Effect of enzymatic extraction treatment on physicochemical properties, microstructure and nutrient composition of tartary buckwheat bran: A new source of antioxidant dietary fiber

The effect of enzymatic treatment with amylase and cellulase on Tartary Buckwheat (F. tataricum Gaertn) bran dietary fiber was evaluated by studying its chemical composition, physicochemical property and microstructure. Tartary buckwheat bran flour, obtained from residues of tartary buckwheat processing exhibited high contents of dietary fiber (44.2 +/- 0.3%), starch (31.94 +/- 0.27%), lipid (5.18 +/- 0.14%) and total ash (2.91 +/- 0.04%), and a low level of crude protein (3.12 +/- 0.11%). The contents of hemicellulose, cellulose and klason lignin were 23.80 +/- 0.21%, 17.48 +/- 0.25% and 4.06 +/- 0.21%, respectively. Total polyphenols and total flavonoids contents were 13.32mg GAE/g and 37.43mg RE/g, respectively. The water holding capacity (WHC) and swelling capacity (SC) were 2.22 +/- 0.07 g/g and 2.33 +/- 0.10 mL/g. After the extraction process with amylase, the dietary fiber, total polyphenols, total flavonoids contents of crude enzymatic extract were increased to 83.5 +/- 0.27%, 27.61 mg GAE/g, 52.14 mg RE/g, respectively. Its WHC and SC also grew up to 2.38 +/- 0.12 g/g and 4.67 +/- 0.09 mL/g, while the starch content was decreased significantly. The crude enzymatic extract from tartary buckwheat bran was modified by cellulase. After the modification treatment, the increasing proportion of soluble dietary fiber (SDF) against total dietary fiber (TDF) was detected, and its WHC and SC also grew up to 2.58 +/- 0.11 g/g and 5.13 +/- 0.12 mL/g respectively. By Small angle X-ray scattering (SAXS) analysis, it was also learned that the size of DF particles were decreased, which had a positive correlation with WHC and SC. The SEM photos showed that the modification processing increased the surface area of DF.