600. Further observations on the volatile compounds associated with oxidized flavour in skim milk

Abstract

The C6–C11 2,4–dienals have been identified in distillates from skim milk with oxidized flavour. The C4–C11 2–enals were isolated from the same distillates in a previous investigation. The most abundant individual compounds in the two groups were 2–octenal, 2–nonenal, 2–4–heptadienal and 2,4–nonadienal. These compounds when flavour–tested in skim milk in dilutions of 10–7–10–9 closely resembled oxidized (cardboard) flavour. It is concluded that they are the main constituents of this flavour defect and that they originate from the oxidation of the more highly unsaturated fatty acids in milk lipids.

CARBONYLS IN OXIDIZING FAT. I. SEPARATION OF STEAM VOLATILE MONOCARBONYLS INTO CLASSESa

“…Maxima were generally sharp and corresponded to those characteristic for saturated aldehyde, 2-en-l-al, and 2,4-dien-l-a1 classes. Braude and Jones (5) and others (14,15,26) have determined the characteristic range of maxima in ethanal and chloroform of the classes of 2,4-DNPH's. These values, along with determinations by the authors in carbon tetrachloride, ethanal, and alcoholic alkali, are shown in Table 1.…”

“…These data illustrate particularly well the rapid increase and change in relative amounts of the monocarbonyl classes during the early stages of oxidation. Data shown in Figure 7 for cured bacon from the same animal (see Figure 7) are considerably different, although the fat was presumably similar in composition .Comparing Figures 6 and 7 over the same range of oxidation (peroxide [12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30], the rate of change and relative amounts of the classes are obviously different. It would appear that the pro-oxidant, salt, may influence the formation of oxidation products in some manner.…”

“…A number of investigators have recently reported identification of carbonyls in food products (12,14,15,39,48). A quantity of individual compounds of the expected types of carbonyls were found by Forss, Pont, and Stark (14,15) in off-flavored skim milk, and by Pippen, Nonaka, Jones and Stitt (39) in a simmering mixture of chicken muscle tissue and water.…”

“…I n general, applications of the above methods have indicated a close relationship between peroxides and carbonyl values. Total carbonyl values, therefore, also appear not to be specific for rancidity.Consideration of these facts, together with the well-known sensitivity of taste, leads to the assumption that rancid flavors may be due to some particular type of carbonyls (8,9,14,15,27), the proportions and rate of formation of which are influenced by the composition of the glycerides, catalysts, enzymes, and anti-oxidants present, and processing and storage conditions. Henick, Benca, and Mitchell (23) have developed a method for determination of total saturated and unsaturated carbonyls as hexanal and crotonaldehyde.Applications (23,38) of this method showed the rate of increase of saturated carbonyls exceeded that of the 2-enal class.…”

Mechanisms of formation of aroma compounds in milk and milk products

“…Ironically, one of the first comprehensive studies of oxidized flavour in milk products (26,27), which showed that alkanals, alk-2-enals and alka-2,4-dienals were responsible, was done on skim-milk supposedly devoid of fat, but actually containing a high proportion of phospholipid rich in polyunsaturated acids.…”