TECHNICAL AND ECONOMIC OPTIMIZATION OF PRODUCTION PROCESSES OF COOKED MUSSEL FLESH

Table of contents

• 1. Introduction
• 1.1. BACKGROUND
• 1.2. COOKING LINE
• OBJECTIVES
• METHODOLOGY OF THE TESTS CONDUCTED
• 1.3. INTRODUCTION
• 1.4. TRIAL 1: SAMPLING OF THE THREE SIZE CLASSES
• 1.4.1. Pre-cooking batch characterization
• 1.4.2. Operating parameters
• 1.4.3. Sampling
• 1.5. TRIAL 2: SAMPLING OF SMALL MUSSELS (UNDER 47 MM)
• 1.5.1. Pre-cooking batch characterization
• 1.5.2. Operating parameters
• 1.5.3. Sampling
• 1.6. TRIAL 3: SAMPLING OF MEDIUM MUSSELS (47–60 MM)
• 1.6.1. Pre-cooking batch characterization
• 1.6.2. Operating parameters
• 1.6.3. Sampling
• 1.7. LABORATORY ANALYSES
• 1.7.1. Morphometric measurements and dry weight
• 1.7.2. Sensory property evaluation and salt content analysis
• 1.8. STATISTICAL ANALYSES
• RESULTS
• 1.9. TRIAL 1: SAMPLING OF THE THREE SIZE CLASSES
• 1.9.1. Characterization of mussels before cooking
• 1.9.2. Characterization of mussels after cooling
• 1.9.3. Temperature of cooked mussels
• 1.9.4. Characterization of flesh-shell separation
• 1.9.5. Characterization of accepted and rejected flesh
• 1.9.6. Length of stages on the cooking line
• 1.9.7. Characterization of the finished product (IQF)
• 1.10. TRIAL 2: SAMPLING OF SMALL MUSSELS (UNDER 47 MM)
• 1.10.1. Characterization of mussels before cooking
• 1.10.2. Characterization of mussels after cooling
• 1.10.3. Temperature of cooked mussels
• 1.10.4. Characterization of flesh-shell separation
• 1.10.5. Characterization of accepted and rejected flesh
• 1.10.6. Characterization of the finished product
• 1.10.6.1. Salt analysis in the laboratory
• 1.10.6.2. Sensory evaluation (panel)
• 1.11. TRIAL 3: SAMPLING OF MEDIUM MUSSELS (47–60 MM)
• 1.11.1. Characterization of mussels before cooking
• 1.11.2. Characterization of mussels after cooling
• 1.11.3. Temperature of cooked mussels
• 1.11.4. Characterization of flesh-shell separation
• 1.11.5. Characterization of accepted and rejected flesh
• 1.11.6. Characterization of the finished product
• 1.11.6.1. Salinity assessment
• 1.11.6.2. Sensory evaluation
• DISCUSSION
• 1.12. TRIAL 1: SAMPLING OF THE THREE SIZE CLASSES
• 1.12.1. Effect on peeling rate
• 1.12.2. Effect on yield and quality of cooked mussel flesh
• 1.12.3. Effect on finished product quality (mussel flesh frozen individually (IQF))
• 1.13. TRIAL 2: SAMPLING OF SMALL MUSSELS (UNDER 47 MM)
• 1.13.1. Effect on peeling rate
• 1.13.2. Effect on yield and quality of cooked mussel flesh
• 1.13.3. Effect on finished product quality (mussel flesh frozen individually (IQF))
• 1.14. TRIAL 3: SAMPLING OF MEDIUM MUSSELS (47–60 MM)
• 1.14.1. Effect on peeling rate
• 1.14.2. Effect on yield and quality of cooked mussel flesh
• 1.14.3. Effect on finished product quality (mussel flesh frozen individually (IQF))
• OVERALL CONCLUSION
• BIBLIOGRAPHIC REFERENCES
• OTHER ITEMS OF INTEREST

1.  Introduction

1.1. Background

Blue mussel aquaculture represents the second largest aquacultural activity in Canada in terms of volume (DFO, 2008). On the North American market, which is relatively small compared to the European market and the lack of diversity in Canadian products with regard to packaging and format, mussels have a relatively low economic value. Despite the increased interest in mussels in general, the consumption of live mussels is stagnating, the trend being an increase in demand for frozen and processed mussels (MAPAQ, 2009). This is why processed mussel imports, in particular from Chile and New Zealand, are up.

The ability to produce cooked mussel flesh in Canada at a competitive price will open the door to development of several high-quality further-processed products. These products will make it possible to expand internal and export markets for Canadian mussels while increasing the extent to which this species is developed. It will now be possible to market new cooked products that meet consumers' expectations of practicality or to market frozen processed products that can be exported to Europe, a rapidly growing market (+4%/year) with better prices. This will decrease competitive pressure that currently weighs on our businesses and, as a result, consolidate the entire mussel industry.

Mussels in Quebec are mainly farmed in the Gaspé Peninsula and on the Magdalen Islands. This production is growing because of improvements in farming techniques. The volumes produced have increased by 25 to 30% per year since 1996 and this expansion is expected to continue (MAPAQ, 2009). Moreover, the implementation of an experimental fresh mussel processing line at the Pêcheries Rivière-au-Renard (Menu-Mer Ltée) plant in 2003 as part of a partnership between the company, MAPAQ, SODIM and Halieutec created an opportunity to start commercial processing of this mollusc in the Gaspé Peninsula.

The production of cooked mussel flesh is a profitable opportunity to cut losses associated with fresh mussel production management. Cooking mussels conserves their initial quality and once the flesh is peeled, it can be frozen or cured and sold for various uses. Moreover, because of cooking, production can be optimized by using mussels under 47 mm that are currently rejected by processors because of a lack of demand on the fresh market. This decrease in rejects would also contribute to the environmental sustainability of the industry. Moreover, cooked flesh targets different markets than the fresh product and opens up the possibility of developing new processed products. Cooked flesh production should therefore increase total volume of mussels harvested by producers.

1.2. Cooking line

The cooking unit was acquired through the École des pêches et de l'aquaculture du Québec's (ÉPAQ) program to support the development of technology in mariculture (DTM) in Quebec and installed for experimental purposes at Menu-Mer. There are only two cookers of this kind in Canada; the other is in Newfoundland at Allen's Fisheries. This equipment, manufactured by the Dutch company Wisse Kramer BV, is used to steam cook mussels in a chamber pressurized to 3 atm. The mussels are then mechanically peeled in a brine pool. Pressure cooking can result in a peeling rate of 98% without manual intervention. The cooking line is fully automated, with a basket rotation and loading system run by electronic sensors that operate it with only two or three employees assigned to monitor and inspect the finished product. The system is also small and fitted to adapt to capacities for fresh mussel processing (fall-off and debyssing) already present in most Canadian plants (1000 to 2000 lbs/h). This new principle has a definite technological benefit, but it involves exhaustive R&D and fine-tuning to enable users to fully benefit from these capacities.

To our knowledge, no Canadian plant currently uses a steam cooking unit for mussels. A continuous steam cooking line manufactured by Charlottetown Metal Products (P.E.I.) was tested by the Prince Edward Island Food Technology Centre, but this piece of equipment operating at atmospheric pressure did not enable peeling rates to exceed 90% (Jim Reeves, personal communication). It is new in Canada, but the Dutch technology is recognized and used on an industrial scale in some plants in the Netherlands, as we saw on a technological information mission. However, this cooking equipment is normally used with fished mussels that are smaller and have a thicker shell than farmed mussels (Aquamossel, personal communication). A different raw material often leads to unexpected results, even if the basic principle is known. Moreover, Canadian Food Inspection Agency (CFIA) and European Union regulatory requirements differ in terms of organoleptic quality, as do North American and European consumer expectations. Transposing operating parameters from one country to another is not easy; major technological uncertainties therefore exist.

