Effect of preparation conditions on the characteristics of whey protein - xanthan gum complexes

The effect of two parameters: the protein-to-polysaccharide [P:PS] ratio (5:1, 10:1, 15:1, and 20:1) and the intensity of a dynamic high-pressure pretreatment of xanthan (4, 8, or 12 passes through a microfluidizer) on whey protein-xanthan gum complexes characteristics (size, composition, and flow behaviour) were studied in view of producing a fat substitute. It was found that the P:PS ratio strongly influenced the size and the composition of the complexes. Low P:PS ratios (5:1 and 10:1) produced principally small complexes (40% were < 20 mu m(2)), whereas in higher ratios (15:1 and 20:1) 40-44% of particles were >300 mu m(2). The protein and polysaccharide measured on the complexed fractions resulted in higher P:PS ratios than in initial ratios, suggesting the presence of complexes with a protein multilayer and/or the formation of protein microparticles, particularly for the 20:1 ratio. The high-pressure pretreatment of xanthan was essential to prevent the formation of fibrous complexes, presumably by disrupting the association pattern of xanthan molecules. An increase in the P:PS ratio and in the number of xanthan passes through the microfluidizer resulted in a decrease in the zero shear viscosity and the pseudoplastic character of uncomplexed WPI-xanthan solutions. After complexation, the solutions presented the same trend except for the 20:1 ratio, which had an increased viscosity, presumably due to the presence of protein aggregates. Although microfluidization of xanthan affected the viscosity of solutions and was indispensable 10 produce particulated complexes, no significant differences were found on the size or composition of the complexes fabricated with xanthan microfluidized different number of times. (C) 2000 Elsevier Science Ltd. All rights reserved.