Comparisons between True Digestibility of Total Nitrogen and Limiting Amino Acids in Vegetable Proteins Fed to Rats

Abstract

Values (%) for true digestibility (TD) of protein and individual amino acids in some vegetable proteins were determined by the rat balance (fecal) method. Diets containing 8% crude protein (N X 6.25) from soaked and autoclaved samples of Trapper and Century field peas, lentil, pinto bean, seafarer bean, black bean or fababean and autoclaved samples of soybean, peanut, sunflower, rolled oat, rice + soybean and corn + pea were tested in two rat balance studies. In the case of blends, each protein source provided 50% of total protein. The beans, peas and lentil proteins were limiting in sulphur amino acids, tryptophan and threonine, whereas sunflower and rolled oat were most limiting in lysine. In beans, peas and lentil, the TD values of methionine (51-82), cystine (46-85), tryptophan (47-90) and threonine (62-84) were considerably lower than the TD values of total nitrogen (72-90). Similarly, in sunflower and rolled oat, the TD values of lysine (81-83) were lower than the TD values of total nitrogen (90-91). These data suggested that crude protein digestibility may not be a good predictor of bioavailability of limiting amino acids in vegetable proteins. Amino acid scores of the vegetable proteins were 62-96%. The corrections for true digestibility of protein and individual amino acids lowered the scores by 6-15 and 11-47 percentage units, respectively.

In‐vitro protein and sulphur amino acid availability as a measure of bean protein quality

“…The need for this double correction, and the better prediction thus offered, may be explained by the differences between total nitrogen digestibility and SAA availability, which are always lower in legumes (Sarwar and Peace 1986). The in-vitro results given here confirm this discrepancy only for cystine values; in fact, while cystine 'availability' was always lower than protein digestibility, methionine 'availability' was higher, except for the red varieties.…”

Digestive utilisation of protein and amino acids from raw and heated lentils by growing rats

“…The values reported herein are in general agreement with figures published by other authors. 41,49 Methionine þ cysteine are not only the most limiting AAs in lentil, but also those with lowest digestibility. 41 Sulphur AAs are abundant in the albumin protein fraction of legumes, which has lower digestibility than the globulin fraction.…”

Organs relative weight and plasma amino acid concentrations in rats fed diets based on whole legume (faba bean, lupin, chickpea, defatted soybean) seed meals or their fractions

“…Finally, it is also possible that the ileal absorption of one or several essential amino acid(s) in legume proteins is low, even under high total N digestibility. 37 The ünal result of these processes might be the increased activity of amino acid degrading enzymes15 with an increased urea production3,4 and loss of amino acids for protein synthesis in legume-fed animals.…”