Menu-Mer staff and the technical team at the Centre technologique des produits aquatiques (CTPA) conducted cooking process validation tests in the summer of 2008 to set critical limits and establish control of biohazardous threats (risks associated with Listeria monocytogenes) at this stage. The purpose of this work was essentially to control factors that can affect the product's internal temperature in order to meet the requirements of an HACCP plan that is to the CFIA's satisfaction. However, during this process, it was noted that factors affecting the product's heating rate also have an impact on the peeling rate and the quality and characteristics of the cooked flesh, especially its texture and its external aspect (unpublished data). The Halieutec team and the CTPA then conducted three sets of samplings in the cooking line in July 2009, December 2009 and April 2010. An analysis of the results is presented in this report.

Objectives

The main objective of this project is to optimize processes for producing cooked mussel flesh and finished products. The specific objectives are to:

1. Identify and test the effect of various cooker operating parameters in relation to mussel size on:
   
   
   • the peeling rate (flesh-shell separation);
   • the yield and quality of the cooked mussel flesh;
   • the quality of the finished products (mussel flesh frozen individually (IQF) and cured mussel flesh);
     
     
2. Set reproducible production standards.

Methodology of the tests conducted

1.3. Introduction

The first step in the project (i.e., evaluating the basic production plan and identifying controllable factors) was accomplished during a visit to the Menu-Mer processing plant on May 27, 2009. To do this, the current cooked mussel flesh production system had to be defined. This involved examining product specifications, putting together process flow sheets, looking into technical problems and coordinating all practices regarding the process, input, equipment and formulations.

Once the technical field was defined, the impact of the operating parameters on peeling rates (flesh-shell separation), production yield, quality of flesh from cooked mussels and quality of flesh from individually frozen mussels (IQF) were studied through a series of trials. The trials were conducted within the critical limits set for cooking control. These limits guarantee that the mussels remain at the minimum internal temperature sought (79°C) for six seconds (FDA, 2001). Therefore, for Trial 1, the cooking parameters were set at 2.5 bars and 115 seconds of cooking. For Trials 2 and 3, various time/pressure combinations were chosen by checking the product's internal temperature until it reached a minimum of 79°C.

Three trials were then conducted at Menu-Mer in 2009 and 2010 (July 16 and December 16, 2009, and April 8, 2010). The purpose of the first was to compare the effect of cooking for three different mussel size classes (under 47 mm, 47–60 mm and over 60 mm) while the two other trials dealt with only one size class. The objective was therefore to optimize cooking for each of them by testing various pressure and cooking time combinations. Therefore, in December 2009, only small mussels were used, whereas in April 2010 sights were set on medium commercial mussels. There were no tests for mussels over 60 mm in size. After discussion with the various stakeholders, these tests seemed less relevant because this size class is not often part of the batches received at the Menu-Mer plant, unless customers are specifically looking for this type of mussel. Moreover, the project had to be finished in April, which resulted in this final test not being carried out.

At the same time that Halieutec was conducting trials, Menu-Mer ran a few cooking tests of its own. This led the plant to make adjustments to the cooking line for Trials 2 and 3 (salinity, depressurization with the addition of a valve, etc.). These changes are discussed in further detail in the following paragraphs.

1.4. Trial 1: Sampling of the three size classes

Trial 1 was conducted on July 16, 2009. The steps below were followed for taking measurements at the plant.

1.4.1. Pre-cooking batch characterization

The mussels that were cooked and peeled throughout the trial were harvested on July 15, 2009, in Maria. Longline socking was done in the spring of 2007 on 2006 spat. The raw material weighed 186 kg (410 lbs) for mussels under 47 mm and 113.4 kg (250 lbs) for the other two size classes (47–60 mm and 60 mm and over). Since mussels from the same batch are divided into three size classes and put in tanks before being cooked, samples had to be taken from each tank before being put in the cooking line in order to accurately characterize the processed mussels.

The analysis of mussels before cooking (commercial flesh yield, dry weight and morphometric measurements) also ensures that the effect on production yield truly comes from the cooking parameters, not from the heterogeneity of the samples. A sample of 50 mussels was therefore taken from isothermal tanks before each class was sent to the process conveyor in the cooking line. These samples were chilled and sent to ÉPAQ, where their commercial flesh yields were calculated.

1.4.2. Operating parameters

During cooking treatment, the path of mussels of the same size class was followed by precisely determining the reject points and the extent, nature and cause of losses. The following parameters were noted:

• Cooking parameters (pressure and length of the cooking cycle);
• Product's internal temperature when the cooker was opened;
• Water temperature in the cooling tank; cooling time (conveyor speed);
• Mixing flow; time spent in the flesh-shell separator (conveyor speed);
• Brine concentration;
• Soaking time in the transition pool (conveyor speed);
• Rinsing time (conveyor speed) and freshwater flow from the nozzles.

The cooking parameters were read directly from the cooking line's control panel. The internal temperature of the product and of the water in the cooling tank was taken using a thermograph probe available at Menu-Mer. Time (duration) data was taken using a stopwatch. Water flow was calculated by sampling a quantity of water for an exact time (noted on the stopwatch). Water samples were taken from the flesh-shell separation tank and sent to ÉPAQ for brine concentration measurement.

1.4.3. Sampling

Analyzing the samples taken identifies operating parameters that have an impact on peeling rate (flesh-shell separation), cooked mussel flesh production yield and quality, and quality of the finished product (i.e., individually frozen mussel flesh (IQF)).

Mussel samples were taken by counting the live mussels with the aid of graduated containers and the frozen mussels with the aid of an electronic scale. The mussels were placed in a freezer bag (Ziploc) marked with a number and kept on ice in a refrigerator before being sent to ÉPAQ. Three of the frozen samples (IQF) were sent to the CTPA for organoleptic analysis. The acceptability panel was conducted on site in the case of accepted flesh. Three mussels were randomly selected at the end of the cooking line three times for each size class. Characteristics regarding taste, texture and appearance were noted by an observer.

1.5. Trial 2: Sampling of small mussels (under 47 mm)

The second trial was conducted on December 16, 2009, on small mussels (under 47 mm).

1.5.1. Pre-cooking batch characterization

To check whether the batch corresponded to the size class targeted by the trials, a sample of about 100 mussels was collected from among the fresh ones (i.e., those not yet cooked). This sample was sent to ÉPAQ and kept fresh before being analyzed the next day.

The batch used for Trial 2 was harvested on November 20, 2009, and came from the Pêcheries R. Allard mussel culture site on Chaleur Bay. The socking date was not determined. This batch was wet stored for 22 days. The weight of the raw material was 1450 lbs.

1.5.2. Operating parameters

Before Trial 2, the processing plant added a valve to the pressure cooker so that the change in pressure at the end of the cycle would be more gradual because the depressurization predicted initially by the manufacturer was quite fast (3–4 seconds). The objective was to decrease the number of cracked mussels observed in Trial 1 (see results of that trial.). Moreover, the salinity of the separation tank (brine) was decreased and set to 62 degrees. This step was recommended following Trial 1 to ensure that the mussels were not too salty (see discussion portion of Trial 1).

The following parameters were noted:

• Cooking parameters (pressure and length of the cooking cycle);
• Product's internal temperature when the cooker was opened;
• Water temperature in the cooling tank; cooling time (conveyor speed);
• Brine concentration;
• Total weight of the live mussels that were cooked for the trial;
• Total number and weight of rejected and accepted flesh.

