Quality of frozen cooked snow crab (Chionoecetes opilio) meat: The effect of the pre-processing condition

Food Research International 26 (1993) 333-342

Quality of frozen cooked snow crab (Chionoecetes opilio) meat: The effect of the pre-processing condition J. R. Botta, S. L. Keats & B. E. Squires Canada Department of Fisheries and Oceans, Inspection Branch, Seafood Quality Investigations Division, PO Box 5667, St John’s, Canada, NF Al C 5X1

Controlled studies were conducted to assess the effect of the pre-processing condition of raw crab upon the quality of cooked snow crab (Chionoecetes opilio). The results of two different methods of assessing raw snow crab (i.e. (i) visual assessment of the heart action of raw snow crab, and (ii) visual assessment of leg movement of raw snow crab immediately after the raw snow crab were electrically stimulated) were compared to the results of sensory assessment of crab meat from the same snow crab that were cooked, shucked, frozen, stored at -26°C thawed and served. These results clearly revealed that visual assessment of heart action was not a relevant method. In contrast, visual assessment of electrical stimulation was revealed to be a reliable method as well as being an inexpensive, non-destructive, portable and rapid method. Since this study was conducted, the electrical stimulation method has been commercialized. Kev words: Criticallv weak. dead. decomposed, electrical stimulation, heart action, hedonic, lively, preference, quality, sensory assessment, snow crab, weak.

INTRODUCTION

reported that post-mortem queen crab can be preserved at an acceptable grade for about 30 h at 3°C or for 3 h at 13°C. Consequently, the Seafood Quality Investigations Division of the Inspection Branch, Canada Department of Fisheries and Oceans, was requested to investigate the relevance of observed heart action upon the quality of commercially produced frozen snow crab meat, and, if necessary, develop a new method of predicting the quality of commercially produced frozen snow crab meat. The relevance of heart action was assessed by commercially processing snow crab which had been previously classified into a number of different stages of physical condition and by conducting sensory evaluation on this experimentally processed crab meat. The development of a new method of predicting the quality of snow crab meat involved assessing the Crab Life Detector (recently reported by Botta et al. (1992)). This detector consisted of (i) a power source and holster attached to a belt; (ii) a gunshaped stimulator; (iii) two probes; (iv) a lever at the back of the ‘gun’ to adjust the distance between

With the different crab species caught in North America and Europe, it is important, because of either commercial practice or government regulations, that the crab be alive when processed (Edwards, 1979; Department of Fisheries and Oceans, 1982; Early and Stroud, 1982; Anon. 1985, 1987, 1988a, 1989 and 1990; Uglow et al., 1986; Spence, 1989; Ward, 1990). The most common methods of determining if crab are dead are (i) observing the lack of movement of the crab’s legs, which is the practice used in the Alaskan commercial crab fishery (Kramer, D. E., 1989, pers. comm.), and (ii) removing the carapace to observe the absence of heart action, which is the common practice used in the Canadian commercial crab fishery (White, D. R. L., 1990, pers. comm.). It is suspected that in some cases crab remain in an acceptable condition for a period of time after the cessation of the heartbeat. Ke et al. (1981) Food Research International 0963-9969/93/$06.00 0 1993 Canadian Institute of Food Science and Technology 333

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the two probes; (v) a trigger rent of 60 V and 160 mA probes, for a predetermined (vi) a buzzer to indicate that ing between the two probes. This paper describes these the results.

