Characterization of a Spray-Dried Soymilk Powder and Changes Observed During Storage

Physical characterization of a soymilk powder was carried out by electron microscopy. Chemical characterization was analyzed by proximate analysis, mineral composition by atomic absorption spectrometry, fatty acid composition by gas chromatography and protein composition by electrophoresis. The powder consists of large granules of 60-80 μm, which may be hollow, with smaller granules of 10-20 μm attached to them. Powder particles are covered by a layer of fat. During storage at 25 °C fat is spreading over the surface, while at -12 °C the fat is contracting. This change affected chemical stability, resulting in high level of fat oxidation when stored at 4 °C or 25 °C as well as a decrease in unsaturated fatty acids. Storage also affected the chemical properties of the re-constituted soymilk; the pH of a 12% soy powder suspension increased from 6.68 ± 0.05 to 7.06 ±0.08 after 12 months of storage. Storage temperature did not affect the pH of the suspension and this change could also not be ascribed to protein aggregation.