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.     

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.     

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.     

EFFECTS OF RETORTING AND STORAGE ON LIQUID MASS TRANSFER IN CANNED SKIPJACK (KATSUWONAS PELAMIS) MUSCLE

Mass loss of precooked tuna muscle during retorting and storage in cans impacts cannery yield and throughput. Changes in moisture content and mass of frozen, thawed, precooked tuna muscle chunks, canned in water, were determined after retorting and through five weeks of subsequent storage. Canned tuna pieces were retorted to equivalent lethality (F_o-value of four) for different time and temperature processes. Retorting at a lower temperature, longer time resulted in less mass loss than higher temperature, shorter time processes. Canned storage of up to five weeks had no effect on muscle mass or moisture content.     

QUANTITATIVE ANALYSIS OF FLAVANOIDS IN BARLEY,HOPS AND BEER BY HIGH-PERFORMANCE LIQUID CHROMATOGRAPHY (HPLC)

This work describes a method for the quantitative analysis of flavanoids of barley, hops and beer by HPLC. This method requires only about 4 h and it gives representative and reproducible results. A few results obtained by this method are given for barley and hops.     

TEMPERATURE ACCLIMATION OF ATLANTIC COD (GADUS MORHUA) AND ITS INFLUENCE ON FREEZING POINT AND BIOCHEMICAL DAMAGE OF POSTMORTEM MUSCLE DURING STORAGE AT 0° and -3°C

The freezing point of muscle fluid from Newfoundland Atlantic cod held at ambient sea water temperature was as low as - 1.30°C in March and as high as - 0.80°C in July. Muscle fluid from cod held live at 0°C for 3 weeks had a freezing point of - 1.02°C in contrast to a muscle fluid freezing point of - 0.90°C for cod acclimated at 10°C prior to sacrifice. Muscle fluid from cold acclimated cod exhibited 0.40°C thermal hysteresis indicating freezing point depression was influenced by antifreeze substances. The following indices of deterioration were measured in muscle sections stored at 0°C or - 3°C for 21 days: extractable protein (EP), free drip (FD), extracellular area (EA), trimethylamineoxide (TMAO), trimethylamine (TMA), dimethylamine (DMA), free amino acids (AA), and pH. Muscle sections at the anterior end of fillets, from myotomes 9–20, prepared using aseptic technique and treated with antibiotic showed less evidence of biochemical deterioration: (a) when stored at - 3°C compared to 0°C with respect to EP, AA, EA; (b) when prepared from fish acclimated at 0°C compared to at 10°C and stored at 0°C or - 3°C with respect to EP, EA, FD, AA. Negligible changes in pH, TMA and DMA occurred during 21 days storage at either temperature. TMAO decreased more during storage at-3°C than at 0°C.     

QUALITY CHANGES IN PEACH PUREE BY BROWN ROT (MONILINIA FRUCTICOLA) AND BIOCONTROL AGENTS1

Tissue loss of peach fruit and quality changes of peach puree caused by Monilinia fructicola were assessed along with use of Bacillus subtilis, Pseudomonas cepacia, and Pseudomonas corrugata as biocontrol agents. Fruits were inoculated with a conidial suspension (10⁶/mL) of M. fructicola and held at room temperature (25 ± 1C) for four days. On day 4, a 3. 7 cm diameter lesion corresponded to 8.8% pulp loss. Peach puree was prepared with noninoculated peaches (control) and with inoculated peaches containing 0 (control), 1, 3 and 5% diseased tissue. As percentage of diseased tissue increased, puree color became darker and less yellow; pH, soluble solids/acidity ratio increased; while acidity, soluble solids, and viscosity decreased. Fruits were treated with suspensions (10⁸–10⁹ colony forming units/mL) of either B. subtilis, P. cepacia or P. corrugata and then challenged with the pathogen M. fructicola. B. subtilis provided the best inhibitory effect with 98% control followed by P. corrugata and P. cepacia with 60 and 23% control, respectively. Following removal of diseased tissue and processing, the     

CHEMICAL COMPOSITION AND POSTMORTEM CHANGES IN SOFT TEXTURED MUSCLE FROM INTENSELY FEEDING ATLANTIC COD (GADIUS MORHUA, L)

Soft textured fillets from postspawning Atlantic cod caught during the influx of capelin exhibited significantly more drip than fillets from fish caught at other times of the 1983 inshore fishing season. The extent and rate of pH decline, protein, collagen and temperature of the muscle were not distinctive in fish caught during the influx of capelin. The muscle from these fish were unique in exhibiting a rapid and relatively low ultimate pH together with a stable pH after the onset of rigor mortis. The number of capelin present in the stomach of cod at the time of catch was positively related (r = 0.92) to the amount of free drip recovered from the fillets.     