J. R. Botta, S. L. Keats, B. E. Squires

to allow a direct curto flow between the period of time; and this current was flowstudies and discusses

MATERIALS AND METHODS Raw materials During the week of 26 September 1988, raw snow crab (Chionoecetes opilio) were purchased from Beothic Fish Processors Ltd, Badger’s Quay, Newfoundland, Canada. The raw crab were then sorted into lively and critically weak stages of physical condition as described by Botta et al. (1989). In order to determine that the crab were critically weak and not dead, the carapace had to be removed; thus killing the crab. These were the crab that were processed shortly thereafter (just dead), 12 h later (dead 12 h), and 20 h later (dead 20 h). Except for the decomposed crab (Botta et al. 1989) which were left in an open container on the wharf for 48 h, all of the snow crab were sorted and stored in the holding room (3.3”C to 6.l’C). Once sorted, the 103 1 kg of raw snow crab in six different stages of physical condition were processed, using normal commercial procedures. The order in which the six different groups were processed was as follows: lively, critically weak, just dead, dead 12 h, dead 20 h, and decomposed. The processing plant and the equipment (which was dismantled prior to being rinsed) were thoroughly rinsed between processing of each group, to prevent cross-contamination. During the processing of each group, the amount of raw crab entering the processing Iine and the amount of packaged products leaving the processing line were carefully weighed. The leg meat and the claws were processed manually with the aid of mechanical rollers whereas the body meat was automatically shucked using an automatic crab meat extraction drum manufactured by Charlottetown Metal Products, Charlottetown, Prince Edward Island, Canada. Once separately packaged, the body meat, claws and leg meat were frozen in a plate freezer for 3 h and then packed in master cartons and stored at -20°C. A week later the master cartons were placed inside insulated containers and transported to the Northwest Atlantic

Fisheries Centre, St Johns, Newfoundland, Canada, and stored at -26°C. The frozen body meat, claws and leg meat were sampled after 0, 3, and 6 months of storage at -26°C. Immediately after being removed from storage, the body meat, claws and leg meat were divided into separate samples of sufficient crab to serve 10 sensory panellists. The samples of body meat and leg meat were wrapped in oxygen-impermeable film whereas the samples of claws were stored inside sealed plastic bags. All samples were stored at -70°C until required for sensory analyses, within 3 months. During the week of 9 September 1991, snow crab were caught by the fisheries research vessel Shamook in St Mary’s Bay, Newfoundland, Canada. Approximately 300 snow crab were caught and immediately placed inside two 0.7 m3 insulated containers, each with a perforated false bottom and an insulated cover. The crab were iced three parts crab to one part ice. Within 18 h of being caught, the crab in the insulated containers were unloaded at Riverhead, St Mary’s Bay, Newfoundland, Canada and transported to St John’s, Newfoundland, Canada where the live snow crab were transferred into two 2700 litre live holding tanks. Each tank was equipped with a constant flow-through system (6.5 litres of sea water per min) with the temperature regulated at 5°C. During the next 5 weeks, nine different batches of snow crab were removed from the holding tank and each batch was stored at one of nine different combinations of temperature and relative humidity as described in Table 1. Prior to being held at one of the aforementioned conditions, 15 snow crab were stored at room temperature until each crab exhibited no physical movement and very heavy drooping of the legs. A sharp needle was inserted through the carapace into the heart and moved in all directions to ensure the heart was destroyed. Each crab was then immediately placed in the chill room (Table 1) and electrically stimulated every hour, for up to 45 h until the crab failed to physically respond to the stimulation. Whenever the detector was used to determine if snow crab were alive, each probe was placed on a different joint (between a leg and the body) of the same crab and the electrical current was immediately activated. Any movement of the crab’s legs or claws, while the buzzer was ringing, indicated the crab was alive. No movement in the crab’s legs or claws (while the buzzer was ringing) indicated that the crab was not alive.

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Quality of frozen cooked snow crab meat

Table 1. Length of storage time (h) at which raw snow crab, stored at nine different combinations of temperature and relative humidity, physically responded to electrical stimulation (Crab Life Detector) Temperature

5 5 5 8 8

8 11 11 11

(“C)

Relative humidity W)

