Aroma Substances

Besides the medicinally used herbal mixtures, there arc also the so-called household teas which are preferred by people who are sensitive to coffee or who do not wish to drink a caffeine-containing beverage on a regular basis. Household teas are made up from drugs which, apart from small amounts of tannins, have only aroma substances and possibly also plant acids bramble leaves, raspberry leaves, hibiscus flowers, hips and haws, and apple skins arc frequent components of such teas [4]. 

Aroma compounds are often heat sensitive and their purification by membrane processes, which work at near ambient conditions, can be attractive. Alternatively, when pervaporation is used then temperatures can be kept low. A variety of aroma substances from aqueous solutions have been recovered. Baudot and Marin (1997) and Baudot et al. (1999) have made an extensive study of this subject. Hydrophobic low boilers to very hydrophobic high boilers have been studied. 

Nature-identical aroma substances are, with very few exceptions, the only synthetic compounds used in flavors besides natural products. The primary functions of the olfactory and taste receptors, as well as their evolutionary development, may explain why artificial flavor substances are far less important. The majority of compounds used in fragrances are those identified as components of natural products, e.g., constituents of essential oils or resins. The fragrance characteristics of artificial compounds nearly always mimic those of natural products. 

Aliphatic monoketones are of minor importance as fragrance and aroma substances. 2-Alkanones (C3-C15) have been found in the volatile fractions of many fruits and foodstuffs, but they do not contribute signiflcantly to their aroma. An exception are the odd-numbered methyl ketones Cy, C9, Cn which possess a characteristic nutty note they are used, e.g., in cheese flavor compositions. In... 

Chemical Properties. Hydrogenation of menthols yields / -menthane oxidation with chromic acid or catalytic dehydrogenation yields menthones. Dehydration under mild conditions yields 3-/ -menthene as the main product. Reaction with carboxylic acids or their derivatives yields menthyl esters, which are used mainly as aroma substances and in pharmaceutical preparations and formulations. The esterification of menthols with benzoic acid is used on an industrial scale in the resolution of racemic menthol. 

The next step of the biotechnical sequence, yeast fermentation, is of the utmost importance to the chemistry of winemaking as well as to the formation of flavor substances. We have investigated this previously using 14C-tagged compounds (16). Amino acids, for example, enter the yeast fermentation with a quasi biochemical valence with regard to the formation of metabolic side products like alcohols and esters. In that respect, the composition of the fermentation substrate, the grape must, is highly important to the formation of aroma substances by yeasts. 

The skins also contain tannins and aroma substances. These are soluble in the dilute alcohol of partially fermented wines. Certain tannin materials—those which give rise to harsh or hard tastes—tend to be... 

The separation of alcohol from different raw materials like cider [13], wine fermentation broth [14], alcohol-water mixtures [15-18] and wine [19-22] is an interesting alternative to distillation processes especially if heat sensitive substances are present. Separex company separated the aroma substances out of whisky and cognac, which gives a very interesting product for food industry. 

Other fruit components. Other fruit components that may be used in tile manufacture of non-carbonated beverages, particularly dilutables, include pectins and aroma substances obtained during the concentration of fruit juices. These components do not normally count towards the fruit content of products as they are usually classifted as types of permitted additives. 

Bruemmer, J. H. Aroma substances of citrus fruits and their biogenesis. In "Geruch-und Geschmackstoffe". F. Drawert, ed. Verlag Hans Carl, Nurnberg, Germany, 1975, p 167-176. 

TABLE 6.6 Volatile compounds associated with botrytized wines as characteristic aroma substances... 

Wine is one of the most complex and interesting matrices for a number of reasons. It is composed of volatile compounds, some of them responsible for the odor, and nonvolatile compounds which cause taste sensations, such as sweetness (sugars), sourness (organic acids), bitterness (polyphenols), and saltiness (mineral substances Rapp and Mandary, 1986). With a few exceptions, those compounds need to be present in levels of 1%, or even more, to influence taste. Generally, the volatile components can be perceived in much lower concentrations, since our organs are extremely sensitive to certain aroma substances (Rapp et ah, 1986). Carbohydrates (monosaccharides, disaccharides, and polysaccharides), peptides, proteins, vitamins, and mineral substances are among the other wine constituents. 

Among the fragrance and aroma substances a great variety of mono- and polyole-finic aliphatic alcohols, aldehydes, ketones, carboxylic acids, and their esters, as well as lactones are found 158). Of these aroma substances, (J5)-2-alkenals, ( )-2-alkenoic acids, ( )-2-alkenoic esters as well as (JS)-2-alken-l-ols are predestinated for the synthesis via the Wittig reaction because of the ( )-stereoselectivity of the olefination using resonance-stabilized ylides. 

