Extraction and Film Properties of Kafirin from Coarse Sorghum and Sorghum DDGS by Percolation

The high cost of kafirin and zein restricts their use for bioplastic and food applications. Effective, simple and rapid kafirin/zein isolation processes are required. Here a percolationtype aqueous ethanol solvent extraction process from coarse meals (grits) and coarse sorghum DDGS for kafirin and zein isolation employing a low ratio of extractant to meal (2.5:1) was investigated, which is potentially applicable in the grain bioethanol industry. Post-extraction filtration times were more than twice as fast using coarse meals compared to fine flours. Washing the meals to prior to extraction to remove starch improved protein preparation purity to 73-85% compared to 68-72% for unwashed meals. Hence, no subsequent filtration or centrifugation step is required to clean up the kafirin/zein solution prior to solvent evaporation. With a single extraction step, kafirin/zein yields were 48% (protein basis) for DDGS and 53-70% for washed sorghum/maize meals. Cast films were used as a model bioplastic system to evaluate extracted kafirin/zein functional properties. DDGS kafirin films had rough surfaces but had the lowest water uptake and in vitro digestibility, due to heat induced disulfide crosslinking during DDGS processing. Extraction by percolation using coarse meal/DDGS has potential to improve kafirin/zein viability.