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Chemical and Flavor Changes in Sterile Concentrated Milk During Storage¹

Department of Dairy and Poultry Science, Kansas State University, Manhattan

ABSTRACT

Three lots of concentrated milk (ultra-high temperature, high-temperature short-time, and conventionally sterilized) were stored at 4, 20, and 37 C for eight months, and examined monthly for changes in flavor, volatile compounds as detected by GLC, acid degree values, and severity of browning, One lot of sterile concentrated skimmilk also stored at 4, 20, and 37 C was analyzed occasionally during the eight months.

Flavor deterioration was rapid at 20 and 37 C, with cooked, scorched, and stale flavor defects most apparent. The ultra-high temperature milk had a flavor advantage initially, but after storage flavor scores for all processed milks were at similar levels. Some methyl ketones, furan, and methyl furan increased during storage at 20 and 37 C. Milk fat was the precursor of 2-heptanone and 2-pentanone. Increases in acetone, butanone, acetaldehyde, furan, and methyl furan concentration during storage appeared to come from the nonfat portion of milk. Methyl sulfide was derived from the serum phase, but did not increase in concentration during storage. Methyl sulfide was the only volatile compound found at concentrations greater than its threshold value in milk. Acid degree values were high in all freshly sterilized milks and increased slightly at 20 C and rapidly at 37 C. Browning reaction values increased at 37 C storage.

¹ Contribution no. 707, Department of Dairy and Poultry Science, Kansas Agricultural Experiment Station, Manhattan, Kansas 66502.