Abstract

The effect of acid and alkaline pH shift processes on biochemical and physicochemical characteristics of protein isolates from bigeye snapper (Priacanthus tayenus) head by-product (HB) was investigated. Approximately 30% protein yield with the significant reduction of lipid and ash (P<0.05) was obtained from both processes. However, partial denaturation of resulting isolates was noticeable in both processes as shown by the decreases in reactive SH content and Ca2+-ATPase activity (P<0.05). Acid process recovered less total pigments with lowered heme iron content resulting in a greater whiteness of the isolate (P<0.05). The highest haem-globin destruction indicated by the disappearance of a soret peak of myoglobin spectra was noticeable in the acid process. The oxidation of residual lipids in both protein isolates measured by TBARS was markedly lowered than in HB (P<0.05) even though the PV was not significantly different among treatments (P>0.05). Both acid and alkaline methods effectively removed TVB-N and fishy odour and lowered the TCA-soluble peptides from HB (P<0.05). Therefore, the pH shift processing can be used as a powerful tool to recover proteins from HB. However, properties of the protein isolate were influenced by solubilisation method. Acid process gave a protein isolate with better overall quality compared to alkaline version.