Physicochemical and gelling properties of short-bodied mackerel (Rastrelliger brachysoma) protein isolate prepared using alkaline-aided process

This study demonstrated the characteristics and gel properties of short-bodied mackerel (Rastrelliger brachysoma) surimi prepared by the conventional washing process and protein isolate prepared by alkaline solubilization process without and with prewashing. A decrease in Ca2+-ATPase activity (P < 0.05), with changes in the tryptophan fluorescence intensity of natural actomyosin, was observed in protein isolate from alkaline solubilization process. However, higher reactive sulfhydryl (SH) content was found in protein isolate, compared with that in conventional surimi (P < 0.05). Generally, the higher amounts of lipid and myoglobin in fish mince were removed by using the alkaline-aided process, compared with the conventional process (P < 0.05). Protein isolate from the alkaline solubilization process formed gels with higher breaking forces than conventional suirmi, especially with 2-step heating (40 °C, 30 min/90 °C, 20 min) (P < 0.05). The lowest expressible moisture was found in the gel of protein isolate prepared by alkaline solubilization process (P < 0.05). However, the highest whiteness was found in the conventional surimi gel prepared by 2-step heating (P < 0.05). Protein isolate prepared by the alkaline solubilization process yielded superior gels compared with the conventional surimi. Therefore, it can be concluded that the gelling properties of surimi or protein isolate are governed by the physicochemical properties of proteins and are affected by processing conditions.