The core temperature of the flesh as it exited the cooker was randomly taken on three mussels with the aid of a Fluke 51 thermocouple for each of the three baskets sampled per scenario. However, the mussel temperature after cooling was not noted.

The cooling tank temperature was continuously recorded with the aid of a Vemco thermograph (8-bit minilog temperature logger) placed in the tank.

Unlike in Trial 1, the flow and the time spent in the various tanks was not noted. The plant continuously modified the conveyor speeds throughout the trial. An Ertco salinometer was used to record the salinity of the separation tank. The unit indicated in the results is that used by the plant: degree of salinity. In the text, we converted it to grams of salt per litre of water.

1.5.3. Sampling

As stated above, the objective of Trial 2 was to optimize the cooking of small mussels. To do that, Halieutec tested several time/pressure combinations (or scenarios) at Menu-Mer. The results obtained were then statistically analyzed to determine the best scenario to recommend to the plant.

The cooking scenarios were chosen based on the results of Trial 1. Accordingly, the pressure and/or time were lowered to obtain cooked, undamaged flesh based on plant requirements. For every pressure, several times were tested to find an optimal scenario. Between each scenario, the cooker's control panel was used to adjust the pressure and the cooking time.

Three 50-lb baskets of mussels were cooked for each scenario and three samples were taken at various cooking stages. Before starting to cook the three baskets, a "test" basket was tested to confirm whether or not the chosen scenario was effective in cooking the flesh. For that, the basket of mussels was put in the cooker and the team tasted some of the mussels. If they were cooked, the cooking scenario was retained for three other baskets. This helped to eliminate some of the initial scenarios and to ultimately keep four scenarios.

The samples were sent to ÉPAQ in marked Ziploc bags that were kept in an icebox and cold stored until their analysis the next day.

1.6. Trial 3: Sampling of medium mussels (47–60 mm)

This trial was conducted on medium mussels (between 47 and 60 mm). Because of a lack of mussel availability, this could not be done earlier in the winter; the team therefore waited until April 8, 2010.

1.6.1. Pre-cooking batch characterization

As in Trial 2, a sample of 100 mussels was analyzed to check the consistency of the batch with the required size class. The batch used that day was harvested on March 29, 2010, at the Grande-Entrée Aquaculture mussel culture site on the Magdalen Islands. The socking date was not determined. The samples were wet stored for 7 days before the trial was conducted. The test required 1000 lbs of fresh mussels.

1.6.2. Operating parameters

The valve put in during Trial 2 was also used for Trial 3. The salinity of the separation tank was increased and set at 71 degrees to increase the flesh's buoyancy. Had the same salinity as that for Trial 2 been used, the flesh from 47–60 mm mussels would be runny because it is denser than small mussels' flesh.

The following information was noted:

• Cooking parameters (pressure and length of the cooking cycle);
• Flesh temperature after cooking and cooling;
• Cooling tank water temperature (measured continuously with a thermograph);
• Time each basket was put in the cooling tank;
• Brine concentration;
• Total weight of the live mussels cooked for the tests;
• Total quantity and weight of rejected and accepted flesh for each scenario (to calculate production yield).

A Fluke 51 thermocouple was used to take the core temperature of the mussels a few seconds before they were removed from the cooker and after they were placed in the cooling tank. As in Trial 2, this data was taken on three mussels at random in each of the baskets sampled.

The flow and the time spent in the various tanks were not noted in this trial either because the conveyor speed was continuously adjusted.

1.6.3. Sampling

The objective of this trial was to find the best cooking scenario(s) for mussels measuring 47–60 mm; several time/pressure combinations were applied. These combinations were chosen first and foremost based on the results obtained in Trial 1. This enabled us to determine whether or not both cooking parameters had to be raised or lowered. The maximum number of scenarios that could be tested was then determined based on the raw material available for the project. From there, the tests began from lowest to highest pressure. The team proceeded as it did for Trial 2 (i.e., each scenario was tested with the aid of a test basket). If the cooking met plant expectations, it continued and sampling could begin.

1.7. Laboratory analyses

1.7.1. Morphometric measurements and dry weight

Commercial flesh yield, morphometric measurements, weight and characterization of mussels' attachment to shells were conducted in the ÉPAQ laboratory starting the day after the sampling.

Live mussels' shell lengths were measured individually.

Dry weight was determined after drying in the oven for 48 hours at 60°C to check whether the flesh's water content could explain some of the results obtained. Commercial flesh yield was calculated after the mussels were cooked in a steam cooker (Ibarra et al., 2000). The samples whose dry weight was to be analyzed were frozen at -18°C because they were not run through the oven (48 hours at 60°C) the next day for each trial.

The attachment of the flesh to its shells was evaluated as follows: Flesh attached by the muscle or not falling from the shell when it is shaken off manually was considered "attached." In addition to flesh that was found free from the shell in a sample or in a shell but was falling from it easily, this quantity constituted "present" flesh.

The percentage in number of flesh inside shell remnants was converted to percentage in weight (through the calculated commercial flesh yield) in order to compare size classes.

1.7.2. Sensory property evaluation and salt content analysis

MAPAQ's Centre technologique des produits aquatiques (CTPA) in Gaspé evaluated the samples' sensory properties and analyzed the samples' salt content. For all tests, the CTPA had planned a sensory evaluation with a broad panel. Mussel samples were taken from IQF frozen flesh, placed in plastic Ziploc bags, saved in Styrofoam iceboxes and sent to the CTPA the same day. When they arrived, the containers were placed in a freezing chamber at -18°C until they were to be evaluated. For Trials 1, 2 and 3, sensory analyses were conducted on October 2, 2009, February 25, 2010, and April 15, 2010, respectively. A sensory analysis involves two steps:

Before a taste panel is conducted, a pre-evaluation is always carried out to:

• check that the product is compliant in terms of food safety;
• check to see if the product allows an evaluator to detect basic sensory characteristics;
• check to see if the product is presentable to a consumer panel;
• check to see if the product is homogeneous;
• prepare the evaluation protocol.

The pre-test is also used to prepare the protocol and adapt the form, if necessary. The CTPA can also take another look at the size of the sample and the order of presentation (if it is foreseeable as from least salty to most salty). It also helps in confirming the choice of analysis: hedonic, triangular or descriptive (Sztrygler et al., 1990).

The taste panel is the next step. When this was applied, a consumer panel was preferred over a restricted panel consisting of experienced evaluators. The panelists were recruited from members of the regular taste panel at the Direction de l'innovation et des technologies (DIT). On the day before the tasting, the samples were thawed in a cold chamber at 4°C. On the morning of the tasting, the mussels were drained through a sieve for 10 minutes to eliminate excess water. Before being presented to the panelists, the mussel flesh was left for 30 minutes at an ambient temperature. For this project, the tasting tray presented a numbered plate with three samples of eight mussels of a total weight of 13 to 16 g each from the retained cooking scenarios. The evaluators gave their personal assessment of the appearance, texture, intensity of saltiness, and overall taste by rating their acceptability on a nine-level scale. Evaluation sessions were conducted in tasting booths in accordance with standard sensory evaluation methods (Meilgaard et al., 1991).
 
Moreover, the CTPA chemistry lab determined the salt content of the flesh in order to check the saltiness of the mussels based on the chemical criteria for Trials 2 and 3. On December 21, 2009, the CTPA took two random 50-g samples of frozen mussels for each basket cooked at the plant (six samples per scenario). For the April 8, 2010 samples, the CTPA took one 50-g sample per basket (three samples per scenario) and sent them to the chemistry lab for a salt analysis. In the results, the salinity is given in percentage (i.e., in grams of salt per 100 grams of sample).

