ALTERATION IN LIPID OXIDATION OF CHANNEL CATFISH DURING FROZEN STORAGE IN RESPONSE TO ASCORBATE APPLICATIONS

Channel catfish were treated with ascorbate via metabolic absorption and vacuum tumbling. The fillets were subjected to varying periods (0, 1.5, 3, 4.5, and 6 months) of frozen storage at −6C. When muscle ascorbic acid levels were increased two fold by both methods, TBA-RS values were significantly lower than that of the control after 6 months of storage. Vacuum tumbled fillets with muscle ascorbic acid that increased by four fold were found to be the least stable to oxidation. The possible fate of the ascorbic acid in the fish tissue was discussed.     

SOME OBSERVATIONS ON MYOGLOBIN AND LIPID OXIDATION IN FROZEN BEEF

SUMMARY –The observed curvilinear correlation between metmyoglobin formation and lipid oxidation in beef gluteus medius samples (3 mm thick) stored in polyethylene at -5°C was dependent (P < 0.001) on initial treatment, namely freeze-thawing, delayed freezing or mincing. However, these initial treatments accelerated both metmyoglobin formation and lipid oxidation. In slices initially held in 1% oxygen at 0°C to increase the relative amount of metmyoglobin, the concentration of this pigment was first reduced during frozen storage at -5°C before increasing again. High initial metmyoglobin concentrations had no effect on the rate of lipid oxidation.     

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.     

EFFECT OF DIFFERENT STORAGE CONDITIONS ON THE LIPID FRACTION OF A VEGETABLE CREAM

Fatty acids (free and esterified), diglycerides, peroxides and total sterols were determined in a vegetable cream. Cream samples were analyzed when fresh and after storage for 3 and 6 months at 4, 15, 30C and room temperature (10–25C). The product showed a higher amount of unsaturated fatty acids ( ≈ 50% of total fatty acids) with respect to milk fat and a low level of cholesterol ( < 0.01%). The phytosterol content ( ≈ 14 mg/100 g of cream) was not high enough to contribute to a decrease in cholesterolemia. Lipid oxidation remained low during storage (peroxides: 2.0–3.0 meq O₂/kg of fat), but a small increase was observed at room temperature after 6 months (about 6.0 meq O₂/kg of fat). Free fatty acids never exceeded 0.3% of fat. Storage at 4C and 15C delayed lipolysis in comparison to storage at 30C and room temperature.

PRACTICAL APPLICATIONS

The analysis of a vegetable cream demonstrated that it was a shelf-stable product, showing a high stability toward lipid oxidation and lipolysis. Such a product might be employed as vehicle for healthy fat compounds like long-chain polyunsaturated fatty acids, phytosterols and fat-soluble vitamins.