Volatile enzymatic degradation

Nonvolatile Inhibitors. Glycosides A number of toxic constituents are known to be released by the enzymatic degradation of various glycosides. Some of the volatile components have been mentioned previously—i.e., isothiocyanates from mustard oil glycosides and hydrogen cyanide from cyanogenic glycosides. 

Volatile compounds formed by anabolic or catabolic pathways include fatty acid derivatives, terpenes and phenolics. In contrast, volatile compounds formed during tissue damage are typically formed through enzymatic degradation and/ or autoxidation reactions of primary and/or secondary metabolites and includes lipids, amino acids, glucosinolates, terpenoids and phenolics. 

The fruit of the cucumber plant Cucumis sativus) is mainly eaten raw or as pickle. Approximately 30 volatile compounds have been detected in the volatile fraction of cucumber, with aliphatic alcohols and carbonyl compounds being most abundant [35]. Fresh cucumber flavour develops as a result of enzymatic degradation of linoleic and linolenic acid rapidly after the tissue is disrupted (Scheme 7.2), by which ( ,Z)-2,6-nonadienal and ( )-2-nonenal mainly are formed [184]. ( ,Z)-2,6-Nonadienal is the main flavour volatile of cucumber fruit, with ( )-2-nonenal as the second most important compound (Table 7.7) [185, 186]. 

Secondary metabolites in plant cell culture are typically stored within the vacuolar compartments of the cells. Small amounts of metabolites are usually excreted into the medium or may appear in the medium due to cell lysis. In some cases, active transport of metabolites adjusts intracellular and extracellular levels in response to cellular conditions. Poor yields of secondary substances released into the medium may be caused by several factors. In those cases where low yield is due to cellularly mediated regulation of the ratio between intracellular and extracellular product concentrations, processes which reduce net medium concentrations such as enzymatic or non-enzymatic degradation, or volatility, should increase net production by depleting the level of the secondary substances in the culture medium. By using the so-called in situ extraction method, the accumulation of a secondary substance inside the cell, in the culture medium, and in the extraction phase should approach an equilibrium, which... 

Traditionally fermented dairy products have been used as beverages, meal components, and ingredients for many new products [60], The formation of flavor in fermented dairy products is a result of reactions of milk components lactose, fat, and casein. Particularly, the enzymatic degradation of proteins leads to the formation of key-flavor components that contribute to the sensory perception of the products [55], Methyl ketones are responsible for the fruity, musty, and blue cheese flavors of cheese and other dairy products. Aromatic amino acids, branched-chain amino acids, and methionine are the most relevant substrates for cheese flavor development [55]. Volatile sulfur compounds derived from methionine, such as methanethiol, dimethylsulflde, and dimethyltrisul-fide, are regarded as essential components in many cheese varieties [61], Conversion of tryptophan or phenylalanine can also lead to benzaldehyde formation. This compound, which is found in various hard- and soft-type cheeses, contributes positively to the overall flavor [57,62]. The conversion of caseins is undoubtedly the most important biochemical pathway for flavor formation in several cheese types [62,63]. A good balance between proteolysis and peptidolysis prevents the formation of bitterness in cheese [64,65],... 

It could be concluded a number of possible modes of tolerance to toxic compounds, which described by Pilon-Smits (2005) and may involve any of six mechanisms these include differences in adsorption, conjugation, sequestration, enzymatic modification, enzymatic degradation and volatilization. Tolerance in Se accumulator plants appears to be due to a number of mechanisms as follows ... 

In a preliminary study, the volatile fraction of cork samples at different stages of processing (raw material and finished stoppers) was analyzed [43]. One hundred seven components were identified by GC-MS, several of which had not been previously reported in cork. Predominant volatiles were hydrocarbons, alcohols, acids, and carbonyl compounds. A natural origin, such as chemical or enzymatic degradation of the cork, could explain the occurrence of many substances. All the identified compounds with a phenyl ring and with a linear structure, e.g., vinylbenzene, benzyl alcohol, and 2-hydroxybenzaldehyde, could be derived from suberin and lignin. 

Elucidating the enzymatic steps in the formation of volatile homoterpenes has been a subject of continual investigation. Cn- and Cxg- homoterpenes are acyclic ter-penes that are produced by degradation of C15- and C20- precursors. Initial smdies by Boland and co-workers [61] with deuterium-labeled precursors administered to... 

OMD offers major advantages in comparison with the conventional thermal concentration techniques. The low temperature employed can help avoid chemical or enzymatic reactions associated with heat treatment [85] and prevent degradation of flavor, color, and loss of volatile aroma [38]. The low-operating pressure (atmospheric pressure) results in low investment costs, low risks of fouling, and low limits on compactive strength of the membrane. Since the separation is based on vapor-liquid equilibrium, only volatile compounds which can permeate the membrane and the nonvolatile solutes such as ions, sugars, macromolecules, cells, and colloids are totally retained in the feed. These factors make OMD an attractive alternative to traditional thermal routes currently used for concentration of liquid foods or aqueous solutions of thermally labile pharmaceutical products and biologicals [86]. 

Main components 1.5-2.5% sinalbin, a glucosinolate, which, after the addition of water, is degraded enzymatically by myrosinase into p-hydroxybenzyl isothiocyanate (not water-vapour volatile), glucose and sinapin hydrogensulphate. Sinapin constitutes the choline ester of sinapinic acid. Moreover, the plant contains app. 30% vegetable oil, mainly the glycerides of erucic acid, mucilage, steroids and proteins. 

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