Ethanolic duea ching extract in combination with microbial transglutaminase: Strengthening effect on mince gel and cross-linking of myofibrillar proteins from Indian mackerel

Surimi or fish mince gel are popular seafood products worldwide. Lean fish are commonly used as raw material, while dark fleshed fish, especially Indian mackerel, has high fat content and dark color associated with poor gel quality. To improve gel strength, plant extract, particularly from duea ching (Ficus botryocarpa Miq.), rich in polyphenols and calcium could be used as natural protein cross-linker to strengthen gel network. Effect of ethanolic duea ching extract (EDCE) at varying levels in the absence and presence of microbial transglutaminase (MTGase) on gel property of Indian mackerel mince gel prepared from fillets pre-washed for different times (1 and 3 times) was studied. Heat-induced aggregation of myofibrillar protein (MP) from Indian mackerel fillets under different conditions was also investigated. Mince gel prepared from fillets pre-washed for 3 times added with 0.10 % EDCE and 0.5 unit/g of MTGase (3-PWM-MT-0.10) showed the highest breaking force, deformation and textural properties (P < 0.05). Lower autolysis of mince gel was obtained when EDCE, MTGase or in combination were added. However, addition of ECHE decreased whiteness of mince gel, particularly at higher concentrations (P < 0.05). Electrophoretic images revealed the disappearance of myosin heavy chain when MTGase or EDCE in conjunction with MTGase was incorporated. Addition of 0.10 % EDCE, MTGase or both could induce aggregation and enhance setting phenomenon of MP solution as indicated by higher absorbance at 660 nm and storage modulus (G′), respectively. Based on microstructure study, 3-PWM-MT-0.10 had more compact, finer and interconnected structure than other gels. Therefore, the use of EDCE and MTGase at the appropriate levels could be used for improving quality of mince gel from pre-washed Indian mackerel fillets.