FOOD FLAVOR CHEMISTRY: Flavor of Foods You Love

Flavor is the sensory impression of a food or other substance, and is determined mainly by the chemical senses of taste and smell. The "trigeminal senses", which detect chemical irritants in the mouth and throat as well as temperature and texture, are also very important to the overall Gestalt of flavor perception. The flavor of the food, as such, can be altered with natural or artificial flavorants, which affect these senses.

Flavorant is defined as a substance that gives another substance flavor, altering the characteristics of the solute, causing it to become sweet, sour, tangy, etc.

Of the three chemical senses, smell is the main determinant of a food item's flavor. While the taste of food is limited to sweet, sour, bitter, salty, umami (savory) pungent or piquant, and metallic – the seven basic tastes – the smells of a food are potentially limitless. A food's flavor, therefore, can be easily altered by changing its smell while keeping its taste similar. Nowhere is this better exemplified than in artificially flavored jellies, soft drinks and candies, which, while made of bases with a similar taste, have dramatically different flavors due to the use of different scents or fragrances. The flavorings of commercially produced food products are typically created by flavorists.

Although the terms "flavoring" or "flavorant" in common language denote the combined chemical sensations of taste and smell, the same terms are usually used in the fragrance and flavors industry to refer to edible chemicals and extracts that alter the flavor of food and food products through the sense of smell. Due to the high cost or unavailability of natural flavor extracts, most commercial flavorants are nature-identical, which means that they are the chemical equivalent of natural flavors but chemically synthesized rather than being extracted from the source materials. Identification of nature-identical flavorants are done using technology such as headspace techniques.

The History of Tastes

Before digging into the main course—the methods of preparation—let us make a little detour useful to understanding how we eat, because we will be better cooks if we know how to distinguish the various sensations that dishes produce: tastes and flavors, colors, scents, aromas.

Aristotle knew everything, but what did he know about tastes? Let us entrust ourselves to this old philosopher. Tirelessly traversing the lyceum with his disciples, he worked up an appetite and turned his metaphysical mind toward gourmand meditations: there are “in the tastes as in the colors, on the one hand, the simple kinds which are also the opposites, that is, the sweet and the bitter; on the other hand, the kinds derived either from the first, like the unctuous, or from the second, like the salty; finally, halfway between these last two flavors, the sour, the pungent, the astringent, and the acid, more or less; these seem to be, in effect, the different tastes.”

Aristotle is not the only authority to have appreciated oral sensations. In particular, in the eighteenth century the great Linnaeus also applied his talents to tastes, but paradoxically the most famous of systematicians, the father of botanical classification, lacked some systematic spirit, because he mixed together the moist, the dry, the acid, the bitter, the fatty, the astringent, the sweet, the sour, the viscous, the salty. He put them all pell-mell in the same bag for us, this mix of tastes and mechanical sensations.

A Frenchman deserves the credit for establishing a little order in the domain of oral impressions. In 1824 the great chemist Michel-Eugene Chevreul (1786-1889), famous especially for his work on fats, distinguished the olfactory, gustatory, and tactile sensations. He recognized that the perception of hot or cold is distinct from that of sweet or bitter. He separated out the tactile sensations of the oral cavity, as well as the proprioceptive sensations (for example, toughness). With Chevreul, the taste of physiologists—one component of flavor—was distinguished from everyday sensation, where all the sensations associated with the absorption of food and drink are mixed.

In the same period but in a different circle, among the gourmands centered around Brillat-Savarin, the only confusion that continued to reign was between tastes and smells. The tongue was known to perceive tastes, but the nose was also believed to be a receptor. Apart from a few more or less harmless errors, the remarks made in the Treatise on the Physiology of Taste are as insightful as their author is passionate about cooking: “The number of tastes is infinite, since every soluble  body has a special flavor which does not wholly resemble any other. Up to the present time there is not a single circumstance in which a given taste has been analyzed with stern exactitude, so that we have been forced to depend on a small number of generalizations such as sweet, sugary , sour, bitter, and other like ones which express, in the end, no more than the words agreeable or disagreeable.” On the other hand, a bit later, Brillat-Savarin adds that “any sapid substance is perforce odorant.” He had forgotten that some molecules that are hardly volatile at all at ambient temperatures and thus odorless nevertheless bind easily to taste receptors on the tongue and palate and therefore have a taste. Salt, for example, is sapid but odorless.

