2.2.2. Glucose, Arabinose, Xylose, Total B-Glucans, Total Arabinoxylans, and Resistant Starch Determination

According to the manufacturer's protocol, the BSG extract and the three soluble fiber dry residues previously described, obtained in the total dietary fiber assay, were prepared for carrying out the determination of (1) free glucose, (2) glucose deriving from rapidly digestible starch and slowly digestible starch, (3) glucose from resistant starch, (4) arabinose, (5) xylose, (6) AXs, and (7) β-glucans using the commercially available kits for the measurements of xylose, arabinose, glucose, and mixed linkage β-glucan (Neogen, Lansing, MI, USA).

As far as the BSG extract is concerned, glucose, arabinose, and xylose, present in the extract before hydrolysis, were quantified by spectrophotometric analysis [24,25], using three calibration curves prepared with standard compounds at known concentrations. The results of these analyses provided the content of free simple sugars originally present in BSG extract. Then, BSG extract was submitted to hydrolysis with α-amylase and α-glucosidase at 60 ◦C for 30 min and for 4 h to obtain the content of glucose derived from rapidly digestible starch and slowly digestible starch and from resistant starch, respectively. Subsequently, glucose, and arabinose and xylose present in the extract after the hydrolysis of β-glucans and AXs, respectively, were quantified by spectrophotometric analysis. BSG extract β-glucan and AX concentrations were calculated on the basis of glucose, and arabinose and xylose concentrations, minus free glucose, and free arabinose and xylose, originally present in the extract before the enzymatic hydrolysis.

With regards to the soluble fiber dry residues obtained from the total fiber assay, glucose, and arabinose and xylose, present in the dry residue after the hydrolysis of β-glucans, AXs, and resistant starch, respectively, were quantified by spectrophotometric analysis, and β-glucan, AX, and resistant starch concentrations were calculated on the basis of glucose, and arabinose and xylose concentrations.
