Improved heat stability of whey protein isolate stabilized emulsions via dry heat treatment of WPI and low methoxyl pectin: Effect of pectin concentration, pH, and ionic strength

Abstract

In this study, Whey Protein Isolate (WPI) was conjugated with Low Methoxyl Pectin (LMP) as a means to improve the heat stability of whey protein stabilized oil in water (o/w) emulsions. Hereby, the emulsifying activity and heat stability of the emulsions (10% w/w of oil) stabilized by 0.5% WPI-LMP conjugates were compared to the stability of emulsions stabilized by either 0.5% WPI, 0.5% of a mixture of WPI-LMP, or 0.5% dry heated WPI. The influence of LMP concentration, pH (i.e. 6.5 versus 5), and ionic strength (i.e. 0 and 30 mM of NaCl) on the stability of the emulsions was studied. It was found that unheated emulsions stabilized by WPI-LMP conjugates had a relatively small droplet size and were stable against creaming, irrespective of the pH and ionic strength of the emulsions. Results also showed that not only the pH sensitivity, but also the heat-sensitivity of WPI-stabilized emulsions could be significantly improved by application of pectin. Upon heating at 80 °C and 120 °C up to 20 min, there was almost no change in the particle size distribution of the conjugate-stabilized emulsions after heating. Viscosity measurements showed a similar trend; heat treated emulsions stabilized by conjugates did not show any change in consistency. This pronounced heat stabilizing effect of LMP, however, was not observed in emulsions stabilized by a mixture of WPI-LMP. With regard to the dry heat incubation time, a 2 days incubation period was sufficient to produce a WPI-derived emulsifier with superior stability towards both pH and heat treatment.