Investigation of the composite system of β-lactoglobulin and pectin in aqueous solutions

The compatibility in aqueous systems of beta-lactoglobulin (beta-lg) with low and high esterified-sodium polypectates (LMP and HMP) was investigated. The mixture did not separate into two co-existing liquid phases in any case studied. At pH above the isoelectric point (IP) of beta-lg, the behavior of LMP and HMP was similar when mixing with beta-lg. Pectins and beta-lg were co-soluble was around a particular ionic strength (mu) (0.07 M for HMP and 0.3 M for LMP). In these circumstances, the flow behavior of pectin was hardly affected by the addition of beta-lg. At all other mu, the mixture formed a liquid phase containing both beta-lg and pectin and a small amount of beta-lg precipitates, Here, the viscosity of the liquid phase was slightly higher than the viscosity of a solution containing the same concentration of pectin. At pH 3.5, i.e, pH less than or equal to IP of beta-lg, the behavior of LMP and HMP was different when mixing with beta-lg, LMP formed insoluble complexes with beta-lg at low mu (less than or equal to 0.25 M), but precipitation was suppressed at high mu (0.5 M). The composite system of beta-lg/HMP formed a white, homogeneous and stable dispersion at low mu (0.07 M). The viscosity of this dispersion was much higher than the additive viscosity of individual solutions would be. Probably, the oppositely charged beta-lg and HMP formed soluble complexes, which further associated into large aggregates. This complexation was also suppressed at high mu (0.5 M). (C) 2000 Elsevier Science Ltd. All rights reserved.