Flavoring agents, Chemistry tutorial

Introduction:

Flavor signifies to a mixed sensation of touch, taste, smell, sight and sound. By the expansion of technology in the flavor industry, most of the artificial or imitation flavors have been made. Cough syrups, sedatives, laxatives, antihistamines, antibiotics, vitamins and pediatric formulations are now available in a range of flavors that successfully mask unpleasant tastes without influencing chemical and physical stability.

Flavoring Agents:

Flavor is the complex effect of taste, odor and feeling factor that is, touch, sight and sound, to produce physicochemical and psychological actions which affect the perception of a substance. There are four fundamental flavors which the nerve endings in the taste buds on the tongue can detect: sour, sweet, salty and bitter. 

1) Taste:

There is a close co-relationship between the chemical structure and taste. Sour taste is because of acidic nature and lipid solubility of substance. Illustrations are vinegar, lemon, citric acid, malic acid and apple. Salty taste is because of cationic species, halide salts. Illustrations are sodium chloride, sodium bromide and sodium iodide. The increase in molecular weight of halide yields in increase in bitter taste. Illustrations are ammonium salts and potassium bromide. Sweet taste is because of polyhydroxy compounds and aqueous solubility. Illustrations are glycerin, sugar and alpha amino acids.

2) Odor:

Odor is stated as 'Taste from a distance'. This is very closely related to taste. Odorous volatile substances produce vapors that interact with olfactory cells and elicit receptors. The brain obtains impulses from a group of microscopic olfactory receptors in the nose which it co-ordinates by the gustatory stimuli to generate the mingled sensation which is recognized as the flavor of the substance. 

3) Feeling factor

Feeling factor is the combination of sight, sound and touch that is, texture (soft/hard), cooling/ warmth, irritation sensation, viscosity and so on. For illustration, flavored viscous multi-vitamin liquid provides mouth feel effect, menthol in mouthwash provides cooling effect. 

Types of Flavoring agents:

Flavors are joined by the sweetening agents such as sucrose, sorbitol, invert syrup, saccharine and so on to improve the flavoring effect. There are two main kinds:

  • Natural flavoring agents
  • Artificial flavoring agents

1) Natural Flavoring agents:

Volatile oils like anise, caraway, dill, ginger, cinnamon, clove, lemon, orange and peppermint are employed as flavoring agents in the diversity of forms. The vehicles of mixtures are often aromatic waters whereas alcoholic or hydro alcoholic solutions of oils (that is, tinctures or spirits) give convenient concentrated preparations for flavoring purposes (that is, lemon, peppermint and compound orange spirits and strong ginger tincture are illustrations). Flavors having aromatic oils (apart from lemon and orange) are more appropriate than fruit syrups for neutral preparations. Fruit flavors are made from fruit juices peel of citrus fruits.

Lemon and orange oils keep badly and build up an unpleasant turpentine-like taste. By eliminating most of the Terpenes, terpeneless oils are generated which, compared by the natural oils are around 20 times stronger in flavor and odor, are more readily soluble and have better stability. 

For solid dosage form, vanillin crystals and dried lemon extract are employed. For liquid dosage form, alcoholic, aqueous and hydro alcoholics (that is, tinctures or spirits) are employed.

2) Synthetic Flavoring agents:

These are made via chemical reactions. Moreover to synthetic sweeteners, other synthetic chemicals are employed in flavoring. These are often favored to natural materials due to their more constant composition, more ready availability, lower cost, greater stability and more predictable incompabilities. For illustration, esters (that is, methylsalicylate), aldehydes (synthetic vanillin, benzaldehyde and cinnamaldehyde), fatty alcohols, ketones, lactones and alcohols are employed. Chloroform consists of an agreeable, warm, sweet taste and is employed as a vehicle Chloroform water BP. For emulsified products, soft flavors such as benzaldehyde and vanillin are most appropriate. Benzaldehyde consists of the odor of bitter almonds and is a substitute for wild cherry syrup and volatile bitter almond oil. Benzaldehyde gives the odor and flavor of fresh almonds.

Cinnamaldehyde is the oil of cinnamon and vanillin and is the key flavoring agent of vanilla beans. Vanillin is helpful when, as with liquid paraffin emulsions, the medicament has bland taste. Fractionated coconut oil, a non-aqueous vehicle for the oral preparations, is difficult to flavor due to its oily nature; imitation ground almond oil and olive oil are appropriate flavors. 

The esters of ethyl, methyl, amyl, propyl and benzyl alcohols by acetic, propionic, butyric, salicylic, formic, caproic, valeric and anthranilic acids are broadly employed to characterize fruit flavors. Anethole consists of the taste of anise and licorice, benzyl acetate tastes similar to raspberry or cherry, and allylcaproate is utilized for pineapple flavors. The other common compounds employed for flavorings are diacetyl (that is, butter), menthol (that is, mint) and isoamyl acetate (that is, banana).

Production of Flavoring agents:

1) Benzaldehyde:

Commercially, benzaldehyde is prepared by several techniques and in two grades, technical and refined. The refined chlorine-free grade is needed for flavoring use and it is economically manufactured by the direct vapor-phase oxidation of toluene. Though, this oxidation is at times taken out in the liquid state.

