Studies on Oxidized Milk Fat. II. Preparation of 2,4–Dinitrophenylhydrazones from the Volatile Material from Oxidized Milk Fat

Abstract

In a previous paper (3), it was reported that the vacuum distillation of oxidized milk fat yielded material containing a high concentration of the characteristic odor compounds of oxidized fat. The preparation of 2,4-dinitrophenylhydrazones showed promise as a means of obtaining identification data on the volatile carbonyl compounds which seemed to be the predominant odor and flavor compounds from the oxidized fat. This paper reports a continuation of the chemical study of the volatile flavor material from oxidized milk fat. EXPERIMENTAL Ten gal. of fresh raw cream (40 per cent fat) were diluted with four volumes of tap water and rcseparated into cream (40 per cent fat). This water-washing procedure was repeated once and the washed cream cooled and held at 13 ° C. for 4 hr. before churning into butter. The butter was passed through a cream separator after mixing with hot tap water (71 ° C.) until a clear, curd-free oil was obtained from the centrifuge. This fat had a bland flavor. After standing at room temperature for 48 hr., the fat was filtered through cheese cloth by gravity and gave about 8 lb. of solid fat and 16 lb. of liquid fat. Three kg. of the precipitate or solid fat were placed in a loosely stoppered 4-1. pyrex Erlenmeyer flask on a hot plate exposed to northwest sunlight. The temperature of this fat was maintained at about 60 ° C. on the hot plate which was lined with asbestos boards to prevent excessive localized heating of the fat. Three kg. of the liquid fat, from the above filtration through cheese cloth, were placed in a loosely stoppered Erlenmeyer flask and similarly exposed to sunlight, but maintained at room temperature. The remainder of the fat, solid and liquid, was placed in cold storage (5 ° C.) for subsequent control experiments. The separation of the whole milk fat by the above procedure resulted in a liquid fat fraction which was considerably deeper in yellow color than the highermelting solid fraction. After 4 wk. the fat held at 60 ° C. was completely bleached. The fat held at room temperature was bleached in 10 wk. After 10 wk. the fat stored at 60 ° C. was distilled at about 0.5 ram. of mercury from an oven (160 to 180 ° C.), in the manner described previously (3), using successive 400-g. portions. Three kg. of this fat gave about 3 g. of volatile material.