Influence of processing conditions on the formation of whey protein-citrus pectin conjugates in extrusion

To investigate the formation of whey protein-citrus pectin conjugates during extrusion processing, extrusion trials were performed by a co-rotating twin screw extruder. The processing conditions such as mechanical stress, reaction time and temperature, are varied by varying screw configuration (with/without reverse elements), and barrel temperature (80 °C-180 °C). Biopolymer reactions, such as protein and pectin degradation, protein aggregation as well as conjugation were examined by SDS-PAGE and fluorescence spectroscopy. The highest formation of conjugates was observed in the samples treated with reverse elements and the barrel temperature of 140 °C. As a measure for the processing conditions, material temperature at the die Tm, specific mechanical energy SME, and residence time distribution RTD were measured. The analysis of these parameters showed that Tm and SME are of significant influence on conjugate formation and degradation. Nevertheless, further analyses at defined conditions (time, temperature, shear stress) are necessary to get a better insight on the reactions taking place in extrusion.