Amyloglucosidase

Buckwheat flour was obtained from Liangchen Century Grain Co., Ltd. (Wuxi, China). Psyllium fibre was provided by Xuzhou Nature Food Co., Ltd. (Xuzhou, China). Instant dry yeast was purchased from Angel Yeast Co., Ltd. (Yichang, China). Maize oil and salt were obtained from local stores in Wuxi, China. Pepsin (P7000) and pancreatin (P7545) used for starch digestion assays were obtained from Sigma–Aldrich Chemical Co., Ltd. (St. Louis, MO, USA). Amyloglucosidase was obtained from Megazyme Inc. (Bray, Ireland). The glucose quantification kit, which employs the glucose oxidase method, was obtained from Nanjing JianCheng Bioengineering Institute (Nanjing, China).

Sand rice (Agriophyllum squarrosum) was harvested in the Gansu province of China. The ɑ‐amylase from the hog pancreas (50 U/mg) was obtained from Sigma‐Aldrich (China) Co., Ltd. The amyloglucosidase (200 U/ml) was purchased from Megazyme International Ireland Ltd. Glucose oxidase‐peroxidase assay kit was bought from the Applygen Technologies Inc. All other chemicals of analytical grade were obtained from Sinopharm Chemical Reagent Co., Ltd.

The in vitro digestibility kinetics of starch was determined as described by Goñi et al. (10 (link)) with slight modifications. 15-mL sodium acetate buffer solution was mixed with 200 mg starch (dry basis). Then Amyloglucosidase (15 U/mL) and porcine pancreatic α-amylase (290 U/mL) (total 10 mL) (Megazyme) and seven glass were added to that solution. The mixed liquids were reacted in a shaking bed (37°C, 150 rpm). At 10-, 20-, 30-, 60-, 90-, 120- and 180-min, absolute ethanol (4 mL) was added to the supernatant (0.5 mL). This solution was centrifuged at 6,000 × g for 15 min at 10°C, and the supernatant was transferred to glucose oxidase-peroxidase to analyze the glucose content. The percentage of enzymatic hydrolysis was calculated as follows (11 (link)):
where 0.9 is the transformation coefficient from starch to glucose (162/180 w/w), 25 is the dilution factor, and glucose concentration within t min was defined as G_t.
The equilibrium concentration (C_∞) and speed rate constant (k) (h⁻¹) were obtained from the enzyme hydrolysis curves, and the first-order formulas were as follows:
where AUC is the area under the fitted curve, t₀ and t_f are the initial and final times of hydrolysis, and t is the time of in vitro digestibility kinetics (min).

A total of twenty-one commercial beer samples were purchased from local RT-Mart in Tai’an, and Jingdong online mall, China, including fifteen wheat and six barley malt beers. Amyloglucosidase (Enzyme Commission (EC) number 3.2.1.3) and β-glucan assay kit (K-BGLU) were purchased from Megazyme International (Bray, Ireland). Monosaccharide standards including L–arabinose, D–xylose, D–galactose, D–mannose, and D–glucose were obtained from Sigma-Aldrich Co. (Saint Louis, Missouri, USA). All other chemicals such as phenol, sulfuric acid, ammonium hydroxide, sodium borohydride, trifluoroacetic acid, 1–methylimidazole, acetic anhydride, and dichloromethane were of at least analytical grade.