Using the results of the chemical amino acid analyses of the unconventional proteins blood, collagen and wool and the conventional proteins soya, maize and casein, protein mixtures were developed. The quality of the protein mixtures was estimated in feeding experiments with growing male Sprague-Dawley rats and expressed as protein efficiency ratio (PER). Different blood parameters and the weight of some organs were also recorded. Blood, collagen and wool protein are very poor in different essential amino acids, therefore their quality is very low, it can however be significantly improved when they are fed in mixtures with other animal or plant proteins of higher quality. In mixtures of three components only containing blood (10--40%), collagen (10--25%) and casein (50 to 70%) the deficit in the content of essential amino acids cannot be compensated. Rats fed with such diets showed, however, decreased food intake and depressed growth. The relative PER values of those mixtures were 44--69% of that of casein. The best supplementing effect on the imbalanced amino acid patterns was achieved when the protein mixture was developed from 4 or 5 different proteins. The quality of these five-component-mixtures amounted to 94--100% of that of casein. In these mixtures the percentage of casein in the protein mixture amounted to only 35% and soya or maize to 15%. Exactly 50% of the protein supply could be derived from hydrolysates of the unconventional proteins blood, collagen and wool.

The quality of protein mixtures on the basis of blood protein, collagen, wool and other proteins was tested using different chemical and biological criteria of protein evaluation. Before mixing the single proteins were hydrolysed enzymatically by means of acid or alkaline proteinases. In this study the influence of both hydrolysis processes on the bioavailability of the protein mixtures was also considered. The N-balance experiments were carried out with weanling Sprague-Dawley rats in groups of n = 6 animals each. The estimated BV's showed that the protein quality was significantly affected by both hydrolysis procedures especially when the hydrolysates were compared with the non-hydrolysed protein components. The BV's also showed that the quality of all mixtures of protein hydrolysates was less than that of casein (reference protein) and the availability of the alkaline hydrolysed proteins better than that with acid proteinase treated proteins. This result could be confirmed by the calculated chemical criteria E/T- and E/N-ratios, EAA-Index and Arnould-Index. The results of the growth-criteria PER, NPR and RNV did neither correspond with each other nor they were of good agreement with N-balance based BV and NPU.