Formation of electrostatic complexes involving mixtures of lentil protein isolates and gum Arabic polysaccharides

Formation of electrostatic complexes involving a mixture of lentil protein isolates (LPI) and gum Arabic (GA) as a function of pH (1.50-8.00) and biopolymer mixing ratio (1:4-10:1 LPI:GA) were investigated by turbidimetric analyses during an acid titration. The nature of interactions was also studied in the presence of destabilizing agents (e.g., 100 mM urea and NaCl), at an elevated temperature (60 degrees C), and as a function of lentil processing (e.g., hulled vs. dehulled). Complex formation followed two pH-dependent structure forming events associated with the formation of soluble and insoluble complexes. For the 1:1 LPI:GA ratio, soluble and insoluble complexes formed at pH 5.87 and 3.62, respectively, with maximum formation occurring at pH 3.50. The addition of GA also resulted in a shift from of LPI's isoelectric point (pH 4.70) to a lower pH (3.17) as chains complexed to the surface of the protein, as measured by electrophoretic mobility versus pH. As the biopolymer mixing ratios increased, critical pHs shifted towards higher pH until reaching the 1:1 mixing ratio, afterwards becoming relatively ratio independent. Complex formation was found to be primarily driven by electrostatic attractive forces with secondary stabilization by hydrogen bonding. Hydrophobic interactions were thought to play a role in the stabilization of LPI-LPI aggregates as part of the formed complexes, rather than in its formation. Removal of the hull resulted in an isolate product with higher surface hydrophobicity than that with the hull. Complex formation shifted slightly to higher pH within the mixture containing isolates derived from dehulled lentil than with, thought to be associated with the higher surface hydrophobicity on the surface. Knowledge of mechanisms driving complex formation within LPI:GA mixtures could lead to improved utilization as food and/or biomaterial ingredients. (C) 2012 Elsevier Ltd. All rights reserved.