55 15 95 55 15 95 55 75 95

Storage which failed to electrical

time (h) at first crab respond to stimulation 19 24 26 8 I 11 2 3 7

Once the storage of the crab at all nine different combinations of temperature and relative humidity was completed, a tenth batch of crab was stored at the combination that kept the crab alive for the longest period of time (Table 1). Shortly after each crab of this tenth batch failed to physically respond to the Crab Life Detector, the crabs were cooked in boiling water for 10 min and cooled in cold potable water. The leg meat was shucked manually with the aid of mechanical rollers whereas the body meat was shucked by hand. The leg meat and body meat were separately packaged in O-45 kg capacity waxed cardboard boxes, appropriately labelled, frozen in a plate freezer and stored at -50°C. An eleventh batch of snow crab was removed from the live holding tank, observed to be ‘lively’ (Botta et al., 1989) and immediately cooked for 10 min, cooled, shucked, packaged, labelled, frozen in a plate freezer and stored at -50°C as previously described. Assessment of microbiological quality During the 1988 study, samples of leg meat and body meat from crabs of each of the six conditions were aseptically sampled for microbiological analyses. These samples were placed inside plastic bags and immediately frozen. Upon being thawed, the samples were microbiologically analysed for faecal coliforms, coagulase-positive staphylococci and Listeria monocytogenes using the procedures of Anon. 1988b, 1988~ and 1988d, respectively. Assessment of sensory quality Within each of the nine different combinations of frozen storage time and product categories,

Storage time (h) at which 500/oof crab failed to respond to electrical stimulation

Storage time (h) at which 100% of crab failed to respond to electrical stimulation

23 28 34 10 15 12 8 10 8

25 31 45 13 19 16 10 11 13

samples from each of the six different stages of physical condition were compared with each of the other five different stages of physical condition. With snow crab caught during 1991, leg meat from crab stored at 5°C and 95% relative humidity was compared to leg meat from lively (Botta et al., 1989) snow crab. Similarly, body meat from crab stored at 5°C and 95% relative humidity was compared to body meat from lively (Botta et al., 1989) snow crab. Prior to being evaluated by the sensory evaluation panel, each 1988 and 199 1 sample was removed from -70°C and -50°C respectively, and stored at -10°C for 16-19 h, thawed at 3°C for 3 h and divided into 10-15 g portions which were placed inside glass Petri dishes and coded with three-digit random numbers. Both the 1988 sensory panel and the 1991 sensory panel consisted of 30 untrained panellists. The evaluations were conducted in partitioned booths under ‘north light’ fluorescent lighting. The panellists used room temperature potable water for rinsing their mouths between samples. The sensory evaluation of the body meat, claws and leg meat was conducted using affective testing. During each sensory evaluation session, two samples of the same product category (body meat, claws or leg meat) from crab of different treatments were evaluated. First the panellists evaluated one sample using a nine-point hedonic scale. When the individual panellists were finished with the first sample, the first sensory evaluation form was removed. The panellists then evaluated the second sample using the hedonic scale of the second form (Table 2) but when the hedonic scale of the second form was completed, the panellists had to decide (without looking at the first form) which sample they preferred (Table 2).

J. R. Botta, S. L. Keats, B. E. Squires

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Table 2. The sensory evaluation form used to evaluate the second sample of a set of two samples of crab product and to evaluate which of the two samples the judge preferred during any particular sensory evaluation session Name

Code

Date

Please circle the term that best reflects attitude about the product whose code matches the code on this scoresheet. Like extremely Like very much Like moderately Like slightly Neither like nor dislike Dislike slightly Dislike moderately Dislike very much Dislike extremely Now that you have evaluated both sample and sample you prefer? Please circle the code of the sample which you preferred:

, which sample do

Code Code

YOU MUST MAKE A CHOICE!

