بررسي ميكروبيوتاي قابل كشت و پويايي آن در طي تخمير سيب

Vinegar is one of the most widely consumed fermented condiments in the world, which has abundant microbial resources and is obtained through a two-stage fermentation process. In the first stage, fermentable sugars are converted into ethanol by yeasts, and in the second stage, acetic acid bacteria oxidize ethanol to acetic acid. Both stages occur spontaneously by fermentation. Several factors affect the quality and properties of fermented foods. Vinegar is also known as a natural preservative due to the antimicrobial activity of acetic acid. In the competitive arena, maintaining the quality of fermented foods is of particular importance. Investigating the presence of pathogenic bacteria in fermented products during different stages of production and also examining the dynamics of the microbial population involved in fermentation are among the important factors affecting the quality of fermented foods. In this study, a six-month fermentation process of apple cider vinegar was considered in four tanks with different treatments (1- washed apples, 2- unwashed apples, 3- containing Saccharomyces cerevisiae yeast starter, 4- containing Acetobacter sengalnis starter) and for six months and after pulping, periodic microbial tests including periodic cultivation of yeasts, lactic acid bacteria and acetic acid bacteria were performed every fifteen days and the colonies were examined. Finally, the isolates were identified by molecular methods. The yeasts isolated in the fermentation tanks without adding starter were identified as Pichia species, while in the six-month fermentation process of the fermentation tank containing Acetobacter bacteria, no yeast was counted and only Acetobacter was counted in this tank. The lactic acid bacteria in the fermentation tanks without adding starter were identified as Lactobacillus faraginis and Lactobacillus paracasei. Also, the bacteria identified from fermentation tanks 1, 3 and 4, which grew on the medium related to Lactobacillus, were identified as Acetobacter pastorianus. Indicative pathogenic bacteria such as coliforms and Bacillus cereus were detected and identified. Non-fecal and culturable coliforms were eva‎luated in specific media of the Enterobacteriaceae family. Coliforms were present only at time 1 and the beginning of fermentation, which was detected by the MPN method as more than 1100 coliforms per ml. And with the beginning of the fermentation process and after it, the presence of coliforms was reported to be less than 3 per ml and then negative. Bacillus and its resistant spores can be detected in the specific culture medium for Bacillus (MYP Agar). Tests related to Bacillus cereus in the specific culture medium indicated the absence of this bacteria at the beginning and during the fermentation process. During this six-month period and after that, periodic chemical tests including pH measurement and titration measurement were eva‎luated. In periodic chemical tests, the measured pH of the fermentation tank containing Acetobacter bacteria had a lower range than the other tanks, while the amount of acetic acid produced by titration was measured to be the highest in the tank. In GC mass analysis of the initial compounds of apple juice, no compounds were found, while after the final fermentation of the fermentation tank containing Acetobacter starter, acetic acid, ethanol and methanol were identified. According to the results obtained, a starter is needed to start the fermentation process and without adding a starter, the fermentation process does not proceed well and severe contamination with Fusarium mold occurs. Also, according to the tests conducted, there is no need to worry about using homemade vinegar if hygiene issues are not observed.

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