1.8. Statistical analyses

Statistical analyses were conducted to check the differences between the size classes and scenarios for the following variables: percentage of flesh attached to its shell (after cooling), percentage of flesh accepted and percentage of flesh rejected (after cooling), percentage of flesh in the shell remnant sample, percentage of flesh attached to shells in the shell remnant sample, and water content (%) of the accepted and rejected flesh on the sorting table.

We used descriptive analyses (averages) to compare the results between size classes and scenarios. We determined whether the differences were significant by checking whether the 95% confidence intervals overlapped. Moreover, some linear regressions were done and their R2 was calculated to check whether the size class explains the variance of the variable studied in the case of Trial 1.

Results

1.9. Trial 1: Sampling of the three size classes

1.9.1. Characterization of mussels before cooking

Three characteristics were measured on mussels sampled before being cooked at the plant: average length, commercial flesh yield and water content.

First, average mussel length closely corresponded to the targeted size class. The average length for mussels under 47 mm, between 47 and 60 mm, and over 60 mm was 43 mm, 56 mm and 65 mm, respectively.

Second, it was noted that the commercial yield for mussels 60 mm and over was higher (38%) than that for the two other size classes (about 28% for mussels under 47 mm and 27% for mussels between 47 and 60 mm).

Third, the water content of mussels in the various size classes was quite similar. It was around 73% for both the under 47 mm class and the 60 mm and over class, and 71% for medium mussels.

1.9.2. Characterization of mussels after cooling

Just before flesh-shell separation, samples were taken from the conveyor located past the cooling tank. For each size class, the total number of shells was counted. The quantity of flesh still attached was used to calculate the percentage of flesh attached. Moreover, the accepted and rejected flesh were separated based on the same criteria as those for the sorting table in order to calculate their percentage (out of the total shells).

The percentage of flesh attached to its shell ranged from 1.9% to 4.5%, the highest being that for medium mussels. Since the confidence intervals overlap, it cannot be deduced that the percentage of flesh attached to its shell varies with the size class analyzed. There was very little variation in cooling time among the size classes (about 30 seconds).

The percentage of flesh accepted seems to vary with size class. Although the confidence intervals overlap among the three size classes, it cannot be concluded that there is a major difference. This means that the size class explains 69% of the variance in the quantity of flesh accepted. It is observed that this regression decreases with size class; in other words, the larger the mussels are, the less their flesh is accepted and the more it is rejected.

Brief taste tests based on texture, flavour and appearance criteria were also done on mussels after cooling. Small mussels have a good texture and taste, but a rather poor appearance (cracked). Medium mussels are firm; although the largest of these mussels are rather floury (heterogeneity between samples), they taste and look good. Large mussels present negative characteristics: unpleasant texture, tastelessness and poor appearance.

1.9.3. Temperature of cooked mussels

It is noted that for all size classes, the mussel temperature before cooling exceeded 79°C (the lower limit to ensure the mortality of Listeria monocytogenes). It cannot be concluded through analysis of the confidence intervals that the temperatures are vastly different.

1.9.4. Characterization of flesh-shell separation

Although the flesh in the sample of rejected shells seemed larger for small mussels, the confidence interval analysis shows that this variable is not related to size class. As for flesh attached to its shell, this variable seems to increase with size class (the larger the mussels are, the more flesh attached). The linear regression done on the data shows an R2 of 0.98, which means that the size class explains almost the entire variance in flesh attached to its shell. There does not seem to be any major difference among the size classes with regard to attached flesh.

The flow from the various nozzles on the cooking line and the salinity of the separation tank were measured when cooking began for each size class. These variables are rather inconsistent among the size classes. Flows vary from 42.3 mL/s to 62.9 mL/s for the flesh-shell separation tank nozzles and from 17.6 mL/s to 24.1 mL/s for the rinsing conveyor nozzles. The salinity ranged from 57 to 80%. However, note that for mussels between 47 and 60 mm, the salinity was increased after the data was taken (from the second basket onward). It can therefore be said that the salinity ranged between 70 and 80%.

1.9.5. Characterization of accepted and rejected flesh

Weight analyses conducted on accepted and rejected flesh on the sorting table enabled the water content to be calculated for each size class. The confidence interval analysis shows that water content does not vary with size class for accepted or rejected flesh.

The weight of mussel flesh that arrived on the sorting table enabled calculation of the production yield (weight of cooked flesh on the sorting table/weight of the raw material) from cooking mussels at the plant. The yield is about 25% for small mussels, 23% for medium mussels and 27% for the largest mussels. Medium mussels seem to have the worst yield, whereas the 60 mm and over size class has the best yield.

Conversely, if the proportion of accepted and rejected flesh in relation to total flesh weight before sorting is examined, mussels over 60 mm had almost twice as much flesh rejected (10%) as mussels under 47 mm (4%) and mussels between 47 and 60 mm (5%). However, it must be noted that during sampling, it was observed that when small mussels (under 47 mm) were sorted, a large proportion of mussels considered "accepted" may have been "rejected" because they presented unacceptable characteristics: broken flesh, damaged hepatopancreas, etc.

1.9.6. Length of stages on the cooking line

The time that cooked mussels spent in the cooling tank did not vary much for the first mussels to be taken out of the tank (between 24 and 30 seconds). However, we did not measure the longest time that the mussels could have spent in this tank because a second basket was dumped onto the preceding one even though there were still mussels left in the tank.

Time spent in the flesh-shell separator was quite fast: four to six seconds for all size classes with a maximum of 10 seconds noted. Soaking time in the transition pool was quite stable: 19–20 seconds. Rinsing time was noted only for mussels 60 mm and over: 41–43 seconds.

1.9.7. Characterization of the finished product (IQF)

The mussels were first weighed to check that the samples corresponded to the size classes indicated. It can be observed that the flesh weight increased with size class.

The finished product was then characterized. Contrary to what was initially planned, there was no taste panel. The CTPA noted a lack of homogeneity, but more particularly the very high intensity of salt in the finished product. The result was therefore too predictable and the panelists would have proceeded to a second evaluation with some apprehension. This point is addressed in the discussion. The characterization of the product was therefore limited to a categorization based on external criteria for mussels after thawing.

The mussels were therefore put in two categories based on different criteria. Class A corresponds to a full product (mussel flesh) that would be compliant and acceptable for (panel) evaluation were the mussels less salty. Mussels that had a major flaw (broken flesh, damaged, cracked, granular appearance, damaged hepato) and were not acceptable for evaluation were placed in Class B. The lowest proportion (29%) of mussels that could have been accepted for evaluation were in samples of small mussels (under 50 mm). The larger the mussels were, the more this percentage increased. It reached 64% for mussels over 60 mm (the larger the mussels were, the lower the percentage of those rejected for evaluation).

1.10. Trial 2: Sampling of small mussels (under 47 mm)

1.10.1. Characterization of mussels before cooking

The average length of mussels before cooking was 46.1 mm. This corresponds well to the targeted size class (under 47 mm).

Only one mussel commercial flesh yield was calculated before cooking because there was only one size class. The commercial yield here was 15.15%.

Water content could not be determined because the sample was lost.

1.10.2. Characterization of mussels after cooling

The average percentage of attached flesh ranged from 2.26% to 6.59%. Most of the flesh was attached by the byssus (88% on average for attached flesh), not by the muscle. As confidence intervals overlap, there does not seem to be any variation in the percentage of attached flesh if the mussels were cooked based on combinations of 2 bars for 95 seconds¹, 2.5/90 and 1.5/125. However, there is a major difference between the 2/115 and 1.5/125 combinations and between the 2/115 and 2/95 scenario. The lowest percentage (2.26%) of mussels still attached after cooling is found in the 2/115 cooking scenario and the highest percentage (6.59%) is found in 1.5/125.

