The total dietary fibre (TDF) content was determined using the enzymatic–gravimetric method [Method 985.29, AOAC (1997)]. The defatted samples were gelatinised with α-amylase at 95 °C for 15 min, followed by enzymatic digestion by protease for 30 min at 60 °C. The protein and starch contents were removed with amyloglucosidase at 60 °C for 30 min. The residue obtained from the first filtration was insoluble dietary fibre (IDF). The filtrate was then added with four volumes of 95% ethanol (pre-heated to 60 °C) to precipitate the soluble dietary fibre (SDF) overnight at room temperature. The precipitates were filtered and washed successively with 78% ethanol, 95% ethanol and acetone. The residue was then oven-dried (105 °C) overnight.
The values obtained using the enzymatic method was then corrected by determining the nitrogen content with the Kjeldahl method and ashing at 525 °C.