Thermally derived aromas

Isolation, concentration, separation, and Identification of thermally-derived aromas 1s an Important area. These aromas are frequently associated with other non-volatile products Including pigments, fats, carbohydrates, and proteins. Techniques are required to separate the volatiles from the non-volatiles without causing chemical deterioration. 

Volatiles in thermally-derived aromas are frequently present at levels of parts per million. It is generally necessary to concentrate the aroma by many orders of magnitude prior to Identification. 

Results of this study indicated that eugenol, 1,8-cineol, linalool, and 2-isopropyl-3-methoxypyrazine are characteristic aroma compounds of the essential oil and fresh leaves of O. sanctum. Meanwhile, heating or cooking of fresh herb caused formation of additional thermally derived aroma compounds, such as )S-damascenone and other thermally derived com-... 

Thermally Generated Aroma from D-Fructosamine Derivatives or the Respective Model Systems ... 

Sugar degradation products were determined as benzimidazole derivatives after reaction with o-phenylenediamine. More than 120 amino-acid specific Maillard products have been isolated and identified from the reaction of L-proline, hydixn roline, < teine and methionine with monosaccharides at 150° for 1-1.5 h, in connection with studies of thermally generated aromas. Proline derived components were important constituents of bread, malt and beer, and cysteine and methionine derived components were predominant in roasted coffee and meat flavours. The effects of temperature, pH, and the relative concentration of rhamnose and proline on the quantity of specific volatiles produced in the Maillard reaction of these substrates have been studied, and the data have been analysed 1 computer methodology. The glucosylated cyclopentenone (44) was one of the products of decomposition of the Amadori product 1-deoxy-l-piperidino-maltulose in warm water. ... 

For AEDA, the essential oil sample mentioned previously was first diluted in dichloromethane (l 50w/v), and then serial dilutions (l 3v/v) were prepared in dichloromethane. Likewise, the aroma extract of the fresh herb underwent ternary (1 3 v/v) dilutions in dichloromethane. Aroma extract dilution analysis (AEDA) was conducted by two experienced panelists using a published procedure [11]. On-column injection was used during AEDA to minimize possible generation of thermally derived artifacts. 

The aroma and red color of the spice saffron are partly due to the style-specific accumulation of carotenoid cleavage products produced by both enzymatic and thermal degradation. M. Giaccio reviewed the renewed interest in saffron as a colorant, spice, and nutraceutical. " Crocetin is a C20 apocarotenoid derived from zeaxanthin (Figure 5.3.4B). ... 

The aroma of DMHF is pineapple-like, and is not considered too detrimental. However, it can mask the fresh orange-like aroma at levels above 0.05 ppm. Shu et al. (41) noted that DMHF is a precursor of various flavor materials when reacted with amino acids at high temperatures. Many acyclic carbonyl and 3(2H)-furanone derivatives can be formed as primary and secondary degradation products during thermal degradation of DMHF (42). 

Other investigators (7-9) have identified a large number of carbonyls from heated fat. The remaining meat aroma components derived by heating lipids are esters, lactones, alkan-2-ones (methyl ketones), benzenoids and other alkylfurans. Several investigators have analyzed volatile compounds formed during thermal degradation of fatty acids (10-12). 

Heterocyclic aroma compounds found in meat primarily arise from interactions between mono- and dicarbonyl compounds, H2S and ammonia. The carbonyl compounds are derived from the Maillard reaction, including Strecker degradation of amino acids, oxidation of lipids and aldolization reactions. H2S is produced by thermal degradation of sulfur amino acids and ammonia by amino acid pyrolysis. 

In heated foods the main reactions by which flavors are formed are the Maillard reaction and the thermal degradation of lipids. These reactions follow complex pathways and produce reactive intermediates, both volatile and non-volatile. It has been demonstrated that lipids, in particular structural phospholipids, are essential for the characteristic flavor development in cooked meat and that the interaction of lipids with products of the Maillard reaction is an important route to flavor. When model systems containing amino acids and ribose were heated in aqueous buffer, the addition of phospholipids had a significant effect on the aroma and on the volatile products. In addition a number of heterocyclic compounds derived from lipid - Maillard interactions were found. The extent of the interaction depends on the lipid structure, with phospholipids reacting much more readily than triglycerides. 

