Aldehyde flavor

The overwhelming consideration in regard to lipid deterioration is the resulting off-flavors. Aldehydes, both saturated and unsaturated, impart characteristic off-flavors in minute concentrations. Terms such as painty, nutty, melon-like, grassy, tallowy, oily, cardboard, fishy, cucumber, and others have been used to characterize the flavors imparted by individual saturated and unsaturated aldehydes, as well as by mixtures of these compounds. Moreover, the concentration necessary to impart off-flavors is so low that oxidative deterioration need not progress substantially before the off-flavors are detectable. For example, Patton et al (1959) reported that 2,4-decadienal, which imparts a deep-fried fat or oily flavor, is detectable in aqueous solution at levels approaching 0.5 ppb. 

Murray, W.D. Duff, S.J.B. Lanthler, P.H. Production of natural flavor aldehydes from natural source primary alcohols C2-C7, USP, 4871669,1989. 

Guzman-Chozas, M., Vicario, I.M., andGuiUen-Sans, R. Spectrometric profiles of off-flavor aldehydes by using their reactions with 2-thiobarbituiic acid. J. Agr. Food Chem. 45, 2452-2457 (1997)... 

Speirs, J., et ah (1998) Genetic manipulation of alcohol dehydrogenase levels in ripening tomato fruit affects the balance of some flavor aldehydes and alcohols. Plant Physiol. 117, 1047-1058... 

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). 

Other botanical varieties are caUed cassia, but the leaves of these varieties differ in flavor components from those of the bark. Saigon cinnamon, C. loureirii Nees, from Viet Nam, closely resembles Chinese cassia in appearance but is grown on the other side of the mountains and has an entirely different flavor character, containing no orthomethoxy cinnamic aldehyde. C. burmani B/ume, ie, Korintje or Kerintje cinnamon and Padang or Batavia cinnamon, is from Sumatra and Indonesia. C. sintok B/ume is native to Malaysia and of minor commercial importance. 

Zeylanicum. The second type of cinnamon is the dried inner bark of the shoots of the tree Cinnamonium lanicum Nees, a moderately sized coppiced evergreen bush of the laurel family cultivated in Sri Lanka. The bark is stripped, roUed into quills, dried, and then shipped in large bundles. The aroma and flavor of the lanicum type, which contains eugenol as well as cinnamic aldehyde, is much milder than the cassia type. 

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). 

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. 

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. 

There are at least two routes currently being used to produce natural benzaldehyde. Principal flavor houses are reported to market a product which is derived from cassia oil. The chief constituent of cassia oil is cinnamic aldehyde which is hydrolyzed into its benzaldehyde and acetaldehyde constituents. This is a fermentative retroaldol reaction. Whether this hydrolysis allows the final benzaldehyde product to be considered natural is of great concern. The FDA has reportedly issued an opinion letter that benzaldehyde produced from cassia oil is not natural (15). 

Yeast (qv) metabolize maltose and glucose sugars via the Embden-Meyerhof pathway to pymvate, and via acetaldehyde to ethanol. AH distiUers yeast strains can be expected to produce 6% (v/v) ethanol from a mash containing 11% (w/v) starch. Ethanol concentration up to 18% can be tolerated by some yeasts. Secondary products (congeners) arise during fermentation and are retained in the distiUation of whiskey. These include aldehydes, esters, and higher alcohols (fusel oHs). NaturaHy occurring lactic acid bacteria may simultaneously ferment within the mash and contribute to the whiskey flavor profile. 

Much work has been reported and summarized ia the Hterature on the matufing of various whiskeys ia charred or uncharred white-oak barrels (4—7). The early Hterature iadicates that total acids, aldehydes, esters, soHds, and color iacreased with aging time and that their concentrations were iaversely proportional to proof. Thus aging at higher proofs (over 127°) yields less color and flavor. The maximum allowable entry proof for straight whiskeys was iacreased from 110° to 125° by the U.S. Treasury Department ia 1962. 

Since the acetal exists in equiUbtium with the aldehyde, it is possible for the aldehyde to be released when water is added in a mixed drink, changing the balance and giving a burst of freshness to a mixed drink. Ethyl esters of terpene alcohols in citms oils and other botanicals, plus the ethyl esters of fatty and volatile acids, are formed during prolonged exposure to ethyl alcohol. Certain beverage alcohol products that need to contain milk, eggs, or other protein containing materials must be developed carefully and the added flavors must be considered to prevent the precipitation of the protein and separation of the product. 

Pyrolytic Decomposition. The pyrolytic decomposition at 350—460°C of castor oil or the methyl ester of ricinoleic acid spHts the ricinoleate molecule at the hydroxyl group forming heptaldehyde and undecylenic acids. Heptaldehyde, used in the manufacture of synthetic flavors and fragrances (see Elavors and spices Perfumes) may also be converted to heptanoic acid by various oxidation techniques and to heptyl alcohol by catalytic hydrogenation. When heptaldehyde reacts with benzaldehyde, amyl cinnamic aldehyde is produced (see Cinnamic acid, cinnamaldehyde, and cinnamyl... 

Formaldehyde, as a gas or in water solution, has a distinctly unpleasant odor. Higher aromatic aldehydes such as those shown in Figure 22.10 (p. 594) are a lot more pleasant to deal with they are used in flavorings and even perfumes. 

There are also methods based on the detection of aldehydic substances, for the typical odor and flavor of rancidity seem to be associated with the liberation of aldehydic materials during the oxidative deterioration. The Kreis test (18), perhaps the best known of these methods, consists of treating the fat with concentrated hydrochloric acid and a solution of phloroglucinol. The red color formed is attributed to a condensation product of epihydrin aldehyde with phloroglucinol. Historically, the chief difficulty with this method has been that fats which are not rancid will often give a positive Kreis test. It has been shown that if this test is quantitatively correlated with the induction period... 

Aldehydes occur naturally in essential oils and contribute to the flavors of fruits and the odors of plants. Benzaldehyde, C6H5CHO (8), contributes to the characteristic aroma of cherries and almonds. Cinnamaldehvde (9) is found in cinnamon, and vanilla extract contains vanillin (10), which is present in oil of vanilla. Ketones can also be fragrant. For example, carvone (Section 18.1) is the essential oil of spearmint. 

In plant tissues, various enzymes convert the hydroperoxides produced by LOX to other products, some of which are important as flavor compounds. These enzymes include hydroperoxide lyase, which catalyzes the formation of aldehydes and oxo acids hydroperoxide-dependent peroxygenase and epoxygenase, which catalyze the formation of epoxy and hydroxy fatty acids, and hydroperoxide isomerase, which catalyzes the formation of epoxyhydroxy fatty acids and trihydroxy fatty acids. LOX produces flavor volatiles similar to those produced during autoxidation, although the relative proportions of the products may vary widely, depending on the specificity of the enzyme and the reaction conditions. 

---