In vitro digestibility of 15N-methionine incorporated into soy protein.

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  • ｀１５´Ｎ‐メチオニン導入大豆たんぱく質の人工消化
  • 15N メチオニン ドウニュウ ダイズ タンパクシツ ノ ジンコウ ショウカ

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Abstract

Applying the one-step process developed by Fujimaki., 15N-methionine (15N-Met) was incorporated into soy protein isolate (SPI) using Papain (EC 3.4.4.10) to obtain a 15N-Met incorporated plastein, with its Met level enhanced to that of whole egg protein.<BR>This plastein contained 2.56mg Met/16mg N, which was equivalent to about twice that of the original SPI.<BR>Ratios of Met to threonine (Thr) and of sulfur-containing amino acids to Thr in this plastein were higher than those in SPI and the essential amino acid pattern of this plastein was shown to be similar to that of whole egg Protein.<BR>To examine the in vitro digestion process of this plastein, gel filtration on Sephadex G-25 (fine) or G-15 was done With in vitro digesta using Pepsin or pepsin-pancreatin. The 15N concentration was also determined on each fraction.<BR>As the pepsin or pepsin-pancreatin digestion proceeded, 15N concentration in the fractions containing relatively small peptides increased.<BR>Thus, this finding suggests that 15N-Met incorporated plastein is easily digested by these proteolytic enzymes.<BR>Another experiment using these enzymes was undertaken to compare in vitro digestibility of this Plastein with that of SPI.<BR>It was demonstrated that this plastein contains low molecular weight peptides soluble in 10% trichloroacetic acid (TCA) than SPI. From the standpoint of the TCA insoluble proteins the in vitro digestibility of SPI is higher than that of plastein.<BR>In conclusion, the Met incorporated plastein appears to be a nutritionally excellent protein-like substance because the incorporated Met shows good digestibility in the in vitro digestion process and contributes to an improvement of nutritional values of constituent amino acids.

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