As indicated previously, the two main factors affecting flavor are taste and odor. In a general way, food flavors can be divided into two groups. The first consists of foods whose flavor cannot be attributed to one or a few outstanding flavor notes; their flavor is the result of the complex interaction of a variety of taste and odor components. Examples include bread, meat, and cheese. The second group consists of foods in which the flavor can be related to one or a few easily recognized components (contributory flavor compounds). Examples include certain fruits, vegetables, and spices. Another way of differentiating food flavors is by considering one group in which the flavor compounds are naturally present and another group in which the flavor compounds are produced by processing methods.

Bread

The flavor of white bread is formed mainly from the fermentation and baking processes. Freshly baked bread has a delightful aroma that is rapidly lost on cooling and storage. It has been suggested that this loss of flavor is the result of disappearance of volatile flavor components. However, it is well known that the aroma may be at least partially regenerated by simply heating the bread. Schoch (1965) suggested that volatile flavor compounds may become locked in by the linear fraction of wheat starch. The change in texture upon aging may be a contributory factor in the loss of flavor. During fermentation, a number of alcohols are formed, including ethanol, rc-propanol, isoamyl and amyl alcohol, isobutyl alcohol, and p-phenol alcohol. The importance of the alcohols to bread flavor is a matter of controversy. Much of the alcohols are lost to the oven air during baking.

A large number of organic acids are also formed (Johnson et al. 1966). These include saturated aliphatic acids, from formic to capric, as well as lactic, succinic, pyruvic, hydrocinnamic, benzilic, itaconic, and levulinic acid. A large number of carbonyl compounds has been identified in bread, and these are believed to be important flavor components. Johnson et al. (1966) list the carbonyl compounds isolated by various workers from bread; this list includes 14 aldehydes and 6 ketones. In white bread made with glucose, the prevalent carbonyl compound is hydroxymethylfurfural (Linko et al. 1962). The formation of the crust and browning during baking appear to be primary contributors to bread flavor. The browning is mainly the result of a Maillard-type browning reaction (Maillard Reaction Mechanism and Its Applications to Your Cooking) rather than caramelization. This accounts for the presence of the carbonyl compounds, especially furfural, hydroxymethylfurfural, and other aldehydes. In the Maillard reaction, the amino acids are transformed into aldehydes with one less carbon atom. Specific aldehydes can thus be formed in bread crust if the necessary amino acids are present. The formation of aldehydes in bread crust is accompanied by a lowering of the amino acid content compared to that in the crumb. Johnson et al. (1966) have listed the aldehydes that can be formed from amino acids in bread crust as a result of the Strecker degradation. Grosch and Schieberle (1991) reported the aroma of wheat bread to include ethanol, 2- methylpropanal, 3-methylbutanal, 2,3-butanedione, and 3-methylbutanol. These compounds contribute significantly to bread aroma, whereas other compounds are of minor importance.

Meat

Meat is another food in which the flavor is developed by heating from precursors present

Aldehydes That Can Be Formed from Amino Acids in Bread Crust as a Result of the Strecker Degradation

Amino Acid	Aldehyde
Alanine	Acetaldehyde
Glycine	Formaldehyde
lsoleucine	2-Methylbutanal
Leucine	Isovaleraldehyde
Methionine	Methional
Phenylalanine	Phenylacetaldehyde
Threonine	2-Hydroxypropanal
Serine	Glyoxal

Source: From J.A. Johnson et al., Chemistry of Bread Flavor, in Flavor Chemistry, I. Hornstein, ed., 1966, American Chemical Society.

in the meat; this occurs in a Maillard-type browning reaction. The overall flavor impression is the result of the presence of a large number of nonvolatile compounds and the volatiles produced during heating. The contribution of nonvolatile compounds in meat flavor has been summarized by Solms (1971). Meat extracts contain a large number of amino acids, peptides, nucleotides, acids, and sugars. The presence of relatively large amounts of inosine-5'-monophosphate has been the reason for considering this compound as a basic flavor component. In combination with other compounds, this nucleotide would be responsible for the meaty taste. Living muscle contains adenosine-5'-triphosphate; this is converted after slaughter into adenosine-5'-monophosphate, which is deaminated to form inosine-5'-monophosphate (Jones 1969). The volatile compounds produced on heating can be accounted for by reactions involving amino acids and sugars present in meat extract. Lean beef, pork, and lamb are surprisingly similar in flavor; this reflects the similarity in composition of extracts in terms of amino acid and sugar components. The fats of these different species may account for some of the normal differences in flavor. In the volatile fractions of meat aroma, hydrogen sulfide and methyl mercaptan have been found; these may be important contributors to meat flavor. Other volatiles that have been isolated include a variety of carbonyls such as acetaldehyde, propionaldehyde, 2-methylpropanal, 3-methylbutanal, acetone, 2-butanone, rc-hexanal, and 3-methyl-2-butanone (Moody 1983).

