Flavor deterioration

Enzymes not only produce characteristic and desirable flavor (79) but also cause flavor deterioration (80,81) (see Enzyme Applications, Industrial). The latter enzyme types must be inactivated in order to stabilize and preserve a food. Freezing depresses enzymatic action. A more complete elimination of enzymatic action is accompHshed by pasteurization. 

Citric acid also inhibits color and flavor deterioration in frozen fmit. Here again the function is to inhibit enzymatic and trace metal-catalyzed oxidation. 

You may have noticed Ca-EDTA on the list of ingredients of many prepared foods, ranging from beer to mayonnaise. EDTA acts as a scavenger to pick up traces of metal ions that catalyze the chemical reactions responsible for flavor deterioration, loss of color, or rancidity. Typically, Ca-EDTA is added at a level of 30 to 800 ppm. 

Included in the above list should be a method for estimating flavor deterioration and degree of desiccation and tests for estimating the adequacy of blanching in the frozen products in which one could have absolute confidence. Suitable methods are not now available their development would be a useful and valuable field for research. 

Carbonated Soft Drinks. Although there is not enough data available to establish maximum levels of dissolved aluminum for each soft drink formulation, Lemelin (20) has reported that cola and lemon-based drinks containing 5-10 ppm aluminum showed no significant flavor deterioration after six months at 78 °F. A relatively high amount of dissolved aluminum will not adversely affect the flavor of soft drinks. 

The levels of pea flour that are most effective for dough improvement are usually less than 5%, and 0.75 to 3% has been recommended. At higher levels, undesirable dough behavior occurs, as well as flavor deterioration. 

Meat flavor deterioration (MFD), formerly referred to as warmed-over flavor, is described as the loss of desirable meaty flavor with an increase in off-flavors (i-5). During this process, the increase in off-flavors is primarily contributed by hpid oxidation reactions. As lipids oxidize, they produce mixtures of aldehydes, ketones and alcohols that contribute to the off-flavors observed. Many of these compounds have been identified and the increase in their intensities during storage have been well documented (7, 4-6),... 

Over the years, scientists have used many types of antioxidants in a variety of foods to retard or inhibit lipid oxidation and, thus, increase shelf-life and preserve quality. These antioxidants include free radical scavengers, chelators, and oxygen absorbers. While there are numerous antioxidants available to food scientists, the objective of this report was to discuss several of these antioxidants as they relate to meat flavor quality research and to show how they were used to retard lipid oxidation and prevent meat flavor deterioration in ground beef patties. 

The flavor quality of food is a primary factor involved in a consumer s decision to purchase a food item. Therefore, food technologists require a thorough understanding of how flavor deteriorates if they are to prepare products that consumers will purchase repeatedly. This knowledge is particularly important in meat and meat products, since the deterioration of meat flavor is a serious and continual process (1-4) that involves both the loss of desirable flavor components 4,5) and the formation of off-flavor compounds (6-9) many of which are associated with lipid oxidation (10). 

Proper sanitary procedures on the farm and in the processing plant, maintenance of a 4°C holding temperature, and reduced holding times before pasteurization have been proposed to control this problem in raw milk (Schipper 1975 Menger 1975). However, more research is needed to determine the role that lipases from microorganisms play in the flavor deterioration of market milk (Richter 1981 Cogan 1980 Stewart et al. 1975). 

The effects of heat treatment of milk on the oxidation-reduction potential have been studied to a considerable extent (Eilers et al 1947 Gould and Sommer 1939 Harland et al 1952 Josephson and Doan 1939). A sharp decrease in the potential coincides with the liberation of sulfhydryl groups by denaturation of the protein, primarily /3-lactoglobulin. Minimum potentials are attainable by deaeration and high-temperature-short-time heat treatments (Higginbottom and Taylor 1960). Such treatments also produce dried milks of superior stability against oxidative flavor deterioration (Harland et al 1952). 

Prolonged storage results in flavor deterioration, drying and fungal growth. A stiff citrus flavored pectin gel applied... 

Blair, J. S. Godar, E. M. Masters, J. E. Riester, D. W. Exploratory experiments to identify chemical reactions causing flavor deterioration during storage of canned orange juice. I. Incompatibility of peel oil constituents with the acid juice. Food Res., 1952, 17, 235-260. 

