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Production of Proline-Rich Proteins by the Parotid Glands of Rats Is Enhanced by Feeding Diets Containing Tannins from Faba Beans (Vicia faba L.)^1,2,

Alfons J.M. Jansman^*,, Andrew A. Frohlich^** and Ronald R. Marquardt^**

^* TNO Nutrition and Food Research, Department of Animal Nutrition and Physiology (ILOB), P.O. Box 15, 6700 AA Wageningen, The Netherlands Agricultural University, Department of Animal Nutrition, Haagsteeg 4, 6708 PM Wageningen, The Netherlands ^** University of Manitoba, Department of Animal Science, Winnipeg, Manitoba, Canada R3T 2N2

Feeding a casein-based diet with either 400 g/kg of tannin-containing faba bean hulls (Vicia faba L.) (1.41% condensed tannins) or 60 g/kg of a tannin-rich hull extract of faba beans (1.99% condensed tannins) to rats over a period of 7 d resulted in a 2.6 and 1.5 fold increase in weight of the parotid glands, respectively, (P < 0.05) and a corresponding 5.5 and 3.7 fold increase in the level of proline-rich proteins in the glands (P < 0.05). In a dose-response experiment, increasing the level of tannin-rich hull extract in the diet (0.0, 3.8, 7.5, 15.0, 30.0 and 60.0 g/kg) resulted in a linear increase in both the relative size of parotid glands (R² = 0.90; P < 0.05) and the quantity of proline-rich proteins in the glands (R² = 0.89; P < 0.05). The apparent digestibility of total (R² = 0.97) and individual amino acids (R² varied from 0.27 to 0.99) decreased linearly (P < 0.05). The quantity of proline-rich proteins in the cecum of rats was estimated from the decrease in digestibility of proline, glycine and glutamic acid. The estimated secretions of proline-rich proteins, when calculated on the basis of the three respective amino acids, were 3.5, 3.5 and 3.9 mg of proline-rich proteins per 10 mg of additional hull extract (21.8% condensed tannins). The results indicate that tannins from faba beans stimulate the parotid glands to increase the secretion of proline-rich proteins in rats. The proline-rich proteins then interact with dietary condensed tannins to reduce their antinutritional effects.

KEY WORDS: • rats • faba beans • tannins • parotid glands • proline-rich proteins

¹ This research was financially supported by the Faculty of Agricultural and Food Sciences of the University of Manitoba in Canada, the National Science and Research Council of Canada, as well as by the TNO Toxicology and Nutrition Institute and the Wageningen Agricultural University in The Netherlands.

² The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore be hereby marked "advertisement" in accordance with 18 USC section 1734 solely to indicate this fact.

Manuscript received 27 January 1993. Revision accepted 27 September 1993.