Tatsuyuki Sugahara

Nitrogen-to-Protein Conversion Factors for Some Cereal Products in Japan

To evaluate a practical method of determining more accurately conversion factors for calculating the protein contents of foods from the total nitrogen content, 19 cereal products found in Japan were analyzed for total nitrogen, amino acid nitrogen, and amide nitrogen, and then the nitrogen-to-protein conversion factors were calculated. The average conversion factors were 5.75 for rice, 5.81 for wheat, and 5.95 for others. These values, corresponding to the proportion of the amino acid residue to amino acid nitrogen recovered from 20 amino acids, were lower than the currently applied factors to these foods, except for wheat flour and amaranth. The use of this factor for estimating the protein content results in a considerable difference from the estimate based on amino acid residue concentrations, due to the wide variations in amino acid composition and to the presence of a significant level of nonprotein nitrogen. The distribution of the protein nitrogen recovered from the amino acids to total nitrogen averaged 93%. Adjusted conversion factors corresponding to the proportion of the amino acid residue to total nitrogen averaged 5.26 for rice, 5.47 for wheat, and 5.54 for other cereal products. Protein contents estimated using these factors are in good agreement with the contents defined as amino acid residues.

Components Characterizing Taste of Konbu-Dashi

こんぶだし汁の味を特徴づける成分を明らかにするため, 分析値をもとに調製したグルタミン酸, アスパラギン酸, 5-AMP, マンニトール, 塩化カリウム, 塩化ナトリウムよりなる合成だし汁から, 一成分ずつを除去し, オミッションテストを行った.また市販の合成だし汁に塩化カリウムと塩化ナトリウムの割合を変えて加え, 味の違いを検討した.結果は, 次のように要約された.1) こんぶだし汁の味に大きく関与する成分は, グルタミソ酸, カリウム, ナトリウムであった.2) 市販の合成だし汁に, 塩化カリウムを添加した塩化ナトリウムを加えたところ, 塩化ナトリウムのみを加えた場合よりも総合評価において高く評価された.