Effect of vacuum frying and atmospheric frying on the quality and protein oxidation of squid (<i>Loligo chinensis</i>)

Squid are commercial marine species that have high nutritional value. This study aimed to compare the influences of vacuum frying and atmospheric frying on the physicochemical properties and protein oxidation of three main parts (ring, tentacle, and fin) of the squid Loligo chinensis. The results showed that the vacuum-fried (VF) group had lower moisture and total fat contents and looser microstructures than the atmospheric-fried (AF) group. The amino acid contents and molecular weight revealed that the proteins were well preserved during vacuum frying. Carbonyl content in the VF ring, tentacle, and fin samples increased nearly 2.53-, 1.54-, and 2.56-fold, respectively, compared to that in the corresponding fresh group, but these increases were lower than those of the corresponding AF group. In addition, the secondary structures of proteins revealed a slight decrease in the α-helix and β-turn contents and a significant increase in the β-sheet content during vacuum frying. Therefore, vacuum frying can be used as an efficient processing method to conserve the high nutritive quality of the product. PRACTICAL APPLICATION: As a developing alternative technology to prepare healthier fried products, vacuum frying has been the focus of recent researches. Vacuum frying produced squid products that had lower TBARS values, carbonyl contents, and Schiff base substances compared to atmospheric frying. And the protein secondary structures of the vacuum-fried group retained better. The study proved that vacuum frying could be an effective method with the advantages of high protein stability and product quality.