Roasting, model

The product was previously identified in beer by Andrews (1987) and in human sweat by Polak et al. (1988), and characterized as sunstruck or lightstruck off-flavor. The cause has been attributed to the degradation of bitter isohumulones from hops under the influence of ultraviolet light (Bondeel et al., 1987). By photofragmentation trans-isohumulone liberates a prenyl radical which can trap a thiol radical, producing an undesired flavor for beer. Holscher et al. (1992) have also shown that 3-methyl-2-buten-l-thiol and 3-mercapto-3-methylbutanol are principally formed under pyrolytic conditions in roast model reactions of prenyl alcohol and sulfur-containing amino acids. 

The model allows to perform thermal calculation of a multi-layer annular structure of a kiln body with a granular mixture-clinker, roasted inside it (Fig 1). 

Model systems indicate that aldehydes may also be produced by the action of polyphenoloxidases on amino acids in the presence of catechin, all of which are present in coffee beans at some stage between green and roasted. For example, valine yields isobutanal, leucine yields isopentanal, and isoleucine yields 2-methyl-butanal.14 Some of these aldehydes probably undergo condensation reactions in the acidic medium of the roasted bean when moisture is present.15 Some dienals in green coffee beans have recently been identified as (E,E)-2,4- and (E,Z)-2,4-nonadienal and (E,E)-2,4- and (E,Z)-2,4-decadienal.18... 

Robbins, P.T. and Fryer, PJ., The spouted-bed roasting of barley development of a predictive model for moisture and temperature, ]. Food Eng., 59 (2003) 199-208. 

Just how one decides whether one is in the mood for broiled salmon or roast duck isn t the concern of the decision sciences, at least not unless the way it is done turns out to conflict in some fashion with the rest of the model of rational choice. It sometimes seems to me - to me... 

Schieberle, P. 1995b. Quantification of important roast-smelling odorants in popcorn by stable isotope dilution assays and model studies on flavor formation during popping. J. Agric. Food Chem. 43 2442-2448. 

Alkylpyrazines have been recognized as important trace flavor components of a large number of cooked, roasted, toasted and deep-fat fried foods (3). As a rule, alkylpyrazines have a roasted nut-like odor and flavor. Formation pathways for alkylpyrazines have been proposed by numerous researchers (4, 5, 6). Model studies suggest that they are minor products of the Maillard reaction. 

Many 2-alkylpyridines were isolated and identified in roasted lamb fat (45). 2-Alkylpyridines were proposed to form from the corresponding unsaturated n-fatty aldehyde reacting with ammonia upon heat treatment. Ammonia, arising from glycine, can react with nonanal, arising from beef fat, produced 2-butylpyridine in a beef fat/glycine browning model system (6). The same phenomenon was observed in the formation of 2-pentylpyridine from 1-decanal. Maltol produced 2-ethyl-3-hydroxy-6-methylpyridine as a major product in a reaction with ammonia (12). 

DKP Formation in Model Peptide Systems. The fact that DKPs are formed at relatively lov temperatures suggested that catalyzed peptide decomposition occurs in the weakly acidic milieu produced by cacao fermentation. Reactions of simple peptides were followed at 0.02 M (initial concentration) in refluxing acetic acid (120°C) to simulate the interior of a bean during roasting (Table II). 

A model wheat bread was prepared by a straight dough procedure from wheat flour, salt and water using glucono-delta-lactone as leavening agent (Schieberle, P., in preparation). The bread crust showed an odor note reminiscent of day-old bread and, specifically the cracker-like, roast odor note was lacking. 

This list of volatile constituents continues to grow as demonstrated by Baltes and coworkers (5 1 Improved analytical instruments and data bases of thousands of mass spectra contributed to the detection of volatile constituents in model reactions as well as in roasted foodstuffs. New food constituents are more and more difficult to locate, isolate and identify. 

Furans and reductones are major components in roasted coffee as shown in Figure 3. Arabicas possess higher amounts of furanaldehydes and Furaneol than Robustas, when roasted under comparable conditions. The aldehydes and reductones are Strecker-active components and further transformed into typical aroma and flavor compounds as demonstrated in model experiments. 

In roasted coffee similar reactions seem to be involved forming methylmercaptan by the Strecker degradation of free methionine and forming H S from peptide cysteine. Figure 8 presents additional flavor contributing constituents of roasted coffee. 3-Thiolanone 6 and 2-methyl-3-thiolanone 1 were identified by Stoll et al. (19) and patented as coffee flavors. The two thiolanones 6, T are formed as major constituents in erythrose and xylose/ cysteine model systems, respectively. 

Kahweofuran (2-methyl-3-oxa-8-thiabicyclo(3.3.0)-1.4-octadiene, 8 ) was first isolated by Stoll et al. (19) and its structure later confirmed by synthesis (3J ). This compound possesses a roasty/sulfury-note as do the related ethyl- and dimethyl derivatives are unique to coffee. So far, the ethyl and dimethyl compounds have not been detected in the roasted foods or in monosaccharide/cysteine model experiments. 

The heat processing of tea leads to many complex chemical changes in tea. Tea s taste and aroma is affected by heat in at least three ways by reducing the content of bitter soluble catechins, by the development of roast aromas and by the thermal degradation of 0-carotene. Studies pertaining to the heat-induced changes in tea and appropriate model systems are reviewed. 

In summary, model studies are very efficient for the identification and structure elucidation of important flavor components. Most of the compounds reported here have not been identified in meat and have not yet been reported as constituents of food volatiles. Nevertheless, there are good reasons to believe that minute traces of these sulfur-containing components are present in roasted and/or cooked meat volatiles because our model system was based solely on naturally occurring precursors. We believe that only minute trace amounts of these types of components need to be present in natural products to be of prime significance due to their extremely low odor threshold values. 

Sotolone and abhexone to a lesser extent make important contributions to roast coffee aroma. They have been shown to be formed in model systems of 2-oxobutanoic acid and 2-oxopropanoic acid by Kobayashi214 (see Scheme 5.1). 

W. Baltes and G. Bochmann, Model reactions on roast aroma formation. IV. Mass spec-trometric identification of pyrazines from the reaction of serine and threonine with... 

K.-H. Wagner, S. Derkits, M. Herr, W. Schuh, and I. Elmadfa, Antioxidative potential of melanoidins isolated from a roasted glucose-glycine model, Food Chem., 2002, 78,375-382. 

Dynamic reactions like processes in blast furnaces, roasting processes or the solidification of liquid alloys can be simulated using the REACTOR MODEL... 

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