Litchi (Litchi chinensis Sonn.) seed starch as a sustainable feedstock for vinegar fermentation: enhancement of quality and bioactive properties

Litchi (Litchi chinensis Sonn.) seeds, a major by-product of litchi processing, represent an important source of starch and bioactive components. This study systematically investigates the effects of different hydrolysis methods on starch hydrolysates and their subsequent conversion into vinegar. The results indicated no significant differences in the parameters between acid and enzymatic hydrolysates. However, the enzymatic method produced higher ethanol and total acid concentration than the acid method. Additionally, the content of total phenolic, total flavonoid, and DPPH radical scavenging capacity were increased by 13.67 %, 12.01 %, and 11.40 %, respectively, in the enzymatic hydrolysates. The vinegar yield was fourfold the raw material mass, with a total acidity exceeding 50 g/L. Furthermore, enzymatic fermented vinegar enriched with over 20 active components, such as epicatechin and naringenin 7-O-glucoside. The lactic acid to acetic acid ratio increased from 0.29 to 2.17 in vinegar fermented with Acetobacter oryzoeni compared to that fermented with Acetobacter pasteurianus. Lactic acid emerged as the dominant organic acid, and the fermented vinegar was characterized by the presence of isoamyl acetate, geraniol, limonene, and other flavor components typical of litchi. The research results established an important foundation for the resource utilization and development of characteristic fermented products of litchi seed starch.