Effect of Process- and Storage-Times and Temperatures on Concentrations of Volatile Materials in Ultra-High-Temperature Steam Infusion Processed Milk 1 .

Effect of various processing times and temperatures on the composition and subsequent changes in concentration of volatile compounds in UHT milk during storage was investigated. Milk samples were sterilized in a DASI Free Falling Film steam infusion system utilizing the combinations of 138, 146, and 154°C for 1.5, 3.4 and 9.0 s. After processing, aseptically collected samples were stored at refrigeration (2-5°C) and room (25°C) temperature for analysis at monthly intervals. Gas chromatographic analysis showed that processing times and temperatures used had little effect on initial concentrations of most volatile compounds in UHT milk. However, changes in their concentrations during storage appeared to be related to processing temperatures and temperature of storage, Acetaldehyde and n-pentanal increased more rapidly in the milk sterilized at 154°C/3.4 s than 146°C/3.4 s, whereas n-hexanal concentrations were lower in milk sterilized at 154°C/3.4 s. In addition, changes in concentrations of volatile compounds during storage at room temperature occurred primarily in aliphatic aldehydes. Increases in acetaldehyde, n-pentanal, and n-hexanal were closely related to the rapid decrease in product acceptability that was mainly due to increase in the intensity of stale flavor. Relatively little change occurred in the concentration of these aldehydes in milk stored at refrigeration temperature.