Pacific oysters (*Magallana gigas*) are globally favored for their nutritional value but suffer from short shelf life and contamination by pathogens like *Salmonella enterica* and *Vibrio parahaemolyticus*. These pathogens accumulate due to the oysters' filter-feeding nature. Biopreservation, using microorganisms or their metabolites, offers a sustainable alternative to chemical preservatives. Lactic acid bacteria (LAB), particularly *Lactiplantibacillus plantarum* 299V, are attractive candidates due to their generally recognized as safe (GRAS) status and production of postbiotics with antimicrobial properties. Previous research has shown the efficacy of LAB and their postbiotics in extending the shelf life of various food products, including fish fillets. However, the cost-effectiveness of producing sufficient LAB and metabolites for large-scale biopreservation remains a challenge. This study addresses this challenge by using soy whey, a by-product of tofu production, as a cost-effective medium for *L. plantarum* 299V fermentation. The abundance of soy whey, a significant food waste stream, coupled with its potential to support LAB growth and its inherent antimicrobial components, makes it an ideal candidate for this application. This research investigates the use of *L. plantarum* 299V-fermented soy whey (FSW) as a biopreservation strategy for Pacific oysters, comparing the effects of FSW, its cell-free supernatant (FSW-CFS), and the bacterial cells (FSW-cells) on oyster safety and shelf life. The study also includes sensory evaluation to assess consumer acceptance of the treated oysters.

Extensive research supports the use of lactic acid bacteria (LAB) in food biopreservation. LAB produce various postbiotics, including organic acids, hydrogen peroxide, and peptides, which inhibit spoilage and pathogenic microorganisms. Studies have demonstrated the effectiveness of LAB-based biopreservation techniques in extending the shelf life and improving the safety of various food products. For instance, Hua et al. (2022) employed a postbiotic-fortified probiotic coating to successfully inhibit *Listeria monocytogenes* and extend the shelf life of salmon fillets. Other research highlights the use of LAB in oyster depuration to prevent *V. parahaemolyticus* growth (Khouadja et al., 2017). Bacteriocins, antimicrobial peptides produced by LAB, are also widely used in the food industry for their biopreservation potential. Studies have shown the efficacy of nisin and pediocin in reducing bacterial counts in various food products (Guerra et al., 2005; Mauriello et al., 2010; Meira et al., 2017). The use of soy whey as a fermentation medium for LAB has also been explored. Studies indicate that soy whey provides adequate nutrients for LAB growth, comparable to traditional media (Mitra et al., 2010; Zhou et al., 2022). Furthermore, soy whey contains natural antimicrobial substances, which can enhance the effectiveness of LAB-based biopreservation strategies. This existing body of work provides a strong foundation for investigating the use of *L. plantarum* 299V-fermented soy whey for oyster preservation.

The study used *L. plantarum* 299V, a commercially available probiotic strain, to ferment pasteurized soy whey. Three different initial inoculation levels (~6.5, ~7.5, and ~8.5 log CFU/mL) were tested, with fermentation carried out at 37 °C for 72 h. Viable cell counts and pH were monitored at intervals. The most cost-effective inoculation level (~6.5 log CFU/mL) was selected for further experiments. Three treatment groups were prepared: FSW (fermented soy whey), FSW-CFS (cell-free supernatant), and FSW-cells (bacterial cells). Pacific oysters were harvested, rinsed, and individually packaged with 40 mL of one of the three treatment solutions or sterile DI water (control). To simulate natural pathogen contamination, oysters were first acclimated in artificial seawater and then exposed to *V. parahaemolyticus* and *S. enterica* cocktails before treatment. The oysters were stored at 4 ± 1 °C, and microbial and chemical analyses were performed on days 0, 4, 8, and 12. Microbial analysis involved enumerating LAB, psychrophilic bacteria, *Pseudomonas* spp., *Enterobacteriaceae*, *Salmonella*, and *V. parahaemolyticus* using appropriate selective media. Total volatile basic nitrogen (TVB-N) was measured using a modified semimicro steam distillation method. Biogenic amines (BAs) were quantified using high-performance liquid chromatography (HPLC) after derivatization. Oyster texture was assessed using a texture analyzer, and color was measured using a colorimeter. Finally, a sensory evaluation was conducted using a 9-point hedonic scale to assess consumer acceptance of the treated oysters.

The *L. plantarum* 299V fermented soy whey exhibited significant antimicrobial activity against both *V. parahaemolyticus* and *S. enterica*. In the FSW and FSW-CFS treatment groups, both pathogens were reduced to below the detection limit (<2.0 log CFU/g) within 2–4 days. The FSW-cells group showed less pronounced antimicrobial effects. The fermented soy whey effectively controlled the growth of spoilage-related microorganisms, including psychrophilic bacteria, *Pseudomonas* spp., and *Enterobacteriaceae*, keeping their counts significantly lower compared to the control group throughout the 12-day storage period. TVB-N levels, a crucial indicator of seafood freshness, remained significantly lower in the FSW and FSW-CFS treated oysters compared to the control. Biogenic amines, associated with seafood spoilage and potential health risks, were also significantly reduced in the FSW treated oysters. Texture analysis revealed that FSW treatment helped maintain oyster texture attributes, with hardness, cohesiveness, and chewiness values comparable to the control group on day 4 even on day 12. Color analysis showed that FSW treatment effectively preserved oyster color, maintaining L* and a* values similar to day 0 even on day 12. Sensory evaluation indicated high consumer acceptance of the FSW-treated oysters, with more than 60% of participants giving positive scores for overall acceptance, appearance, smell, and taste.

The results demonstrate the effectiveness of *L. plantarum* 299V-fermented soy whey as a biopreservation solution for Pacific oysters. The significant reduction in pathogenic and spoilage bacteria, coupled with the maintenance of desirable sensory and textural properties, highlights the potential of this approach for enhancing oyster shelf life and safety. The superior performance of FSW and FSW-CFS compared to FSW-cells suggests that the postbiotics produced during fermentation, rather than the live bacterial cells, are primarily responsible for the observed antimicrobial effects. This is likely due to the low metabolic activity of mesophilic *L. plantarum* 299V at the chilled storage temperature (4 °C). The use of soy whey as a fermentation medium offers a sustainable and economically viable alternative to traditional media, reducing waste and production costs. The high consumer acceptance further reinforces the commercial potential of this technology. This study contributes to the development of sustainable food preservation strategies, reducing food waste and improving food safety.

This study successfully demonstrated the application of *L. plantarum* 299V-fermented soy whey as a sustainable and effective biopreservation strategy for Pacific oysters. The fermented soy whey significantly improved the safety and extended the shelf life of oysters while maintaining desirable sensory attributes. The use of soy whey as a fermentation substrate reduces food waste and production costs. Future research could explore the optimization of fermentation parameters, investigating different LAB strains and soy whey processing methods to further enhance the effectiveness of this biopreservation approach. Further studies could also investigate the long-term stability of the postbiotics and their potential health benefits to humans.

The study was conducted under controlled laboratory conditions, and the results may not fully reflect the performance of the biopreservation solution under real-world conditions. The scope of the sensory evaluation was limited, and a larger scale study with a more diverse consumer panel would be beneficial. While the study focused on *V. parahaemolyticus* and *S. enterica*, other potential oyster pathogens were not investigated.