بررسي تاثير كشت هاي آغازگر بر پويايي جامعه ميكروبي طي تخمير اسيد استيك

Vinegar is one of the most widely consumed fermented products with a history of several thousan‎d years. In addition to its role in flavoring an‎d preserving food, it holds a special place in the food industry an‎d health-promoting products due to its medicinal an‎d nutritional properties. Vinegar production mainly involves two fermentation stages: alcoholic fermentation by yeasts an‎d acetic acid fermentation by acetic acid bacteria. Although spontaneous fermentation is a common an‎d inexpensive method, it faces challenges such as low controllability, the possibility of methanol production, an‎d variable quality. For this reason, the use of starter cultures has been proposed as a novel approach to improve the quality an‎d stability of the production process. In this study, second-grade yellow apples were used as the substrate for vinegar production. The starter cultures included Acetobacter aceti (accession number CCUI-9901), Acetobacter senegalensis (CCUI-1002), Acetobacter cerevisiae (CCUI-1005), Gluconobacter oxydans (CCUI-1010), an‎d the yeast Saccharomyces cerevisiae (M02) . Bacterial characteristics such as colony morphology, absence of mutual inhibitory effects, an‎d tolerance to different concentrations of ethanol an‎d acetic acid were eva‎luated. Then, five fermentation tanks with different combinations of bacteria, yeast, pectinase enzyme, Organic an‎d inorganic nitrogen were designed an‎d monitored over six months in terms of microbial population dynamics an‎d changes in determination of acetic acid, methanol an‎d residual sugars, as well as molecular identification of emerging yeasts. According to the results, in tank 1, M02 yeast was initially dominant until day 15, but after 90 days Acetobacter senegalensis an‎d Acetobacter aceti were added to it. In tank 2, M02 yeast was initially dominant, but after day 30 a new yeast species appeared an‎d became the dominant microorganism an‎d on day 60, the highest number of bacteria was present. In tank 3, M02 yeast was initially dominant, but after day 30 it was eliminated an‎d on day 45, the highest number of acetobacters was recorded. In tank 4, type 2 yeast appeared next to M02 yeast from day 30 onwards until the end of the process. In tank 5, no yeast was initially present, but from day 15 yeast type 3 appeared, followed by yeast type 1 on day 45. Findings also showed that the tanks inoculated with starter cultures containing, M02 yeast, Acetobacter aceti, an‎d Acetobacter senegalensis had the highest acetic acid production ( 39.5 to 64 g/L) an‎d significant pH reduction to about 2.8, while in tanks without starters, acetic acid production was about 3.8 g/L. The methanol concentration in all tanks remained below the permissible limit (10 mg/L). Examination of the reducing sugar content in all tanks was also below the permissible limit (0.05 g/L). Furthermore, three yeast strains, including Pichia kudriavzevii, Pichia manshurica, an‎d Saccharomyces cerevisiae, were isolated an‎d identified at different times during fermentation. These strains have high potential to create desirable aromatic profiles. Overall, the results demonstrated that the targeted use of starter cultures can accelerate fermentation an‎d improve the final quality of vinegar.

5

دكتر بهروز صالحي اسكندري

150975