The first two sections of this book provide the reader with a background on the thermal generation of aromas. Included in these sections are perspectives on the regulatory aspects and the analytical methodologies at the forefront of aroma research. Subsequent sections present original research on aromas derived from various food sources. In addition, we have included a section on mechanistic studies to provide insights into aroma formation through thermal decomposition of lipid, carbohydrate, and amino acid precursors. The final section is entirely... 

Although most of the alkylpyrazines are formed through thermal Interactions of components in food, methoxy-substltuted pyrazlnes are mainly derived from biosynthetic pathways. 2-Isobutyl-3-methoxy-pyrazine Isolated from bell pepper by Buttery at al. (14) is one of the most significant flavor compounds discovered. This characteristic bell pepper aroma compound has an extremely low odor threshold of 0.002 ppb in water (15). 

Aldoses undergo the Amadori rearrangement and subsequently turn into caramels, the natural brown food colorants, and/or heteroaromatic compounds — derivatives of pyrrole, imidazole, and pyrazine. Ketoses react similarly into ketosylamino acids or ketosylamines, which, in the first step, undergo the Heyns rearrangement (5.17-5.23). These rearrangements are the first steps of either thermal or enzymatic (the Maillard reaction) reactions resulting in the browning of food and the aroma of roasted, baked, or fried foodstuffs. 

In strongly acidic media, saccharides produce furan derivatives in a sequence of reactions that are rearrangements and dehydrations followed by cyclization. Similar products are available thermally. Pentoses and hexoses give furan-2-aldehyde and 5-hydroxymethylfuran-2-aldehyde, respectively. Both of these products are responsible for the specific aroma of caramel and burnt sugar. 

The overall aroma produeed fi om thermally degraded D-fructosamine derivatives depends mostly on the nature of the aglycon rather than on the earbohydrate, as exemplified in Table VI. 

Some of the compounds identified in YEs which are formed either by the thermal degradation of thiamine or on the interaction of thiamine degradation products with other components are shown in Fig. 2. They include aliphatic sulfur compounds, furans, thiophenes and thiazoles. 2-Methyl-3-furanthiol and 2-methyl-3-thiophenethiol have been identified in YEs 9,13 14) and are well known thermal degradation products of thiamine (29). As well as possessing meaty aromas and low odor threshold values 34), these compounds are key precursors of several other sulfur-substituted furans and thiophenes, including the derivatives in Fig. 2. Most possess meaty aromas at low concentrations and several have been identified in YEs (see Tables I and III). 

Essential oils are volatile compounds responsible for the aromas commonly associated with many plants (see essay "Terpenes and Phenylpropanoids")- The chief constituent of the essential oil from cloves is aromatic and volatile with steam. In this experiment, you will isolate the main component derived from this spice by steam distillation. Steam distillation provides a means of isolating natural products, such as essential oils, without the risk of decomposing them thermally. Identification and characterization of this essential oil will be accomplished by infrared spectroscopy. 

A large number of furan derivatives are produced in non-enzymatic browning reactions as dehydration products of carbohydrates and related compounds, such as ascorbic acid (y-lactones can also be considered furan derivatives). Most furans are common to many thermally processed foods. Higher levels of these compounds are also present in acid protein hydrolysates. Furan-2-carbaldehyde has the characteristic pleasant woody aroma resembling nuts, which arises from pentoses and ascorbic acid, and 5-methylfuran-2-carbaldehyde, which is a product of 6-deoxyhexoses. A fatty herbal type flavour is provided by 5-hydroxymethylfuran-2-carbaldehyde arising from hexoses. 2-Acetylfuran arising from hexoses and pentoses is an important component of a number... 

Thermal treatment during the production and processing of foods leads to a variety of desired changes in color, taste and aroma but also enhances the formation of Advanced Glycation End Products (AGE), formed by the reaction of amino acids and reducing carbohydrates. Carboxymethyl-lysine (CML), a lysine derivative and major AGE, has been detected in dairy products and in a multitude of other foods Various studies indicate that food derived AGEs are absorbed in the intestines with the transephitelial uptake based on passive diffusion... 

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