Fish

Fish contains sugars and amino acids that may be involved in Maillard-type reactions during heat processing (canning). Proline is a prominent amino acid in fish and may contribute to sweetness. The sugars ribose, glucose, and glucose-6-phosphate are flavor contributors, as is 5'-inosinic acid, which contributes a meaty flavor note. Volatile sulfur compounds contribute to the flavor of fish; hydrogen sulfide, methylmercaptan, and dimethylsulfide may contribute to the aroma of fish. Tarr (1966) described an off-flavor problem in canned salmon that is related to dimethylsulfide. The salmon was found to feed on zooplankton containing large amounts of dimethyl-2-carboxyethyl sulfonium chloride. This compound became part of the liver and flesh of the salmon and in canning degraded to dimethylsulfide according to the following equation:

(CH3)2-SH-CH2-CH2-COOH ->

(CH3)2S + CH3-CH2-COOH

The flavor of cooked, fresh fish is caused by the presence of sugars, including glucose  and fructose, giving a sweet impression as well as a umami component arising from the synergism between inosine monophosphate and free amino acids. The fresh flavor of fish is rapidly lost by bacterial spoilage. In fresh fish, a small amount of free ammonia, which has a pH level of below 7, exists in protonated form. As spoilage increases, the pH rises and ammonia is released. The main source of ammonia is trimethylamine, produced as a degradation product of trimethylamineoxide. The taste-producing properties of hypoxanthine and histidine in fish have been described by Konosu (1979). 5'-inosinate accumulates in fish muscle as a postmortem degradation product of ATP. The inosinate slowly degrades into hypoxanthine, which has a strong bitter taste. Some kinds of fish, such as tuna and mackerel, contain very high levels of free histidine, which has been postulated to contribute to the flavor of these fish.

Milk

The flavor of normal fresh milk is probably produced by the cow's metabolism and is comprised of free fatty acids, carbonyl compounds, alkanols, and sulfur compounds. Free fatty acids may result from the action of milk lipase or bacterial lipase. Other decomposition products of lipids may be produced by the action of heat. In addition to lipids, proteins and lactose may be precursors of flavor compounds in milk (Badings 1991). Sulfur compounds that can be formed by heat from (3-lactoglobulin include dimethyl sulfide, hydrogen sulfide, dimethyl disulfide, and methanethiol. Some of these sulfur compounds are also produced from methionine when milk is exposed to light. Heterocyclic compounds are produced by nonenzymatic browning reactions. Bitter peptides can be formed by milk or bacterial proteinases. The basic taste of milk is very bland, slightly sweet, and salty. Processing conditions influence flavor profiles. The extent of heat treatment determines the type of flavor produced. Low heat treatment produces traces of hydrogen sulfide. Ultra-high temperature treatment results in a slight fruity, ketone-like flavor. Sterilization results in strong ketone-like and caramelization/sterilization flavors. Sterilization flavors of milk are caused by the presence of 2-alkanones and heterocyclic compounds resulting from the Maillard reaction. Because of the bland flavor of milk, it is relatively easy for off-flavors to take over.

Cheese

The flavor of cheese largely results from the fermentation process that is common to most varieties of cheese. The microorganisms used as cultures in the manufacture of cheese act on many of the milk components and produce a large variety of metabolites. Depending on the type of culture used and the duration of the ripening process, the cheese may vary in flavor from mild to extremely powerful. Casein, the main protein in cheese, is hydrolyzed in a pattern and at a rate that is characteristic for each type of cheese. Proteolytic enzymes produce a range of peptides of specific composition that are related to the specificity of the enzymes present. Under certain conditions bitter peptides may be formed, which produce an offflavor. Continued hydrolysis yields amino acids. The range of peptides and amino acids provides a "brothy" taste background to the aroma of cheese. Some of these compounds may function as flavor enhancers. Breakdown of the lipids is essential for the production of cheese aroma since cheese made from skim milk never develops the full aroma of normal cheese. The lipases elaborated by the culture organisms hydrolyze the triglycerides to form fatty acids and partial glycerides.

