Enzymatic Flavor Changes

One must remember that virtually all foods were once living. These living entities depended on enzymes for metabolism and subsequent growth. Therefore, foods contain a variety of enzymes. While many are inactivated by processing or may be inactive due to inadequate conditions for functioning (e.g., low-water activity, temperature, and pH), some foods do contain active enzymes, which may cause OF to develop in the food product. The three enzymes most commonly associated with OF in foods are lipoxygenase, lipase, and various proteases. 

Lipoxygenase is an enzyme that will attack cis-cis double bonded, methylene interrupted fatty acids (most commonly linoleic and linolenic acids). This enzyme 

FIGURE 7.5 Photodegradation of iso-a- humulones in a cysteine model system. (From Saxby, M.J., S. Wragg, Ind., p. 310, 1985. With permission.) 

Lipoxygenase enzymes are quite common to plant tissues. The legumes (especially soybeans) contain substantial quantities of lipoxygenase enzymes. The beany flavor of soybeans is believed to be due to lipoxygenase activity in the bean once tissue damage has occurred [102-104], The reversion flavor of soybean oil is also believed to be due to lipoxygenase activity in the oil. Hsieh et al. [155] have shown that 2-pentylfuran is the primary oxidation product responsible for this OF. 

Lipoxygenase also plays a role in the deterioration of frozen vegetables. Many vegetables must be blanched prior to frozen storage in order to inactivate lipoxygenase enzymes, which otherwise result in oxidized OF [105] during storage. 

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Abstract Overcoming the complexity of cheese matrix to reliably analyze cheese composition, flavor, and ripening changes has been a challenge. Several sample isolation or fractionation methods, chemical and enzymatic assays, and instrumental methods have been developed over the decades. While some of the methods are well... 

HP reduces the total counts similar to a mild blanching (which at 150 sec. is sufficient for a complete inactivation of the polyphenoloxidase an enzyme involved in the enzymatic browning of the products). Obviously and in line with the present state of the art", spores cannot be inactivated sufficiently at temperatures up to 50°C by a HP-treatment but temperatures above 65°C [6] are needed. However, this leads to heat-induced changes in the texture, flavor etc. A product treated under these conditions,... 

Garlic develops its aroma from enzymatic reactions, as described before. When garlic slices are deep fried, microwave heated, or oven baked, the aroma changes (Yu et al., 1993) and contributes a different kind of garlic flavor to foods. A novel... 

Specific changes in color, aroma, flavor, texture, stability, and acceptability of raw and processed food products have been associated with relatively narrow a ranges (Huang et al, 1989 Chang et al, 1991). The a may have direct uncomplicated effects upon various chemical reactions (Labuza, 1980), enzymatic reactions (Schwimmer 1980), and the proliferation of microorganisms (Troller, 1972,1980 Troller and Christian, 1978). 

Some of the stated advantages of direct osmosis in comparison with other drying processes include minimized heat damage to color and flavor, less discoloration of fruit by enzymatic oxidative browning, better retention of flavor compounds, and less energy consumption since water can be removed without change of phase. However, products cannot be dried to completion solely by this method and some means of stabilizing them is required to extend their shelf lives. 

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