Formation of milk protein-pectin conjugates with improved emulsifying properties by controlled dry heating

The subject of the present paper is a systematic investigation of the formation of synthetic glycoproteins (conjugates) from milk proteins and pectins by a Maillard-type reaction using an experimental design and a comparison of the results with those of investigations of the thermodynamic compatibility of the proteins and pectins. Whey protein isolate and sodium caseinate were combined with pectins of high and low degree of methylation, incubated at different pH (5.8 and 7.0), temperature (50 and 60 °C), humidity (65 and 80%) and mixing ratio (1:1-1:5) for up to 15 days. The aim was the preparation of a material with out-standing emulsifying properties. The conjugates as well as the pure proteins and the mixtures were tested for their colour, emulsifying activity and emulsion stability. The influence of the protein type was dominating. A conjugate from whey protein isolate and high methoxyl pectin in a mixture ratio of 1:3 at pH 7 and after incubation at high temperature and humidity for 10 days had the best emulsifying properties. Sodium caseinate in combination with any pectin, however, was not suitable for the formation of glycoproteins with improved emulsifying properties. An influence of the thermodynamic compatibility between the protein and the pectin component on the formation and the resulting properties of the conjugates is probable.