Assessment of data For each of the three different 1988 product categories-frequencies of three degrees of likeness/ dislikeness (likeness, neither like nor dislike, and dislikeness) and mean and standard deviation of the assigned hedonic scores were tabulated for each of the 18 different stages of physical condition/length of frozen storage treatment combinations. The results of the paired preferences were analysed for the effect of stage of physical condition within each product category and storage time, using Friedman analysis (Meilgaard et al., 1991). When the Friedman analyses indicated significant differences, comparisons of the different stages of physical condition, within each product category and storage time, were made using Tukey’s honestly significant difference (HSD) procedure for rank data (Meilgaard et al., 1991). Within each of the two different 1991 product categories-(i) frequencies of three degrees of likeness/dislikeness; (ii) preference results; and (iii) means and standard deviations of the assigned hedonic scores were calculated for each of the two treatments. The results of the paired preferences were compared to tabulated critical numbers of correct answers in order to determine if there was a significant difference between treatments (Meilgaard et al., 1991). The yields of the individual final products and

the combined yields of all final products were also tabulated.

RESULTS AND DISCUSSION Relevancy of observed heart action All samples analysed microbiologically were observed to have ~30 faecal coliforms MPN (most probable number) per 100 g and to have < 10 Staphylococcus aureus per gram. In addition, Listeria monocytogenes were not detected in any samples analysed. The Canadian minimum acceptable levels for faecal coliforms, coagulase-positive staphylococci and Listeria monocytogenes are 400/ 100 g, 1000/g and zero, respectively (White, D. R. L., 1990, pers. comm.). Thus, all the cooked and frozen leg meat, body meat were microbiologically acceptable. When evaluated at 0 and 3 months of storage at -26”C, the sensory quality of leg meat (regardless of the physical condition of raw snow crab) was very good (Table 3). With each of these 12 different treatment combinations, over 87% of the samples were liked and less than 10% of the samples were disliked (Table 4). Even when stored at -26°C for 6 months, all of the leg meat (except that from crab which had been assessed to be decomposed) were liked by at least 90% of the

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Quality of frozen cooked snow crab meat

significant differences concerning preferences involved leg meat from crab which were decomposed in the raw state (Table 4). With leg meat stored 6 months at -26°C the significant differences (p I 0.05) concerning preferences involved leg meat from crab which were decomposed in the raw state, or crab which were dead 12 h in the raw state (Table 4). However, the significant differences (p I 0.05) that did not involve leg meat from crab which were decomposed in the raw state have little practical meaning as 90% of leg meat from crab which were dead 12 h prior to being processed were liked (Tables 3 and 4). The quality of the body meat at each of 0, 3, and 6 months storage at -26°C steadily decreased as the stage of physical condition changed from lively to decomposed (Table 5). At 0 months of

panellists (Table 3). However, with leg meat from decomposed snow crab that were stored for 6 months, only 66% of the samples were liked, over 23% of the samples were disliked and the mean sensory score was 59 (Table 3). Only leg meat from crab that were decomposed in the raw state developed lines of blackening on some leg meat after 6 months of frozen storage at -26°C. Lines of blackening were not observed in any other samples. Statistical analysis of the results of preference testing of leg meat stored at -26°C for 0, 3 and 6 months revealed that within each storage time, the physical condition of snow crab in the raw state significantly (p I 0.05) affected the preference of the cooked and frozen leg meat (Table 4). Except for leg meat stored 6 months, all of the

Table 3. Frequencies (%) of three degrees of likeness/dislikeness of snow crab leg meat for each of 18 different stages of physical condition/length of frozen storage treatment combinations

Disliked (%)

Mean + SD

Liked (X)

Neither liked nor disliked (“XI)

0 months of storage Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

95.3 93.3 98.0 94.0 94-o 87.9

2.0 3.3 0.7 3.3 2.6 2.7

2.7 3.3 1.3 2.1 3.4 9.4

7.37 7.34 I.52 7.29 7.20 6.74

* + * f f f

1.13 1.10 0.95 1.05 1.13 1.32

3 months of storage at -26°C Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

94.3 92.0 91.5 92.1 94.6 87.8

2.1 4.1 2.1 3.3 0.6 4.3

2.7 3.4 6.4 4.1 4.6 I.9

7.42 7.24 7.19 7.07 7.21 6.51

f + f f f *

1.08 1.24 1.29 1.19 1.23 1.35

6 months of storage at -26°C Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

