Effects of heat treatment and homogenisation pressure during sweetened condensed milk manufacture on product quality

Commercially produced low-, medium- and high-heat skim milk powders (SMP) w ere examined for their suitability for recombined sweetened condensed milk (RSCM) manufacture. The viscosity indices of the powders were obtained usin g the Australian and Dutch standard methods. The powders were used for manu facture of RSCM (74% total solids: 20% milk solids non-fat, 8% fat, 46% suc rose) on a pilot scale using heat treatments of 88 degreesC/30 s, 92 degree sC/30 s, 88 degreesC/5 min or 92 degreesC/5 min and homogenisation pressure s of 2 or 10 MPa for processing of the RSCM mix. Although the apparent visc osity of RSCM determined by the Australian method was greater than that of RSCM determined by the Dutch method, there was a significant correlation (p <0.05) between these two methods. However, neither of these methods is suf ficiently reliable for predicting the viscosity of RSCM made from the powde rs under a variety of RSCM processing conditions. Although increasing time and temperature of heat treatment and increasing homogenisation pressure ge nerally increased viscosity, the effects of these processing variables were different, depending on the heat treatment applied during powder manufactu re as well as other factors such as the inherent viscosity characteristics of the individual powders.