Not all data for accepted and rejected flesh from the samples taken after cooling was recorded. The little data thus obtained does not allow us to provide proportions of accepted and rejected flesh based on the cooking scenarios. However, the few measures taken show that for all of the scenarios combined, the percentage of accepted flesh is close to 89.8% and that of rejected flesh is 7.8%.

1.10.3. Temperature of cooked mussels

In all scenarios tested, the mussel temperature before cooling exceeded 79°C (the lower limit for ensuring the destruction of Listria monocytogenes). The temperature seems to have been higher at 2/115, but it is not significant.

The water temperature in the cooling tank was 5.3°C before cooking began. However, it never exceeded 11.5°C. For the duration of the testing, it was 8°C on average.

1.10.4. Characterization of flesh-shell separation

In the samples of rejected shells, the percentage of flesh present ranged from 0.56% to 1.26%. It cannot be concluded from the results that the percentage of flesh present is vastly different depending on the type of scenario, except between cooking at 2/115 and 1.5/125. It seems that the 2/115 scenario is that for which there is less flesh present in the rejects.

The percentage of flesh attached after separation ranges from 0.23% to 0.71%. There is a major difference between the 2/115 and 1.5/125 scenarios. The average percentage seems lower for the former. Even there, however, we cannot highlight a particular combination based on the results.

The brine water tank had an average salinity of 60 degrees. According to the scenario, the values ranged between 59 (or about 188 grams of salt per litre of water) and 61 degrees (195 g/L). The average temperature of this tank was 11.62°C. Based on the cooking, the lowest average temperature was 11°C and the highest was 14°C.

1.10.5. Characterization of accepted and rejected flesh

After dry weight analysis, the water content of the mussel flesh does not seem to vary with scenario, the exception being scenario 1.5/125, which seems to have a water content much higher than the others in the case of rejected flesh.

Because the accepted and rejected flesh were not weighed for each scenario, an overall production yield was calculated for the entire batch of mussels cooked on that day (including mussels cooked outside the trial period). The yield was about 14%. This made it possible to calculate the overall proportion of accepted flesh in comparison with the total weight of the flesh before sorting. This proportion is about 93% for accepted flesh and 7% for rejected flesh.

On two occasions, Menu-Mer then cooked the rest of the mussels in the batch that were not used on December 16. This provided other production yield results for one scenario in particular. Accordingly, on March 9, 2010, small mussels were cooked at 2/115 and the plant got yields of 18% and 19% with a proportion of rejected flesh of 0.05% and 1.1%, respectively.

1.10.6. Characterization of the finished product

1.10.6.1. Salt analysis in the laboratory

The salinity of the flesh after being cooked at 2/115 and 2/95 did not differ much. However, the same is true for mussels in the 2/95, 2.5/90 and 1.5/125 combinations. Conversely, those cooked at 2.5/90 and 1.5/125 differ greatly from the 2/115 scenario. Mussels cooked at 2.5/90 and at 1.5/125 are therefore saltier than those cooked at 2/115. The variability for one scenario is quite low according to the confidence intervals.

1.10.6.2. Sensory evaluation (panel)

Three of the four cooking scenarios tested were evaluated by 34 panelists. The fourth cooking test (1.5/125) was not evaluated, given the softer, less pleasant texture of the flesh noted in the pre-evaluation. As a result, after discussion with Halieutec, the scenario was not retained for the taste panel.

For each criterion analyzed, the products received a mean acceptability score higher than 6. These scores range from 6.2 to 7.1 for mussels cooked at 2/115, 6 to 6.4 for mussels cooked at 2/95 and are similar for mussels cooked at 2.5/90. These mean scores are between "slightly pleasant" (6) and "moderately pleasant" (7). The overall appearance criterion for the three batches of mussels was judged a bit more harshly than the other criteria because the panelists agreed that the mussels were quite small. The intensity criteria scores for salty taste and overall taste are somewhat similar. If the salty taste satisfied the panelist, he/she will like the overall taste of the mussel. Panelists preferred mussels cooked at 2/115 but if the standard deviations are taken into account, this is not significant. The panelists were less approving of mussels cooked at 2.5/90; these were deemed too salty but again, not significant.

During preparation of the samples, the CTPA technician noted that there were a few more cracked mussels in the 2.5/90 batch than in the two others. These mussels were not presented to the panelists.

The results show that in all cases, the panelists found the mussels slightly pleasant.

1.11. Trial 3: Sampling of medium mussels (47–60 mm)

1.11.1. Characterization of mussels before cooking

The average mussel length was 61.85 mm, which is more than the targeted size class (47–60 mm). The team noted that the mussel flesh was quite fat and that the shells were quite large in relation to the targeted size class.

Initial commercial flesh yield was 31.9%, which is higher than it was in July 2009 (27.2%).

The water content in the sample of live mussels was about 69%.

1.11.2. Characterization of mussels after cooling

The average percentage of attached flesh in the mussel samples collected after cooling ranged between 5.47% (the 2/145 scenario) and 3.1% (the 2.5/115 scenario). Almost all of the attached flesh was free but it remained inside the shells. Very little flesh was attached by the muscle and even less was attached by the byssus. The very large variability among the samples (confidence intervals overlap) does not allow for major differentiation of the cooking scenarios.

The 1/185 scenario presents, on average, the most accepted flesh after time spent in the cooling tank and this number is much higher than it is for the 2/145 and 2.5/115 scenarios. This result does not differ much from the 1.5/160 scenario, however.

Among the total flesh in the samples, the 1/185 combination presents an average rejected flesh percentage that is lower than that for the other scenarios. However, this result is not significant.

1.11.3. Temperature of cooked mussels

After spending time in the cooling tank, the mussels have a somewhat variable temperature. On average, mussels in the 1/185 scenario were hotter, although this does not differ much from the 2/145 and 2.5/115 scenarios.

During the cooking cycle, the temperature of the cooling tank was 4.3°C on average. Compared to July 2009 (about 15°C), the water in the cooling tank was much colder at this time of year because the water used came from an outside source. Therefore, before cooking tests began, the temperature was 3.4°C.

1.11.4. Characterization of flesh-shell separation

The percentage of flesh found in shell remnants does not differ much among the cooking scenarios. It is also observed that the averages do not differ much among the combinations because they range from 3.3% for the 2/145 scenario to 4.17% for the 1.5/160 scenario.

Among the flesh present, the quantity of attached flesh was calculated. There is no major difference among the scenarios, the exception being 2.5/115 when compared with 1.5/160 and 2/145. Most of the attached flesh was inside the shell but not attached by muscle or byssus. The flesh inside the shells was quite fat and did not come out of them, even though they were opened and the flesh was placed in the separation tank.

The salinity of the separation tank was 72 degrees on average (234 g/L) and ranged between 70 (226 g/L) and 72. The temperature of the brine pool was 12°C on average, ranging between 10 and 14°C.

1.11.5. Characterization of accepted and rejected flesh

There is no major difference among the scenarios, the exception being 1/185 and 2/145. The water content of the accepted flesh ranged from 73 to 73.4%, which presents few variations. The results for the rejected flesh are similar. They show little variation (between 73 and 73.4% water) and the scenarios present no major differences, the exception being between cooking at 1/185 and 2/145.

The 2/145 combination had the highest yield (32.8%) and was followed by 2.5/115 (30.6%). The 1.5/160 scenario had the lowest yield (25.4%).

The pressure/time combination used with the 1/185 scenario yielded the highest quantities of flesh accepted after sorting (93.2%). However, cooking at 2/145 and 2.5/115 yielded quite poor results (only about 50% of flesh accepted). The proportion of rejected flesh is quite a bit higher than that for July 2009 (5.4%). Here, with regard to the last three scenarios, the flesh was broken.