94.2 94.0 86.9 90.0 91.5 65.8

2.9 5.3 7.7 2.1 4.3 10.8

2.9 0.7 5.4 7.9 4.3 23.3

7.40 I.43 6.96 6.90 I.22 5.90

* 1.15 f 1.02 f 1.26 f 1.31 _+1.22 * 1.64

Physical condition

Table 4. Results of preference testing of leg meat processed from snow crab

Condition

of the raw snow crab

Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

Length of time leg meat stored at -26°C” 0 months

3 months

6 months

60,Oa 52.la 57.3a 50.7a 50,Oa 29.3b

56,Oa 55.3a 53.3a 45.3ab 52,Oa 31.3b

62.0a 56,Oab 40,Oab 41.3b 50.6ab 12.oc

“The values are percentages of the samples evaluated that were preferred. Within each of the different storage times, values not sharing the same letter were significantly different (p 2 0.05).

J. R. Botta, S. L. Keats, B. E. Squires

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Table 5. Frequencies (“/) of three degrees of likeness/dislikeness of snow crab body meat for each of the 18 different stages of physical condition/length of frozen storage treatment combinations Physical condition

Liked W)

Neither liked nor disliked (%)

Disliked (%)

0 months of storage Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

37.3 26.0 20.7 24.7 11.4 2.9

20.0 18.0 10.0 11.3 8.7 5.0

42.7 56.0 69.3 64.0 79.9 92.1

4.76 4.13 3.71 4.14 3.06 2.12

f f + f + +

3 months of storage at -26’C Lively Critically weak Just dead Dead 12 h Dead 20 h Rotten

21.4 11.3 13.3 7.3 2-7 0.0

12.7 13.3 8.7 8.0 5.3 1.3

66.0 75.4 78.0 84.7 92.1 98.6

4.03 3.47 3.13 3.19 2.49 1.54

* 1.62 f 1.48 + 1.68 +I 1.43 + 1.36 f 0.84

6 months of storage at -26°C Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

14.0 12.0 10.0 12.7 8.0 0.7

18.7 16.7 10.7 9.3 6.0 1.3

67.3 71.3 79.3 78.0 86.1 97.3

3.79 3.63 3.35 3.23 2.80 1.85

+ f + f f +

frozen storage, the body meat from snow crab that were lively in the raw state was liked by 37.3% of the panellists, disliked by 42.7% and had a mean sensory score of 4.76 (Table 5). However, body meat from snow crab that were decomposed in the raw state and stored at -26°C for 6 months after being processed was liked by 0.7% of the panellists, disliked by 97.3% and had a mean sensory score of 1.85 (Table 5). The body meat from crab that were dead 20 h in the raw state was slightly dark and had developed a few black specks only after 6 months of frozen storage at -26°C. However, the body meat from crab that were decomposed in the raw state was quite dark with a large number of small black specks throughout the meat, even at 0 months of frozen storage.

Mean f SD

I.56 1.82 1.84 1.63 1.68 1.36

1.54 1.56 1.50 1.64 1.57 I.20

Statistical analysis of the results of preference testing of body meat stored at -26°C revealed that with 27 of the 45 comparisons, the condition of raw crab significantly (p I 0.05) affected the preference of cooked body meat (Table 6). The vast majority of these significant comparisons involved cooked and frozen body meat from snow crab that were decomposed, dead 20 h, dead 12 h, and just dead, respectively, in the raw state (Table 6). Although often preferred (Table 6) the sensory quality of body meat, from both critically weak crab and lively crab, was low (Table 5). Depending upon the length of storage (at -26”Q 42.7% to 75.4% of these samples were disliked (Table 5). Thus, even when the stage of physical condition was good, the sensory quality of all of the cooked

Table 6. Results of preference testing of body meat processed from snow crab Condition

of the raw snow crab

Length of time body meat stored at -26’C” 0 months

Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

72.7a 59.3abc 50.7bc 62.7ab 43.3c 8.0d

3 months

6 months

76.7a 72,Oa 52.6b 53.3b 38,Ob 7.3c

70.0a 66.7ab 57.3ab 49.3bc 36.0cd 20.0d

“The values are percentages of the samples evaluated that were preferred. Within each of the different storage times, values not sharing the same letter were significantly different (p 5 0.05).

