Flavors enzymes

Function Color enzyme flavoring agent humectant nutritive sweetener stabilizer thickener and texturizer. 

Another, perhaps more promising, application of enzymic flavor modification is the conversion of specific undesirable flavor compounds to... 

Initially, researchers focused on studies of non-enzymic flavor formation (3,4). More recently, a renaissance of investigations of biogenesis of plant aromas is evident. The reasons for this new trend are obvious. Worldwide, an increasing quantity of natural flavors is required, and - as the natural sources are no longer sufficient - new ways of production are needed, e.g., plant cell or tissue cultures, microorganisms or enzymes (5,6). At present, these efforts are rather limited, since only a few experimentally demonstrated biogenetic pathways are known for plant volatiles (1,2). 

Each trial consisted of a vat of control cheese (butterfat capsules contained only phosphate buffer), a vat of cheese with the encapsulated enzymic flavor generating system, and a vat of cheese containing both butterfat capsules with only phosphate buffer and 15 ml of the unencapsulated reaction mixture (i.e., enzyme, substrate, and cofactor). Such an experimental design allowed assessment of Influences of both the addition of free methioninase systems and encapsulated methioninase systems on the... 

Although xanthine oxidase does not mediate sulfhydryl oxidations per se, it is activated by the binding of hydrogen sulfide and perhaps other simple thiols (82). Thus, the effects of this enzyme also might be useful in fabricating enzymic flavor-generating systems where it could serve as an assist in limiting free thiols in the medium. 

Biotransformations, biocorrversions impact on the whole range of biological, biotechnological arrd biomedical applications, such as in the analysis of genes and transcripts, the therapeutic treatment of abnormal molecules in diseases, the construction of specific enzymes and proteins for therapy, analysis, production, the assembly and constixiction of synthetic bio-synthetic pathways in organisms for the synthesis of intermediates, antibiotics, vitamins, enzymes, flavors. 

Nature has provided us with various food-dispersed components some are liquids (water-in-oil or oil-in-water emulsions), and some are semisolids or solids (dispersed fats, proteins, and carbohydrates). Some components are dissolved in continuous phases, and others are dispersed in various complex molecular and physical macro- or microstructured networks. This infinite number of structural combinations are organized and arranged in very complex types of assemblies such as dispersions, emulsions, foams, and gels. In addition, foods contain hundreds of small molecules as minor ingredients and various other added compounds termed food additives. Additives act as vitamins, antioxidants, preservatives, acidulants, enzymes, flavors, colorants, amphiphiles, and so on. 

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. 

FlavorFicpunct. A substance used in or with a flavor but not essentially a part of it. These include solvents, antioxidants, enzymes, adjusting agents, emulsifiers, and acidulants. 

In general, many species of algae have cell walls resistant to digestive enzymes, dark colors, and bitter flavor. AH of these characteristics must be altered to make an acceptable food or feed product. 

Hydrolyzed Vegetable Protein. To modify functional properties, vegetable proteins such as those derived from soybean and other oil seeds can be hydrolyzed by acids or enzymes to yield hydrolyzed vegetable proteins (HVP). Hydrolysis of peptide bonds by acids or proteolytic enzymes yields lower molecular weight products useful as food flavorings. However, the protein functionaHties of these hydrolysates may be reduced over those of untreated protein. 

Use of ultrafiltration (UF) membranes is becoming increasingly popular for clarification of apple juice. AH particulate matter and cloud is removed, but enzymes pass through the membrane as part of the clarified juice. Thus pasteurization before UF treatment to inactivate enzymes prevents haze formation from enzymatic activity. Retention of flavor volatiles is lower than that using a rack-and-frame press, but higher than that using rotary vacuum precoat-filtration (21). 

