The quality of surimi gel can be improved using protein cross-linkers, especially from plant extracts. Apart from the presence of phenolic compounds, Duea ching fruit is rich in calcium, which can activate indigenous transglutaminase or form the salt bridge between protein chains. Its extract can serve as a potential additive for surimi. The effect of different media for the extraction of Duea ching was studied and the use of the extract in sardine surimi gel was also investigated. The Duea ching fruit extract (DCE) was prepared using distilled water and ethanol (EtOH) at varying concentrations. The DCE prepared using 60% EtOH (DCE-60) had the highest antioxidant activity and total phenolic content. When DCE-60 (0–0.125%; w/w) was added to the sardine surimi gel, the breaking force (BF), deformation (DF) and water holding capacity (WHC) of the gel upsurged and the highest values were attained with the 0.05% DCE-60 addition (p < 0.05). However, the whiteness of the gel decreased when DCE-60 levels were augmented. The gel containing 0.05% DCE-60, namely D60-0.05, showed a denser network and had a higher overall likeness score than the control. When the D60-0.05 gel was packed in air, under vacuum or modified atmospheric packaging and stored at 4 °C, BF, DF, WHC and whiteness gradually decreased throughout 12 days of storage. However, the D60-0.05 gel sample showed lower deterioration than the control, regardless of the packaging. Moreover, the gel packaged under vacuum conditions showed the lowest reduction in properties throughout the storage than those packaged with another two conditions. Thus, the incorporation of 0.05% DCE-60 could improve the properties of sardine surimi gel and the deterioration of the resulting gel was retarded when stored at 4 °C under vacuum packaging conditions.

Squid (Loligo vulgaris) is commonly prone to spoilage, leading to a short shelf-life. High-pressure processing (HPP) can play a role in maintaining the quality and freshness of squid. Along with HPP, food preservatives from natural sources such as mint extract (ME), which are effective, safe, available, and cost-effective, are required. The present study aimed to investigate the combined effect of ME and HPP on the quality of refrigerated squid mantle cuts (SMC) over a period of 15 days. The time-kill profiles of ME and planktonic cell inactivation by HPP were assessed. ME (400 mg/L) inhibited bacterial growth, while planktonic cells treated with HPP (400 MPa) exhibited a reduction at 5 min. Physicochemical and microbial qualities of SMC treated with ME (0, 200, 400 mg/L) followed by HPP (0.1, 200, 400 MPa) for 5 min were monitored during refrigerated storage. Samples treated with ME (400 mg/L) and HPP (400 MPa) exhibited lower weight loss, cooking loss, pH changes, volatile base content, microbial counts, and higher textural properties than other samples. Based on next-generation sequencing results, Brochothrix campestris from family Listeriaceae was the predominant spoilage bacteria in treated sample after 12 days of storage. Therefore, ME and HPP combined treatments exhibited effectiveness in extending the shelf-life of refrigerated SMC.

Surimi and its products have been consumed widely, especially in Japan and Southeast Asia. Market value and consumer acceptability are mainly determined by the textural properties of surimi gel. Textural and gelling properties are governed by the type of fish, lipid content, processing conditions, and presence of endogenous protease and transglutaminase. In addition, several additives such as protein cross-linkers, hydrocolloids, protease inhibitors, etc. have been used in surimi to improve their gelling properties. Cross-linking is the promising method for protein modification to obtain desirable surimi-based gel products possessing unique textural properties. Endogenous transglutaminase (TGase) plays a profound role in protein cross-linking during setting in surimi paste. For surimi from fish with low setting phenomenon, microbial TGase (MTGase) has been widely used. Plant polyphenols have also been employed for protein crosslinking to strengthen the surimi gel. Polysaccharides mainly the hydrocolloids also strengthen the gel network and increase water holding capacity (WHC) of gel. During heating, endogenous heatactivated proteases that are firmly attached to muscle proteins are active in hydrolyzing myofibrillar proteins. This results in a weaker gel with low WHC. Protease inhibitors form plants as well animals could impede the protease activity, thus maintaining the myofibrillar proteins responsible for the gelation. In addition to the additives, processing methods such as highpressure technology or ohmic heating in combination with those additives have a positive impact on the gel properties. For this review, the role of various kinds of additives namely protein crosslinkers, hydrocolloids and protease inhibitors in surimi gel improvement was revisited.