Amyloglucosidase

The sauce-flavored high-temperature Daqu samples were provided by Kweichow Moutai Co., Ltd. (Zunyi, China). At the end of Daqu fermentation on day 40, 39 samples were randomly collected from different parts of the Daqu fermentation rooms. After treatment with liquid nitrogen, the samples were stored at −40°C for later use. Among them, BQ 1, BQ 2, and BQ 3 were three parallel samples of BQ; YQ 1, YQ 2, and YQ 3 were three parallel samples of YQ; and WQ 1, WQ 2, and WQ 3 were three parallel samples of WQ. These nine samples were used to evaluate the metabolites of Daqu. BQ I-X, YQ I-X, and WQ I-X were the other 10 samples of BQ, YQ, and WQ, respectively, used to determine the content of melanoidins. The raw materials wheat and mother Daqu for Daqu-making were provided by Kweichow Moutai Co., Ltd.
The chemical reagents used in the experiment were of analytical or chromatographic grade. Methanol, acetonitrile, ammonium acetate, and formic acid were purchased from CNW Technologies (Düsseldorf, Germany). α-Amylase, amyloglucosidase, dispase, and Flavourzyme were purchased from Shanghai Yuanye Biological Technology Co., Ltd. (Shanghai, China). DNS color reagent (3,5-dinitrosalicylic acid) was purchased from Beijing Soleibao Technology Co., Ltd. (Beijing, China). Ninhydrin and reduced ninhydrin were purchased from Sangon Biotech Co., Ltd. (Shanghai, China).

Sweet potatoes (cultivar “Xinxiang”) were purchased from a local market in Hangzhou, Zhejiang Province, China. Taka-diastase, amyloglucosidase, pancreatin, d-glucose, and inulin were purchased from Yuanye Bio-Tech Co., Ltd. (Shanghai, China). de Man, Rogosa and Sharpe (MRS) broth was purchased from Hope Bio-Technology Co., Ltd. (Qingdao, China). Monosaccharide standards (l-arabinose, l-fucose, l-rhamnose, d-galactose, d-glucose, d-mannose, d-ribose, d-glucuronic acid, and d-galacturonic acid) and SCFA standards (acetic acid, propionic acid, and n-butyric acid) were purchased from Sigma-Aldrich Chemical Co. (Shanghai, China). All other chemicals and reagents used in this study were of analytical grade. L. plantarum (RBHZ 68), L. reuteri (MFHZ 18), L. acidophilus (GFHZ 41), and L. rhamnosus (MFHZ 77) were gifted by the Vegetable Processing Laboratory at the Food Science Institute at the Zhejiang Academy of Agricultural Sciences.

Fresh, pest- and disease-free sweet potatoes were peeled (Longshu No.9, purchased from Yonghui Supermarket). Then, they were combined with water in a 1:2 (w/w) ratio in the pulping wall-breaker (SP301S, Zhejiang Supor Co., Ltd., Hangzhou, China). The slurry of sweet potato was kept at 95°C for 2 h after 10 U/g of high-temperature amylase (20,000 U/mL, provided by Shanghai Yuanye Bio-Technology Co., Ltd.) addition and then kept at 40°C for 3 h after 20 U/g amyloglucosidase (100,000 U/mL, provided by Shanghai Yuanye Bio-Technology Co., Ltd.). The sweet potato slurry was then split into 250 mL shake flasks containing 100 mL of liquid. The liquid is then pasteurized and stored at 4°C for future fermentation studies.