Evaluation of antioxidant effect of gallic acid and its alkyl esters on freeze-dried scallop with different packaging by lipid stability, predicted shelf life, and thermodynamic study

Antioxidant effect of gallic acid alkyl esters in emulsions or complex food systems has a “cut-off effect”. However, it is unclear whether this phenomenon can occur in food under low-oxygen environment. The present work compared the effects of gallic acid, octyl gallate, and hexadecyl gallate on lipid stability, predicted shelf life, and thermodynamic parameters of freeze-dried scallop with vacuum polyamide/polyethylene packaging (VPP) and non-vacuum polyamide/polyethylene packaging (NPP) during storage for 16 days. The results showed that regardless of the packaging type, the octyl gallate group showed the lowest peroxide value, thiobarbituric acid reactive substances value, and free radical levels, and loss of eicosapentaenoic acid and docosahexaenoic acid contents (46.5, 39.3, 35.7, and 22.6% lower than those of deionised water-treated sample (control group), respectively). Moreover, the octyl gallate group had the longest induction period and shelf life (6.9 and 1.3-fold longer than those in control group, respectively). These results indicated that the antioxidant capacity of gallic acid and its alkyl esters increased with the chain length (C0 to C8), and then decreased (C8 to C16). Thus, the “cut-off effect” existed in freeze-dried scallop with VPP or NPP. Thermodynamic analysis indicated that lipid oxidation of freeze-dried scallop during storage was an endothermic (ΔH++ > 0) and non-spontaneous (ΔG++ > 0) process, and the addition of octyl gallate in combination with VPP had the strongest antioxidant effect. The shelf life of freeze-dried scallop treated with octyl gallate and VPP was extended to about 120 days. The present work would be helpful for the reasonable selection of antioxidants and packaging to prolong shelf life of dried seafood during long-term storage.