Quality of frozen cooked snow crab meat

and frozen body meat was low (Table 5). The lower sensory quality of the cooked and frozen body meat is believed to be a result of the method of processing. During the processing of the body meat, the sections of the crab which contained the body meat was automatically washed extensively to remove the meat from the shell. Most of the panellists felt the body meat was ‘washed out’. The legs and claws were not subjected to this extensive washing as they were processed manually. In general, the quality of the claw meat was not as good as that of the leg meat, but it was better than that of the body meat (Tables 3, 5, and 7). With claws that were stored at for 0 months, the claw meat from crab that were lively in the raw state was liked by 88% of the panellists, disliked by 6% of the panellists and had a mean sensory score of 7.12 (Table 7). As the treatment changed from lively to decomposed at 0 months of frozen storage, the acceptability decreased until the claw meat was liked by 5 1.3% of the panellists, disliked by 47.6% and had a mean sensory score of 4.96 (Table 7). However, when claw meat from crab of the lively treatment were stored at -26°C for 6 months, the meat was liked by 67.6% of the panellists, disliked by 26.4% and had a mean sensory score of 5.92% (Table 7). Regardless of the physical condition of the raw snow crab, storing the processed claws for 3 and 6 months, respec-

339

tively, at -26°C always caused a noticeable decrease in the percentage of panellists that liked the samples (Table 7). The claws from the crab that were decomposed in the raw state, developed some lines of blackening on the edges of the meat only after 3 and 6 months of frozen storage at -26°C. Similar lines of blackening were only observed in a few of the claws from crab that had been dead 20 h in the raw state, and had been stored frozen for 3 and 6 months at -26°C. Statistical analysis of the results of preference testing of claw meat stored at -26°C revealed that with 15 of the 45 comparisons, the condition of raw crab significantly (p I 0.05) affected the preference of cooked and frozen claw meat (Table 8). The vast majority of these significant comparisons involved meat from snow crab that were decomposed in the raw state (Table 8). The combined yield of snow crab that were lively in the raw state was noticeably lower (at least 1.0 percentage point) than that of crab which were critically weak, just dead, or dead 12 h in the raw state (Table 9). This lower yield of crab in the lively treatment appeared to be primarily caused by a low yield of leg meat (Table 9). Since these raw crab were lively when processed, this lower yield was probably caused by the meat being more firmly attached to the shell (of the leg) than was the meat of the crab that were critically weak, just

Table 7. Frequencies (%) of three degrees of likeness/dislikeness of snow crab claws for each of 18 diKerent stages of physical condition/length of frozen storage treatment combinations Liked (%)

Neither liked nor disliked (%)

Disliked (%)

0 months of storage Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

88.0 88.0 85.0 92.0 73.7 51.3

6.0 6.0 4.0 2.0 3.8 1.3

6.0 6.0 11.0 6.0 22.5 47.6

7.12 6.97 6.86 7.08 6.06 4.96

f f * f f +

1.32 1.29 144 1.27 1.92 2.18

3 months of storage at -26°C Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

71.0 78.0 81.1 76.0 64.4 39.0

3.0 4.0 4.4 8.0 4.4 10.0

26.0 18.0 14.4 16.0 31.2 51.0

5.99 6.40 6.55 6.50 5.49 4.57

f f f f + +

2.04 1.61 1.71 1.71 2.23 2.17

6 months of storage at -26T Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

67.6 66.7 76.0 73.0 61.8 35.0

6.3 8.9 7.0 8.0 5.6 3.0

26.4 24.4 17.0 19.0 32.6 62.0

5.92 5.91 6.37 6.23 5.53 4.07

f 2.04 f 1.98 f 1.66 Z!I1.79 f 2.18 f 2.47

Physical condition

Mean f SD

J. R. Botta, S. L. Keats, B. E. Squires

340

Table 8. Results of preference testing of claw meat processed from snow crab Condition

of the raw snow crab

Length of time claw meat stored at -26°C”

Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

0 months

3 months

6 months

75,Oab 53,Oabcd 52.0cd 62.0bcd 33.8de 13.8e

58,Oab 53,Oab 65.6a 61,Oab 43.3bc 2o.oc

52.5a 58.9a 64.5a 58,Oa 41.5ab 25.0b

“The values are percentages of the samples evaluated that were preferred. Within each of the different storage times, values not sharing the sake letter were significanily different (p 5 0.05).

dead, or dead 12 h in the raw state. However, as the physical condition of the raw crab changed from dead 12 h to dead 20 h to decompose, the yield of both body meat and leg meat decreased dramatically (Table 9). These changes were probably due to autolysis.

sory quality of leg meat from control samples (Table 10). Similarly, with body meat, the sensory quality of treated samples did not significantly differ (p > 0.05) from that of control samples (Table 10). General discussion

New method of predicting the quality of snow crab meat The length of time until raw snow crab failed to physically respond to electrical stimulation (Crab Life Detector) was highly dependent upon both temperature and relative humidity (Table 1). Relative humidity appeared to have the greatest affect at the lowest temperature whereas temperature appeared to have the greatest affect at the highest relative humidity (Table 1). At a high temperature (1 l°C) and a low relative humidity (55%), snow crab failed to physically respond to electrical stimulation 2-10 h after the heart stopped beating (Table 1). In contrast, at a combination of low temperature (5’C) and a high (95%) relative humidity, snow crab failed to physically respond to electrical stimulation 2G45 h after the heart stopped beating (Table 1). However, the sensory quality of all leg meat from treated samples was not significantly different (p > 0.05) from the sen-

During the 1988 study, body meat was 100% commercially processed body meat whereas, typically, commercially processed body meat is mixed with tip meat and broken leg meat and sold as ‘salad’. Thus, depending upon the exact mixture of body meat, tip meat and broken leg meat, the sensory quality of salad from commercially processed snow crab would be much higher than that of the corresponding body meat in the 1988 study. The conclusions of Dewar et al. (1969) and the statements of other researchers (Early, 1965; McAllister, 1967; Blackwood et al., 1969; Dassow & Learson, 1976; Dewar, 1980) clearly specify that the processing of dead crab will only yield a reject product or an inferior product with a very short shelf-life. The results of both the 1988 study and the 1991 study do not support these previously published results/statements. Factors that individually, at least partially, explain this discrepancy are as follows: (i) during the 1988 study the dead

Table 9. Yield (%) of individual final products and combined yield of processed snow crab Physical condition of raw crab

Weight (kg) of raw crab processed

Yield (%) of individual final products Claws

Body meat

Tip meat

Leg meat

Broken meat

Combined yield (%) of all final products

Lively Critically weak Just dead Dead 12 h Dead 20 h Decomposed

183.6 196.4 153.6 165.5 182.7 149.1

4.2 4.7 4.4 4.8 3.9 4.3

7.8 7.3 7.6 7.2 5.3 2.3

2.4 2.4 2.3 2.3 1.5 1.1

4.6 5.9 6.2 6.8 6.3 4.0

1.3 1.2 0.8 0.85 0.5 1.3

20.3 21.5 21.3 21.95 17.5 13.0

Quality of frozen cooked snow crab meat

341

Table 10. Frequencies (%) of three degrees of likeness/dislikeness of leg meat and body meat from lively snow crab (control samples) and from snow crab that had been stored, at 5°C and 95% relative humidity, until the crab failed to physically respond to electrical stimulation (treated samples) Liked WJ)

Neither liked nor disliked (“XI)

Disliked (o/o)

