Effect of storage temperature on the physicochemical and sensory properties of regular and lactose-reduced low-fat UHT milk

UHT milk is stable towards spoilage for months, but chemical and enzymatic reactions occur during storage. This study evaluated whether changes over storage (at 4, 20 or 30 degrees C, for 30-90 d) of regular as well as lactose-reduced UHT milk were discernible by untrained and trained sensory panelists, and which physicochemical parameters they were associated with. Most changes were of low magnitude, such as significant increases in non-protein nitrogen (in both milk types) and lactulose (in regular UHT milk). However, the color of lactose-reduced UHT milk noticeably changed due to browning. Trained panelists evaluated lactose-reduced samples stored at 30 degrees C as significantly different in color than those stored at lower temperatures and untrained panelists correctly distinguished between fresh and stored lactose-reduced UHT milk in a tetrad-test already after 30 d. Further research is needed to evaluate if consumers detect such changes and therefore dispose of UHT- milk.