PURIFICATION AND CHARACTERIZATION OF PHENOLOXIDASE ISOFORMS FROM TAIWANESE BLACK TIGER SHRIMP (PENAEUS MONODON)1

Two phenoloxidase (PPO) isoforms were purified from Taiwanese black tiger shrimp (Penaeus monodon) purified via ammonium sulfate precipitation and high performance hydrophobic interaction chromatography on phenyl Sepharose CL-4B. Optimal DL-ã-3, 4-dihydroxyphenylalanine (D, L-DOPA) oxidation by these isoforms was observed to occur at pH 6.0, and at 45°C. The isoforms showed both mono- and di-PPO activities, and preferential medabolism of both monoand di-phenolic substrates lacking a carboxyl group either directly attached to the ring, or in the side chain moiety of the phenolic structure.     

QUALITY ASSESSMENT OF FARMED BLACK TIGER SHRIMP (PENAEUS MONODON) IN SUPPLY CHAIN: ORGANOLEPTIC EVALUATION

Organoleptic quality of the farmed shrimp ( Penaeus monodon ) throughout the supply chain was investigated under two conditions – normal practices using no ice and under experimental conditions using ice at the ratio of 1:1 (ice : shrimp). Overall, organoleptic acceptability score ranged between highly acceptable and moderately acceptable (shrimp farm  =  8.8, depot  =  5.47, commission agent  =  6.67 and processing plant  =  6.33 in a scale of 10) for shrimp under normal practices and a relatively better score and quality of shrimp under experimental conditions as judged by the organoleptic evaluation. The overall organoleptic score between the two experiments did not differ significantly ( P ≤  0.05).

PRACTICAL APPLICATIONS

From the moment the shrimp is caught, the deterioration process starts and its quality is affected. The most frequent problem is temperature fluctuation in raw materials due to (1) mishandling after harvest, (2) lengthy transportation times to processing plants or (3) manual processing where shrimp are kept for several hours waiting under each stakeholder supply chain. These result in uncertainty of the shelf life and lower quality products. A score sheet is prepared based on well-defined characteristic changes (appearance, flavor, odor and texture) that occur in the deteriorative process of shrimp. Demerit points are assigned to attributes and the resulting scores prescribe overall acceptable quality. Considering food safety, organoleptic evaluation is one of the most often used simple methods for assessing freshness and quality in the fish and shrimp inspection services, and routinely applicable on all levels of marketing from harvesting to the processing plants.     

IMMUNOHISTOCHEMICAL LOCALIZATION OF PHENOLOXIDASE IN HEPTOPANCREAS, MUSCLE AND EPIDERMIS OF GRASS SHRIMP (PENAEUS MONODON F.)

The in vivo sites of melanogenesis in grass shrimps (black tiger shrimp, Penaeus monodon F.), unirradiated and irradiated (5 kGy), was investigated by determining the location of phenoloxidase in heptopancreas, muscle and epidermis using an immunocytochemical technique with electron microscopy. Specific labelling by gold-IgG complex particles was observed over the microvillar border, apical surface and endoplasmic reticula in hepatopancreas, sarcoplasmic reticula in muscle and chromatophores in epidermis. These results suggest that phenoloxidase is synthesized in R-cells of heptopancreas, or chromatophores in epidermis and transferred to muscle. There was no difference in the location of phenoloxidase in shrimp tissues that were nonirradiated and irradiated. Consequently, R-cells in heptopancreas and chromatophores in the epidermis were considered to be important in studying melanogenesis in shrimps.     

BIOCHEMICAL AND MORPHOLOGICAL CHANGES IN GRASS SHRIMP (PENAEUS MONODON) MUSCLE FOLLOWING FREEZING BY AIR BLAST AND LIQUID NITROGEN METHODS

Grass shrimp (Penaeus monodon) at prerigor stage were frozen at rates ranging from 3.41 to 16.1 cm/h by using an air blast freezer at –35C or a liquid nitrogen freezer at – 80, – 100 and – 120C. Immediately after freezing, the spacing between muscle fiber bundles was larger (21.3 ± 5.7 μm) in shrimp frozen at 3.4 cm/h than in shrimp frozen at 8.6 ～ 16.1 cm/h (6.0 ± 0.6 to 8.8 ± 1.1 μm, respectively). The spacing between fibers increased during frozen storage at – 20C and remained different for slow and fast frozen samples within 4 weeks. The lysosomal fraction from fresh shrimp had more cathepsin D-like activity (187 units/mg protein) than that from shrimp frozen at 10.2 cm/h (179 units/mg protein) and at 3.4 cm/h (86 units/mg protein). During frozen storage at – 20C the cathepsin D-like activity of intact lysosomes decreased and was negligible after 4 weeks. The solubility of muscle protein in 0.6 M KCl was not consistently different in samples frozen by different methods and stored at – 20C for 4 weeks. Liquid nitrogen freezing produced frozen shrimp of higher muscle integrity than air blast. But the differences disappeared after one-month storage at – 20C.     

