Optimising substrate conditions for microbial fermentation of vinegar residue

Abstract

The aim of this study was to investigate the effects of additives on the nutritional value of fermented vinegar residue. Molasses, urea, and wheat bran were added to the vinegar residue fermentation system as a carbon source, nitrogen source, and a combined source of both carbon and nitrogen, respectively. Molasses was added at the following proportions: 0, 1.5, 3 and 4.5%, urea at 0, 0.5, 1.0 and 1.5%, and wheat bran at 0, 5, 10 and 15%. Fermentation was performed using five strains of fermenting bacteria in laboratory silage bags. After four weeks, the quality of vinegar residue fermentation was evaluated using sensory index, pH value, raw ash, and crude protein contents, as well as levels of ammonia-nitrogen and short-chainfatty acids (including lactic, acetic, propionic, and butyric acids). The results revealed that the addition of 3 and 4.5% molasses significantly improved the pH value, and lactic acid concentration in the vinegar residue (P < 0.05). The addition of 4.5% urea significantly increased the pH value, lactic acid concentration, ash and crude protein contents, while decreasing the acetic acid concentration in the vinegar residue (P < 0.05). The inclusion of 15% wheat bran significantly elevated the sensory index and crude protein content, but reduced the pH value, dry matter content and acetic acid concentration in the vinegar residue (P < 0.05). So, the nutritional quality of vinegar residue can be improved by incorporating carbon and nitrogen sources into the fermentation system. The addition of 15% wheat bran appears to be an optimal choice for stimulating vinegar residue fermentation, surpassing the effectiveness of utilising carbon (molasses) and nitrogen (urea) sources individually.