Quality of cereal proteins in animal nutrition

The aim of this work was to asses the quality of proteins in wheat, spelt, oats and maize by chemical methods and biological tests in model animals. The following parameters were assessed by chemical methods: nitrogen content by Kjeldahl method, protein content as described by Barnstein, protein fractions by extraction method as described by Golenkov, modified by Michalik et al., amino acid content after acid hydrolysis 6 MHCl in AAA-400, methionine and cysteine content after hydrolysis in AAA-400, other nutrients (fibre, fat, ash, starch) after the Decree of the Slovak Ministry of Agriculture, Biological tests were performed following the methods for quality assessment of proteins in experiments with rats and the following parameters were assessed: digestibility of crude protein (CP), balance of nitrogen, biological protein value (BPV) in 7-day balance experiment, net protein utilization (NPU), utilizable proteins by calculation UP = CP x NPU, protein efficiency ratio (PER) in 21-day feeding trial, feed consumption per one gram gain, live weight gain within 21 days, The maintenance requirement of nitrogen (MRN) and metabolic nitrogen in excrements (MNE) were calculated from regression equations, MRN = 0.222w + 22.93, MNE = 0.081w + 3.01, where w is the average weight of the rat in balance period. Wistar rats of about 75 g body weights were used in the experiment. The grain of the tested cereals was the only source of nitrogen in the experimental diet, crude protein of feeds representing 10% dry matter in the feed ration. The different nutritive quality of cereals was manifested in all studied parameters. Good feed conversion and the highest PER value (2.16) was observed in animals fed with oats. The quality of proteins in maize and wheat is lower, which was proved also by lower net values of protein utilization (NPU 57.3) and utilizable proteins (UP 5.6). The different protein composition became evident in the content and representation of individual amino acids. Higher proportion of protoplasmic proteins condition also higher concentration of limiting amino acid in cereals (lysine). The prolamine proteins have a decisive effect on amino acid composition of the whole grain, and their total content limits the content of lysine.