Organoleptic, Chemical and Microbiological Changes in Ultra-High-Temperature Sterilized Milk Stored at Room Temperature1

Abstract

The effects of carton materials on flavor of ultra-high-temperature sterilized milks stored 100 days at 22 ± 2 C was investigated. Flavor scores of stored milk decreased concurrent with an increase in stale flavor. At the same time propanal, pentanal, hexanal, and an unidentified compound increased; cooked flavor along with methyl sulfide and another unidentified compound decreased. Differences in browning were observed between ultra-high-temperature sterilized and reference (freshly pasteurized) milks and between 2- and 12-day-old ultra-high-temperature sterilized milks. Thiobarbituric acid values did not increase (indicating no lipid oxidation) until after the milk had been stored 22 days; however, those values were below that which would be detected organoleptically. Abnormally high acetaldehyde concentrations were related to the ethylene oxide sterilizing pretreatment of the carton board. Reference milk was superior in flavor to milk from all other treatments. Aluminum foil-lined cartons were less permeable to gases than were polyethylene-lined cartons. Milk in aluminum foil-lined cartons retained desirable flavor characteristics longer than did that stored in polyethylene-lined cartons. Wrapping cartons with Saran and aluminum foil was detrimental to flavor in all instances. Analysis of variance of microbiological data established that there were no differences in numbers of microorganisms in the different types of cartons during 42 days.