چكيده لاتين
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.
