High-efficiency fungistatic activity of vegetable waste-based humic acid related to the element composition and functional group structure

Vegetal foods are one of the most consumed commodities globally, accounting for more than 40 % of total food wastage. Hydrothermal conversion is an innovative transformation method towards effective utilization for vegetal waste to generate value-added products which are more eco-friendly and sustainable. In this study, the vegetable wastes of Chinese cabbage (C), broccoli (B) and sweet potato (S) were used to prepare humic acids (HAs) by hydrothermal conversion. The KOH concentration was the key factor affecting the preparation of HA. There was a significant difference in S element (p < 0.05), which followed the order of S-HA (1.48 %) > C-HA (0.57 %) > B-HA (0.43 %). The proportions of HAh, HAm, and HAl with molecular weights of > 100, 10–100, and < 10 kDa were 49.89–52.62 %, 23.70–27.92 %, and 18.75–21.13 %, respectively. HAs were rich in oxygen-containing functional groups such as CO, CC, and COOH. The fungistatic activities of Botrytis cinerea and Phytophthora capsici Leonian by S-HA were higher than those of other HAs. Through Mantel analysis and redundancy analysis, it was shown that element S and structure of aliphatic compounds had important effects on the fungistatic activity. In summary, hydrothermal conversion provided a new theory and technical guidance for the high-value utilization of vegetable waste.