Analysis of grain protein, tryptophan and lysine contents of quality protein maize (qpm) lines

Abstract

The nutritional well being and health of all people are vital prerequisites for the development of societies. However, malnutrition still remains a widespread problem, and is particularly severe in developing countries with low per capita income. Maize (Zea mays L.) plays a very important role in human nutrition in a number of developed and developing countries, worldwide. Maize proteins, however, have poor nutritional value for humans, because of reduced content of essential amino acids such as lysine, tryptophan and threonine. Maize proteins contain on an average about 2% lysine, which is less than one-half of the concentration recommended for human nutrition. Therefore, healthy diets for humans must include alternate sources of lysine and tryptophan. Significant advances have been made in genetic enhancement of maize for nutritional value. It is in this context that the value of Quality Protein Maize (QPM) assumes significance, as it signifies a breeding achievement of enhancing grain protein quality in maize. In view of the growing importance of QPM in human nutrition, the objective of this study was to analyze the protein, tryptpphan and lysine contents of QPM lines so as to utilize these genotypes in developing hybrid varieties and bringing its nutritional benefits to fruition. METHODS: The seeds for this work were obtained from a field experiment conducted in winter 2000 at Hyderabad and in summer 2000 at New Delhi. A total of 89, 50 and 31 genotypes including three checks were selected and evaluated for their endosperm protein, tryptophan and lysine contents using Microkjeldahl, Colourimetric and ELISA methods respectively. RESULTS: Endosperm protein content ranged from 6.9 to 11.3 (mg/100 mg flour) and genotypes were significantly different from each other (p<0.01). A large majority of the Indian as well as CIMMYT Quality Protein Maize (QPM) inbreds displayed higher levels of tryptophan per 100 mg protein in comparison with the non-QPM checks (p<0.01). The EF-1 concentration (estimator of lysine content) of a vast majority of the QPM genotypes analyzed was significantly superior to the non-QPM cultivars, except DMRQPM-56 x DMRQPM-44 (0.37) and DMRQPM-66 x DMRQPM-60 (0.39). Endosperm protein content showed a highly significant and negative correlation with tryptophan content in endosperm protein, whereas tryptophan content in flour and in protein showed highly significant and positive correlation.