EFFECT OF SEASONAL VARIATIONS ON PROTEIN FUNCTIONAL PROPERTIES OF FISH DURING FROZEN STORAGE

Influence of seasonal variation (February, July and October), time elapsed before freezing, and type of processing of the muscle on several functional properties (protein solubility, emulsifying capacity, and viscosity) in two species of fish with differing seasonal behavior (hake and sardine) were studied. Correlations between the changes in these functional properties during frozen storage were established. Although proximate analyses of the hake muscle were similar throughout the year, significant differences were observed in viscosity and protein solubility during storage between lots of fish caught in different seasons. Changes in the functional properties were less evident in sardine, which undergoes wide seasonal variations. The larger differences in the functional proprities of hake muscle, depending on season, were related to differences in the dimethylamine content after the fifth month of frozen storage. High correlations were established between functional properties in fish caught in the same or different seasons. Any of the three functional properties studied can be used as a suitable index of the quality of frozen fish, irrespective of the different conditions studied.     

PACKAGING AND STORAGE EFFECTS ON THE FUNCTIONAL PROPERTIES OF FROZEN VENISON

The functional stability of vacuum- and nonvacuum-packaged venison semimembranosus muscle was determined after 0, 1, 2, 3, 6 and 9 months of frozen storage. Vacuum-packaged samples had higher emulsion stability, chroma, shear force values, cooked batter torsion stress, strain and tensile stretch, lower malondialdehyde (MDA) and lower hue angle compared with nonvacuum-packaged samples. The two packaging methods did not vary in the other functional attributes of venison measured. Total protein solubility, cooked batter torsion strain and tensile strength increased in the first month of storage and then decreased thereafter. Sarcoplasmic protein solubility increased ( P <  0.05) in the first 6 months and declined in the ninth month . Reactive sulphydryl contents ( P <  0.1) and moisture loss in raw ( P <  0.001) and in cooked venison ( P <  0.01) increased with storage time and peaked at 3 months and declined thereafter. MDA increased during the first 2 months, then declined and increased again at 9 months ( P <  0.001). The results of this study suggest that most of the changes in frozen venison manufacturing functionality took place within the first month of storage and this peak functionality was extended to 3 months when venison was vacuum-packaged.

PRACTICAL APPLICATIONS

The following are some of the practical applications of this research: (1) Frozen venison has better functional properties for manufacturing purposes compared with fresh unfrozen venison immediately postrigor. (2) This functionality tends to peak at 1 month of frozen storage, with longer storage up to 9 months having little or no further effect on the functionality. (3) The peak functionality can be extended to 3 months through vacuum packaging.     

EFFECT OF FROZEN STORAGE ON THE QUALITY OF AKARA, FRIED COWPEA (VIGNA UNGUICULATA) PASTE

Akara, a fried food of West African origin, is made from whipped cowpea paste flavored with fresh onion, fresh hot or bell pepper, and salt. Akara has potential for U.S. markets as a fully cooked, frozen, reheatable product. Akara was stored at ?18°C for 9 months and compared to freshly prepared akara in selected quality characteristics. Frozen, thawed akara had a higher moisture and lower crude fat content, required significantly less force to shear, and had a lighter, less intense color than freshly prepared product. Frozen/thawed/reheated akara received lower senson scores for color, moistness and flavor than the fresh product. Analysis of headspace volatiles of freshly prepared akara and akara frozen 3, 6 and 9 months resulted in fifteen peaks. Two peaks were significantly affected by frozen storage.     

GEL-FORMING ABILITY OF COMMON CARP FISH (CYPRINUS CARPIO) MEAT: EFFECT OF FREEZING AND FROZEN STORAGE

Effect of freezing and frozen storage on gel‐forming ability of muscle from fresh water fish, common carp (Cyprinus carpio), was investigated. Fresh carp meat had good gel‐forming ability as revealed by large strain test (gel strength of 1027 g·cm) and dynamic viscoelastic behavior. Freezing and frozen storage at ?18C for 180 days significantly (P < 0.01) reduced the gel‐forming ability of common carp meat. Reduction in protein solubility and calcium‐activated adenosinetriphosphatase enzyme activity of common carp meat during frozen storage was also significant (P < 0.05). Structural change of proteins during frozen storage was evident from reduced viscosity and gel filtration profile. Higher drip loss and reduction in gel‐forming ability of carp meat is attributed to denaturation of proteins during frozen storage.     

EFFECT OF PROCESSING ON BACTERIAL POPULATION OF CUTTLE FISH AND CRAB AND DETERMINATION OF BACTERIAL SPOILAGE AND RANCIDITY DEVELOPING ON FROZEN STORAGE

Processing techniques like cooking and freezing exhibited significant (P < 0.001) reduction in the bacterial load of cuttlefish, Sepia pharaonis, and marine crab, Portunus pelagicus. Raw cuttle fish had 2.4 × 10⁷ cfu/g which on cooking reduced to 9.7 × 10⁶ cfu/g. Freezing reduced the bacterial load further as cooked frozen product had only 9.9 × 10⁴ cfu/g. Similarly, raw crab had 2.6 × 10⁷ cfu/g which on cooking reduced to 6.5 × 10⁶ cfu/g. A further reduction in bacterial load was seen after freezing as cooked frozen crab exhibited only 7.3 × 10⁴ cfu/g. Escherichia coli and Staphylococcus aureus were present in the limit of acceptability for fish and fish products. Salmonella typhimurium and Vibrio cholerae were absent even in raw stage. Biochemical analysis performed on stored frozen products of cuttle fish and crab exhibited a significant (P ≤ 0.05) increase in bacterial spoilage and rancidity with increasing days of storage. Total volatile base nitrogen, trimethylamine, thiobarbituric acid and free fatty acid contents in frozen products of cuttle fish and crab increased significantly with 120 days of frozen storage.     

THE EFFECTS OF FROZEN STORAGE AND PROTECTIVE STORAGE WRAP ON THE RETAIL CASE-LIFE OF PORK LOIN CHOPS

Loin chops from 60 pork carcass sides were utilized to evaluate the influences of frozen storage and protective storage wrap upon factors contributing to the retail case-life of thawed chops. The composite results of this study indicated that pork loin chops could be frozen and stored for 168 days or less at ?30° C and have a retail case-life of at least 6 days, under the conditions employed in the present study. The possible exception is an amount of drip in the packages of chops stored in certain protective wraps which may be unacceptable when displayed for prolonged periods.     

THE EFFECT OF PRESSURE COOKING ON THE MICROSTRUCTURE AND EXPANSION OF FISH CRACKER ('KEROPOK')

The effect of pressure cooking on microstructure of wheat and tapioca starch in keropok gel and expansion of fried keropok slices were studied. The morphology of the starch granules in the keropok gel at different steaming temperature was examined using scanning electron microscopy (SEM). Linear expansion of keropok made with wheat starch increased with increasing steaming temperature, but that of keropok made with tapioca starch decreased with increasing steaming temperature. The linear expansion results correlate with the sensory evaluation of the products.