Experimental procedures have been described in which the desired reactions have been carried out either by whole microbial cells or by enzymes (1—3). These involve carbohydrates (qv) (4,5) steroids (qv), sterols, and bile acids (6—11) nonsteroid cycHc compounds (12) ahcycHc and alkane hydroxylations (13—16) alkaloids (7,17,18) various pharmaceuticals (qv) (19—21), including antibiotics (19—24) and miscellaneous natural products (25—27). Reviews of the microbial oxidation of aUphatic and aromatic hydrocarbons (qv) (28), monoterpenes (29,30), pesticides (qv) (31,32), lignin (qv) (33,34), flavors and fragrances (35), and other organic molecules (8,12,36,37) have been pubflshed (see Enzyp applications, industrial Enzyt s in organic synthesis Elavors AND spices). 

Irradiation. Although no irradiation systems for pasteurization have been approved by the U.S. Food and Dmg Administration, milk can be pasteurized or sterilized by P tays produced by an electron accelerator or y-rays produced by cobalt-60. Bacteria and enzymes in milk are more resistant to irradiation than higher life forms. For pasteurization, 5000—7500 Gy (500,000—750,000 tad) are requited, and for inactivating enzymes at least 20,000 Gy (2,000,000 rad). Much lower radiation, about 70 Gy (7000 tad), causes an off-flavor. A combination of heat treatment and irradiation may prove to be the most acceptable approach. 

The leaves of Camellia sinensis are similar to most plants in general morphology and contain all the standard enzymes and stmctures associated with plant cell growth and photosynthesis (10—12). Unique to tea plants are large quantities of flavonoids and methylxanthines, compounds which impart the unique flavor and functional properties of tea. The general composition of fresh tea leaves is presented ia Table 1. 

Fermentation. The term fermentation arose from the misconception that black tea production is a microbial process (73). The conversion of green leaf to black tea was recognized as an oxidative process initiated by tea—enzyme catalysis circa 1901 (74). The process, which starts at the onset of maceration, is allowed to continue under ambient conditions. Leaf temperature is maintained at less than 25—30°C as lower (15—25°C) temperatures improve flavor (75). Temperature control and air diffusion are faciUtated by distributing macerated leaf in layers 5—8 cm deep on the factory floor, but more often on racked trays in a fermentation room maintained at a high rh and at the lowest feasible temperature. Depending on the nature of the leaf, the maceration techniques, the ambient temperature, and the style of tea desired, the fermentation time can vary from 45 min to 3 h. More highly controlled systems depend on the timed conveyance of macerated leaf on mesh belts for forced-air circulation. If the system is enclosed, humidity and temperature control are improved (76). 

Diacetyl, acetoin, and diketones form during fermentation. Diacetyl has a pronounced effect on flavor, with a threshold of perception of 0.1—0.2 ppm at 0.45 ppm it produces a cheesy flavor. U.S. lager beer has a very mild flavor and generally has lower concentrations of diacetyl than ale. Diacetyl probably forms from the decarboxylation of a-ethyl acetolactate to acetoin and consequent oxidation of acetoin to diacetyl. The yeast enzyme diacetyl reductase can kreversibly reduce diacetyl to acetoin. Aldehyde concentrations are usually 10—20 ppm. Thek effects on flavor must be minor, since the perception threshold is about 25 ppm. 

In the wet method, as practiced in Colombia, freshly picked ripe coffee cherries are fed into a tank for initial washing. Stones and other foreign material are removed. The cherries are then transferred to depulping machines which remove the outer skin and most of the pulp. However, some pulp mucilage clings to the parchment shells that encase the coffee beans. Fermentation tanks, usually containing water, remove the last portions of the pulp. Fermentation may last from twelve hours to several days. Because prolonged fermentation may cause development of undesirable flavors and odors in the beans, some operators use enzymes to accelerate the process. 

Coffee bioconversions through enzymatic hydrolysis have been used to modify green coffee and improve the finished product (60). Similarly, enzymes have been reported which increase yield and improve flavor of instant coffee (61). Fermentation of green coffee extracts to produce diacetyl [431 -03-8] a coffee flavor compound, has also been demonstrated (62). 

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