Reaction flavors

Further evidence of the importance of the Halliard reaction in the formation of volatile flavorants from meat precursors is gleaned by examining ingredients in reaction mixtures patented as synthetic meat constituents. Ching (31), examined 128 patents of meat flavor and found that 55 specified use of both amino acids and sugars. Cysteine, cystine, and glutamic acid were used in 39 such mixtures. Over 80 patents describe meat flavor "reaction products" (32). 

Quantitative studies on the enzymatic generation of methanethiol from methionine showed that methioninase obtained from Pseudomonas putida could be used for the development of flavors. Reactions carried out under anaerobic conditions yielded only methanethiol while aerobic conditions favored conversion of substantial amounts of methanethiol to dimethyl disulfide. Incorporation of free or fat-encapsulated methionine/methioninase systems into Cheddar cheeses resulted in the formation of volatile sulfur compounds, including carbon disulfide, and accelerated rates of development of aged Cheddar-like flavors. Methanethiol, when present alone, was observed not to cause the true, Cheddar-like flavor note in experimental cheeses. 

Maga (17D06) has reviewed the occurrence of oxazoles and oxazolines in a variety of processed food systems. Most of them possess green, sweet, and nutty aroma qualities and have been identified in coffee, soy sauce, wheat, and cooked beef and some of them have very low odor thresholds. In 1976, LefflngweU discussed how certain flavorants (reaction products) can be produced in tobacco and tobacco smoke (2337). 

Cakes Catty off-flavor Reaction of ketones with sulfur compounds in food 4... 

Chloroacetate esters are usually made by removing water from a mixture of chloroacetic acid and the corresponding alcohol. Reaction of alcohol with chloroacetyl chloride is an anhydrous process which Hberates HCl. Chloroacetic acid will react with olefins in the presence of a catalyst to yield chloroacetate esters. Dichloroacetic and trichloroacetic acid esters are also known. These esters are usehil in synthesis. They are more reactive than the parent acids. Ethyl chloroacetate can be converted to sodium fluoroacetate by reaction with potassium fluoride (see Fluorine compounds, organic). Both methyl and ethyl chloroacetate are used as agricultural and pharmaceutical intermediates, specialty solvents, flavors, and fragrances. Methyl chloroacetate and P ionone undergo a Dar2ens reaction to form an intermediate in the synthesis of Vitamin A. Reaction of methyl chloroacetate with ammonia produces chloroacetamide [79-07-2] C2H ClNO (53). 

Many other acrolein derivatives produced via Diels-Alder reactions are classified as flavors and fragrances. Among those of commercial interest are lyral, (1) [31906-04-4] (91,92) andmyrac aldehyde, C 3H2oO, (2) [80450-04-0] (92,93). 

Diluent Portion. The diluent portion of a flavor compound is the carrier for the color and the flavor, ie, the solvent for the flavor portion. It keeps the flavor homogenous, ie, keeps soflds in solution retards chemical reactions from occurring and regulates flavor strength, ie, the greater the amount of solvent, the weaker the flavor. 

Other examples are glycine — formaldehyde, alanine — acetaldehyde, valine — isobutyraldehyde, phenylalanine — phenylacetaldehyde, and methionine — methional (106). Products such as dried skim milk, dried eggs, and dehydrated vegetables and fmits are particularly susceptible to deteriorative flavor changes ascribed to this reaction (Table 10). 

Hydroxybenzaldehyde has an agreeable aromatic odor, but is not itself a fragrance. It is, however, a useful intermediate in the synthesis of fragrances. The methyl ether of -hydroxybenzaldehyde, ie, -anisaldehyde, is a commercially important fragrance. Anisaldehyde can be made in a simple one-step synthesis from hydroxybenzaldehyde and methyl chloride. Another important fragrance, 4-(p-hydroxyphenyl)butanone, commonly referred to as raspberry ketone, can be prepared from the reaction of -hydroxybenzaldehyde and acetone, followed by reduction (see Flavors and spices). 

Direct oxidation yields biacetyl (2,3-butanedione), a flavorant, or methyl ethyl ketone peroxide, an initiator used in polyester production. Ma.nufa.cture. MEK is predominandy produced by the dehydrogenation of 2-butanol. The reaction mechanism (11—13) and reaction equihbtium (14) have been reported, and the process is in many ways analogous to the production of acetone (qv) from isopropyl alcohol. 

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). 

