Protein mixtures and their nutritional properties optimized by response surface methodology

Three protein ingredients (hydrolyzed gelatin, HG, wheat gluten, WG and soybean protein isolate, SPI) were mixed at different proportions in order to partially replace milk proteins in food formulations. The nutritional quality of the mixtures was evaluated by the Protein Digestibility-Corrected Amino Acid Score (PDCAAS) and Net Protein Ratio (NPR) methods. The results obtained experimentally were used to elaborate polynomial equations that would describe the effect of the proportion of each component on the final nutritional quality of the product. The PDCAAS method showed good correlation with the NPR method in terms of growth (r = 0.85). A optimum formulation containing 25% HG, 15% WG and 60% SPI, supplemented with calcium, was developed and used to substitute about 42% of the milk proteins in the formulation that is usually consumed by Nutrition Programs. The reformulated product showed the same nutritional quality, evaluated by the PDCAAS method, as the original product formulated with only integral milk, and its cost was cheaper. The Mixture Response Surface Methodology proved to be an indispensable tool for the optimization of the nutritional quality of protein mixtures. (C) 2000 Elsevier Science Inc.