The most abundance of anti-Salmonella lactic acid bacteria (LAB) was found in feces of naturally born, exclusively breastfed Thai infants. Six strains of Lactobacillus plantarum and one strain of Lactobacillus paracasei were selected and identified. In the co-cultivation assay, L. plantarum subsp. plantarum I62 showed the strongest and broadest antibacterial activity against Escherichia coli, Shigella sonnei, Salmonella Paratyphi A, and Salmonella Typhimurium SA 2093 under the mimicked proximal colon condition, in which glucose and other nutrients were limited. According to GC-MS analysis, the major antibacterial contribution of organic acids secreted by L. plantarum I62 grown in the presence of glucose was dramatically reduced from 95.8 to 41.9 % under glucose-limited niche. The production of low-pK a acids, such as lactic, 1,2-benzenedicarboxylic, and 3-phenyllactic acids, was remarkably dropped. Surprisingly, higher-pK a acids such as 5-chlorobenzimidazole-2-carboxylic, pyroglutamic, palmitic, and oleic acids were enhanced. Moreover, cyclic dipeptides, ketones, alkanes, alcohols, and miscellaneous compounds, which were pH-independent antibacterial metabolites, became dominant. The electron microscopy strongly supported the synergistic attacks of the multiple antibacterial components targeting outer and cytoplasmic membranes leading to severe leakage and cell disruption of Salmonella Typhimurium. This strain poses to be a potential probiotic candidate for effectively controlling and treating human foodborne bacterial infection.
This study evaluated the effects of autochthonous starters on the quality characteristics of budu. The effects of individual or combined inoculation of Virgibacillus halodenitrificans PS21 and Staphylococcus simulans PMRS35 were compared to those of non-inoculation during 150 days of budu production. The starters directly affected characteristics of budu with browner colour and enhanced proteolysis and lipolysis as indicated by degree of hydrolysis and free fatty acid contents. The combined starter inoculation resulted in a high aspartic acid, glutamic acid and lysine levels. Additionally, key desirable volatiles, including 2-methylbutanal, 3-methylbutanal, benzaldehyde and 2-ethyl furan, were dominant in the starter-inoculated budu. In a sensorial analysis, the highest scores for appearance, colour, taste and flavour were assigned for inoculated budu with combined starters. Therefore, the addition of starters (V. halodenitrificans PS21 and S. simulans PMRS35) in budu production improved the quality characteristics and reduced the fermentation period.
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