The effect of product formulation and homogenization on the physical properties of the milk-fat globule and acid milk gels

Abstract

The elect of homogenization pressure and product formulation on the composition physical and chemical properties of acid milk gels was evaluated. Nonfat dry milk, whey protein concentrate (WPC), cream, Span 60 and Tween 20, were combined to prepare formulations with 1.5% fat and 4.5% total protein that were homogenized at 15, 30 and 45 Mpa. Particle size analysis, protein load on the milk fat globules, fat globule membrane composition, dynamic yield stress, and apparent viscosity were determined for each formulation. The specific surface area (SSA) of the milk fat particles increased as the homogenization pressure increased. The SSA of the fat particles in samples which contained WPC was greatest after homogenization at 30 Mpa but the greatest specify surface area of the fat panicles in the control was after homogenization at 45 Mpa. The SSA of samples with Tween 20 and WPC was greater than the SSA of the other formulations. The sample containing Span 60 and WPC had the smallest SSA after homogenization at 45 Mpa. Increasing the homogenization pressures caused the average diameter for volume-surface (dvs) of the fat globules to decrease. Homogenization at 15 MPa caused the samples containing only WPC and Span 60 with WPC to have a larger dvs than the samples containing Tween 20 and WPC and the control. Protein load was greatest after homogenization of the sample containing Tween 20 and WPC at 15 Mpa, no differences were found between the protein load of other treatments. The yield point and yield stress of the gels increased as the homogenization pressure was increased. Span 60 with WPC increased gel armless after homogenization at 45 Mpa, when compared to the other treatments homogenized at 45 Mpa. Homogenization at 45 Mpa caused the yield stress of the samples with only WPC and Tween 20 and WPC to be less than the yield stress of the samples with Span 60 and WPC. The slope of the apparent viscosity regression and the initial viscosity of the gels made from samples which contained Tween 20 and WPC were less than the slopes and initial viscosities measured for all other treatments. The addition of WPC, Tween 20 and Span 60, as well as homogenization pressure change the rheological and chemical properties of acid milk gels.