Effect of chemical modification on some structural and functional properties of pennisetin, a major seed storage protein from pearl millet

Nine different types of amino acids of pennisetin, a major storage protein in pearl millet, were modified separately and the effect of this modification was assessed by determining certain structural and functional properties. With modification of histidine, tyrosine, methionine and cysteine, there was an increase in intrinsic viscosity [eta] from 16.8 to 20.5 ml g-1 while that of serine led to a decrease [eta] from 16.8 to 14.9 ml g-1 indicating alterations in the molecular dimensions of pennisetin. The CD spectra of pennisetin modified at serine, lysine, methionine and cysteine residues showed changes in molar ellipticity values reflecting some changes in its secondary structure. The water holding capacity of pennisetin showed a maximum increase in the case of serine modification (1.76-4.32 g of H2O g-1 of pennisetin) and a maximum decrease in lysine modification (1.76-1.26 g of H2O g-1 of pennisetin). The thermostability of pennisetin remained unaffected with modification of amino acids except in the case of glutamic and aspartic acid. This is the first report where a specific seed storage protein of an important food crop is chemically modified and its effects are studied with respect to its structural and functional properties.