Essential Oils. Essential oils are produced by distillation of flowers, leaves, stems, wood, herbs, roots, etc. Distillations can be done directly or with steam. The technique used depends mosdy on the desired constituents of the starting material. Particular care must be taken in such operations so that undesired odors are not introduced as a result of pyrolytic reactions. This is a unique aspect of distillation processing in the flavor and fragrance industry. In some cases, essential oils are obtained by direct expression of certain fmits, particular of the citms family. These materials maybe used as such or as distillation fractions from them (see Oils, essential). 

Another significant use of 3-methylphenol is in the production of herbicides and insecticides. 2-/ f2 -Butyl-5-methylphenol is converted to the dinitro acetate derivative, 2-/ f2 -butyl-5-methyl-4,6-dinitrophenyl acetate [2487-01 -6] which is used as both a pre- and postemergent herbicide to control broad leaf weeds (42). Carbamate derivatives of 3-methylphenol based compounds are used as insecticides. The condensation of 3-methylphenol with formaldehyde yields a curable phenoHc resin. Since 3-methylphenol is trifunctional with respect to its reaction with formaldehyde, it is possible to form a thermosetting resin by the reaction of a prepolymer with paraformaldehyde or other suitable formaldehyde sources. 3-Methylphenol is also used in the production of fragrances and flavors. It is reduced with hydrogen under nickel catalysis and the corresponding esters are used as synthetic musk (see Table 3). 

MaillardReaction (Nonenzymatic Glycation), Browned reaction products ate formed by heating amino acid and simple sugar. This reaction is important in food science relating to coloring, taste, and flavor enhancement (79), and is iUustrated as follows ... 

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). 

Among chemical properties of cane sugar that affect daily use are color, flavor, sweetness, antioxidant properties, and reactions ia aqueous solution... 

The rate of aspartame degradation in dry mixes is more dependent on the water activity than on the temperature (23). In dry mixes, aspartame may also engage ia Maillard reactions with the aldehyde moieties of flavoting agents, resulting ia the loss of sweetness and flavor. Use of the corresponding acetals of the flavor compounds to avoid this reaction has been reported (24). 

The chemistry of organic sulfur compounds is very rich and organosulfur compounds are incorporated into many molecules. Thiols, or mercaptans as they were originally called, are essential as feedstocks in the manufacture of many types of mbber (qv) and plastics (qv). They are utilized as intermediates in agricultural chemicals, pharmaceuticals (qv), ia flavors and fragrances, and as animal feed supplements. Many reviews have been undertaken on the chemistry of the thiols, regarding both their preparation and their reactions (1 7). 

Mixed sulfides are prepared in the flavor industry by the reaction of thiols, 2inc oxide, and a bromoalkane (39). Some of these mixed sulfides are constituents of allium, asafetida, coffee, and meat flavors. A representative reaction is represented in equation 24. 

Vanillin, being an aldehyde, is able to form acetals and hemiacetals. Therefore, in flavor formulations using high concentrations of vanillin in conjunction with carriers such as propylene glycol, a glc analysis often shows a reduced vanillin peak after storage of the compounded flavor, and the presence of new peaks indicating acetal formation. Addition of about 0.5% of water to the formula reverses the reaction, ie, there is a reduction of acetal, and the reappearance of vanillin peaks. 

Antioxidants are used to retard the reaction of organic materials with atmospheric oxygen. Such reaction can cause degradation of the mechanical, aesthetic, and electrical properties of polymers loss of flavor and development of rancidity ia foods and an iacrease ia the viscosity, acidity, and formation of iasolubles ia lubricants. The need for antioxidants depends upon the chemical composition of the substrate and the conditions of exposure. Relatively high concentrations of antioxidants are used to stabilize polymers such as natural mbber and polyunsaturated oils. Saturated polymers have greater oxidative stabiUty and require relatively low concentrations of stabilizers. Specialized antioxidants which have been commercialized meet the needs of the iadustry by extending the useflil Hves of the many substrates produced under anticipated conditions of exposure. The sales of antioxidants ia the United States were approximately 730 million ia 1990 (1,2). 

Water. The character of the water has a great influence on the character of the beer and the hardness of water (alkalinity) manifests itself by the extent of its reaction with the weak acids of the mash. Certain ions are harm fill to brewing nitrates slow down fermentation, iron destroys the colloidal stabihty of beer, and calcium ions give beer a purer flavor than magnesium or sodium ions (Table 7). 

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