Microbial and Protease Fermentation of Mao-Tai Lees Alters Nutritional Composition and Promotes In Vitro Intestinal Proteolysis

Mao-tai lees (ML) is a by-product produced in the process of Mao-tai liquor production and contains high levels of crude protein, starch and fiber, and large yield. Thus, the ML has the potential to become feedstuffs alternatives in livestock production. The present study evaluated the nutritional values of ML and fermented ML (FML), including the first stage (FML I; microbial fermentation), the second stage (FMTL II; microbial fermentation), and the final stage (FFML; microbial fermentation with proteases), and explored their effects on in vitro intestinal fermentation. The results showed that the FFML had higher contents of acid detergent fiber, acid detergent lignin, crude fiber, crude protein, neutral detergent fiber, starch, Vitamin B 2 , B 6 , and B 12 , whereas the FML II presented higher contents of calcium, copper, iron, manganese, magnesium, and Vitamin B 1 compared with the other groups. Compared with the ML, the total free amino acids (FAAs) and total bioamine contents were higher in the FML II and FFML and had lower total hydrolyzed amino acids and total other free organic acids contents, among which the FFML had higher total FAAs and total bioamine contents. The FMLs had lower n -6: n -3 PUFA ratio compared with the ML; however, the FFML had lower n -6: n -3 PUFA ratio than the other groups. Furthermore, the FFML had higher concentrations of 1,7-diaminoheptane, isobutyrate, isovalerate, putrescine, and spermidine in vitro fermentation, suggesting that the FFML had greater proteolysis than the other groups. Collectively, these findings suggest that microbial fermentation with proteases could alter the nutritional composition and promote in vitro intestinal proteolysis of ML, which may be an effective way for promoting the protein utilization of ML. The study provides an effective potential strategy to develop novel feedstuff alternatives.