1.11.6. Characterization of the finished product

1.11.6.1. Salinity assessment

Frozen mussel samples were analyzed in the laboratory to determine their salt content. This ranges between 1.17% (1.5/160) and 1.70% (1/185). However, it cannot be concluded from the confidence intervals that there is a major difference among the cooking combinations retained. As stated earlier in Trial 2, the consumer sensibility threshold is 1.5%. Cooked at 1/185, mussels seemed relatively saltier than when cooked under the other scenarios.

1.11.6.2. Sensory evaluation

The CTPA team worked with a restricted panel for this trial. About seven evaluators on this panel assessed the mussel samples on April 15, 2010. The consumer panel, made up of about 50 people, is not a very effective tool for evaluating a non-standardized product. For the products presenting as much variability in salinity and texture expression as the mussels in this experiment, the CTPA worked with a restricted panel of experienced evaluators. They can taste a larger quantity of samples to appreciate (or not appreciate) the product's variability. They can also be told about some experimental predispositions, which becomes extremely sensitive with a consumer panel.

The mussels were sorted before being presented to the panel in order to eliminate those that were unacceptable. Acceptable mussels are those with a good appearance or with minor flaws (i.e., when the flesh covering the hepatopancreas was only fissured). Unacceptable mussels had an appearance with major flaws: damaged hepatopancreas, flesh totally or partially cracked, and ripped gonads.

With these criteria, the samples contained a relatively high number of unacceptable mussels. Out of 100 mussels, the number not accepted by the panel ranged between 17% (2.5/115) and 37% (1/185).

The evaluators agreed that for the four treatments, the mussels were too large and the hepatopancreas was full.

The scores awarded by the panelists vary between 2.8 (very unpleasant) and 7.0 (moderately pleasant). Mussels cooked at 2.5/115 and 2/145 looked very similar; many of the mussels were cracked and their flesh was granular. These mussels received scores of 3 and 3.5, respectively. Cooking at 1.5/160 produces a mussel with a more pleasant appearance (score of 4.7), even if several mussels are cracked. The mussels also seemed saltier (score of 4.8) than those in the other scenarios for which the scores range between 5.3 (the 2/145 scenario) and 7 (the 1/185 scenario). The most enticing, still according to the overall appearance criterion, are mussels cooked under the 1/185 scenario (score of 5.3) and their salty taste is much more appreciated (score of 7). However, they look as though they are not cooked thoroughly. The overall taste is relatively similar for all of the scenarios and was evaluated between "slightly unpleasant" (score of 4.5) and "slightly pleasant" (score of 5.5).

Discussion

1.12. Trial 1: Sampling of the three size classes

1.12.1. Effect on peeling rate

The effects of size class on peeling rate are rather difficult to prove. The percentage of flesh attached to its shell in samples taken after cooling seems higher for medium mussels (4.5%), which would explain the low production yield for this size class (23%). However, the considerable heterogeneity among the samples does not allow this to be highlighted significantly.

As for the results from the samples taken in shell remnants, the proportion of attached flesh increases with size class: the bigger the mussels are, the more flesh attached (R2). This result is consistent with the yield results, which show that large mussels lose more flesh than the expected result (details in the next section). Lastly, the quantity of flesh present in shell remnants does not seem to vary with size class.

1.12.2. Effect on yield and quality of cooked mussel flesh

Production yield can be compared with mussels' commercial flesh yield before they are cooked at the plant. Results show that the commercial yield is higher than the production yield for all size classes, revealing a loss of flesh at one stage of the cooking line. Several causes can explain this loss. One is that the pressure cooking method could have induced a water loss in the mussel flesh. Another is that at the flesh-shell separation stage, a high percentage of flesh is found in shell remnants and either stays attached to its shell or is simply taken by the current.

Analyses show that losses between commercial and production yields seem to increase with size class. It is not very likely that the cooking method (pressure) induces a different water loss based on size class (relatively speaking). Moreover, since the water content does not vary with size class, this possibility is to be excluded. However, since the proportion of flesh attached to its shell also increases with size class, an attempt must be made to decrease this level of loss. To do this, an attempt must be made to understand why flesh is found in shell remnants. The quantity of flesh taken by the current can probably be decreased by more precisely adjusting the water flow and the salinity in the flesh-shell separation tank. However, this would have no impact on how much flesh is attached to shells. Instead, this phenomenon seems to result from the parameters that arise before the line: pressure and/or cooking time or even time spent in the cooling tank. For example, it is likely that a relatively large mussel will take more time to cool than a small mussel (as heat moves from the centre towards the edges). Another possibility to explore is the quantity of mussels put together in a basket for cooking. Currently, the plant calibrates its baskets to obtain 50 lbs (23 kg). This ensures that there are more small mussels cooked at the same time as large ones, which probably affects the cooking.

According to analyses conducted on mussels taken after cooling, the larger they are, the less the flesh accepted and the more the flesh rejected. This result is consistent with the analysis of accepted and rejected mussel flesh on the sorting table: it reveals that mussels 60 mm and over had almost twice as much flesh rejected (10%) as mussels under 47 mm (4%) and between 47 and 60 mm (5%). However, it must be noted that during sampling, it was observed that small mussels (under 47 mm) were sorted by only one monitor. However, two people were likely required to sort the largest quantity of mussels. This explains why a large proportion of mussels that presented characteristics of those rejected were not rejected

With regard to mussel quality, brief taste tests (acceptability panel) show characteristics of a granular and floury texture, tastelessness and a cracked appearance for mussels over 60 mm. This result can be explained by the harvesting period. Mussels spawn in the spring and summer (CSMOPM, 2005). In this case, the flesh will have an appearance that differs from that of mussel flesh outside of the spawning period and look granular (Françoise Tétreault, personal communication). Ordinarily, the plant wet stores mussels and does not cook them during this period. Medium mussels (47–60 mm) present positive characteristics. As for small mussels (47 mm and under), only their appearance is lacking. In this case, the market for which this product is intended (i.e., if looking for a better appearance) is relevant. For example, if small mussels are intended for products such as spreads and quiches, their appearance may not be a criterion to worry about, given that taste and texture are acceptable.

The results for mussels under 47 mm and between 47 and 60 mm seem clearly attributable to the correlation between cooking parameters (time and pressure) and mussel size. No relationship can be made between the mussels' water content because this does not vary with mussel size. Similarly, it is difficult to correlate the differences with time spent in tanks and with water temperature and salinity. These parameters undoubtedly varied during cooking, but not significantly among size classes. Lastly, there could be an indication in relation to mussel temperature after cooling; it seems higher for mussels 60 mm and over than for small mussels, although the temperature for mussels between 47 and 60 mm could not be taken and these differences are not significant. It would be logical for large mussels to take more time than small mussels to cool, thereby explaining a lower flesh-shell separation rate. This parameter was monitored during samplings 2 and 3.

1.12.3. Effect on finished product quality (mussel flesh frozen individually (IQF))

Mussel quantities that present characteristics that are unacceptable for a (panel) evaluation are quite high for all size classes in the samples analyzed by the CTPA. In the case of small mussels (under 50 mm), this can be partially explained by sorting being done by only one person. However, this does not explain the results obtained in the other size classes. To be noted is that the criteria used by the CTPA to categorize mussels are not plant criteria because the plant has no specifications for frozen products. However, these criteria are those used for taste panels. If we total the sorting table flesh rejected by the plant and the frozen product flesh rejected by the CTPA, the percentage of rejected flesh is 75% for small mussels, 56.4% for mussels between 50 and 60 mm and 45.8% for the largest mussels, which is considerable. These results therefore support the fact that there are adjustments to be made to the cooking parameters in order to improve the mussels' appearance.

