Thermal interactions, volatile compounds

Amino acids may also undergo thermal degradation, which is almost always coupled with some other food components, particular sugars. The major types of volatile compounds formed from amino-sugar interactions include Strecker degradation aldehydes, alkyl pyrazines, alkyl thiazolines and thiazoles and other heterocycles [35, 36]. As the subject has mainly relevance for baked and roasted vegetable food products, this subject will not be discussed in further detail. 

The extruder is a continuous high-temperature short-time reactor. Ingredients, moisture, temperature, pressure, and shear can interactively produce many Mail lard-type flavor compounds. As the extrudate exits the extruder, many of the volatile reaction products may be lost with steam since the extrudate passes from a zone of relatively high pressure within the extruder to atmospheric pressure. By controlling formulation variables, the extruder can serve as a useful tool to thermally produce volatile and nonvolatile compounds which make significant contributions to overall flavor. 

Among the volatile compounds listed in Table II, only thiazole compounds are derived from the thermal degradation of thiamin. 5-(2-hydroxyethyl)-4-methylthiazole and 4-methyl-5-vinylthiazoIe are well-known thermal degradation products of thiamin. 5-(2-Chloro-ethyl)-4-methylthiazole may form through the interaction of 5-(2-hydroxyethyl)-4-methylthiazole with hydrogen chloride. However, the most abundant product, 4-methylthiazole, has never been identified as a decomposition product of thiamin. The mechanism for its formation is not clear. 

It is formed when heating glucose (Heyns et al., 1966a) and is one of the main aliphatic volatile compounds identified after thermal interaction of glucose and cysteine (Zhang and Ho, 1991). 

Heyns et al. (1966a) identified it in the products formed when heating glucose. 2,3-Pentanedione is the main volatile compound formed by thermal degradation of Furaneol (1.100) after ih at 160°C in water at pH 5.1, it represents nearly half of the volatiles (GC). It is one of the aliphatic compounds identified in the thermal interaction of glucose and cysteine (Zhang and Ho, 1991). 

As many oxazolines (but only one oxazole, trimethyloxazole, L.ll) were identified in beef systems, always heated at lower temperatures than those used for coffee roasting, it seems reasonable to consider them as intermediates in oxazole formation. Hirai et al. (1973) and Peterson et al. (1975) actually observed that the peak area for 2,4,5-trimethyl-3-oxazoline is large to very large in boiled beef extracts. The work of Jassmann and Schulz (1963) had previously shown that this 2,4,5-trimethyl-3-oxazoline results from thermal interaction of ammonia, acetaldehyde and acetoin, all compounds that have been reported to be present in cooked beef, as well as in coffee volatiles. 

Volatile Compounds Cencraled from Thermal Degradation or Thermal Interactions of of Alkfenjyl Cysteine Sulfoxides... 

In addition to the enzymatic pathway of aroma formation, a thermal route also exists. At high temperatures, interactions of amino acids and sngars resnlt in the formation of various aldehydes. After thermal treatment, the tea becomes more tasty and pleasant, and has a better aroma. An essential source of secondary volatiles, formed during tea leaf processing, is oxidative. o-Quinone resulting from the oxidation of catechins can oxidize, besides amino acids and carotenes, unsaturated fatty acids as well. Linoleic and linolenic acids can be converted into hexenal and trans-hex-2-enal, respectively, and in addition, small amounts of other volatile compounds, especially hexanoic acid and trani-hex-2-enoic acid, can be formed from the same acids, respectively. Also the monoterpene alcohols, linalool and geraniol, play an important role in the formation of the aroma of black tea [38]. 

Volatile Compounds Generated from Thermal Interactions of Inosine-5 -monophosphate and Alliin or DeoxyaUiin... 

As shown in Table II, some volatile compounds identified from the thermal interaction of IMP and alliin were derived from the thermal degradation of alliin (II, 13), and the others were generated from the interactions of IMP and alliin. 

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