The particular flavor of some Italian cheeses can be enhanced by adding enzymes during the cheese-making process that cause preferential hydrolysis of short-chain fatty acids. Apparently, a variety of minor components are important in producing the characteristic flavor of cheese. Carbonyls, esters, and sulfur compounds are included in this group. The relative importance of many of these constituents is still uncertain. Sulfur compounds found in cheese include hydrogen sulfide, dimethylsulfide, methional, and methyl mercaptan. All of these compounds are derived from sulfur-containing amino acids. The flavor of blue cheese is mainly the result of the presence of a number of methyl ketones with odd carbon numbers ranging in chain length from 3 to 15 carbons (Day 1967). The most important of these are 2- heptanone and 2-nonanone. The methyl ketones are formed by p-oxidation of fatty acids by the spores of P. roqueforti.

Fruits

The flavor of many fruits appears to be a combination of a delicate balance of sweet and sour taste and the odor of a number of volatile compounds. The characteristic flavor of citrus products is largely due to essential oils contained in the peel. The essential oil of citrus fruits contains a group of terpenes and sesquiterpenes and a group of oxygenated compounds. Only the latter are important as contributors to the citrus flavor. The volatile oil of orange juice was found to be 91.6 mg per kg, of which 88.4 was hydrocarbons (Kefford 1959). The volatile water-soluble constituents of orange juice consist mainly of acetaldehyde, ethanol, methanol, and acetic acid. The hydrocarbons include mainly Dlimonene, p-myrcene, and a compound of composition C15H24. The esters include isovalerate, methyl alphaethyl-n-caproate, citronellyl acetate, and terpinyl acetate.

In the group of carbonyls, the following compounds were identified: w-hexanal, H-octanal, w-decanal, and citronella; and in the group of alcohols, linalool, a-terpineol, rc-hexane-1-ol, noctan- 1-ol, rc-decan-1-ol, and 3-hexen-l-ol were identified. The flavor deterioration of canned orange juice during storage results in stale off-flavors. This is due to reactions of the nonvolatile water-soluble constituents. As in the case of citrus fruits, no single compound is completely responsible for any single fruit aroma. However, some organoleptically important compounds characteristic for particular fruits have been found. These include amyl esters in banana aroma, citral in lemon, and lactones in peaches. The major flavor component of Bartlett pears was identified by Jennings and Sevenants (1964) as ethyl /ratt5--2-d,y-4-decadienoate.

Vegetables

Vegetables contain an extensive array of volatile flavor compounds, either in original form or produced by enzyme action from precursors. Maarse (1991) has reviewed these in detail. Onion and garlic have distinctive and pungent aromas that result mostly from the presence of sulfur-containing compounds. A large number of flavor compounds in vegetables are formed after cooking or frying. In raw onions, an important compound is thio-propanal s-oxide—the lachrymatory factor. The distinctive odor of freshly cut onions involves two main compounds, propyl methane-thiosulfonate and propyl propanethiosulfonate. Raw garlic contains virtually exclusively sulfur compounds: four thiols, three sulfides, seven disulfides, three trisulfides, and six dialkylthiosulfinates.

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Tea

The flavor of black tea is the result of a number of compounds formed during the processing of green tea leaves. The processing involves withering, fermentation, and firing. Bokuchava and Skobeleva (1969) indicate that the formation of the aroma occurs mainly during firing. Aromatic compounds isolated and identified from black tea include acrolein, n-butyric aldehyde, ethanol, nbutanol, isobutanol, hexanal, pentanal, 2- hexanol, 3-hexen-l-ol, benzaldehyde, linalool, terpeneol, methylsalicylate, benzyl alcohol, (3-phenylethanol, isobutyric aldehyde, geraniol, and acetophenone. The flavor substances of tea can be divided into the following four fractions: a carbonyl-free neutral fraction including a number of alcohols, a carbonyl fraction, a carboxylic acid fraction, and a phenolic fraction. A compilation (Maarse 1991) identifies a total of 467 flavor constituents in tea. The distinctive flavor of tea is due to its content of lactones, aldehydes, alcohols, acids, and pyridines.

