Multi-criteria assessment of pea protein quality in rats: a comparison between casein, gluten and pea protein alone or supplemented with methionine

The objective of this study was to assess the nutritional quality of pea protein isolate in rats and to evaluate the impact of methionine (Met) supplementation. Several protein diets were studied: pea protein, casein, gluten, pea protein-gluten combination and pea protein supplemented with Met. Study 1: Young male Wistar rats (n = 8/group) were fed the test diets ad libitum for 28 days. The Protein Efficiency Ratio (PER) was measured. Study 2: Adult male Wistar rats (n = 9/group) were fed the test diets for 10 days. A protein-free diet group was used to determine nitrogen (N) endogenous losses. The rats were placed in metabolic cages for 3 days to assess N balance, true fecal N digestibility, and to calculate the Protein Digestible-Corrected Amino Acid Score (PDCAAS). They were then given a calibrated meal and euthanized 6 hours later for collection of digestive contents. The true cecal amino acid (AA) digestibility was determined and the Digestible Indispensable Amino Acid Score (DIAAS) was calculated. Met supplementation increased the PER of pea protein (2.52 vs. 1.14, P < 0.001) up to the PER of casein (2.55). Mean true cecal AA digestibility was 94% for pea protein. The DIAAS was 0.88 for pea protein and 1.10 with Met supplementation, 1.29 for casein and 0.25 for gluten. Pea protein was highly digestible in rats under our experimental conditions, and Met supplementation enabled generation of a mixture that had a protein quality that was not different from that of casein.