Fermented Rainbow Trout Production Using Lactobacillus sakei and Saccharomyces cerevisiae: Effects on Microbiological, Biochemical, and Sensory Quality

The aim of this study was to evaluate the microbiological, biochemical and sensory properties of fermented rainbow trout (Oncorhynchus mykiss) using Lactobacillus sakei ATCC® 15521™ (L), Saccharomyces cerevisiae ATCC® 9080™ (S) and their combination (M) as starter cultures and without starter culture as spontaneous fermentation (F). Rainbow trout slices (94% w/w) were mixed with curing ingredients—sucrose (2% w/w), salt (3% w/w), garlic powder (0.3% w/w), ginger powder (0.3% w/w), and sweet red pepper powder (0.3% w/w)—and kept at 4 °C for 2 days. After the cured trout were dried at 60 °C for 3 hours, starter cultures were evenly injected into the trout slices at a rate of 1% (1 mL starter culture: 100 g cured fish). The fermentation process was conducted at 24 °C for 14 days. During fermentation of the trout, the recommended 6 log CFU/g value for LAB, which is beneficial for gastrointestinal health, was reached on different days depending on the group: on day 12 in the F group (6.07 ± 0.25 log cfu/g), on day 4 in the S group (6.25 ± 0.11 log cfu/g), and on day 2 in the M group (6.52 ± 0.09 log cfu/g). Additionally, the highest value in the L group was 7.21±0.11 log cfu/g on day 2, indicating rapid fermentation. Enterobacteriaceae counts remained low across all groups, with values dropping to <1 log cfu/g by the end of fermentation. The results showed that the pH of fresh fish, initially 6.70, decreased significantly to 4.01, 4.18, and 4.09 in L, S, and M groups, respectively, by the end of fermentation. Nutritional analysis revealed higher protein content and reduced lipid oxidation levels in the M group, which also exhibited the lowest levels of total volatile basic nitrogen and thiobarbituric acid, indicating improved freshness and oxidative stability. Sensory evaluation identified the M group as the most preferred due to its balanced acidity, texture, and flavor. These findings suggest the potential of combining L. sakei and S. cerevisiae to produce highquality fermented trout with enhanced safety, nutritional value, and consumer acceptance. This study represents the first effort to produce the fermentation process specifically for rainbow trout, marking a contribution to the field of fermented fish production.