Impact of pH Readjustment on Gel Properties of Alkaline pH-Shift-Processed Protein Isolate from Farm-Raised Hybrid Catfish (Clarias Macrocephalus × Clarias Gariepinus)
While limiting the accumulation of undesirable volatile compounds (such as geosmin, 2-methylisoborneol, hexanal, (E)-2-nonenal, (E)-2-heptenal, 2-butanone, and hexadecane), the alkaline pH-shift method can be utilized to isolate gel-forming proteins from hybrid catfish. However, it is necessary to enhance the gel properties of alkaline pH-shift-processed protein isolate. In general, a number of variables, including pH, have an impact on how fish protein gels. As a result, this study sought to determine how gel characteristics of alkali-made protein isolate (previously precipitated at pH 5.5) would change with a pH alteration (ranging from 4.5 to 8.0). The characteristics of alkaline-protein isolate gel were shown to be substantially pH dependent. The maximum hardness and whiteness were found in the alkaline-produced protein isolate at pH 5.5 (p < 0.05). While metmyoglobin production was highest in the gel with the highest alkalinity (pH 8.0), the content of thiobarbituric acid reactive substances (TBARS) was highest in the gel with the lowest alkalinity (pH 4.5) (p < 0.05). The gels with pH adjustments of 7.5 and 8.0 had the lowest protein carbonyl concentration (p < 0.05). When the pH was changed away from 6.5, a drop in the total sulfhydryl content was seen, indicating disulfide formation at pH levels lower and higher than this one. At pH 7.0, a compact and consistent gel of protein isolate was produced. The lowest volatile compounds, including hexanal, heptanal, 1-octen-3-ol, octanal, and nonanal, were detected by SPME-GC-MS/MS analysis at pH 6.5 to 7.0, while their retention was found in the more acidic and alkaline sides. As a result, it appeared that changing the protein isolate's pH to 7.0 would best increase the gel-forming properties of the pH-shifted protein isolate from hybrid catfish. The study improves the overall sustainability of protein production and consumption globally by assisting the aquaculture industry in catalyzing the switch from terrestrial to aquatic protein production systems. Additionally, the pH-shift procedure followed by the pH adjustment of the protein isolate can be an alternative method of enhancing the sustainable use of fish protein by purifying the gel-forming protein from farmed hybrid catfish.