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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^1,2,

Nutrition Research Division, Bureau of Nutritional Sciences, Food Directorate, Health Protection Branch, Health Canada, Ottawa, Ontario, Canada K1A 0L2

Protein digestibility and quality of six enteral nutrition products sold in Canada were studied by rat balance and growth methods. Casein + L-methionine, 0.2 g/100 g diet (control) and six enteral products (freeze-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 for a period of 2 and 1 wk, respectively. A protein-free diet was also included in the feeding studies to permit calculations of true protein digestibility and net protein ratio values. Values for true digestibility 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 young rats. The 2-wk relative protein efficiency ratio values (42–56%) or the relative net protein ratio values (61–74%) of the enteral products were considerably lower compared to those of the control (100). Supplementation of an enteral product with cysteine, cysteine + tryptophan, cysteine + threonine or cysteine + tryptophan + threonine caused significant improvement in protein quality; suggesting that the product was limiting in these three amino acids. The protein digestibility-corrected amino acid scores for the enteral products were 43–46, 69–75 and 86–93% by using whole egg, casein and the FAO-WHO (1991) pattern as reference proteins, respectively. The results indicate that these enteral products are inferior to casein in protein quality.

KEY WORDS: • enteral nutritionals • medical foods • protein digestibility • amino acid adequacy • rats

¹ Presented in part at the 206th Meeting of the American Chemical Society, August 22–27, 1993, Chicago, IL [Sarwar, G., Peace, R. W. & Botting, H. G. (1993) Protein digestibility and quality of liquid diets (used in nursing homes) fed to rats.].

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.

³ To whom correspondence should be addressed at: Nutrition Research Division, Bureau of Nutritional Sciences, Room 364, Banting Research Centre, Tunney's Pasture, Ottawa, Ontario, Canada K1A 0L2.

Manuscript received 18 November 1993. Revision accepted 13 May 1994.