Combined effect of microbial transglutaminase and ethanolic coconut husk extract on the gel properties and in-vitro digestibility of spotted golden goatfish (Parupeneus heptacanthus) surimi gel

The combined effects of microbial transglutaminase (MTGase) and ethanolic coconut husk extracts (ECHE) at various concentrations on gelling properties of spotted golden goatfish (SGG) (Parupeneus heptacanthus) surimi were investigated. When gel was added with MTGase at various levels (0.5–2 U/g paste), the gel containing 1 U/g paste (MT-1) had the highest increase (284%) in breaking force (BF), compared to that of the control gel (CON). Similarly, with ECHE incorporation (0.05–0.25%, based on protein content), BF was increased to the maximum value with the addition of 0.1% ECHE (EC-0.1), in which BF was augmented by 59% than the CON. When MT-1 sample was incorporated with 0.15% ECHE (MT-EC), BF was increased by 709% as compared to that of CON. Gel added with ECHE alone had lower whiteness than the CON (p<0.05). However, MTGase increased the whiteness of all gel samples, regardless of ECHE addition. MT-EC samples had higher water holding capacity than the CON (p<0.05). Electrophoretic studies showed the disappearance of myosin heavy chain (MHC) bands with the incorporation of both additives at all levels used. MT-EC sample showed the highest Gʹ value, followed by MT-1. Impact of in-vitro digestion on antioxidant activity of selected SGG surimi gels was also elucidated. During in-vitro digestion, the MT-EC and MT-1 samples had the lowest TCA-soluble peptide content. The highest antioxidant activity was obtained for MT-EC and EC-0.1 samples (p<0.05). Hence, the combination of MTGase and ECHE at appropriate levels could yield a gel with improved gelling properties and enhanced antioxidant potential after the in-vitro digestion.