Vegetative volatiles

Vegetables contain some flavor compounds, the concentrations of which are mostly too low to obtain essential oils. In the tissues of some vegetables, volatile compounds are enzymatically produced when they are disrupted. Vegetables have the function of flavoring only after their cells are disrupted or after being oil-fried. Vegetable flavors are classified in the category of savory flavor, while fruit flavors are classified as sweet flavors. 

The enzymic formation of aldehydes, ketones, alcohols, and oxoacids (from linoleic and linolenic acids) on disruption of plant tissues is an important biosynthetic pathway by which fruit and vegetable volatiles are formed. Some examples are (E)-2-hexenal ("leaf aldehyde") and ( )-3-hexenol ("leaf alcohol") in tea (E)-2-hexenal in apples (E,Z)-2,6-nonadienal ("violet Teaf aldehyde") and (E)-2-nonenal in cucumber ( Z)-5-nonenal in musk melon (Z,Z) -3,6-nonadienol in water melon, and 1-octen-3-ol ("mushroom alcohol") in certain edible mushrooms and Fungi. The enzyme system is highly substrate specific to a (Z,Z)-1,4-pentadiene system (like lipoxygenase) splitting the >C = C< double bond at the W - 6 and/or W - 9 position. Therefore linoleic-, linolenic-, and arachidonic acids are natural substrates. It seems to be a common principle in leaves, fruits, vegetables, and basidiomycetes. 

Fig. 7.2 Monoterpenes/monoterpenoids from floral and vegetative volatile emissions of Nicotiana spp. (Solanaceae)...

Potable Water Treatment. Treatment of drinking water accounts for about 24% of the total activated carbon used in Hquid-phase apphcations (74). Rivers, lakes, and groundwater from weUs, the most common drinking water sources, are often contaminated with bacteria, vimses, natural vegetation decay products, halogenated materials, and volatile organic compounds. Normal water disinfection and filtration treatment steps remove or destroy the bulk of these materials (75). However, treatment by activated carbon is an important additional step in many plants to remove toxic and other organic materials (76—78) for safety and palatability. 

Drying is an operation in which volatile Hquids are separated by vaporization from soHds, slurries, and solutions to yield soHd products. In dehydration, vegetable and animal materials are dried to less than their natural moisture contents, or water of crystallization is removed from hydrates. In freeze drying (lyophilization), wet material is cooled to freeze the Hquid vaporization occurs by sublimation. Gas drying is the separation of condensable vapors from noncondensable gases by cooling, adsorption (qv), or absorption (qv) (see also Adsorption, gas separation). Evaporation (qv) differs from drying in that feed and product are both pumpable fluids. 

The early measurements therefore identified NHj volatilization, and were followed in the f920s by studies which demonstrated NHj emission by vegetation. The measurement of emission of NjO and NO from agricultural sites has been... 

The nutmeg must first be moistened with ether, otherwise the extraction takes much longer. The author has found this a])])aratus to be generally satisfactory for the extraction of vegetable drugs with volatile solvents. 

Volatile hydrocarbo ns Motor vehicles Vegetation damage (especially... 

An absolutely scientific definition of the term essential cr volatile oils is hardly possible, but for all practical purposes they may be defined as odoriferous bodies of an oily nature obtained almost exclusively from vegetable sources, generally liquid (sometimes semi-solid or solid) at ordinary temperatures, and volatile without decomposition. This definition must be accepted within the ordinary limitations which are laid down by the common acceptation of the words, which will make themselves apparent in the sequel, and show that no more restricted definition is either advantageous or possible. Many essential oils, for example, are partially decomposed when distilled by themselves, and some even when steam distilled. 

Similar information for other foods would be of great value. With dehydrated vegetables and fruits, large errors are not to be expected, because these foods do not normally contain much nonaqueous volatile matter and some of it will have been lost in the process of dehydration. 

The lyophilization procedure, as described, is suitable for materials such as vegetables, that do not usually contain much nonaqueous volatile matter. For other materials, rich in these volatiles, a modification of the procedure would be required. The volatiles could in some cases be extracted with a solvent and dried separately (28), or the substances evolved in the drying could be collected and analyzed for the amount of nonaqueous material. 

Foods such as meat, fish, and some vegetables contain sulfur-bearing amino acids that form volatile sulfur compounds during processing and storage. When these compounds react with iron, a black precipitate forms on the container and in most instances darkens the food. A small piece of aluminum welded to the tinplate can has been used to prevent container corrosion and sulfide staining in commercially canned hams. In this case, the aluminum acts as a sacrificial anode and stops the reaction with tin and iron that otherwise could occur at the small exposed tinplate areas (14). 

Nutrient Losses Associated With Biomass Burning. Nutrient losses associated with slash fires occur through volatilization and convective losses of ash. Elements with low temperatures of volatilization (e.g. N, K, S, and some organic forms of P) will be lost in the highest quantities (Table III) (57). Conversely, Ca and Mg have volatilization temperatures higher than that recorded during most vegetation fires. Almost all fire-induced losses of these elements are due to particulate transfer by convective processes. 

Volatile hydrocarbons Motor vehicles Solvent processes Chemical industry Vegetation damage (especially unsaturated hydrocarbons) Some are irritants Adverse health effects... 

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