Grilling of sardine fillets. Effects of frozen and thawed modality on their protein quality

Abstract

Sequential freezing, thawing and cooking may affect the protein quality of fish fillets. Fillets of fresh raw sardine (R) were stored frozen, thawed at 4°C in a refrigerator (RR) or in a microwave oven (MR), and subsequently grilled (G). Proximate and amino acid compositions, solubility in sodium dodecylsulphate+ β-mercaptoethanol, –SH group content and amino acid chemical score were determined. Freezing–thawing increased ( p<0.05) (in wet matter basis) fat and decreased protein content in RR samples and ash content in RR and MR samples. Grilling produced a drip-loss phenomenon that causes loss of moisture that was more prominent after thawing (RG and MG samples). Thawing in refrigerator decreased the protein solubility, but grilling reversed that effect increasing and decreasing it in RG and MG samples, respectively. Every step of all processes caused a decrease in –SH group, cyst(e)ine and methionine giving rise to the lowest chemical score in RG and MG samples. The cholesterolemic index given by the arginine/lysine ratio and the smallest changes in the protein quality suggest that consuming grilled fresh raw sardine fillets is better than consuming refrigerator or microwave thawed–grilled sardine fillets.