CHANGES IN QUALITY DURING STORAGE OF VACUUM-PACKED SEA BASS (DICENTRARCHUS LABRAX, Linnaeus, 1758) COOKED BY DIFFERENT METHODS

This work evaluates the chemical, microbiological and sensorial characteristics of vacuum-packed sea bass processed by different cooking methods under different time/temperature conditions and storage at 2C. The heat treatments applied in core were: 5 min, at 180C for frying, 30 mi, at 230C for baking, and 16 min at 2450 MHz for microwave cooking. Chemical, microbiological and sensory quality changes were investigated periodically. In all groups; the total viable and psycrophilic bacteria counts increased throughout the storage period of vacuum-packed sea bass. Total viable counts of fried, baked and microwave-cooked sea bass reached 6.06, 7.00, 7.24 log cfu/g, respectively, after 15 days. On day 15, the total volatile base nitrogen (TVB-N) value of microwave-cooked sea bass exceeded the allowable limit of 38.72 mg/100 g, whereas the TVB-N value of fried and baked sea bass reached 22.46 and 29.85 mg/100 g, respectively. Therefore, it can be concluded that frying at 180C for 5 min in core is the most effective cooking method to ensure the safety and extend the shelf life of fried sea bass, preserving its microbiological guality.

PRACTICAL APPLICATION

This study establishes the chemical, microbiological and sensory quality of vacuum-packed sea bass and emphasizes the relevance of the quality changes of the different cooked sea bass. Heat treatments and storage temperatures are very important to ensure the safety of the fish product.     

EFFECTS OF TRIMMING AND COOKING BY SEVERAL METHODS ON POLYCHLORINATED BIPHENYLS (PCB) RESIDUES IN BLUEFISH

Bluefish were captured in the Atlantic Ocean near Long Island to study the effects of trimming and cooking on reduction of residues of polychlorinated biphenyls (PCBs). The mean concentration (standard error) of PCBs in the raw untrimmed fillets of the fish captured was 1.76 ± 0.17 ppm on a dry weight basis with range of 0.58 to 7.47. A direct relation between the concentration of PCBs in the raw fish fillets and their fresh weight showed a correlation coefficient of only 0.39. About twice the concentration of PCBs were found in the skins as compared to the dorsal and ventral sections of the raw fillets. Trimming the fillets resulted in a reduction in PCB residues averaging 59.4% with a further average reduction of 7.4% from baking, broiling, frying or poaching. There were no significant (p > 0.05) differences among the combined trimming and various cooking methods in the magnitude of reduction of PCB residues. The total quantities of PCBs found in the oil collected after baking, broiling or frying the fillets were less than could be accounted for as total cooking losses thus indicating that vaporization of PCBs during cooking may also occur.     

CHOLESTEROL AND PROXIMATE COMPOSITION OF CHANNEL CATFISH (ICTALURUS PUNCTATUS) FILLETS – CHANGES FOLLOWING COOKING BY MICROWAVE HEATING, DEEP-FAT FRYING, AND OVEN BAKING

Effects of microwave heating, deep-fat frying, and conventional oven baking on proximate composition and concentration of cholesterol in channel catfish fillets were examined. The paired fillet technique was employed to control the variability among fish. A total of fifteen catfish were randomly assigned to the three cooking methods. All cooking procedures resulted in moisture loss. Fillets that were deep-fat fried showed the lowest moisture content but the highest fat content, respectively, among three cooking methods. The three cooking methods, on a dry weight basis, all significantly affected cholesterol concentration of cooked catfish compared with raw fillets. Deep-fat frying resulted in a significant decrease of cholesterol and showed the lowest concentration of cholesterol among three cooking methods probably due to leaching of cholesterol into frying oil.     

CHANGES IN FRESHNESS OF CHILIPEPPER ROCKFISH (SEBASTES GOODEI) DURING STORAGE AS MEASURED BY CHEMICAL SENSORS AND BIOSENSORS

ABSTRACT Trimethylamine (TMA) and ammonia contents in Chilipepper rockfishes were determined by ion specific electrodes, as a late indicator of fish freshness. After 9 days of storage in ice, TMA contents significantly increased, indicating that bacterial spoilage was in progress. The pattern of changes in ammonia contents was similar to that of TMA. Determination of ATP degradation products in Chilipepper rockfish by HPLC showed that AMP and hypoxanthine levels were low and did not change much during storage. The concentration of IMP initially increased and then continuously decreased as inosine accumulated. Only trace amounts of hypoxanthine were detected in rockfish tissues. Chilipepper rockfish appears to differ from other Sebastes species in that ATP degradation results in inosine accumulation rather than hypoxanthine.