Heat-induced glycosylation with dextran to enhance solubility and interfacial properties of enzymatically hydrolyzed zein

In order to increase aqueous solubility and emulsification properties, zein partially hydrolyzed by trypsin was conjugated to dextran with molecular weight of 2.5 or 6 kDa by Maillard reaction in aqueous mixtures at 90 °C. Change in free amine content, gel electrophoresis bands, and infrared spectra confirmed conjugation of the hydrolysates after 1, 3, and 6 h of heating. Conjugation increased aqueous solubility of zein hydrolysates up to 30% and decreased surface hydrophobicity up to 53%. In comparison to hydrolysates, conjugation reduced air-water interfacial tension and increased foaming capacity, foam stability, emulsifying activity index, and emulsion stability index. Properties were most improved for hydrolysates conjugated with 2.5 kDa dextran after 3 h heating, although emulsion stabilization was comparable for conjugates prepared with 6 kDa dextran. Emulsion droplet size and adsorbed content both decreased with dextran and were further reduced for samples with greater conjugation, implying surface activity of conjugates was greater than unconjugated hydrolysates.