Antimicrobial and antioxidant activities of Quillaja saponin and its impact in enhancing storage stability and microbiome modulation of refrigerated surimi gels

Surimi, a concentrated myofibrillar protein, serves as the raw material for several gel products that are prone to spoilage during refrigerated storage. Saponin exhibits several biological activities that may retard spoilage and improve product stability when incorporated into foods. This study evaluated the antimicrobial and antioxidant activities of Quillaja saponin and its effectiveness in enhancing the shelf life of surimi gels during refrigerated storage. Based on minimum inhibitory concentration (MIC) and bactericidal concentration studies, saponin exhibited a bactericidal effect against both spoilage and pathogenic bacteria. Time-kill assays confirmed that microbial inactivation was concentration and time-dependent. Scanning electron images revealed that saponin, at 2 × MIC, induced morphological changes and pore formation in bacterial cells. Saponin exhibited antioxidant activity when tested by multiple in vitro assays. Surimi gels supplemented with two selected concentrations of saponin (1%-SPN1 and 2.5%-SPN2.5) were stored at 4 °C. The SPN2.5 sample maintained total viable counts within acceptable limits up to day 15 compared with day 12 for the control and SPN1. However, both SPN1 and SPN2.5 samples exhibited significantly lower peroxide value and thiobarbituric acid reactive substances than the control, indicating enhanced oxidative stability. Next-generation sequencing analysis revealed that psychrotrophic spoilage bacteria were dominant in the control sample, whereas the SPN2.5 sample had a lower relative abundance of spoilage-associated microbial taxa and overall diversity. Overall, incorporating saponin into surimi gel effectively delayed microbial growth and reduced lipid oxidation. Overall, saponin addition provided measurable antioxidant and antimicrobial effects, resulting in a slight delay of microbial proliferation during refrigerated storage.