This expression is a realistic approximation even though it is assumed here that no diffusion of the aroma substances into the atmosphere takes place. The relative solubility KP/Fof the aroma substance in the packaging material can play an important role in critical cases (high A/mF values) where the ratio mP/mF assumes a maximum... 

Fragrance creation is not necessarily confined to natural aroma substances and many rely heavily on artificial compounds. Therefore, classical perfumes categorized into fundamental types along with the representative natural products are covered here (Table 13). 

Rapp, A., Marais, J. (1993). The shelf life of wine Changes in aroma substances during storage and ageing of white wines. In Shelf Life Studies of Foods and Beverages. Chemical, Biological, Physical and Nutritional Aspects. Ed. (pp. 891-923). Charalambous, Elsevier, Amsterdam,. 

Dufour, C., Bayonove, C.L. (1999a). Influence of wine structurally different polysaccharides on the volatility of aroma substances in a model system. J. Agric. Food Chem., 47, 671-677. 

VoUley, A., Beghin, V, Charpentier, V, Charpentier, C., Peyrond, D. (1991). Interactions between aroma substances and macromolecules in a model in a model wine. Food Sci. Technol-Leh, 24, 469 72... 

This study demonstrated the influence of natural colloids from wine (mannoproteins released from yeast) on the volatility of aroma compounds and therefore the possible role of these minor components of a wine matrix on sensory properties of wine. The physico-chemical interactions between aroma substances and exocellular yeast material depend on the nature of volatile compounds and of the macromolecules. 

Yeast Cell Walls. Interactions between aroma substances and yeast walls induce to a modification of the volatility of some aroma compounds in the model wine (76/Yeast walls do not bind a specific chemical class of volatile compounds (Table II). The volatility of octanal, an aldehyde and of ethyl hexanoate, an ester, decreases by 14% with yeast walls at 1 g/L. The effect of walls is greater on the volatility of ethyl octanoate than that of the other aroma compounds the partition coefficient decreases by 45% for ethyl octanoate in the presence of 1 g/L yeast cell walls. 

Several lactic acid derivatives were used by Gessner et al. for the determination of the enantiomeric purity of flavor substances such as chiral alcohols from natural sources. Diastereomeric 0-acetyl-, propionyl-, and hexanoyllactic acid esters of the chiral alcohols were separated by GLC (155). A report from the same laboratories described characterization of several chiral aroma substances that are S-lactones. The lactones were hydrolyzed to the corresponding hydroxy acids, and the acid moiety was esterified to the isopropyl ester. The remaining hydroxyl group was esterified with (R)-2-phenylpropionic add chloride or [30], and the diastereomeric derivatives were separated using preparative silica gel LC. The derivatives were also separated on an analytical scale by GLC (156). 

Rapp, A. (1988) Wine aroma substances from gas chromatographic analysis. In Modern methods of plant analysis, H.F. Linskens and J.F. Jackson (Eds), Springer Verlag, Berlin. 

Rothe, M., Thomas, B. (1963) Aroma substances of bread (in German). Z. Lebensm. Unters. Forsch. 119, 302-310... 

Low alcohol or alcohol-free beers of 0.5-1.3% alcohol may be produced by interruption of the fermentation, by boiling of the beer to distill part of the alcohol, by vacuum distillation, or by alcohol removal by reverse osmosis. The first two methods are the most common [16]. However, these methods result in the loss of desirable aroma substances along with the alcohol. This is remedied with used yeast, which is a reservoir of aroma substances. This is added at 2-10 mg/L to the dealcoholized beer just before filtration to restore the beer aroma. 

The chemical composition of honey (Table 2.3) is dominated by glucose and fructose. Honey also contains many other valuable components, like enzymes, organic acids, mineral elements, nonprotein nitrogenous compounds, vitamins, aroma substances, and pigments. 

Many microbial metabolites are volatile compounds and in terms of their sensory properties can be broken into two broad categories odorants and tastants (Table 1). Tastants include salty, sour, sweet, and bitter compounds such as amino acids, peptides, and sugars. Primary odorants typically are quite volatile and include carbonyl compounds, esters, and terpenes. There is considerable overlap between the two categories lactones, for example, have both taste and odor properties. In keeping with the theme of this symposium, volatile aroma substances will be the primary focus. 

Monoterpenes, Ci3-norisoprenoids, and some benzenoid compounds are the most important grape aroma substances present in the pulp and skin of berries in both free and glycoside forms. Profiles of these compounds in the grape are mainly dependent on the variety, even if environmental variables and agricultural practices influence their contents (Marais et al., 1992). These compounds are transferred to the wine in winemaking and depend on the process used. 

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