After discussion at a meeting in November 2009, the project participants agreed to work size class by size class during the tests that followed in order to optimize the cooking scenario in relation to all of these classes; the plant then validated the scenario.

The salinity problem encountered in the finished product may simply be due to too much salt in the separation tank (brining). This could also be due to variability among different batches. The plant decreased the quantity of salt in the fall of 2009 and, according to the company, the cooked mussels that arrived on the sorting table had a reasonably salty taste when tasted randomly. As mussel saltiness was not evaluated in the laboratory, it was done for the following tests to get a better idea of its variability in samples from one batch.

1.13. Trial 2: Sampling of small mussels (under 47 mm)

1.13.1. Effect on peeling rate

Cooking at 2/115 seems to give the best results with less flesh attached after cooling. This stands out considerably in relation to the 1.5/125 and 2/95 combinations. It seems that from 2 bars upward, the quantity of attached flesh tends to increase when time decreases. Although this is not significant in relation to the 2.5/90 combination, a trend is observed in this sense because the quantity of flesh attached is larger on average (6.38%) than that at 2/115 (2.26%). However, at a pressure below 2 bars (i.e. 1.5 bars) and despite an increase in cooking time to 125 seconds, the quantity of flesh attached is higher. This shows that a decrease in pressure and cooking time lowers the peeling rate. A comparison with the results of Trial 1 confirms that. In Trial 1, the proportion of attached flesh was 1.9% for a 2.5/115 combination. When the pressure was lowered to 2 bars in Trial 2, the rate increased to 2.26%.  

The results of the quantity of flesh present and the attached flesh in the shell remnant sample are abundant in the same way. Therefore, with cooking at 2/115, the proportion of flesh still present in the remnants seems to be lower when compared with cooking at 1.5/125. However, the result does not vastly differ in relation to the other scenarios by virtue of the large variability of the samples, the exception being with cooking at 1.5/125.

Compared to tests conducted in July, the decrease in pressure to 2 bars did not considerably increase the quantity of flesh attached when the mussels came out of the cooker (1.9% in Trial 1 vs. 2.26% in Trial 2) and in the shell remnants (0.28% in Trial 1 vs. 0.23% in Trial 2). The quantity of flesh still present in shell remnants decreased significantly, from 2% in July to 0.56% in December.

However, the peeling rate obtained in the various trials (1 and 2) is as good as, if not better than, that recommended by the cooking line manufacturer (at least 98%).

1.13.2. Effect on yield and quality of cooked mussel flesh

As stated in the Results section, production yield was calculated for all mussels cooked on December 16. Since yields are not calculated for all scenarios, it is impossible to compare them. However, the production yield (14%) is roughly equal to the commercial flesh yield (15%). It can therefore be believed that no flesh is lost during cooking.

The difference between commercial yield and production yield (1%) is less than that found in Trial 1, which could lead us to believe that cooking in December improved production yield. However, the commercial yield obtained here is less than what was found during the initial trials (about 28%). It is therefore difficult to compare these two trials.

There could be several reasons to explain the results of the commercial and production yields in the December 16, 2009 test. Wet storage for 22 days could have caused some water loss in mussels. However, this hypothesis does not seem to be confirmed by the Menu-Mer plant because wet storage in the fall seems to have no impact on mussel quality (Françoise Tétreault, personal communication). However, it could come from the result itself because this production yield was calculated from the whole batch, not just from the cooking scenarios. Lastly, with regard to the result differences between the July and December tests, yield also depends on mussel harvesting season. Therefore, in Chaleur Bay, production yield would seem lower in winter than in fall (Françoise Tétreault, personal communication).

Lastly, the results lead us to believe that the quality of the flesh after cooking in December is slightly lower than what we found with cooking in July 2009 (93% of flesh accepted vs. 96%). There again, the seasonality of the harvest can explain not only this difference, but also the sorting problem stated in section 5.1.2. Therefore, if the tests conducted by Menu-Mer in March 2010 are taken into consideration, the proportion of accepted flesh was 99.95% and 98.9%. However, it is difficult to compare these results with those obtained in December because the tests were not conducted at the same time.

1.13.3. Effect on finished product quality (mussel flesh frozen individually (IQF))

The strong salt taste problem detected in July 2009 is not found in Trial 2 because of salinity being reduced to 62 degrees.

According to the CTPA lab results regarding the salt content in the flesh, mussels cooked at 2/115 seem to be much less salty than flesh cooked with the other scenarios. This was confirmed through sensory evaluation because the panelists preferred cooked mussels with these parameters regarding the "salty taste criterion" (score of 7). Mussels cooked at 2.5/90 that have flesh containing 1.7% salt were the least appreciated and were considered too salty.

The consumer sensibility threshold for salt is generally 1.5% (CTPA, personal communication). The panelists can therefore clearly detect a salty taste if total salt content exceeds that percentage. The flesh obtained with the 2.5/90 and 1.5/125 scenarios presented a salt content of 1.7 and 1.53%, respectively. This can certainly explain why this flesh is less appreciated in comparison with that from mussels cooked at 2/115 that present a salt rate lower than the sensitivity threshold (1.37%).

It is difficult to justify the salt content variation in the mussel flesh. However, a brine variation in the tank probably changes the salt proportion in the flesh. When the average salinity in the separation tank according to the cooking scenarios is reviewed, the salt content in the tank is lower for the 2/115 scenario. It also seems that even a small difference in salinity in the brine may be noticeable in the finished product. However, it must be noted that only an informed consumer may see this difference because the consumer panel in Gaspé is used to eating mussels. It must also be remembered that the evaluator assigns individual scores for the three simultaneous samples and may therefore find it difficult to make a clear comparison among the three.

Mussels cooked at 2.5 bars may be hotter when they come out and therefore absorb more salt in the separation tank. However, this does not correspond to the flesh temperatures before cooling because they were not higher than those for the other cooking scenarios. It would also have been interesting to have the temperatures after the flesh was placed in the cooling tank. It is also impossible to use Trial 1 to check this because the temperature of the mussels cooked at 2.5/115 was even lower (92°C) than what was found in Trial 2.

On the basis of the mean acceptability test scores and considering the test's interpretation limits, the results show that the consumer panel saw no truly observable difference among the three mussel cooking tests. These mean scores are between "slightly pleasant" and "moderately pleasant." When the panelists were invited to conduct this evaluation, they should have been informed that the mussels to be assessed were of a size under 47 mm, unlike the size class generally sold to consumers (over 47 mm), because when the tray was presented, the reaction was rather negative (they found the mussels too small).

1.14. Trial 3: Sampling of medium mussels (47–60 mm)

1.14.1. Effect on peeling rate

The results of the flesh analyses taken after cooling and in the shell remnants do not allow for significant differentiation of the cooking scenarios or to determine whether one of the pressure/time combinations enables better peeling of the flesh after cooking. However, the loss of flesh in the remnants did not decrease; it stayed the same as or was better than what was found in Trial 1.

During the analyses, the team noted that the vast majority of flesh considered attached simply remained in the shell. As stated in the Results section, the flesh was quite fat and did not come out of its shell. However, the peeling rate stays above 98%.

In April 2010, for all cooking scenarios tested, the averages for the flesh present and attached in the shell remnants were much higher compared to the July 2009 results. Trial 3 therefore did not improve the peeling of the flesh.

