ABSTRACT
Investigation of the colloidal behaviour of protein-polysaccharide systems is becoming increasingly important to provide a foundation for their applications in areas such as production of biopolymer micro-and nano-particles, designing food analogues, and microencapsulation technology. The aim of the present study was to investigate the pH-induced critical transitions during associative phase separation between beta -lactoglobulin [BLG] and tragacanthin [T]. The formation of electrostatic complexes in BLG/T dispersions [0.3wt.% total concentration; BLG:T ratio 2:1] was investigated as a function of pH [2.00-6.00] by spectrophotometry and particle size analysis. In addition, coupling of slow in situ acidification of the blend, with gluconodelta-lacton, and rheometry were used to monitor the structural transitions during the associative phase separation. The influence of salt type and concentration on the formation of micro-particles were also determined. The formation of soluble complexes started at pH -5.20, and at pH -4.85 the aggregation of intrapolymeric complexes occurred, followed by a bulk phase separation at pH -4.30. The data indicated that coacervation occurred at pH 4.15. Finally, the mixture returned to a mono-phasic system at pH 2.5. Particle size analysis showed that the assembled structures experienced a contraction process upon complexation. Rheometry provided deeper insights into the colloidal behaviour of the system and the results were in good agreement with quiescent pH-induced transitions established by HCl titration. The formation of the micro-particles was strongly salt-dependent. Under controlled pH conditions, electrostatic interactions between beta -lactoglobulin and tragacanthin can be used to form a variety of biopolymer particles. These biopolymeric micro- and nanoparticles may be used in the food industry as natural delivery systems or fat-replacers