EFFECT OF TRISODIUM PHOSPHATE ON LISTERIA MONOCYTOGENES ATTACHED TO RAINBOW TROUT (ONCORHYNCHUS MYKISS) AND SHRIMP (PENAEUS SPP.) DURING REFRIGERATED STORAGE

The potential of using trisodium phosphate (TSP) to reduce bacterial populations in fresh fishery products was explored since TSP has recently been approved by USDA for its usage in poultry processing to eliminate Salmonella contamination. Fresh headed shrimp and rainbow trout fillets were inoculated with L. monocytogenes before dipped in tap water, 10% TSP, or 20% TSP solutions and overwrap-packaged. Surface pH values, psychrotrophic plate counts, and L. monocytogenes counts of inoculated shrimp and trout fillets were determined after 0, 3, 6, and 9 days of storage at 4C. The TSP treatment resulted in relatively high residual surface pH values (11–12) initially in both shrimp and trout fillets. Compared to tap water dipping, TSP treatment did not significantly reduce psychrotrophic or Listeria populations in shrimp. However, the 20% TSP treatment significantly (p < 0.05) lowered 0-day psychrotrophic and L. monocytogenes counts of trout fillets and remained effective for 6 days during storage at 4C .     

A NEW APPROACH TO CORRELATE TEXTURAL AND COOKING PARAMETERS WITH OPERATING CONDITIONS DURING DOUBLE-SIDED COOKING OF MEAT PATTIES

Cooking and textural parameters during double-sided cooking of hamburger patties were correlated with volume-averaged temperature at the end of the cooking process and gap thickness between plates. Frozen patties were cooked in a clamshell grill set at different plate surface temperatures (177C; 191C; 204C; 218C), for different gap thicknesses (9.65 mm; 10.55 mm; 10.55 mm; 11.05 mm) for 120 s. A decrease in the gap thickness and an increase in the plate surface temperature resulted in an increase in the cooking loss values (24–36%) and in a decrease of press juice values (8–25%). The values of peak load (183–215 N), modulus (16–19 N/mm), work needed in shearing (2300–2800 Nmm), hardness (25–32 N), cohesiveness (0.76–0.83), and chewiness (107–152 Nmm) of the patties increased when the gap thickness decreased and the plate surface temperature increased. There was no effect of the variables studied on springiness. The correlation equations involving the operating variables and quality parameters obtained are simple and useful in developing optimal process conditions.     

SHELF-LIFE EXTENSION OF RAW BROWN SHRIMP (PENAEUS AZTECUS) WITH POTASSIUM SORBATE IN ICES AND DIPS

The shelf-life of shrimp, as indexed by psychrotrophic bacterial counts, was extended approximately 1.0, 1.9, and 3.1 days using levels of 0.05%, 0.1%, and 0.2% potassium sorbate-containing ice, respectively. Shelf-life was extended an additional 0.5 to 2.5 days when a 3% potassium sorbate dip was administered prior to storage on modified ice. In all cases, potassium sorbate extended the lag phases of the spoilage bacteria.     

TEXTURE AND COLOUR CHANGES IN MEAT DURING COOKING RELATED TO THERMAL DENATURATION OF MUSCLE PROTEINS1

Differential scanning calorimetry was used to select temperatures that diferentiated between thermal denaturation of the three major structural protein species in bovine muscle: myosin, collagen and actin. Samples of m. semimembranosus, m. semitendinosus and m. psoas major were heated to those different temperatures and evaluated sensorially. Three groups of sensory properties were needed to describe the main texture changes observed in the meat: 1. Firmness 2. Fiber cohesivity, bite-off force, residual bolus 3. Juiciness Firmness increased with thermal denaturation of the myofibrillar proteins (myosin; 40-60d?C and actin; 66-73d?C). Fiber cohesivity etc. decreased with collagen denaturation (56-62d?C). Reduction in juiciness was primarily associated with actin denaturation, while cooking loss increased over the whole temperature range. The property “total chewing work”, a composite of the first two texture groups mentioned, yielded like the judges' “total texture preference”, optimal texture in the 60-67d?C temperature region, implying denatured myosin and collagen but native actin. This meat was light pink-gray in colour, while the cooking juice released was dark red.     

MODELLING THE MECHANICAL AND HISTOLOGICAL PROPERTIES OF CARROT TISSUE DURING COOKING IN RELATION TO TEXTURE AND CELL WALL CHANGES

A tensile test was used to measure four mechanical properties of carrot tissue cooked under various time-temperature conditions. A kinetic model describing the changes of these mechanical properties measured during cooking was developed. The histological properties of the rupture surfaces caused by the mechanical testing were investigated. The kinetic model was found capable of predicting the changes in the rupture mechanism of the cell walls. Determining the percentage of cell wall ruptures proved to be an accurate method to assess the textural state of carrot tissue during cooking as compared to the measurement of the mechanical properties.     

