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 pret reatment of xanthan (4, 8, or 12 passes through a microfluidizer) on whey p rotein-xanthan gum complexes characteristics (size, composition, and flow b ehaviour) 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 compl exes (40% were < 20 mu m(2)), whereas in higher ratios (15:1 and 20:1) 40-4 4% 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 r atios, suggesting the presence of complexes with a protein multilayer and/o r the formation of protein microparticles, particularly for the 20:1 ratio. The high-pressure pretreatment of xanthan was essential to prevent the for mation of fibrous complexes, presumably by disrupting the association patte rn 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 ze ro shear viscosity and the pseudoplastic character of uncomplexed WPI-xanth an solutions. After complexation, the solutions presented the same trend ex cept for the 20:1 ratio, which had an increased viscosity, presumably due t o the presence of protein aggregates. Although microfluidization of xanthan affected the viscosity of solutions and was indispensable 10 produce parti culated complexes, no significant differences were found on the size or com position of the complexes fabricated with xanthan microfluidized different number of times. (C) 2000 Elsevier Science Ltd. All rights reserved.