2.9.5. Determination of reducing power
The reducing power of rice extract was measured according to the method reported by Yen and Duh (1993) with some modifications. Each rice extract (2.5 ml) was mixed with 2.5 ml of 0.2 M sodium phosphate buffer (pH 6.6). The diluted sample was then mixed with 2.5 ml of 1% potassium ferricyanide and the dispersion was incubated at 50 °C for 20 min. Trichloroacetic acid (2.5 ml, 10%) was added to the dispersion, which was then centrifuged at 6000×g for 10 min. The upper solution (2.5 ml) was mixed with distilled water (2.5 ml) and 0.5 ml of ferric chloride (1.0%). The absorbance was measured at 700 nm.
2.10. Mineral content
Mineral analysis was determined using the method of Bhol and Bosco (2014) with some modifications. The analysis was performed using WD-XRF (Wavelength dispersive spectrometer-X-ray fluorescence), Bruker AXS, S4-Pioneer Germany. Two grams of powdered sample was mixed with 0.5 g boric acid (granulated) with a mortar and pestle. The prepared sample was then made into a 34 mm diameter pellet with the help of a 40 ton hydraulic press (10 ton pressure, 20 min pressing time). The pellets were then introduced into the sample slots of WD-XRF and analysed for the composition of elements in the samples.
2.11. Statistical analysis
The data were analysed statistically using SPSS software (SPSS PASW 18.0) and the means were separated using the Duncan’s multiple range test (P < 0.05). All the data are presented as the mean with the standard deviation.
3. Results and discussion
3.1. Length/breadth ratio, bulk density and colour
The length/breadth ratio of brown rice at different stages of puffing showed non significant (P < 0.05) variation among raw and parboiled rice kernels, whereas the expanded grain showed significant difference (P < 0.05) among the puffing stages ( Table 1). In raw rice the highest length/breadth ratio was observed in SKAU-345 (2.49) and lowest in SKAU-382 (2.34). Puffing significantly decreased the length/breadth ratio due to expansion of rice with highest in SKAU-345 (2.16) followed by SKAU-382 (1.96) and Jehlum (1.95).
Table 1.
Physical properties of brown rice at different stages of puffing.