Coffee

The flavor of coffee is developed during the roasting of the green coffee bean. Gasliquid chromatography can be used to demonstrate the development of volatile constituents in increasing amounts as intensity of roasting increases (Gianturco 1967). The total number of volatile compounds that have been isolated is in the hundreds, and many of these have been identified. To determine the flavor contribution of each of these is a Herculean task. Many compounds result from the pyrolytic decomposition of carbohydrates into units of 2, 3,4, or 5 carbons. Other compounds of carbohydrate origin are 16 furanic compounds, cyclic diketones, and maltol.

Roasting of the proteins of the coffee bean can yield low molecular weight products such as amino acids, ammonia, amines, hydrogen sulfide, methyl mercaptan, dimethylsulfide, and dimethyl disulfide. A series of furanic and pyrrolic compounds identified include the following: furan, furfural, acetylfuran, 5-methylfuran, 5-methylfurfural, 5-methyl-2-acetylfuran and pyrrole, 2-pyrrolaldehyde, 2-acetylpyrrole, Af-methylpyrrole, Af-methyl-2-pyrrolaldehyde, and Af-methyl-2-acetylpyrrole. Differences in the aroma of different coffees can be related to quantitative differences in some of the compounds isolated by gas chromatography, may be different. Pyrazines, furanes, pyrroles, and thiophen derivatives are particularly abundant in coffee aroma. Furfurylmethyl- sulfide and its homologs are important contributors to the aroma of coffee.

It is impossible to compare the aroma of different coffees on the basis of one or a few of the flavor constituents. Computer-generated histograms can be used for comparisons after selection of important regions of gasliquid chromatograms by using mathematical treatments. Biggers et al. (1969) differentiated the beverage quality of two varieties of coffee (arabica and robusta) on the basis of contributions of flavor compounds. Recent studies have identified 655 compounds in the flavor of coffee, the principal ones being furans, pyrazines, pyrroles, and ketones (Maarse 1991). The distinctiveness of coffee flavor is related to the fact that it contains a large percentage of thiophenes, furans, pyrroles, as well as oxazoles, thiazoles, and phenols.

Alcoholic Beverages

In distilled beverages, one of the major flavor compounds is acetaldehyde. Acetaldehyde represents about 90 percent of the total aldehydes present in beverages like whiskey, cognac, and rum. Together with other shortchain aliphatic aldehydes, it produces a pungent odor and sharp flavor, which is masked by other flavor components in cognac, fruit brandies, rum, and whiskey. In vodka the presence of acetaldehyde may result in an off-flavor. Propanol and 2-methylpropanol, as well as unsaturated aldehydes, are also present in distilled beverages. The aldehydes are very reactive and can form acetals by reacting with ethanol. This reaction results in a smoother flavor profile. Another important flavor compound in distilled beverages is the diketone, 2,3-butanedione (diacetyl), which is a product of fermentation. Depending on fermentation and distillation conditions, the level of diacetyl varies widely in different beverages.

Fusel alcohols, which are present in most distilled beverages, influence flavor. They are formed during fermentation from amino acids through decarboxylation and deamination, and include 1-propanol, 2-methylpropanol, 2-methylbutanol, 3-methylbutanol, and 2-phenylethanol.

Distilled beverages also contain fatty acids—from acetic acid (which is one of the major fatty acids) to long-chain unsaturated fatty acids.

Maturation in oak barrels has a major effect on flavor of distilled beverages. Maturing fresh distillates in oak barrels can transform a raw-tasting product into a mellow, well-rounded beverage. The reactions that take place during maturation involve reactions between components of the distillate and reactions between distillate components and compounds present in the oak wood. The alcoholic solution in the barrel extracts lignin from the oak to form an alcohol-soluble ethanol- lignin. Alcoholysis converts this to coniferic alcohol and then by oxidation to coniferaldehyde. Similarly, sinapic alcohol is converted to sinapaldehyde. These aldehydes then produce syringaldehyde and vanillin. The latter compound is important in the flavor of cognac and whiskey. A similar process occurs in the aging of wines in oak barrels to produce the distinctive smoothness of oakaged wines.

