Forward osmosis concentration of milk: Product quality and processing considerations

Concentration of milk in the dairy industry is typi-cally achieved by thermal evaporation or reverse osmo-sis (RO). Heat concentration is energy intensive and leads to cooked flavor and color changes in the final product, and RO is affected by fouling, which limits the final achievable concentration of the product. The main objective of this work was to evaluate forward os-mosis (FO) as an alternative method for concentrating milk. The effects of fat content and temperature on the process were evaluated, and the physicochemical prop-erties and sensory qualities of the final product were assessed. Commercially pasteurized skim and whole milk samples were concentrated at 4, 15, and 25 degrees C us -ing a benchtop FO unit. The FO process was assessed by monitoring water flux and product concentration. The color of the milk concentrates was also evalu-ated. A sensory panel compared the FO concentrated and thermally concentrated milks, diluted to single strength, with high temperature, short time pasteur-ized milk. The FO experimental runs were conducted in triplicate, and data were analyzed by single-factor ANOVA. Water flux during FO decreased with time under all processing conditions. Higher temperatures led to faster concentration and higher concentration factors for both skim and whole milk. After 5.75 h of FO processing, the concentration factors achieved for skim milk were 2.68 +/- 0.08 at 25 degrees C, 2.68 +/- 0.09 at 15 degrees C, and 2.36 +/- 0.08 at 4 degrees C. For whole milk, after 5.75 h of FO processing, concentration factors of 2.32 +/- 0.12 at 25 degrees C, 2.12 +/- 0.36 at 15 degrees C, and 1.91 +/- 0.15 at 4 degrees C were obtained. Overall, maximum concentration levels of 40.15% total solids for skim milk and 40.94% total solids for whole milk were achieved. Additionally, a triangle sensory test showed no significant differences between regular milk and FO concentrated milk diluted to single strength. This work shows that FO is a viable nonthermal processing method for concentrating milk, but some technical challenges need to be overcome to facilitate commercial utilization.