THE PROTEIN-QUALITY OF SOME ENTERAL PRODUCTS IS INFERIOR TO THAT OF CASEIN AS ASSESSED BY RAT GROWTH METHODS AND DIGESTIBILITY-CORRECTED AMINO-ACID SCORES

Protein digestibility and quality of six enteral nutrition products so ld in Canada were studied by rat balance and growth methods. Casein L-methionine, 0.2 g/100 g diet (control) and six enteral products (fre eze-dried) were fed as the sole source of protein in diets containing 8.61-9.12 g/100 g protein (N x 6.25) to weanling and 18 mo-old rats fo r a period of 2 and 1 wk, respectively. A protein-free diet was also i ncluded in the feeding studies to permit calculations of true protein digestibility and net protein ratio values. Values for true digestibil ity of protein as determined in old rats for the control diet and the test products were 95 and 89-93%, respectively. Compared with old rats , protein digestibility values were 5-7 percentage units higher in you ng rats. The 2-wk relative protein efficiency ratio (42-56%) or the re lative net protein ratio (61-74%) of the enteral products were conside rably lower compared to, those of the control (100). Supplementation o f an enteral product with cysteine, cysteine + tryptophan, cysteine threonine oi cysteine + tryptophan + threonine caused significant impr ovement in protein quality; suggesting that the product was limiting i n these three amino acids. The protein digestibility-corrected amino a cid scores for the enteral products were 43-46, 69-75 and 86-93% by us ing whole egg, casein and the FAG-WHO (1991) pattern as reference prot eins, respectively. The results indicate that these enteral products a re inferior to casein in protein quality.