Spices and Herbs

Spices and herbs are natural vegetable products used for adding flavor and aroma to foods. They are usually highly flavored themselves and are used in small quantities. There is no clear distinction between spices and herbs, other than the general rule that spices are produced from tropical plants and herbs from plants grown in cooler climates. Spices and herbs provide aroma because of the presence of aromatic constituents; in addition, spices often provide pungency or hotness. The flavor and pungency of spices can be provided by the dried or ground products themselves, by their essential oils (produced by steam distillation), or by their oleoresins (produced by extraction with solvents). Essential oils contain only volatile compounds; oleoresins also include nonvolatile fats or oils.

Spices and herbs differ in the nature of their volatile constituents (Boelens 1991). Spices contain higher levels of phenylpropanoids such as eugenol, dillapiol, and cinnamaldehyde. Herbs have higher levels of para-menthanoids, such as menthol, carvone, thymol, carvacrol, and cuminaldehyde. Numerous volatile compounds have been identified in the essential oils of spices. Maarse (1991) has reported the number of hydrocarbons, alcohols, aldehydes, ketones, esters, phenols, acids, and others. Ginger contains about 2 percent of volatile oil, composed mostly of sesquiterpene hydrocarbons. Other constituents are oxygenated sesquiterpenes, monoterpene hydrocarbons and oxygenated monoterpenes. The pungent component of ginger is gingerol, which is a series of compounds consisting of zingerone-forming condensation products with saturated straight-chain aldehydes of chain lengths 6, 8, and 10. Fresh ginger has a lemony flavor resulting from the presence of citral and terpineol compounds. The lemony character may be lost because of flashing off during drying.

Pepper aroma and flavor are determined by the composition of the steam volatile oil (Purseglove et al. 1991). The steam volatiles consist of monoterpene hydrocarbons and smaller amounts of sesquiterpene hydrocarbons. The major pungent compound in pepper is piperine. Also contributing to pungency are five minor alkaloids. Nutmeg oil, which is obtained by steam distillation, contains the following major components: monoterpene hydrocarbons, oxygenated monoterpenes, and aromatic ethers. The monoterpene hydrocarbons contain alpha- and betapinene and sabinene. The aromatic ether fraction has as major constituent myristicin; this fraction is thought to

Number of Volatile Components in the Essential Oils of Some Spices

Spice	Number
Cinnamon	113
Cloves	95
Ginger	146
Nutmeg	80
Pepper	122
Vanilla	190

Source: Reprinted with permission from H. Maarse, Volatile Compounds in Foods and Beverages, p. 1991, by courtesy of Marcel Dekker, Inc.

forms used as a spice. The composition of the pungent Capsicum fruits varies widely and is influenced by the species, cultivars, growing conditions, stage of maturity at harvest, and postharvest processing. The bell peppers possess no pungency, and paprika is mainly used for its coloring power. The main pungent principle of hot chilies is capsaicin. In addition, Purseglove et al. (1991) have reported a number of analogs and homologs of capsaicin that contribute to the pungency of chilies.

Vanilla

Vanilla is obtained from dried and cured vanilla beans. These can be used directly, in the form of an alcoholic extract, or as oleoresin. The major flavor compound is vanillin, which is present in the beans at a level of 1.3 to 3.8 percent (Maarse 1991). The extracts contain resins that contribute to the taste and serve in the fixation of flavor. The precursor of vanillin is probably lignin, of which the cured beans contain from 2.1 to 3.9 percent. Numerous other compounds are present at very low concentrations. These include phydroxybenzaldehyde and /?-hydroxylbenzyl methyl ether. The composition of vanilla is influenced by the geographic origin of the beans.

Flavorants or flavorings

Flavorings are focused on altering the flavors of natural food product such as meats and vegetables, or creating flavor for food products that do not have the desired flavors such as candies and other snacks. Most types of flavorings are focused on scent and taste. Few commercial products exist to stimulate the trigeminal senses, since these are sharp, astringent, and typically unpleasant flavors.

