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Assessment of the nutritional quality of proteins: the use of ‘ileal’ digestibilities of amino acids as measures of their availabilities*

Published online by Cambridge University Press:  09 March 2007

S. C. Achinewhu  and
D. Hewitt
S. C. Achinewhu
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading RG2 9AT
D. Hewitt
Affiliation:
National Institute for Research in Dairying, Shinfield, Reading RG2 9AT
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Abstract

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1. A comparative study was made of two biological techniques for assessing protein quality in wheat and barley, and in a soya-bean-protein isolate both as received, and after being heat damaged by autoclaving. Amino acid digestibility was determined by the ‘ileal’ analysis technique while amino acid availability was measured in growth assays. Some chemical and microbiological tests were also done.

2. Heat treatment of the soya-bean-protein isolate caused little change in amino acid composition but the digestibility of all amino acids and the availability of lysine and methionine were severely reduced, lysine being most affected. The reduced availability of lysine was not entirely attributable to impaired digestibility.

3. The amino acids in wheat and barley were highly digestible. The availability of methionine and lysine in barley and of methionine in wheat was high, whereas the availability of lysine in wheat was apparently much lower.

4. The results showed that for methionine, digestibility values are a fair measure of the availability. In heat-damaged soya-bean-protein isolate however, digestibility of lysine over-estimated the availability, indicating that amino acid digestibility may sometimes provide a misleading indication of nutritional value.

Type
Papers on General Nutrition
Information
British Journal of Nutrition , Volume 41 , Issue 3 , May 1979 , pp. 559 - 571
Copyright
Copyright © The Nutrition Society 1979

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