576. The volatile compounds associated with oxidized flavour in skim milk

Abstract

Using chromatographic techniques, a number of compounds was isolated from the steam distillates of skim milk containing oxidized (cardboard) flavour. The following compounds were definitely identified: acetone, acetaldehyde, n–hexanal, crotonaldehyde, and the C5 to C11 2-unsaturated aldehydes. Presumptive evidence for the presence of several 2,4-diunsaturated aldehydes of medium chain length was obtained also. Acetaldehyde and acetone were also isolated from normal skim milk; these two compounds appear to play no part in the defect.2-Enals, in particular the C8 and C9, were considered to be the principal flavour-determining compounds. In milk at dilutions of 1 part in 107 to 109 they impart an oxidized type of flavour resembling that known as cardboard. Evidence was obtained that 2,4-dienals were also present and they produced a similar flavour.It may further be deduced that cardboard flavour in milk is caused by the preferential oxidation of di- and polyunsaturated fatty acids.

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

“…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.…”

Quality and Flavor of Diary Products, Review of Biochemical Properties of Milk and Lipide Deterioration in Milk and Milk Products as Influenced by Natural Varietal Factors

“…The use of Clarase or some other phosphatase is advisable because cooking so)-bean meal for feeds inactivates the natural phosphatase; also the natural phosphatase is not very active at p H 4.. 5. Raw meal contains a phosphatase with optimum activity at pH 6.0 which liberates free thiamine from cocarboxylase on autolysis.…”