Number of samples preferred

Mean & SD

Leg meat Control Treated

83.3 16.1

3.3 10.0

13.3 13.3

19h llh

6.63 + 1.83 6.33 + 1.54

Body meat Control Treated

50.0 56.6

3.3 6.7

46.7 36.1

15” 15h

5.03 + 1.77 5.17 f 1.76

Samples”

un = 30. ‘Not significantly different at the 5% level.

crab was not removed from the chilled holding room until immediately before it was butchered and processed promptly thereafter; (ii) during the 1988 and 1991 studies body meat, leg meat (and claw meat in the case of the 1988 study) were all evaluated separately; and (iii) the results of both studies concern only frozen snow crab, not canned snow crab. The importance of the effect of canning versus freezing upon the quality of crab meat cannot be over emphasized. If any blood is contained in canned crab meat, the copper in the blood causes the crab meat to turn blue or black, but this is not true for crab meat that is frozen (Ward, 1990). However, during 1988 the vast majority of snow crab processed within the Newfoundland region was frozen. In fact, of the 14 crab processing plants operating during 1988, only two plants were canning crab. Although the results of the present studies differ from a number of previously mentioned studies/statements, they are supported by the results of Ke et al. (1981) who reported that post-mortem queen crab (also known as snow crab) can be preserved at an acceptable grade for about 30 h at 3°C and for 10 h at 13°C. Thus, it should be stressed that the sensory results of the 1988 and 1991 studies apply only to crab that are chilled (3-6°C) until immediately before being cooked and processed. Although the results of the 1988 study indicated that the sensory quality of some of the crab meat (particularly leg meat) from crab that were decomposed (Table 1) in the raw state was quite good, these results must be interpreted very carefully as this was a controlled study. The results of the 1991 study clearly revealed that the sensory quality of snow crab meat, from crab that responded to the Crab Life Detector, was equal to that from a snow crab that was lively, immediately prior to being cooked. How-

ever, snow crab that only weakly respond to the Crab Life Detector must be cooked immediately, thereby ensuring the high sensory quality of this crab meat that is physiologically ‘alive’. Since the Crab Life Detector is also portable, very rapid (approximately one second) to use, non-destructive and inexpensive (approximately $800, Canadian funds), it has great potential in the snow crab industry to be used to cull crab prior to being cooked, processed and frozen. The results of the 1991 study strongly indicate that use of the Crab Life Detector would greatly reduce the amount of wastage (discarding crab that were, in fact, acceptable). However, the results of the 1988 study indicate that with snow crab without heart action the yield of the body meat, but not leg meat, decreased after approximately 20 h of chilled storage. The actual time required to reduce yield would depend upon the temperature and humidity at which the crab was stored. The 1991 results support those of Kaneps and Boothroyd (1991) who reported that there was a strong correlation between the capacity of post-mortem lobsters to respond to the Crab Life Detector and the resulting cooked tail meat quality. Since July 1991 the Crab Life Detector has been commercialized (see Acknowledgements). In conclusion, the results of the 1988 study revealed that the procedure of rejecting snow crab to be cooked and frozen, because of absence of heart beat is not relevant. The sensory quality of crab meat produced from snow crab that were dead (lack of heart action) for 20 h, at 3-6°C was quite good as was the crab meat stored at -26°C. The results of the 1991 study revealed that applying the Crab Life Detector (electrical stimulation) to raw snow crab was an effective method of predicting the quality of cooked and frozen snow crab meat.

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J. R. Botta, S. L. Keats, B. E. Squires

ACKNOWLEDGEMENTS The use of facilities and materials and the assistance of management and staff of Beothic Fish Processors Ltd, Badger’s Quay, Newfoundland, Canada is gratefully appreciated. The authors sincerely thank L. Dalton, E. Dawe and B. Wheeler for their technical assistance. The authors recognize the commercialization of the Crab Life Detector by Newtech Instruments Ltd, 63 Thorburn Road, St John’s, Newfoundland, Canada.

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1992)

8 October 1992; accepted 28 December