Metaproteomics reveals protein composition of multiple saccharifying enzymes in nongxiangxing daqu and jiangxiangxing daqu under different thermophilic temperatures

Daqu provides hydrolytic enzymes that saccharifying the macromolecular carbohydrate in fermenting grains. The process of saccharification is the premise of Baijiu production. But little is known about the protein composition associated with the activity of saccharifying enzymes in daqu. This study investigated related proteins between nongxiangxing daqu and jiangxiangxing daqu by metaproteomics. We present that the amylase system (α-amylase, glucoamylase and α-glucosidase) and cellulase system (cellobiohydrolases, endoglucanase and β-glucosidase) are regarded as the main saccharifying enzymes. Combined with protein-based taxonomic annotation, the key proteins involving in amylase system were mainly from Kroppenstedtia, Lichtheimia, Byssochlamys and Thermomyces, while Thermoascu contributed the most to cellulase system. Moreover, it was found that the up-regulated amylase proteins at thermophilic fermentation period in jiangxiangxing daqu in comparison with nongxiangxing daqu were affiliated to Aspergillus, Rhizomucor, Byssochlamys and Thermomyces, along with Thermoascu contributing to cellulase system. These findings will provide clues for improving saccharification efficiency in Baijiu production.