Thai traditional fermented fish products (Plaa-som) from four provinces (Ubon Ratchathani, Surin, Sisaket, and Khon Kaen) in the northeast part of Thailand were collected and analyzed to determine their salt content, total acidity, and pH. Yeasts in all samples were isolated and identified to the genus and species level based on sequence analysis of the D1/D2 of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) region. The results revealed that the salt content, total acidity, and pH values are in the range of 2.01–6.9%, 0.62–1.9%, and 4.4–6.57%, respectively. Moreover, 35 strains of yeast were isolated and identified as eight genera, namely Candida, Diutina, Filobasidium, Kazachstania, Pichia, Saccharomyces, Torulaspora, and Yarrowia with 17 species. The ascosporogenous yeast, Kazachstania, was the most dominant genus found and was widely distributed among the fermented food samples. In addition, a new strain of yeast, Kazachstania surinensis, was also discovered in Plaa-som samples. Thus, this study is the first to report the presence and wide distribution of these yeasts in fish fermentation products.
Protease is a widely used enzyme particularly in the detergent industry. In this research, we aimed to isolate alkaline protease-producing bacteria for characterization as a laundry detergent additive. The screening of alkaline protease production was investigated on basal medium agar plus 1% skim milk at pH 11, with incubation at 30°C. The highest alkaline protease-producing bacterium was 6BS15-4 strain, identified as Bacillus gibsonii by 16S rRNA gene sequencing. While the optimum pH was 12.0, the strain was stable at pH range 7.0-12.0 when incubated at 45°C for 60 min. The alkaline protease produced by B. gibsonii 6BS15-4 using dairy effluent was characterized. The optimum temperature was 60°C and the enzyme was stable at 55°C when incubated at pH 11.0 for 60 min. Metal ions K + , Mg 2+ , Cu 2+ , Na + , and Zn 2+ exhibited a slightly stimulatory effect on enzyme activity. The enzyme retained over 80% of its activity in the presence of Ca 2+ , Ba 2+ , and Mn 2+ . Thiol reagent and ethylenediaminetetraacetic acid did not inhibit the enzyme activity, whereas phenylmethylsulfonyl fluoride significantly inhibited the protease activity. The alkaline protease from B. gibsonii 6BS15-4 demonstrated efficiency in blood stain removal and could therefore be used as a detergent additive, with potential for various other industrial applications.
Two food-grade antimicrobial substances, thymol and nisin were tested for their antimicrobial activity against 4 species of Shigella including S. boydii, S. dysenteriae, S. flexneri and S. sonnei inoculated in sugarcane juice at 4◦C. When used separately, only thymol, but not nisin, exhibited a dose-dependent and species-dependent inhibitory effect on the bacteria. When thymol and nisin were used together, the concentrations of thymol required for complete inhibition were decreased in all cases of the bacteria as the concentrations of nisin were raised, indicating the synergistic antimicrobial activity between both compounds. The effects of bacterial cell number and temperature on the antimicrobial activity of thymol and nisin against S. sonnei in sugarcane juice were investigated. The doses of both compounds required for complete inhibition were directly proportional to the number of bacterial cells in sugarcane juice. Furthermore, they inhibited the bacterium at 30◦C more efficiently than at 4ºC. The sensory evaluation showed that thymol- and nisin-treated sugarcane juice was acceptable to consumers. This study suggests that thymol and nisin can be used as food preservatives with the consideration of their dependence on bacteria species, number of contaminated bacterial cells and temperature
Seven yeast strains (UBIF12-1, UBFB13-1, SRFS56-3, SRFS57-2, SKFS62-1, SKFS66-1 and SKFS67-1) representing a single anamorphic novel yeast species were isolated from traditional Thai fermented foods in Ubon Ratchathani, Surin and Sisaket in the northeast part of Thailand. The results of analysis of the sequences of the D1/D2 region of the large subunit (LSU) rRNA gene and the internal transcribed spacer (ITS) region indicated that the seven strains showed zero to one nucleotide substitutions in the sequences of the D1/D2 region of the LSU rRNA gene, and zero to four nucleotide substitutions in the ITS region. Kazachstania humilis CBS 5658T was the most closely-related species, but with 0.7–0.9% nucleotide substitutions in the D1/D2 region of the LSU rRNA gene, and 2.0–2.2% nucleotide substitution in the ITS region. The results of a phylogenetic analysis based on the concatenated ITS and D1/D2 regions confirmed that the seven strains represented a single species of the genus Kazachstania distinct from the other recognized species of the genus. Furthermore, the morphological, biochemical and physiological properties of the seven strains not only indicated that they represented members of the genus Kazachstania, but that they were separated from K. humilis and K. pseudohumilis, the two most closely related species in the phylogenetic tree. Therefore, the seven strains were identified as representing a novel species, for which we propose the name Kazachstania surinensis f.a., sp. nov. The holotype is TBRC 15053T (isotype: SRFS57-2 and PYCC 9021). The MycoBank number of the novel species is 841892.
<abstract> <p>This research aimed to evaluate the diversity of yeasts recovered from fermented foods gathered from some areas of Northeastern Thailand. The fermented food items included Pla-som, Nham-pla, Kem-buknud, Isan-sausage, Pla-ra, Mhum-neu, Mhum-Khai-pla, Nham-neu, Nham-mu, Kung-joom, Som-pla-noi, and Poo-dong. Their probiotic characteristics were also investigated. A total of 103 yeast isolates of nine genera were identified using 28S rDNA sequencing. The yeast genera were <italic>Candida</italic> (20.3%), <italic>Diutina</italic> (2.9%), <italic>Filobasidium</italic> (1.0%), <italic>Kazachstania</italic> (33.0%), <italic>Pichia</italic> (3.9%), <italic>Saccharomyces</italic> (1.0%), <italic>Starmerella</italic> (28.2%), <italic>Torulaspora</italic> (2.9%), and <italic>Yarrowia</italic> (6.8%). Based on probiotic characteristic analysis of ten selected yeast strains, <italic>Kazachstania bulderi</italic> KKKS4-1 showed the strongest probiotic characteristics in terms of hemolytic activity, antimicrobial activity against pathogenic bacteria, tolerance to low pH and bile salt and hydrophobicity. Isolated yeasts with probiotic characteristics may be useful in fermented food and animal feed production to improve their nutritional values.</p> </abstract>
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