Heat-Induced Volatile Compounds in Milk

Abstract

Milk, preheated at 82[degree]C for 30 min, was heated to 146[degree]C for 4 sec and cooled to 5[degree]C in a tubular heat exchanger. Immediately after heat treatment, the milk was vacuum distilled at 30[degree]C in a semi-continuous, reduced pressure, glass apparatus. Raw milk was distilled in a similar manner for a control. Continuous liquid-liquid ethyl ether extractions were employed to recover the compounds from the aqueous distillates. Gas chromatog-raphy, mass spectrometry, infrared spectrophotometry, and odor confirmation were used to characterize the compounds in the ethereal concentrates. The following compounds were found to be heat induced: The C3 4,5,7,8,9,10,11,13 n-methyl ketones, the C8,10,12 delta-lac-tones, benzaldehyde, furfural, phenylacetaldehyde, vanillin, oct-l-en-3-ol, n-heptanol, 2-butoxyethanol, maltol, acetophenone, benzonitrile, benzothiazole and diacetyl. Other food products could yield these heat-induced compounds provided the basic materials from which they originate were present during the heat treatment. The following novel compounds were found in both heated and raw milk: A dichlorobenzene, a trichlorobenzene, methyl iodide, and diacetyl. Benzonitrile, dichlorobenzene, trichlorobenzene, and methyl iodide were present in the ethereal concentrates in trace amounts. The concentration of diacetyl in heated and raw milk was determined by a modified gas entrainment, on-column trapping GLC [gas-liquid chromatography] technique. The amount of diacetyl in raw milk was 5 ppb while the amount in the heated milk was 38 ppb, which is above the average flavor threshold for diacetyl in milk. Diacetyl may contribute to the rich or heated note in the flavor of heated milk.