Studies on the electrostatic interactions between β-lactoglobulin and tragacanthin:The first step towards fabrication of biopolymeric micro- and nano-particles

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 β-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 glucono-delta-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 β-lactoglobulin and tragacanthin can be used to form a variety of biopolymer particles. These biopolymeric micro- and nano-particles may be used in the food industry as natural delivery systems or fat-replacers. Keywords: β-Lactoglobulin، Tragacanthin، Protein-polysaccharide interactions، Associative phase separation، Biopolymer micro-particles