Whey protein-pectin conjugates: Linking the improved emulsifying properties to molecular and physico-chemical characteristics

Abstract

Abstract The generation of protein-polysaccharide conjugates via dry-heating can overcome several disadvantageous properties of proteins. It has already been demonstrated that conjugates of whey protein isolate (WPI) and pectin yield clearly improved emulsifying properties. However, less attention has been paid to the connection between the amount/portion of conjugates and the emulsifying properties. In addition, the molecular background of the conjugation reaction is yet unknown. This study was focused on the evaluation of the molecular background of conjugate formation. Before further characterization, WPI-pectin conjugates were produced by using various reaction times and analyzed by various approaches. The results were used to select a reaction time which yields high conjugate portions, high solubility and good droplet stabilization. To obtain information about the influence of residual unconjugated WPI in that mixture, a fractionation procedure based on the solubility in different buffers was developed. This approach allowed for the isolation of fractions with increasing portions of conjugated WPI, which was confirmed by analyzing the protein content. In addition, the amino acid profile of the isolated fractions indicated that increasing portions of conjugates correlate with decreasing portions of lysine. Unambiguous evidence for the conjugation of the e-lysine amino groups with pectin was obtained from the isolation and characterization of a corresponding Maillard reaction product. Therefore, the results of this study demonstrated that conjugate formation between protein-bound lysine and pectin is responsible for the improved emulsifying properties of WPI-pectin conjugates. Furthermore, the emulsifying properties of the conjugate-enriched fractions confirmed that increasing conjugate portions allow for the stabilization of smaller droplets.