Optimization of processing parameters for extraction of total, insoluble and soluble dietary fibers of defatted rice bran

Response surface methodology was used to optimize the processing parameters for extraction of total dietary fiber (TDF), insoluble dietary fiber (IDF) and soluble dietary fiber (SDF) of defatted rice bran (DRB). The studied independent factors were concentration of NaOH solution (varying from 0.15 to 0.25 mol/L), soaking time (from 60 to 90 min), alpha-amylase enzyme - substrate (E: S) ratio (from 0.6:100 to 0.9:100 g: g of dry DRB) and alcalase enzyme concentration (from 3.5:100 to 4.7 g: g of dry DRB)) whereas; the dependent variables were extraction yield and purity of TDF, IDF and SDF. Therefore, the three- level four-factor Box-Behnken design was used to establish the optimum conditions and the generated regression quadratic polynomial models and adequacy of each dependent variable were significant (p < 0.0001) with regression coefficient R2 (> 0.90) and lack of-fit was not significant. Moreover, ANOVA showed that most of the linear, interaction and quadratic regression coefficient values were significant (p < 0.05). The optimum processing parameters observed for extraction of TDF, IDF and SDF with high yield and purity were: 0.15 mol/L NaOH solution concentration, 64.3 min soaking time, 0.68:100 and 3.52:100 (g: g) alpha-amylase and alcalase enzyme - substrate ratio (E: S), respectively. Moreover, the alkali pretreatment was the factor amongst the others that significantly (p<0.05) affected the purity of Fiber fractions but did not contribute to improve their yields.