Evaluation of dynamic physicochemical property changes of purple sweet potato (Ipomoea batatas (L.) Lam) vinegar through stepwise fermentation

Tan, Sin Yun (2025) Evaluation of dynamic physicochemical property changes of purple sweet potato (Ipomoea batatas (L.) Lam) vinegar through stepwise fermentation. Final Year Project, UTAR.

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Abstract

Vinegar is a health-beneficial condiment produced from two-stage fermentation involving alcohol conversion and subsequent acetification using high-sugar materials. However, vinegar production from starchy materials, such as purple sweet potato and cassava, has been rarely studied due to the limited conversion of starch to sugar. Since agarwood leaves are an underutilized by-product of agarwood cultivation, their infusion has been incorporated to enhance the physicochemical properties of vinegar, such as total phenolic content. This study aimed to evaluate the effects of different substrates and the presence of agarwood leaf infusion on the physicochemical and biochemical properties of vinegar production. Purple sweet potato and cassava obtained from the local market were saccharified using Aspergillus oryzae, followed by alcohol and vinegar fermentation. During this process, dynamic changes in the biochemical properties of vinegar were monitored, alongside phytochemical qualitative screening and organic acid analysis. Purple sweet potato showed a sugar content of 28.40 %wb, but the amino acid content after saccharification was lower compared to cassava. Vinegar incorporated with agarwood leaves displayed a similar trend in alcohol content as the water-treated samples. Dynamic changes in vinegars showed an increase in pH and a decrease in alcohol content during acetic acid fermentation. The total phenolic content of agarwood-treated vinegar was higher than that of water-treated vinegar. Quantitative analysis revealed that the acetic acid ranged from 1.176 mg/mL to 4.536 mg/mL for both vinegars. Besides, similar acetic acid production was observed in the water-treated and agarwood-treated vinegar at Day 10. The study showed higher potential for purple sweet potato for vinegar production. In addition, the incorporation of agarwood tea improved the biochemical properties of the vinegar while not affecting the alcohol content throughout the fermentation process and acetic acid level at the end of acetic acid fermentation.

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