Effect of Pasteurization Tempertaure on Susceptibility of Milk to Light-Induced Flavor

Milk pasteurized at 73, 80 and 90°C for 16.2 s and homogenized than exposed to 50-foot-candle intensity of fluorescent light in clear glass bottles was compared for flavor and concentrations of acetaldehyde, propanal, n-pentanal and n-hexanal with similarly treated milk in foil-covered glass bottles. Flavor (hedonic scaling by five judges) was influenced by pasteurization temperatures, storage time and exposure to light. Milk pasteurized at 73°C and held in foil-covered bottles through 10 d at 2°C had the most acceptable flavor. However, when milk was pasteurized at this temperature but exposed to light, it had the least desirable flavor during 10 d. At 14 d, flavor score of the 73°C, unexposed milk declined, and that of the irradiated milk increased so that both were almost identical. At pasteurization temperatures of 80 and 90°C, the adverse effect of irradiation was either reduced or eliminated and the incidence of oxidized flavor lessened. Poorer flavor at these pasteurization temperatures from unexposed milks reflected greater intensities of cooked flavor. Concentrations of acetaldehyde, propanal, n-pentanal and n-hexanal increased much more in the light-treated samples than those kept in the dark. However, high-heat treatment (90°C) lessened those increases in propanal and n-hexanal but enhanced increases in acetaldehyde and n-pentanal.