2.3. Process of soybean hulls conversion into dietary fibre powder
The diagram of developing dietary fibre powder from soybean
hulls is shown in Fig. 1(a). Soybean hulls with around 45% moisture
content were ground into 1–1.5 mm particle size. The broken hulls
were digested at pH 1.5–2.0 by the addition of 2 N HCl, 60 C for
2 h. The hulls were then rinsed with water to neutral pH, and the
water subsequently removed by centrifugation of 5000g for
10 min. The dewatered hulls were hydrolysed at pH 10–11 by addition
of 2 N KOH, 60 C for 2 h. Similarly, the alkaline digested hulls
were rinsed with water to neutral pH, and then centrifuged at
5000g for 10 min. After acidic-basic hydrolysis, the hulls were
autoclaved at 121 C with 15 lb pressure for 10 min. Then, the hulls
were dehydrated by hot air at temperature of 60 C in a dehydrator
to reach final moisture content in range of 9–11%. Finally, the dried
hulls were ground by 1093 Cyclotec Mill Unit (Foss, Sweden) in the
size range between 150 and 250 lm as dietary fibre powder for
further analysis.