Change of available lysine in food protein by heating and smoking

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  • Inagami Kaoru
    Laboratory of Food Chemistry, Department of Food Science and Technology, Kyushu University
  • Horii Masaharu
    Laboratory of Food Chemistry, Department of Food Science and Technology, Kyushu University

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Other Title
  • 食品加工のさいにおこる蛋白質中の有効性リジンの損失に関する研究
  • ショクヒン カコウ ノ サイ ニ オコル タンパクシツ チュウ ノ ユウコウセイ リジン ノ ソンシツ ニ カンスル ケンキュウ

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Abstract

1) The amount of available lysine in food protein which was heated with sugar and treated with smoke was determined, and the relation between these treatment and content of the lysine was examined. The available lysine was determined as ε-DNP-lysine by the reaction with 2, 4-dinitrofluorobenzene. 2) Ten per cent of the lysine was destroyed when protein was autoclaved 60 minutes at 100℃, in pH 8.0 solution, and 21% when protein plus glucose was autoclaved. It seems that the available lysine of protein is reduced by two reactions of which one is a destruction of protein and the other is a Maillard reaction. 3) The reduction of available lysine in protein by heating was affected by temperature of treatment, pH of solution and concentration of sugar contained. Twenty per cent of the lysine was destroyed by heating with 3 Mol-ratio of glucose in pH 6.2 solution at 120℃ for 30 minutes. 4) Ascorbic acid, erythorbic acid, formaldehyde, acetaldehyde and furfural reduced the available lysine of protein. Nineteen per cent of the lysine was destroyed when protein was autoclaved with ascorbic acid at 100℃ for 60 min., in pH 7.8, 56% with formaldehyde in pH 6.2, 35% with furfural in pH 7.8. 5) A striking reduction of available lysine was found in sheep meat when it was exposed to smoke for 4 hrs. at 55℃. One gram of meat heated at the same temperature without smoking contained 34.6 mg of available lysine, but one gram of smoked meat contained 23.6 mg of it, so that the loss of lysine was 32%. It has been attempted to prevent from the reduction of lysine on smoking by the addition of polyphosphate and sorbitan fatty acid ester.

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