Chemical Changes in Spray-Dried Skimmilk Held Near Dryer Outlet Temperatures

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Abstract
The hydroxymethylfurfural (HMF) content and fluorescence of spray-dried powders (2.8 to 5.6% H2O) made from pasteurized skimmilk increased during storage at temperatures similar to those encountered in products held in bulk storage without cooling immediately after drying (37 to 60 C). Rate of increase was directly related to the storage at 50[degree]C, an increase of HMF in powders containing 2.8% H2O could be detected, the amount originally present doubling during 16 hours of storage. The powders exhibited changes in the pattern of fluorescence excited by ultra-violet light having wavelengths of 330, 360, and 390 mu. More than a fivefold increase in HMF and a doubling of fluorscence activated at 330 mu was observed before changes in the visible color of the powders became detectable. Since no significant changes were noted in the powders during one week of storage at 37[degree] C, it was concluded that chemical changes in milk constituents during spray drying can be further decreased by cooling powder to this temperature immediately after drying.