Phenols aroma compounds

Phenolic aroma compounds can be generated by the thermal radical degradation of phenolic acids such as ferulic acid (52), which is a constituent of many vegetable raw materials [76]. Fig. 3.32 shows the formation scheme for vinylguaiacol (53), vanilline (54) and guaiacol (55) from 52. 

Turmeric contains two main classes of compounds the curcuminoids responsible for the yellow color and the aroma compounds. The coloring principle of turmeric consists of three major phenolic derivatives curcumin, demethoxycurcumin, and bisdemethoxycurcumin. Commercially available products called curcumins contain curcumin (l,7-bis(4-hydroxy-methoxyphenyl)-l,6-heptadiene-3,5-dione) as the major component (about 77% of total curcuminoids). Some other minor phenohc compounds such as cyclocurcumin and calebin were also isolated from turmeric. See Figure 5.2.1. 

Phenols. See also Phenol Phenolic entries achiral derivatizing agents, 6 96t alkylation, 2 196-197, 212-214 aroma chemicals, 3 243-246 aroma compounds in roasted coffee, 7 256ts... 

Pectinases and (3-glucanases are the only enzymes allowed in wine-making by European legislation. They are used as clarification and filtration agents and also to release aroma compounds that are mostly present in grape as nonvolatile glycosidic precursors. Pectolytic enzymes are also reported to increase extraction of phenolic compounds and wine color... 

A large number of volatile phenols and related compounds occur in vegetables and fruits, and some of them are potent aroma compounds. The majority of volatile phenols and related compounds in plants are formed mainly through the shikimic acid pathway, and are present in intact plant tissue either as free... 

The main aroma compound in vanilla is vanillin. Several other volatile constituents are responsible for its characteristic aroma with sweet, balsamic, creamy, woody, spicy, fruity, herbaceous, phenolic and cinnamonlike notes. A compilation of volatile substances identified has been reported by Maarse et al. (1994) and Ranadive (1994). 

Aroma compounds in cured vanilla beans from different countries, e.g. Madagascar, Tonga, Costa Rica, Java, Indonesia and Mexico, have been documented. Over 100 volatile compounds have been detected, including aromatic carbonyls, aromatic alcohols, aromatic acids, aromatic esters, phenols and phenol ethers, aliphatic alcohols, carbonyls, acids, esters and lactones, of which the aldehyde vanillin is the most abundant. The level of the aldehydes, e.g. vanillin and p-hydroxy-benzaldehyde and their respective acids (vanillic acid and p-hydroxybenzoic acid), in cured vanilla beans is used as an indicator of cured vanilla bean quality for commercial purposes (Klimes and Lamparsky, 1976 Adedeji et al., 1993 Ranadive, 1994). 

It is well known that the secondary metabolites of grapes provide the basis of varietal character in wine. The important secondary metabolites are represented by several groups of compounds that contribute to the distinctive aroma profile of wines made from particular varieties of Vitis vinifera. They include terpenes, Ci3-norisoprenoids, aliphatics, benzene-derivatives, volatile phenols and long-chain polyfuntional thiols. While constituent aroma compounds within these groups occur in most grape varieties, it is only when one or more of these compounds occur at concentrations well above their odour threshold that a distinctive varietal aroma emerges. 

Early studies carried out by King and Solms (1982) documented interactions between phenolic compounds and aroma compounds in water systems. They suggested that hydrophobic interactions between aroma compounds and phenolic compounds increased solubility of aroma compounds thereby decreasing the activity coefficient of the aroma compounds. 

Since yeast lees may adsorb some aroma compounds responsible of off-flavours in wines (volatile phenols), these components have been also proposed such as a cost-effective and efficient approach to remove or to decrease organoleptic defects in wine (Chassagne et al. 2005). 

The smell and taste of plants rely on aroma and fragrance compounds, many of which (besides fhe terpenoids) are derived from phenylpropanoid metabolism. In food and cosmetic industry, such fragrance and aroma compounds play an important economical role. Simple phenolic fragrance compounds are, e.g., eugenol, isoeugenol or (methyl)chavicol (Fig. 4.2), the biosynthesis of which has been clarified recently more complex compounds are phenolic esters. Evolutionary aspects of the bios)mthesis of flavours and scents have been reviewed by Gang (2005). 

Besides the Maillard reaction, fat oxidation and thiamine degradation, more aroma compounds in process flavours are formed by the interaction of these different reactions, as well as from other precursors (e.g. phenol compounds, terpenes) present in the raw materials used. Three examples are given below but are far from being exhaustive. 

The report of the possible presence of phenol-like compounds in Oriental tobacco by Jones and Latimer (1980) at RJRT R D eventually prompted a research project to synthesize a series of phenols in an attempt to find one or more that would impart a pleasant leather-like aroma to cigarette smoke (3235a, 3240a). Some twenty phenols were synthesized. However, none was ever used commercially as a tobacco flavorant or in any extensive in-house panel tests, for the following reasons. 

Hu, W. Studies on pyrolysis of some phenols used as precursor-aroma compounds in the cigarette industry 50th Tobacco Chemists Research Conference, Program Booklet and Abstracts, Vol. 50, Paper No. 56, 1996, p. 53. 

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