Kinetics of Formation and Functional Properties of Conjugates Prepared by Dry-State Incubation of beta-Lactoglobulin/Acacia Gum Electrostatic Complexes

摘要

The formation of conjugates between beta-lactoglobulin and acacia gum based on electrostatic complexes formed at pH 4.2 was investigated upon dry-state incubation for up to 14 days at 60 deg C and 79% relative humidity(RH).By means of SEC-HPLC and RP-HPLC,it was shown that the beta-lactoglobulin incubated alone was able to form polymers with molecular masses higher than 200 kDa until 50% of the initial monomeric protein disappeared after 14 days.In the presence of acacia gum at initial protein to polysaccharide weight mixing ratios of 2:1 and 1:2,only 35% of the initial beta-lactoglobulin monomers disappeared after 14 days.Using RP-HPLC,an apparent reaction order of 2 was found for the disappearance of monomericbeta-lactoglobulin both in the presence or absence of acacia gum.However,the reaction rate was faster in the absence of acacia gum.SDS-PAGE electrophoresis with silver staining confirmed the formation of beta-lactoglobulin/acacia gum conjugates.The solubility curves of the incubated beta-lactoglobulin showed a minimum around pH 4-5.By contrast,the minimum of solubility of the beta-lactoglobulin/acacia gum incubated mixtures shifted to lower pH values compared to initial mixtures.The conjugates exhibited higher foam capacity than the incubated protein as well as lower equilibrium air/water surface tension.Conjugation at ratio 1:2 led to increased interfacial viscosity(300 mN s m~(-1)at 0.01 Hz)compared to beta-lactoglobulin alone(100 mN s m~(-1)at 0.01 Hz),but similar interfacial elasticity(30-40 mN m~(-1)).The foam capacity of the conjugates was significantly higher than that of the incubated beta-lactoglobulin as well as foam expansion and drainage time,especially at pH 5.3,i.e.,higher than the pH of formation of the conjugates.