Volatile compounds sulfur-based

The flavor of fish and seafoods is composed of taste-active low molecular-weight extractives and aroma-active compounds. The taste-active compoimds are more abundant in the tissues of mollusks and crustaceans than fish. The most important non-volatile taste components are fi-ee amino acids, nucleotides, inorganic salts and quaternary ammonia bases. Alcohols, aldehydes, ketones, furans, nitrogen-containing compounds, sulfur-containing compounds, hydrocarbons, esters and phenols are the most important volatiles is shellfish. Alkyl pyrazines and sulfur-containing compounds are important contributors to the cooked aroma of crustaceans. Furans pyrazines, and Lactones have been found in heat-treated seafoods. Dimethyl disulfide, dimethyl trisulfide, heterocyclic sulfiir-containing compounds (alkylthiophenes) have been found in most thermally treated crustaceans like prawn, crab, oyster, crayfish and shrimp (52). 

The headspace technique, a static gas extraction method, is particularly suitable for the enrichment of volatile compounds. It enables the analysis of solid and liquid samples by direct sampling from the gas phase, and can be directly combined with gas chromatography. This principle is based on the distribution of analyte between the matrix and gas phase. It has been used successfully to determine volatile sulfur compounds from various matrices, such as wastewater, body fluids, plants, and animal fatty tissue. 

Based on a survey of the published literature, Maarse and Vischer (1989) listed 213 volatile compounds that had been identified in 50 studies on Cheddar these included 33 hydrocarbons, 24 alcohols, 13 aldehydes, 17 ketones, 42 acids, 30 esters, 12 lactones, 18 amines, 7 sulfur compounds, 5 halogens, 6 nitriles and amides, 4 phenols, 1 ether, and 1 pyran. The concentrations of many of these compounds were reported. The principal volatile compounds identified in Cheddar are listed in Table VII. 

To devise polymeric systems that can conduct protons with little or no water, in addition to possessing good chemical and electrochemical stability above 100 °C, is very challenging and has been the focus of intensive research over the last decade. One of the most successful strategies has been to replace the water with less volatile compounds. For example, strong 0x0 acids, e.g. phosphoric acid or sulfuric acid, have been complexed with basic polymers such as polybenzimidazole (PBI). PEMs based on PBIs doped with phosphoric acid have been used successfully at temperatures well above 100 °C under very dry conditions. However, there is still a risk that the acid will be partly leached out, especially at low temperature and high humidity. 

The Met and Cys sulfur-based amino acids as well as, probably, other precursor compounds are converted into volatile odoriferons com-ponnds. They contribnte to the increasing complexity in a wine s aromas and bonqnet after malolacfic fermentation De Revel et al., 1999. O. oeni produces methanethiol, dimethyl sulfide, 3 (methylsulfanyl) propanol-l-ol, and 3(methyl-sulfanyl) propionic acid. Synthetic solntions of... 

Putrefied animal matter hcis formed the basis for coyote attractants of possible value in pest control programs. Thus, a putrefied fish formulation has been used as a coyote lure and, more recently, attention has been directed to a fermented aqueous suspension of chicken whole-egg powder, developed initially as an attractant for flies (48). The odor components csf this material have been subjected to detailed chemical analysis ty Bullard et al. (49) and are reported to include volatile fatty acids (77% total 13 acids identified), bases (13% total, mainly trimethylamine, 9 amines identified), and headspace volatiles, including esters, aldehydes, ketones, alcohols, alkyl aromatics, terpenes and sulfur compounds (10% total, 76 compounds identified). Based on these data, a synthetic mixture, "synthetic fermented egg" has been formulated, composed largely of a mixture of ten volatile fatty acids (81%), together with a diverse range of amines and other compounds (50). This mixture was found to be as attractive to coyotes as the fermented preparation itself. The volatile fatty acid component alone was found to exhibit substantial coyote attractancy also (50,51). ... 

Thiuram Sulfides. These compounds, (8) and (9), are an important class of accelerator. Thiurams are produced by the oxidation of sodium dithiocarbamates. The di- and polysulfides can donate one or more atoms of sulfur from their molecular stmcture for vulcanization. The use of these compounds at relatively high levels with litde or no elemental sulfur provides articles with improved heat resistance. The short-chain (methyl and ethyl) thiurams and dithiocarbamates ate priced 2/kg. Producers have introduced ultra-accelerators based on longer-chain and branched-chain amines that are less volatile and less toxic. This development is also motivated by a desire to rninirnize airborne nitrosamines. 

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. 

Volatile sulfur compounds. Volatile sulfur compound are best determined in the headspaces using a sulfur selective detector. Different alternatives, based on direct headspace of headspace-SPME, have been developed (Rauhut et al. 1998 Mestres et al. 2000 Lopez et al. 2007). 

The exclusion of selenium from the proteins of accumulator plants is thought to be the basis for their selenium tolerance. Their selenium metabolism is based mainly on water-soluble nonprotein forms such as selenium methylselenomethionine (Jacobs, 1989). The garlic odor characteristic of selenium-accumulator plants reflects the volatile organic compounds dimethylselenide and dime-thyldiselenide. Plants can suffer selenium toxicity as a result of selenium competition with essential metabolites for biochemical sites, replacement of essential ions by selenium, mainly major cations, selenate occupation of the sites of essential groups such as phosphate and nitrate, or selenium substimtion in essential sulfur compounds. 

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