Ethanolic Binahong ( Anredera cordifolia ) Leaf Extract: Antioxidant Activities and Its Influence on the Gel Properties of Sardine Surimi and Oxidative Stability during Refrigerated Storage

Dark-fleshed surimi is an unexploited resource due to its poor gelling property and high susceptibility to lipid oxidation. Hence, the application of natural plant-derived polyphenols has attracted considerable attention as a multifunctional additive to enhance surimi gel quality and oxidative stability. The preparation of an ethanolic extract of binahong (Anredera cordifolia) leaves was carried out using distilled water and ethanol at concentrations ranging from 40% to80% (v/v). The extracts were evaluated for their total phenolic content and antioxidant activities, including 2,2-diphenyl-1-picrylhydrazyl radical-scavenging activity (DPPH-RSA), 2,2’-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) radical-scavenging activity (ABTS-RSA), ferric-reducing antioxidant power (FRAP), and metal-chelating activity (MCA). The binahong leaf extract (BLE) prepared with 80% ethanol (BLE80) had the highest phenolic content and the strongest antioxidant activity. Therefore, BLE80 was added to sardine surimi at levels ranging from 0% to 0.125% (w/w). The addition of 0.075% BLE80 increased the breaking force, deformation, hardness, cohesiveness, and water-holding capacity (P < 0.05), but slightly decreased the whiteness of sardine surimi gel. Scanning electron microscopic (SEM), dynamic rheological, Fourier-transform infrared spectroscopic (FTIR) analyses, and protein patterns indicated the improved protein cross-linking and the formation of a compact and well-ordered gel. However, higher BLE80 levels accelerated excessive protein aggregation, leading to poorer gel texture. Besides, lipid oxidation was effectively inhibited in surimi gel with 0.075% BLE80. BLE80 is a multifunctional natural additive, which improves gel formation and oxidative stability and provides a sustainable strategy to improve the quality and shelf life of surimi made from dark-fleshed fish.