Color formation and Maillard reactions during the spray drying process of skim milk and model systems

The thermal degradation of fresh skim milk, reconstituted skim milk and two model systems with different lactose/WPI ratios in a new design of spray dryer has been investigated. The extent of thermal degradation has been measured by the formation of Advanced Maillard reaction products, as assessed by a fluorometric method. Significant changes have been found when the inlet temperature increased from 180 degrees C to 190 degrees C, suggesting that temperature may play an important role in the kinetics of milk degradation in spray dryers. The non-uniform distribution of particle residence time in the pilot-scale dryer suggested that the design and operation of the spray dryer used for drying may also affect the extent of thermally induced reactions during the spray-drying process. Results from the spray drying of model systems with different lactose/WPI ratios suggested that WPI concentration may be the rate-limiting factor. Colourimetric analysis of the samples suggested a strong correlation between the formation of advanced Maillard reaction products and the color intensities of the spray-dried products. Practical Applications A correlation exists between the color intensity of the spray-dried products and formation of advanced Maillard reaction products, which can be potentially further developed as a rapid, cost-effective quality evaluation method for spray-dried products. The discussion of the effect of spray drying conditions on the wall-deposition and re-entrainment process and thus the particle residence time distribution may also assist in improving the spray-drying process for thermally sensitive products.