Effect of chymotrypsin digestion followed by polysaccharide conjugation or transglutaminase treatment on functional properties of millet proteins

Millet protein was solubilized by chymotrypsin; the soluble protein was conjugated to galactomannan under controlled conditions (60 °C, 76% RH) or polymerised by transglutaminase (TGase). SDS–PAGE patterns showed that the conjugated and polymerised proteins had higher molecular mass bands above the stacking gel. SDS–PAGE patterns also indicated that the digest was conjugated to galactomannan and polymerised by TGase. The free amino groups (OD₃₄₀) of the conjugated and polymerised digest were greatly reduced. Although the chymotrypsin digest was considerably insoluble between pH 2.0 and 5.0, galactomannan conjugate was completely soluble at all levels of pH. TGase polymer was slightly insoluble at pH 4.0. Galactomannan conjugate resisted heat-induced aggregation, even after heating at 90 °C for 20 min, while TGase polymer resisted heat-induced aggregation up to 70 °C, after which its solubility started to decline. The emulsifying properties of the conjugate and the polymerized proteins were greatly improved, compared to the native and chymotrypsin digests.