An improved method for protein determination in persimmon [Diospyros kaki] fruit
1991
Matsui, T. (Kagawa Univ., Miki (Japan). Faculty of Agriculture) | Kitagawa, H.
Different methods of protein determination were examined using persimmon cv. Atago which contains high amount of tannin and is normally astringent. Micro-Kjeldhal is accurate and stable against polyphenols compounds but takes time whereas Lowry, dry reagent and micro-Biuret methods are affected by polyphenol compounds. The protein content determined by the last three methods was lower when astringency was removed by heat treatment. However, micro-Kjeldhal did not detect this difference in protein content between untreated and heat-treated fruits. To protect the protein from polyphenolic disturbance, trichloroaceteic acid (TCA) was added to the fruit extract. The protein value increased in the presence of TCA. Lowry and dye reagent methods sometimes resulted in negative readings and were thus not applicable to protein assay. When the protein of persimmon fruits which contain large amount of tannin will be analyzed by micro-Biuret, the protein value obtained when TCA is added (blank) should be subtracted from the sample reading (without TCA). Micro-Biuret method is rapid and the value obtained was comparable to that of micro-Kjeldhal
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