Complexation of high methoxyl pectin with ethanol desolvated whey protein nanoparticles: physico-chemical properties and encapsulation behaviour

Using a desolvation method, whey protein isolate (WPI) nanoparticles were prepared and mixed with high methoxyl pectin (HMP) solutions (DE 72.8) to form WPI-HMP supramolecular complexes at low pH. Aqueous dispersions containing 5% WPI at pH 9 were desolvated with ethanol, and then diluted in HMP solutions at pH 3. Changes in particle size of the HMP-WPI complexes were studied as a function of HMP concentration. Upon dilution of the WPI nanoparticles in 0.05% HMP at pH 3, the average apparent diameter (d(90)) was around 270 nm, and there were no differences with desolvation level. These nanoparticles would undergo coarsening with storage at room temperature. The complexes showed to withstand homogenization and although heating increased aggregation, the particle size of the heated suspensions improved after homogenization. In addition, the suspensions demonstrated higher interfacial pressures (measured by drop tensiometry) compared to the corresponding unprocessed, desolvated or heated WPI solutions, suggesting their employment as surface active ingredients. The encapsulation efficiency of the desolvated WPI suspensions and desolvated WPI-HMP complex suspensions was studied using a model hydrophilic dye. In all cases, appreciable amounts of dye molecule were encapsulated and retained by the nanoparticles during storage at pH 3.