Physicochemical, volatile compound, and metagenomic analysis on the quality of Malaysia budu (fish sauce)

Inconsistency in product quality has often been a common problem for budu as it relies on spontaneous fermentation. This study aimed on a process improvement by applying a starter culture selected based on metagenomic analysis and hydrolytic activities. The first objective was to assess the process variations and how it affects the quality attributes and compliance with the Malaysia Food Regulation 1985. Chemometricbased analysis clustered budu into raw, heated, and non-heated types with total plate count, Enterobacteriaceae, moisture, protein, ash, salt, total free fatty acids, pH, water activity, and viscosity contributed considerably to the grouping. Budu whose quality complied with regulation standards were further evaluated for its microbial community and metabolite profiles during fermentation in second objective. Budu microbiota altered significantly after 1, 3, 6, and 12 months of fermentation, with Chao1 and Shannon indices indicating a decrease in microbial richness and diversity with time. The canonical correspondence analysis showed that bacterial community explained 84.53% of the variance in volatile metabolites. The high accumulation of 3- methylbutanoic acid with nutty and cheesy notes in the 12-month sample corresponded o the abundance of Lentibacillus, Bacilli, and Halomonas. The metagenome function prediction suggested that protein and lipid degradation pathways were responsible for most budu flavour compound synthesis. Therefore, salt-tolerant microbes with high proteolytic and lipolytic activity were isolated and characterized in the third objective. Five strains identified as Bacillus haikouensis 3M2G, Bacillus sp. 3M3A, Bacillus sp. 6M2A, Bacillus haikouensis 12M1F, and Bacillus licheniformis 12N3A with the highest crude enzyme activity ranged from 124.46-164.78 U (protease), 22.00-30.00 U (lipase), 104.45-155.48 U (esterase) and accounted for 902.33-1993.02 μmol/L glutamic acid production were used as co-culture for a laboratory-scale budu fermentation. In the fourth objective, Bacillus-mixed strains were compared to backslopping and spontaneous fermentation on physicochemical properties, volatiles, and microbial community profiles. Strain-added budu displayed significantly lower total volatile basic nitrogen and higher degree of hydrolysis (p < 0.05) than backslopping and spontaneous fermentation. These samples also exhibited a closer amino nitrogen content, browning intensity, and degree of hydrolysis to commercial samples fermented for 12 months. The addition of strains increased the formation of 3-methylbutanoic acid, 2,6-dimethylpyrazine, hexanal, 3-methylbutanal, heptanal, N, N-dimethylamine and phenylethyl alcohol. Fermentation with Bacillus strains could benefit the industry by improving the flavour profile of budu while controlling unwanted volatile bases formation.

Text 122626.pdf Download (1MB) Official URL or Download Paper: http://ethesis.upm.edu.my/id/eprint/18626

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