Determination of total dietary fiber (TDF)

TDF was measured by the enzymatic-gravimetric AOAC method (Lee et al., 1992). A total of 0.5 g of defatted four types of analog rice was added into an Erlenmeyer flask, with 25 mL of 0.08 M phosphate buffer (pH 6.0) and 50 µL of α-amylase. The mixture was then incubated at 95°C for 30 min and cooled. When the mixture reached pH 7.5, 5 mL of 0.275 N NaOH was added. The mixture was then incubated at 60°C for 30 min in a swaying water bath at pH 4.5 with 0.325 N HCl. Amyloglucosidase (150 µL) was then added and the mixture was further incubated at 60°C for 30 min and filtered. To determine the TDF content, the rice was treated with a 95% (v/v) ethanol (ethanol/rice analog ratio of 4:1) at room temperature for 1 h to precipitate the soluble fiber and remove depolymerized proteins and glucose from starch. The residues were filtered on G4-sintered glass and washed sequentially with 78% and 95% (v/v) ethanol and absolute acetone, and dried to a constant weight at 40°C (Lee et al., 1992; Mandalari et al., 2010).