Formation of native whey protein isolate–low methoxyl pectin complexes as a matrix for hydro-soluble food ingredient entrapment in acidic foods

Whey protein isolate (WPI) and low methoxyl pectin (LMP) may form soluble or insoluble complexes depending on polymer ratios, mode of acidification and final pH. WPI and LMP solutions were blended to obtain protein:pectin ratios of 2:1, 1:1 and 1:2 at a total polymer concentration (TPC) of 0.4% (w/w) with pH adjustment to 4.0, 3.5, 3.0, and 2.5 either before or after blending. WPI–LMP complexes, obtained from the mixing of WPI and LMP solutions at protein:polysaccharide (P:Ps) ratio 2:1, were used as thiamine carriers in the process of thiamine entrapment. Suspension turbidity, particle size, zeta potential, sedimentable-complexes yield (portion of complexes sedimentable by centrifugation), microscopic appearance and thiamine content of the complexes as well as thiamine entrapment efficiency (percent of thiamine entrapped) were evaluated. All observed characteristics were largely dependent on pH, protein:pectin ratios, and whether acidification was performed before or after polymers blending (pre and post-blending acidification). Complex size was constant and lower when acidification was done after mixing the polymers at a protein:pectin ratio of 2:1 compared to when acidification was done before the mixing. The optimum pH for maximum turbidity and sedimentable-complexes yield, at a P:Ps ratio of 2:1, was around 3.0 with both pre and post-blending acidifications. With decreasing protein:pectin ratio, the maximum sedimentable-complexes yield was shifted towards acidic pH. Complex formation with pre-blending acidification produced generally a larger mass of complexes than with post-blending acidification. The optimal thiamine content of the complexes as well as the optimal entrapment efficiency, with all acidification modes, was found at pH 3.5.