Cooked flavor

Amino acids play a role in food processing in the development of a cooked flavor as the result of a chemical reaction called the nonenzymatic browning reaction (228). 

Probably the most important difference between UHT and pasteurized milk is flavor. UHT milk has an intensely cooked flavor immediately after processing that dissipates in about 1 week a stale flavor develops 3 to 4 weeks after the milk is processed and becomes progressively worse. Not all researchers agree on the intensity and significance of the flavor of UHT milk (Anon. 1981B) and the many factors that influence it (Mehta 1980). 

Gould, I. A. and Sommer, H. H. 1939. Effect of heat on milk with especial reference to the cooked flavor. Mich. Agri. Exp. Sta. Bull. 164. 

Hutton, J. T. and Patton, S. 1952. The origin of sulfhydryl groups in milk proteins and their contributions to cooked flavor. J. Dairy Sci. 35, 699-705. 

Josephson, D. V. and Doan, F. J. 1939. Observations on cooked flavor in milk—its source and significance. Milk Dealer 29(2), 35-54,... 

Although batch and HTST pasteurization produces a cooked flavor in milk by activation of whey protein sulfhydryl groups, it is not severe... 

Sulphydryl oxidase, an indigenous milk enzyme, has been proposed for the oxidation of thiols in UHT milk to reduce cooked flavor and also thereby to serve as an antioxidant, in conjunction with lactoperoxidase (to destroy the resultant H2O2), by obviating pro-oxidants resulting from autoxidation of thiols (Swaisgood and Abraham, 1980). 

When freshly squeezed orange juice is allowed to stand, the suspended pectic compounds ("cloud") separate and settle from the juice. This phenomenon can be prevented by heating the freshly squeezed juice to inactivate the pectin methylesterase, producing a "cooked flavor." Alternatively, additional polygalacturonase can be added to the juice (53). Cloud precipitation is caused by Ca + chelating the pectic acid produced by pectin methylesterase. 

Vacreation accomplishes a number of tasks in one operation. Pasteurization of the cream for buttermaking is perhaps the most important of these, followed by steam stripping of off odors. Other functions include destruction of natural milk lipases and development of a slightly nutty or cooked flavor in the resulting butter. 

In unseasoned stewed tomatoes, 2% sucrose reduced seed flavor and grassiness, augmenting sweetness and cooked flavor. An even more interesting effect was the increase of flavor amplitude. Sugar was found complementary to salt, pepper, and butter in the stewed tomatoes. Again, it was noted that sugar reduced saltiness. 

The aim of this research is to utilize the SCD to detect the sulfur compounds found in UHT processed milk. An integrated analytical approach to sampling, detection, and identification is used which includes purge and trap volatile concentration followed by thermal desorption, GC separation, SCD detection, and mass spectral identification. The sulfur compounds identified should be chiefly responsible for the cooked flavor in UHT milk. In addition, the mechanism for the disappearance of this sulfurous flavor will be explored. 

Three approaches were used to raplore cooked flavor fade. The first was to introduce oxygoi into freshly processed UHT milk. The other two were merely to store the pn uct at two differrait temperatures to determine what changes, if any, occur over time. All three showed no dramatic quantitative changes in sulfide or thiol concoitration. Small decreases, however, were observed with noticeable increases of dimethyl sulfone. 

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