There are three principal types of flavorings used in foods, under definitions agreed in the E.U. and Australia:

Type	Description
Natural flavoring substances	Flavoring substances obtained from plant or animal raw materials, by physical, microbiological or enzymatic processes. They can be either used in their natural state or processed for human consumption, but cannot contain any nature-identical or artificial flavoring substances.
Nature-identical flavoring substances	Flavoring substances that are obtained by synthesis or isolated through chemical processes, which are chemically and organoleptically identical to flavoring substances naturally present in products intended for human consumption. They cannot contain any artificial flavoring substances.
Artificial flavoring substances	Flavoring substances not identified in a natural product intended for human consumption, whether or not the product is processed. These are typically produced by fractional distillation and additional chemical manipulation of naturally sourced chemicals, crude oil or coal tar. Although they are chemically different, in sensory characteristics are the same as natural ones.

Regulations on Natural Flavoring

UK Food Law defines a natural flavor as: a flavouring substance (or flavouring substances) which is (or are) obtained, by physical, enzymatic or microbiological processes, from material of vegetable or animal origin which material is either raw or has been subjected to a process normally used in preparing food for human consumption and to no process other than one normally so used.

The U.S. Code of Federal Regulations describes a "natural flavorant" as: the essential oil, oleoresin, essence or extractive, protein hydrolysate, distillate, or any product of roasting, heating or enzymolysis, which contains the flavoring constituents derived from a spice, fruit or fruit juice, vegetable or vegetable juice, edible yeast, herb, bark, bud, root, leaf or any other edible portions of a plant, meat, seafood, poultry, eggs, dairy products, or fermentation products thereof, whose primary function in food is flavoring rather than nutritional.

The European Union's guidelines for natural flavorants are slightly different. Certain artificial flavorants are given an E number, which may be included on food labels.

Smell

Smell flavorants, or simply, flavorants, are engineered and composed in similar ways as with industrial fragrances and fine perfumes. To produce natural flavors, the flavorant must first be extracted from the source substance. The methods of extraction can involve solvent extraction, distillation, or using force to squeeze it out. The extracts are then usually further purified and subsequently added to food products to flavor them. To begin producing artificial flavors, flavor manufacturers must either find out the individual naturally occurring aroma compounds and mix them appropriately to produce a desired flavor or create a novel non-toxic artificial compound that gives a specific flavor.

Most artificial flavors are specific and often complex mixtures of singular naturally occurring flavor compounds combined together to either imitate or enhance a natural flavor. These mixtures are formulated by flavorists to give a food product a unique flavor and to maintain flavor consistency between different product batches or after recipe changes. The list of known flavoring agents includes thousands of molecular compounds, and the flavor chemist (flavorist) can often mix these together to produce many of the common flavors. Many flavorants consist of esters, which are often described as being "sweet" or "fruity".

Chemical	Odor
Diacetyl	Buttery
Isoamyl acetate	Banana
Benzaldehyde	Bitter almond
Cinnamic aldehyde	Cinnamon
Ethyl propionate	Fruity
Methyl anthranilate	Grape
Limonene	Orange
Ethyl decadienoate	Pear
Allyl hexanoate	Pineapple
Ethyl maltol	Sugar, Cotton candy
Ethylvanillin	Vanilla
Methyl salicylate	Wintergreen

The compounds used to produce artificial flavors are almost identical to those that occur naturally. It has been suggested that artificial flavors may be safer to consume than natural flavors due to the standards of purity and mixture consistency that are enforced either by the company or by law. Natural flavors in contrast may contain impurities from their sources while artificial flavors are typically more pure and are required to undergo more testing before being sold for consumption.

Flavors from food products are usually the result of a combination of natural flavors, which set up the basic smell profile of a food product while artificial flavors modify the smell to accent it.

Unlike smelling, which occurs upon inhalation, the sensing of flavors in the mouth occurs in the exhalation phase of breathing and is perceived differently by an individual. In other words, the smell of food is different depending on when you are smelling it in front of you or whether it has already entered your mouth.

Taste

While salt and sugar can technically be considered flavorants that enhance salty and sweet tastes, usually only compounds that enhance umami, as well as other secondary flavors are considered and referred to as taste flavorants. Artificial sweeteners are also technically flavorants.

Umami or "savory" flavorants, more commonly called taste or flavor enhancers are largely based on amino acids and nucleotides. These are typically used as sodium or calcium salts. Umami flavorants recognized and approved by the European Union include:

Acid	Description
Glutamic acid salts	This amino acid's sodium salt, monosodium glutamate (MSG), a notable example, is one of the most commonly used flavor enhancers in food processing. Mono and diglutamate salts are also commonly used.
Glycine salts	Simple amino acid salts typically combined with glutamic acid as flavor enhancers.
Guanylic acid salts	Nucleotide salts typically combined with glutamic acid as flavor enhancers.
Inosinic acid salts	Nucleotide salts created from the breakdown of AMP. Due to high costs of production, typically combined with glutamic acid as flavor enhancers.
5'-ribonucleotide salts	Nucleotide salts typically combined with other amino acids and nucleotide salts as flavor enhancers.

