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Intestinal Zinc and Carboxypeptidase A and B Activity in Response to Consumption of Test Meals Containing Various Proteins by Rats¹

Department of Nutrition, University of California, Davis, CA 95616

Rats were fed test meals containing 23% protein as casein (C), soy protein isolate (SPI) or egg white (EW) to assess effects of dietary protein sources on the amount of zinc and carboxypeptidase (CP, CPA, CPB) activity in the small intestinal contents. Groups of six rats each were killed at 1, 2.5 and 5 h postprandial and six rats fasted for 19 h served as a 0 time control. Consumption of a test meal increased the weight of small intestinal contents at 1 and 2.5 h compared with unfed animals and in a similar manner for all three protein sources. However, at various times during the postprandial period differences in the level of zinc and CP activity within the small intestinal contents among the three dietary protein sources were observed. Both the SPI and EW groups had significantly higher levels of CPA and CPB activity at 1 h postprandial than the C group. Only in the SPI group was the intestinal level of zinc increased at 1 and 2.5 h compared with the unfed group. At 1 and 2.5 h postprandial intestinal zinc was significantly higher in the SPI group than in the C and EW groups. The results indicate that the disappearance of zinc from the intestine is delayed in rats fed SPI, probably because of the presence of phytate.

KEY WORDS: • soy protein isolate • zinc • carboxypeptidase • pancreas • phytate • casein • egg white

¹ Supported in part by a grant from U.S. Department of Agriculture and by National Institutes of Health Grant No. DK20446.

² Present address: ORSTOM-Nutrition, Institute Bouisson-Bertrand, Zolad, rue de la Croix Verte, 34100, Montpellier, France.

³ To whom reprint requests should be sent.

Manuscript received 3 September 1987. Revision accepted 25 January 1988.