Dynamic headspace analysis of light activated flavor in milk

Abstract

Dynamic headspace analysis (DHA) was evaluated for its ability to recover, fractionate and identify the key volatile compounds responsible for development of light activated flavor (LAF) in commercial fluid milk stored in Pyrex test tubes and exposed to 200 foot-candles of fluorescent light for 6 to 48 h at 0–5 °C, with and without headspace during storage. Major volatile compounds recovered and identified from ⩾12 h light exposed milk, presumably resulting from photosensitization and decomposition of riboflavin and oxidation of lipids and sulfur compounds, included: hexanal, pentanal, dimethyl disulfide (DMDS), 2-butanone, and 2-propanol. Formation of all five compounds was favored by providing headspace during light exposure, except for 2-butanone and 2-propanol in 48 h light-exposed milk. DMDS was not detected in 12 h light-exposed milk, but was recovered from 24 and 48 h light-exposed milk at steadily increasing concentrations. DMDS formation was favored by providing headspace during light exposure. A trained sensory panel was not able to detect LAF in 6 or 12 h light-exposed milk without headspace, whereas DHA was able to detect increases in concentrations of two volatile compounds, i.e., pentanal and hexanal, in 12 h light-exposed milk without headspace, which corresponds to commercial milk storage conditions.