Abstract:
Sorghum foods contribute significantly to the protein intake of millions of people in developing countries. One limitation to sorghum’s use as a protein source is that its proteins become less digestible on wet cooking, primarily through the formation of disulphide-linked enzymatically resistant protein polymers. Irradiation of foods can modify bonds involved in stabilizing protein structure, resulting in changes in the protein. The effects of irradiating sorghum cultivars BR7 and Madjeri, and maize cultivar PAN 6043 flours under mild (10 kGy dry) and severe (50 kGy dry and 10 and 50 kGy wet) conditions, followed by cooking into porridge on the digestibility, solubility and some molecular properties of their proteins, were investigated. Pepsin and multienzyme methods of determining protein digestibility (PD) were compared. As expected, pepsin PD of sorghum decreased more with cooking alone (12-18%) compared to maize (4%). Sorghum porridges had more disulphide-bonded prolamin dimers than maize as shown by SDS-PAGE under non-reducing conditions. However, the amounts of disulphide bonds in both porridges appeared similar. Prolamin extractability (PE) decreased more with cooking in sorghum compared to maize. There was no significant correlation between the pepsin and multienzyme methods, suggesting the latter may not simulate in vivo PD that has been reported to correlate positively with pepsin PD. Mild and severe irradiation of sorghum flour before cooking alleviated somewhat the reduction in sorghum PD on cooking. Maize porridge digestibility was unaffected by prior irradiation of dry flour but decreased with irradiation of wet flour. Mild irradiation of sorghum alleviated the reduction in PD with cooking most, almost to the level of uncooked flour. The alleviation in PD coincided with alleviation in the reduction in PE. With severe irradiation, the alleviation in PE was not consistent. Pepsin PD was positively correlated with PE for sorghum BR7 (r=0.83, p<0.01) and Madjeri (r=0.75, p<0.05), but not for maize. Copyright
