Study of the combined effects of a gelatin-derived cryoprotective peptide and a non-peptide antioxidant in a fish mince model system

The combined effect of a gelatin-derived cryoprotective peptide (Pro-Ala-Gly-Tyr) and a non-peptide antioxidant (caffeic acid) in a fish mince model system was investigated. The physicochemical properties (peroxide value, thiobarbituric acid-reactive substances, total sulfhydryl group content and protein carbonyl content), water distribution and thermal properties of Japanese sea bass mince were determined before and after 6 freeze-thaw cycles. Mince supplemented with a combination of a cryoprotective tetrapeptide (12.5 ppm) and 50 ppm caffeic acid had the lowest peroxide value and comparable thiobarbituric acid-reactive substances to 100 ppm caffeic acid. The cryoprotective tetrapeptide at 12.5 ppm also showed the greatest effect when combined with caffeic acid in lowering protein oxidation, in protecting the total sulfhydryl group content and in having the lowest protein carbonylation, which led to least myosin heavy chain denaturation. The state of water was studied using low-field nuclear magnetic resonance. The tetrapeptide reduced the formation of free water in the mince, especially in conjunction with caffeic acid. Thus, the cryoprotective tetrapeptide worked with caffeic acid in retarding the quality losses in the mince induced by freezing and thawing.