1.14.2. Effect on yield and quality of cooked mussel flesh

The overall commercial flesh yield (for all scenarios) obtained is 31.9%. In the end, the highest production yield is for the 2/145 cooking scenario (32.8%) and, in this case, the yield is even slightly lower than the commercial yield. This may be explained by the quantity of flesh in the analyses or by how the live mussel sample was cooked. Cooking was done in water in the laboratory whereas steam was used with the cooking unit. The flesh could therefore have absorbed water. For the other scenarios, a difference of 6.45% (1.5/160) and 1.25% (2.5/115) between yields is noted. The 1.5/160 and 1/185 results are more than what was found in the first test conducted in July 2009. However, the production yields for all of the scenarios are higher (22.8% in July). This observation must be taken with caution because it must be remembered that the April mussels were relatively fat and large and would therefore be closer to the size class of 60 mm and over. From this perspective, it can be compared with the July 2009 results for this size. The yields obtained in April are equal and even higher because the production yield in Trial 1 was 26.6%. The commercial yield is also closer, given that it was 33% in July. The same can be said for the difference in yield of about 6.4% in July, which supports the fact that the mussels could ultimately be categorized in those over 60 mm. The cooking combinations used in April 2010 did not really improve the production yield. Had scenarios been chosen based on the 60 mm and over category, the results would probably have been different.

The differences between scenarios are particularly evident when the results of the sorted flesh are considered. Low-pressure (1 bar) and relatively long cooking (185 seconds) seem to give the best results because the quantity of flesh accepted is higher. The quantity of flesh accepted and rejected obtained after cooling for this scenario also seems highest. However, this is significant only with the 2/145 scenario. The more the pressure is raised by lowering the time, the higher the percentage of flesh rejected. It even becomes quite high because it borders on 50% at 2 and 2.5 bars. These results are much higher than what was found in the first test in the 47–60 mm and 60 mm and over size classes. However, recall that the CTPA then rejected quite a bit of the cooked mussels during this test (56% for medium and 46% for large). The CTPA results for Trial 3 are discussed in the next paragraph.

Mussels being collected in a different season and at another site has an impact on the results and explains why when they were cooked at 2.5/115 in July 2009 and April 2010, their production yields and flesh quality were different. Other studies showed that for mussels from the Magdalen Islands (Trial 3), the yield in the plant is much higher than that for Chaleur Bay mussels (Trials 1 and 2) (Laurent Girault, personal communication). However, that was verified in only one month of the year (December) and this result cannot be generalized.

1.14.3. Effect on finished product quality (mussel flesh frozen individually (IQF))

The average salinity for the scenarios is below the panelists' detection threshold, the exception being for mussels cooked at 1/185. However, this difference is insignificant, despite the temperature of these mussels after cooling being much lower than that of mussels cooked at 1.5/160. The high salinity of the mussels that was noted in July 2009 was therefore improved and lowered because of adjustments made by the Menu-Mer plant between tests (lowering of the separation tank's salinity to 72 degrees) and because of a more controlled brine salinity.

After the sorting done by the CTPA, relatively high rates of flesh were unacceptable because the flesh presented major flaws. Contrary to the results obtained by the plant after sorting, here mussels cooked at 1/185 present the highest rate and the 2.5/115 scenario presents the lowest. However, the conclusion of the sensory evaluation differs somewhat because cooking at 1/185 results in the best flesh from an appearance and salinity perspective, even though the flesh is not completely cooked. This combination is therefore not ideal for cooking flesh in an optimal manner.

In comparison with Trial 1 results, there is less flesh rejected by the CTPA. When the rejected flesh on the sorting table and the flesh rejected by the CTPA is added, the rates are 44% for 1/185, 60% for 1.5/160, 80% for 2/145 and 66% for 2.5/115. Those results are still quite high (near the July 2009 rates). If the mussels being in a category higher than that targeted is taken into consideration, an explanation can be found for these results. The cooking scenarios were chosen based on medium, not large, mussels. However, according to the Kramer company, the hypothesis about depressurization being too fast seems plausible. Nevertheless, use of a pressure graduating valve did not decrease broken flesh. This valve increased the depressurization time so that the change could be made more gradually; the time was increased by about two seconds. There could be a possibility of lengthening this time further. However, this would require changes with regard to programming the line (Françoise Tétreault, personal communication). Lastly, breaking can be related to the quality of the flesh depending on the season. This varies from one season to the next. During the April test, the hepatopancreas was full and the flesh was quite fat, probably made fragile because spawning was approaching. Tests conducted in the fall on medium mussels compared the interseasonal results. However, the plant is required to cook mussels all year long and cannot limit its activity to a given period.

Overall conclusion

This project consisted in testing the production parameters of the cooker installed at Menu-Mer in order to optimize them for three mussel size classes. Given the inconclusive results from Trial 1 with regard to the finished product quality (very high salinity, large quantity of flesh rejected) with mussels cooked at 2.5/115, the team decided to conduct specific tests on small mussels (under 47 mm) in December 2009 and on medium mussels (47–60 mm) in April 2010. The principle consisted in varying the pressure and the time to optimize cooking and be in a position to recommend a final scenario to the plant, which would then validate it. Throughout the tests, the peeling rate was above the manufacturer's recommendations (98%). For small mussels (under 47 mm), after several tests, the team arrived at an interesting scenario. Cooking at 2/115 seems to be the best scenario because it maximizes the peeling rate and the panelists appreciate the finished product more. For mussels between 47 and 60 mm, the conclusion is more difficult because the overall quantity of rejected flesh (at the plant and the CTPA) was still very high for all cooking scenarios. Moreover, the mussel size was above the targeted category and instead corresponded to mussels over 60 mm. Consequently, the scenarios chosen were probably not adapted and the tests did not enable a particular combination to be recommended. However, it appears that the more the pressure is lowered and the time increased, the better the flesh's quality. At 1/185, the finished product is good but needs a bit more cooking. Pressure is a factor that has an impact on the flesh's quality and whether or not this parameter could be improved, especially when it comes to depressurization, must be checked. If this is possible, the cooking line would require adjustments. Lastly, since the flesh is not of the same quality depending on the season (spawning period), it is difficult to generalize the results obtained with the December and April tests and to recommend use of one scenario for all batches cooked by Menu-Mer over the course of a year. If there is further testing, it must be done in the same season to yield results that are more comparable. In this case, the plant will probably have to adjust the cooking in light of the results discussed in this report.

Bibliographic References

Aquamossel, 2010. sales@aquamossel.nl

CSMOPM, 2005. Guide de démarrage d'une entreprise maricole édition 2005. [Document pdf]. 401 p.

Jim Reeves. Project Manager, Fisheries Division. Charlottetown Metal Products. jreeves@cmpequipment.com

CTPA, 2010. Direction de l’innovation et des technologies. MAPAQ. ctpa@mapaq.gouv.qc.ca

FDA, 2001. Appendix 4 - Bacterial Pathogen Growth and Inactivation. Fish and Fisheries Products Hazards and Controls Guidance. Third Edition. [En ligne]. http://www.fda.gov

Girault L., 2010. Halieutec. LGirault@cgaspesie.qc.ca

MAPAQ, 2009. Les pêches et l’aquaculture commerciales. Bilan 2007 et perspectives. [Document pdf]. 64 p.

MPO, 2008. L’aquaculture au Canada. [Document pdf]. 22 p.

Ibarra D., Couturier C., Mills T. (2000). Calculation of meat yields by mussel growers in Newfoundland. Science Tech publishing.

Sztrygler F., SSHA, ISHA and LeMagnen J., 1990. Evaluation sensorielle : manuel méthodologique. Collection Sciences et techniques agroalimentaires. Lavoisier. 328 p.

Tétreault F., 2010. Menu-Mer Ltée. ftetreault@globetrotter.net

Tétreault F., 2004. Rapport des opérations postrécoltes du printemps 2004 et évaluation de l'impact de l'entreposage humide sur la durée de conservation des moules en conditions printanières. [Document pdf].Rapport commandité par la SODIM. 27 p.

Other Items of Interest