Certain organic and inorganic acids can be used to enhance sour tastes, but like salt and sugar these are usually not considered and regulated as flavorants under law. Each acid imparts a slightly different sour or tart taste that alters the flavor of a food.

Acid	Description
Acetic acid	Gives vinegar its sour taste and distinctive smell
Ascorbic acid	Found in oranges and green peppers and gives a crisp, slightly sour taste. Better known as vitamin C .
Citric acid	Found in citrus fruits and gives them their sour taste
Fumaric acid	Not found in fruits, used as a substitute for citric and tartaric acid
Lactic acid	Found in various milk or fermented products and give them a rich tartness
Malic acid	Found in apples and gives them their sour/tart taste
Phosphoric acid	Used in all Cola drinks to give an acid taste
Tartaric acid	Found in grapes and wines and gives them a tart taste

Color

The color of food can affect flavor. For example, adding more red color to a drink increases its sweetness with darker colored solutions being rated 2–10% higher than lighter ones even though it had 1% less sucrose concentration. The effect of color is believed to be due to cognitive expectations.

Dietary Restrictions

Food manufacturers are sometimes reluctant about informing consumers about the source from where the flavor is obtained and whether it has been produced with the incorporation of substances such as animal by-products glycerin (note that glycerin is also available from vegetable sources), gelatin, and the like, and the use of alcohol in the flavors. Many Jews, Jains, Hindus, and Muslims adhere to religious dietary laws, and vegans to personal convictions, which restrict the use of animal by-products and/or alcohol in foods unless subject to oversight and inspection by their respective religious authority or less-strict or circumstantial moral belief.

In many Western countries, some consumers rely on a Jewish Kosher Pareve certification mark to indicate that natural flavorings used in a food product are free of meat and dairy (although they can still contain fish). The Vegan Society's Sunflower symbol (which is currently used by over 260 companies worldwide) can also be used to see which products do not use any animal ingredients (including flavorings and colorings).

Similarly, persons with known sensitivities or allergies to food products are advised to avoid foods that contain generic "natural flavors" or to first determine the source of the flavoring before consuming the food. Such flavors may be derived from a variety of source products that are themselves common allergens, such as dairy, soy, sesame, eggs, and nuts.

Flavor Creation

Most food and beverage companies do not create their own flavors but instead employ the services of a flavor company. Food and beverage companies may require flavors for new products, product line extensions (e.g., low fat versions of existing products) or changes in formula or processing for existing products. In 2011, about U$S10.6 billion were generated with the sale of flavors; the majority of the flavors used is consumed in processed and packaged food.

The flavor creation is done by a specially trained scientist called a "flavorist". The flavorist's job combines extensive scientific knowledge of the chemical palette with artistic creativity to develop new and distinctive flavors. The flavor creation begins when the flavorist receives a brief from the client. In the brief the client will attempt to communicate exactly what type of flavor they seek, in what application it will be used, and any special requirements (e.g., must be all natural). The communication barrier can be quite difficult to overcome since most people aren't experienced at describing flavors. The flavorist will use his or her knowledge of the available chemical ingredients to create a formula and compound it on an electronic balance. The flavor will then be submitted to the client for testing. Several iterations, with feedback from the client, may be needed before the right flavor is found.

Additional work may also be done by the flavor company. For example, the flavor company may conduct sensory taste tests to test consumer acceptance of a flavor before it is sent to the client or to further investigate the "sensory space." The flavor company may also employ application specialists who work to ensure the flavor will work in the application for which it is intended. This may require special flavor delivery technologies that are used to protect the flavor during processing or cooking so that the flavor is only released when eaten by the end consumer.

Determination

Few standards are available or being prepared for sensory analysis of flavors. In chemical analysis of flavors, solid phase extraction (SPE), solid phase microextraction (SPME), and headspace gas chromatography are applied to extract and separate the flavor compounds in the sample. The determination is typically done by various mass spectrometric techniques.

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