2000_Benzaldehyde-Production of Flavoring agents.jpg

Fig: Benzaldehyde-Production of Flavoring agents

Commercially, the oxidation of toluene is completed with air and diluted with nitrogen (to prevent the complete oxidation) at 500oC in the presence of oxides of Mn, Mo or Zr as catalyst. Benzaldehyde can as well be prepared commercially via oxidation of benzyl alcohol. This comprises the treatment of benzyl alcohol by dil. HNO3 or acidic potassium dichromate or chromic anhydride in acetic anhydride or with copper catalyst at around 350o C.

1395_Benzyl alcohol to Benzaldehyde.jpg

Fig: Benzyl alcohol to Benzaldehyde

2) Vanillin:

Vanillin is the key flavoring agent of vanilla bean that is the immature fruit of the orchid Vanilla planifolia. The pods are picked whenever they are just beginning to turn from a uniform green to yellow at the tip and encompass a rather disagreeable odor. The green pods undergo a curing treatment of from 3 to 5 months duration. The cured bean is shaky, pliant and dark-colored. The odor has become full and rich and the treatment might have left white aromatic crystals on the outside of the bean. This is due to the reason that, the glucoside glucovanillin present in the bean has been acted on via ferment and split to glucose, vanillin and other aromatics. Substances recognized in the vanilla bean are anisic acid, alcohol and aldehyde; vanillic acid and alcohol; cinnamic acid and its esters; vanillin, ethyl vanillin and possibly other homolog of vanillin.

As of 2001, the yearly demand for vanillin was around 12,000 tons, however only 1,800 tons of natural vanillin was produced. The remainder was produced via chemical synthesis. As of today, most vanillin is prepared from the petrochemical raw material guaiacol. Some routes exist for synthesizing vanillin from guaiacol. At present, the most important of these is the two-step method practiced by Rhodia since 1970s, in which guaiacol (i) reacts by glyoxylic acid through electrophilic aromatic substitution. The resultant vanillylmandelic acid (ii) is then transformed through 4-Hydroxy-3-methoxyphenylglyoxylic acid (iii) to vanillin (iv) via oxidative decarboxylation. 

1271_Vanillin.jpg

Fig: Vanillin

3) Natural Fruit Concentrates:

Due to the large percentage of water in most common fruits and the presence of considerable amounts of sugar and other simply fermented materials, special methods are used in handling fruit flavors.

Such processes comprise:

a) Distillation and Extraction of the fruit:

The ripe fruit is stoned and comminuted. This is then subjected to steam distillation and rectification till the whole aroma is concentrated in a small part of the aqueous distillate. This part is then extracted by low-boiling petroleum ether, and the ether eliminated under vacuum to leave an essence, or quintessence, of the fruit utilized. Cherry, strawberry, apple and raspberry are treated by this process.

b) Extraction of the juice:

The expressed and filtered juice is extracted directly with no previous distillation. Occasionally, the juice is allowed to ferment slightly prior to extraction. This is assumed to yield in a fuller flavor.

c) Concentration of the juice:

The expressed and filtered juice is concentrated in the vacuum evaporators having a low degree of heat till the water is largely driven off and the sugar concentration is high adequate to slow down bacterial growth. This kind of concentrate often consists of a 'jam' or cooked flavor, particularly in the case of the strawberries. The alternative process of concentration is freezing. After reducing the temperature adequately, the mush of practically pure water ice is filtered off, and the partially concentrated juice is refrozen and re-filtered till the obligatory strength is obtained. This is the optimum process of producing concentrates, as there is little injury from heat and the slight off-flavors from oxidation can be avoided via running the procedure in an atmosphere of carbon-dioxide. 

4) Monosodium Glutamate (MSG):

This compound is a significant flavoring agent, yet consists of no flavor of its own. It accentuates the hidden flavors of food in which it is utilized. Glutamic acid exists in three forms, however just the monosodium salt of L-glutamic acid consists of a flavor-accentuating capacity. Formerly, it was made through hydrolysis of wheat gluten, which consists of around 25% glutamic acid, however presently; it is mostly prepared by submerged bacterial fermentation of the carbohydrates. More and more significant constituents of flavors are being made via the usual chemical synthetic methods. Some of the constituents are chemically synthesized from an isolate or other natural starting material and are categorized as semi synthetics. 

5) Benzyl benzoate:

Benzyl benzoate consists of a faint aromatic odor, boils at 323 to 324°C and is a flavoring material. It takes place naturally in balsams however is made commercially by the esterification of benzoic acid by benzyl alcohol or via the Cannizzaro reaction with benzaldehyde. 

6) Methyl salicylate:

Methyl salicylate (that is, an ester of salicylic acid) is a very significant ingredient in the flavoring industries. It is manufactured as follows: Carbon-dioxide and sodium phenate are reacted under pressure to get the salt of phenyl carbonic acid. This salt is isomerized to sodium salicylate via heating to 120 to 140°C. The ester is prepared from the acid and alcohol.

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