The contribution of lipid oxidative products to off-flavor development has been studied by many workers, and a review of these studies has been presented by Nagy (38). It is generally agreed that the contribution of the lipid oxidative products to the flavor deterioration of processed citrus products is relatively minor when compared to the contributions by the products formed by the acid-catalyzed hydrolysis of flavoring oils and the products of Maillard browning (39,40). 

As might have been expected, flavor deterioration followed the same pattern as did the degradation of ascorbic acid, i.e., the concentrates at 23.9°C deteriorated in flavor acceptability more rapidly than did those at 7.2°C those at 7.2°C deteriorated at a faster rate than did those stored frozen. The products stored at 23.9°C remained acceptable in flavor for about six months those at 7.2°C remained acceptable for eight to ten months. At -17.8°C, the products were still acceptable after a year of storage. 

Flavor changes that occur in citrus juices are the result of heat input into the product over time i.e., they are a function of temperature and time. It is for this reason that canned and bottled juices are generally less preferred by consumers than other processed citrus juices, e.g., frozen concentrates or chilled juices. The canned juices receive more heat input during pasteurization and they remain at relatively high temperatures for extended periods of time because they are discharged from the water coolers at temperatures near 40°C to facilitate drying and to inhibit rusting of the cans. It is well known that the rate of flavor deterioration increases with temperature, so canned juices are stored at a temperature as low as is economically practical before distribution at the retail level to extend their shelf life as much as possible. 

Since several studies identified the aliphatic and heterocyclic sulfur compounds as being important to cooked-beef flavor (9-11). the present report focuses upon a few key sulfur compounds that contribute to flavor of cooked meat as they change with time and temperature. Previous work has been directed to obtaining reliable correlation of sensory panel data with objective instrumental data describing meat flavor deterioration on storage (1). The present study is targeted toward obtaining a reliable, objective assay... 

Volatile profiles of raw and cooked-beef flavor samples, prepared by the procedures of Figure 1, were obtained after capillary GC and FPD. Although the identification of these sulfur containing compounds is as yet incomplete, the chromatograms demonstrated that there were a number of new sulfur compounds produced on cooking that were not present in the raw beef. Three prominent sulfur compounds were identified as markers in subsequent meat flavor deterioration experiments, namely, methional (13.2 min), methyl sulfone (13.8 min), and benzothiazole (25.3 min). Each compound produced an adequate mass spectrum for spectral library search and positive identification. 

A typical cooked-beef flavor deterioration sample was prepared as described in Beef Preparation section to observe changes in key sulfur marker compounds over a period of 0-, 2-, 4-, and 7-day storage. Sulfur markers, methional, methyl sulfone, and benzothiazole were compared with benzothiophene as internal standard to follow the course of free radical reactions taking place in the stored cooked-beef. Results are plotted in... 

Figure 3 plots intensity changes perceived by gd hoc descriptive sensory panelists in intensity analysis for character notes involved in meat flavor deterioration during storage of the grilled beef samples reported in Figure 2 and Table II (12, 13). The loss of intensity for certain descriptors in Figure 3 is in accord with sensory panel experience that the positive notes such as cooked-beef brothy diminish with formation of new off-flavor compounds represented as cardboard and painty. 

Positive cooked-beef flavor components as perceived by descriptive sensory panelists are reduced during free radical catalyzed meat flavor deterioration (MFD) while negative flavor notes with descriptor definitions of cardboard and painty intensify, as reviewed recently by Love (13). Although the cardboard and painty off-flavors correlate well with lipid oxidation products and can be measured easily by gas chromatography (1, 14, 18). much less is known about the fate of the positive cooked-beef flavors in this MFD process (13). 

The effect of storage temperature on the oxidative stability of milk and milk products is unclear. Storage, in air, at 2°C inhibited the development of oxidized flavor in dry whole milk when compared with control samples held at 38°C (Pyenson and Tracy, 1946). Oxidative deterioration of UHT cream occurred two to three times more rapidly at 18°C than at 10°C, while little or no oxidation occurred at 4°C (Downey, 1969). The oxidation-reduction potential of butter and the rate of flavor deterioration have been reported to increase as the storage temperature increased (Weihrauch, 1988). 

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