EFFECT OF FEED DIET ON AMINOPEPTIDASE ACTIVITIES FROM THE HEPATOPANCREAS OF WHITE SHRIMP (PENAEUS VANNAMEI)

White shrimp (Penaeus vannamei) were fed one of seven diets for 30 days. Diets contained 85% of a reference ration and 15% of either anchovy, tuna waste meal, deboned fish meal, langostilla crab meal, soybean meal, menhaden meal A, or menhaden B as a protein replacer. At the end of the feeding trial, animals were sacrificed and 10 aminopeptidase activities of the hepatopancreas tissue were assayed. The hepatopancreas tissues contained Arg-, Leu-, His-, Ile-, Lys-, Met-, Thr- and Val-aminopeptidase activities but no activity was detected for Phe-aminopeptidase. Leu-aminopeptidase activity was inhibited by Zn⁺² and Mg⁺² salts and activity was also inhibited when more than 0.2 mg of hepatopancreas extract protein was included in the assay. Principal component analysis was used to determine whether diet had an influence on hepatopancreas
aminopeptidase activities. The aminopeptidase activities were greater for animals fed a diet containing menhaden fish meal B. This was principally the result of the higher levels of Met-, Val-, Pro-, Lys-, and Leu-aminopeptidase activities in animals fed menhaden fish meal. Menhaden fish meal B had a lower nutritional quality for shrimp than the other protein replacers. Seven of the 10 essential amino acids for shrimp were present at less than 100% of the recommended values. On the other hand, shrimp fed soybean meal replacer contained lower amounts of aminopeptidase activity, notably Gly- and Met-aminopeptidase activities, and the meal was of excellent quality having only one limiting amino acid. The results indicate that the shrimp diet can influence proteolytic activity of the hepatopancreas tissue. This is significant to the seafood technologist since previous studies showed that hepatopancreas proteases can leach into the meat postmortem and cause tissue softening.     

MATHEMATICAL MODEL to PREDICT EFFECT of TEMPERATURE ABUSE IN MAP SYSTEMS APPLIED to PACIFIC HAKE (MERLUCCIUS AUSTRALIS)

This paper describes the development of a mathematical model to predict consequences of temperature abuse on shelf‐life of Pacific Hake packed in modified atmosphere. the model includes simultaneous heat and mass transfer phenomena coupled with a predictive shelf‐life model for packed fish. the model was solved using an explicit finite difference scheme. the simulated results are in good agreement with the experimental results. the model predicted temperature, gas concentration and relative humidity within < 0.6[°C], < 1.43% and 3%, respectively. Shelf‐life model predicts that, even if the fraction of the total storage time at an abusive temperature is small (4.3%), the reduction in shelf‐life can be significant (25%). the predicted shelf‐life without temperature abuse is consistent with literature results. Optimum MAP systems must reach pseudoequilibrium headspace gas composition which maximize the shelf‐life of food considering possible environmental temperature abuses.     

PURIFICATION AND CHARACTERIZATION OF CHYMOTRYPSIN FROM PENAEUS VANNAMEI (CRUSTACEA: DECAPODA)

The purification and characterization of a chymotrypsin from the hepatopan-creas of the white shrimp Penaeus vannamei is described. Only one chymotrypsin was detected in contrast to other shrimp that have two major forms. P. vannamei chymotrypsin has a molecular mass of 33.2 kDa and a pI of 3.1. The molecular mass is high relative to other penaeid chymotrypsins. The proteinase is acid labile and exhibits optimum activity at pH 8. The enzyme is thermostable both at 25 and 37C. It is a serine proteinase. Phenylmethylsulphonyl fluoride and soybean trypsin inhibitor blocked the activity of the enzyme, and it was not affected by chymotrypsin inhibitors such as tosyl-PheCH₂Cl or benzyloxycarbonyl-Phe-CH₂Cl. Protein profiles of the hepatopancreas from two populations varied     

COMPARISON OF METHODS TO VERIFY END POINT COOKING TEMPERATURE OF CHANNEL CATFISH (ICTALURUS PUNCTATUS) FILLETS

Cooking to 63C for 15 s remains an important step to ensure safe fish for human consumption. Methods for heat process verification have not been validated for channel catfish ( Ictalurus punctatus ). The present research compared extractable protein quantification, lactate dehydrogenase, acid phosphatase and catalase activity assays for verification of internal cooking temperature of channel catfish fillets. Ground raw catfish fillet samples (fresh and frozen) were cooked to 55, 60, 62, 63, 64 and 66C. Extractable protein, acid phosphatase and catalase activities decreased as internal cooking temperature increased, but lactate dehydrogenase activity remained unchanged. Samples cooked to 63C had extractable protein concentrations between 9.11 and 10.02 mg/g (95% confidence). Catalase was rapidly inactivated between 55 and 60C and may be suitable for identification of severely undercooked product. Acid phosphatase activity was influenced by method of storage (fresh versus frozen). A method based on total extractable protein appeared to be the most promising for determining the end point cooking temperature of catfish.

PRACTICAL APPLICATIONS

The most precise and reliable method to verify maximum cooking temperature attained during heat treatment of catfish fillets was total extractable protein. This finding may be useful for critical control point verification and may be valuable where claims of foodborne illness associated with catfish consumption are being litigated or investigated. To confirm gross undercooking, an easier test would be to measure catalase activity.