Effects of dietary fiber and tannins on protein utilization in dry beans (Phaseolus vulgaris)

The nutritional value of dry bean (Phaseolus vulgaris) protein is typically lower than that of cereal and animal proteins, but the factors responsible for the low nutritional value of bean protein have not been clearly identified. In this study, the ability of dietary fiber and tannins to lower protein utilization in dry beans was investigated using weanling rats. The rats were fed eight experimental diets containing varying amounts of bean dietary fiber and tannins. Both protein digestibility and net protein ratio (NPR) were determined as measures of protein nutritional value. Soluble dietary fiber significantly increased fecal nitrogen losses (P less than or equal to 0.001) and reduced protein digestibility (P less than or equal to 0.001), while insoluble dietary fiber and tannins had no effect on either fecal nitrogen loss or protein digestibility. However, neither soluble nor insoluble dietary fiber had a significant effect on NPR, but tannins significantly reduced NPR values (P less than or equal to 0.01). Both dietary fiber and tannins appear to contribute to the low nutritional value that is typical of bean protein, with soluble dietary fiber being primarily responsible for the reduction in protein digestibility that is commonly associated with dietary fiber in foods. Copyright (C) 1996 Canadian Institute of Food Science and Technology. Published by Elsevier Science Ltd