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Protein Quality of some Representative Latin American Diets by Rat Bioassay¹

Department of Food Science and Nutrition, University of Massachusetts, Amherst, Mass. 01002

A study of the protein quality of twelve different food-mixtures common to Latin America, was performed by rat bioassay. The individual foods were cooked and dried and then mixed in the appropriate proportions resembling the original meals. Rats of the Sprague-Dawley strain were used for the bioassays. Special emphasis was given to the methodology of the slope-ratio techniques preconized by Hegsted and his associates who have claimed that classical bioassays overestimate the nutritive value of poor quality proteins. RNV and RPV values were calculated using the slope-ratio technique, with and without use of a non protein control group. PER, NPR, relative NPR and utilizable protein were also calculated using the same data. The amino acid composition was determined and the score against the FAO/WHO 1973 pattern was compared with the bioassays. Protein value of the diets was also calculated from food table data. Agreement was good between all the procedures especially for the calculation of utilizable protein although the poorest diet containing little else but maize was somewhat overestimated in its quality by calculation from food table data. Thus, in general, estimates for protein quality of diets by standard bioassay techniques and even by amino acid scoring procedures gave values comparable to those obtained by the slope-ratio assays. The large scale re-evaluation suggested for all protein quality data prior to the slope-ratio techniques may not in fact be necessary.

KEY WORDS: • protein quality • rat growth • slope ratio assays • Latin American diets • amino acid composition

¹ This study was part of a Master's thesis by Jose Felix Chavez.

² Present address: Instituto Nacional de Nutricion, Caracas, Venezuela, Apartado 2049.

Manuscript received 28 August 1975.