The Second Limiting Amino Acid of Ladino Clover LPC in Rats

Abstract

From the same green juice extracted from freshly harvested ladino clover, heat-coagulated and oven-dried LPC (Thermally processed LPC) and directly centrifuged and freeze-dried LPC (Freeze-dried LPC) were prepared. During the thermal processing of LPC, lysine recoverable by acid hydrolysis was reduced. Wistar strain male growing rats were given diets containing one of the LPC_s as the sole protein source with or without supplementary amino acids. Not only the body weight gain, the nitrogen retention and the protein efficiency ratio, but the apparent digestibility of crude protein was also higher in rats fed freeze-dried LPC than in those fed thermally processed LPC. Supplementation of methionine was effective in improving the nutritive value of both the LPC_s, and the rate of the improvement was greater in freeze-dried LPC than in thermally processed LPC. By the lysine supplementation in combination with methionine, the nutritive value of thermally processed LPC was further improved to as high as that of freeze-dried LPC supplemented with methionine. The addition of lysine to freezedried LPC containing supplementary methionine was ineffective. Accordingly, it is clear that lysine is the second limiting amino acid of thermally damaged LPC and LPC prepared without any thermal damages contains enough lysine to meet the requirement of growing rats. Although the plasma amino acid concentrations and the chemical score suggested that threonine or histidine might be the second limiting amino acid of freeze-dried LPC, addition of one of them to the LPC containing supplementary methionine was also ineffective.