Composition and characterisation of kafirin, the dominant protein fraction in grain sorghum

Abstract

Context Sorghum is an important feed grain for chicken-meat production in Australia. However, it is usually considered inferior to wheat – the foremost feed grain. Kafirin, the dominant protein fraction in sorghum, may be a major contributor to this inferiority due to its negative influence on starch digestion and energy utilisation. Aims The objective of this study was to determine kafirin concentrations in sorghum relative to crude protein and amino acid profiles of both kafirin and total sorghum protein. Methods Concentrations of amino acids and kafirin in 19 Premium Grains for Livestock Program sorghum varieties were quantified. These data were combined with that of up to 14 Poultry Research Foundation sorghum varieties to generate the most exhaustive documentation of its kind. The methodology developed to quantify kafirin concentrations in sorghum is thoroughly described. In addition, essential amino acid profiles in 25 grain sorghums from Australian surveys completed in 1998, 2009 and 2016 were compared statistically. Also, consideration was given to relevant near-infrared spectroscopy predicted data from 992 sorghum varieties from 2014 to 2019. Key results The average kafirin concentration of 48.2 g/kg represented 51.9% of the 92.9 g/kg crude protein (N × 5.81) content in 33 varieties grain sorghum. Kafirin holds a substantial 62.7% share of leucine as the concentration was 8.53 g/kg in kafirin as opposed 13.73 g/kg in total sorghum protein. The proposal was advanced that kafirin contents of local sorghum crops have increased during the past two decades from the 1998, 2009 and 2016 surveys of amino acid profiles in grain sorghum. Conclusions Kafirin concentrations in Australian sorghum crops may have increased over the past two decades, which may be having a negative impact on the performance of broiler chickens offered sorghum-based diets. Implications Breeding programs should be directed towards sorghums with lesser kafirin proportions of sorghum protein and/or modified kafirin protein bodies to enhance the nutritive value of sorghum as a feed grain for chicken-meat production.