The effects of calcium regulation of endosperm reserve protein mobilization of the Nigeria sorghum cultivars, ICSV 400 and KSV 8 during malting

Abstract

The effects of steep liquor calcium ion on sorghum endosperm reserve protein mobilization were evaluated using two improved Nigeria sorghum cultivars (ICSV 400 and KSV 8). The key protein modification factors evaluated were free amino nitrogen (FAN), total non protein nitrogen (TNPN) and soluble protein of cold water extract (CWS-P). Ca²⁺ treatment highly significantly (P < 0.001) repressed FAN development in both sorghum cultivars ICSV 400 and KSV 8. TNPN accumulation significantly enhanced in ICSV 400 by Ca²⁺ treatment in contrast to KSV8 malts which showed 23 to 69% repression. Similarly, Ca²⁺ treatment was effective in stimulating peptide accumulation in ICSV 400 at all levels of treatment indicating that the enhancement of TNPN accumulation in this cultivar was derived mainly from the stimulation of peptide accumulation. KSV 8 in contrast showed highly significant repression of peptide accumulation. Protein solubilisation, soluble protein accumulation and cold water soluble protein modification in both cultivars were all highly significantly repressed by Ca²⁺ treatment; although, ICSV 400 appeared to be better modified. Carboxypeptidase development was stimulated significantly by Ca²⁺ treatment in both cultivars. Existence of multiple high points in  carboxypeptidase activity suggests heterogeneity of this enzyme in sorghum while Ca²⁺ treatment caused reduced proteinase development in ICSV 400, the enzyme activity was enhance in KSV 8 albeit marginally.

Key words: Sorghum malt, steep water Ca²⁺ treatment, modification, free amino nitrogen, total non protein nitrogen, carboxypeptidase.