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A colorimetric bran pigment method for determining the degree of milling of rice
Author(s) -
Bhattacharya K. R.,
Sowbhagya C. M.
Publication year - 1972
Publication title -
journal of the science of food and agriculture
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.782
H-Index - 142
eISSN - 1097-0010
pISSN - 0022-5142
DOI - 10.1002/jsfa.2740230203
Subject(s) - absorbance , bran , pigment , chemistry , chromatography , solvent , extraction (chemistry) , brown rice , colorimetry , degree (music) , filter paper , aqueous solution , raw material , mathematics , analytical chemistry (journal) , food science , organic chemistry , physics , acoustics
The alkaline alcohol bran‐pigment extraction method has been developed into a simple and reliable quantitative colorimetric method. A requisite quantity (0.1‐1.0 g, depending on the degree of milling of the sample) of rice powder is soaked overnight with a 1:2 (v/v) mixture of 2% aqueous KOH‐ n ‐propanol (1 ml for each 0.1 g powder). Next day, the balance of 10 ml of the solvent is added, the mixture vigorously shaken and centrifuged. The yellow‐brown solution is read in a Spectronic 20 (filter colorimeters did not give linear readings) at 400 nm. On plotting the absorbance/g/10 ml data expressed as percentage of that of the corresponding brown rice against the degree of milling, the values in three raw and one parboiled rice varieties fell into a single smooth curve. The extent of milling of an unknown sample could, therefore, be determined by testing its absorbance and that of the corresponding brown rice. The extractant chosen, selected from different solvent combinations, gave a clear extract and a negligible difference in reading between normal and red rice kernels. The intensity of the colour was maximum at about pH 10.5 and above, and its λ max was at 360 nm (but 400 nm was used for convenience). The colour was rather unstable, but was more stable in presence of excess rice flour. Hence it was necessary to use a constant rice‐to‐solvent ratio during the extraction for all analyses. The concentration of the extractable pigment in successive layers of bran decreased linearly from the outermost to the innermost layer. The fat content, on the other hand, first increased and then decreased.