Improvement of emulsifying properties of Maillard reaction products from β-conglycinin and dextran using controlled enzymatic hydrolysis

A novel emulsifier was prepared by conjugating soy beta-conglycinin and dextran (MW 67 kDa) under dry-heated Maillard reaction followed by trypsin hydrolysis with the degree of hydrolysis (DH) at 2.2% and 6.5%. The emulsifying properties of beta-conglycinin, beta-conglycinin-dextran conjugates and hydrolysates of beta-conglycinin-dextran conjugates (DH 2.2% and DH 6.5%) were investigated using zeta-potential, droplet size and creaming index of the emulsions. The results showed that hydrolysates of beta-conglycinin-dextran conjugates (DH 2.2%) were capable of forming a fine emulsion (d(43) = 0.62 +/- 0.04 mu m, pH 7.0) which remained stable during 4 weeks of storage. A variety of physicochemical and interfacial properties of beta-conglycinin, beta-conglycinin-dextran conjugates and hydrolysates of beta-conglycinin-dextran conjugates were investigated. Hydrolysates of beta-conglycinin-dextran conjugates (DH 2.2%) had a much higher fraction of protein adsorption (F-ads) and a significantly lower saturation surface load (Gamma(sat)) compared with beta-conglycinin, beta-conglycinin-dextran conjugates and hydrolysates of beta-conglycinin-dextran conjugates (DH 6.5%). This might be due to its higher molecular flexibility, which benefited the adsorption and unfolding of peptide molecules at the droplet interface. These might explain its markedly improved emulsifying capability. The conjugation of beta-conglycinin and dextran effectively enhanced the hydrophilicity of the oil droplets surfaces and improved the steric repulsion between the oil droplets. Therefore the emulsions were still stable after 4 weeks of storage against pH, ionic strength and thermal treatment. This study demonstrated that controlled enzymatic hydrolysis of protein-polysaccharide conjugates could be an effective method for preparing favourable emulsifiers. (C) 2012 Elsevier Ltd. All rights reserved.