Aroma causes

In tomato paste, for example (cf. Table 17.12), it was found that the changes in aroma caused by heating are primarily due to the formation of dimethylsulfide, methional, the furanones HD2F and HD3F and the increase in P-damascenone, and a substantial decrease in (Z)-3-hexenal and hexanal. 

Cheeses with a very pungent aroma caused by bacteria that live in the rind and on the cheese surface (such as Pont lEveque, Limburger or Romadur) contain phenol, cresol, acetophenone and methylth-ioesters of lower fatty acids (8-185), such as methyl thioacetate (R = H), methyl thiopropionate (R =CH3) and methyl thiobu-tyrate (R = CH2CH3) as flavourings. Other important flavouring substances include C4-C1Q fatty acids, especially capric acid, alkan-2-ones (methylketones) and alkan-2-ols. 

When the add and strawberry aroma were turned off either separately (runs 1 and 3) or together (run 5) they had less of an effect on the perceived strawberry intensity than sucrose. Stopping the flow of acids caused the perceived strawberry intensity to fall to just above 50%, whereas removal of the strawberry aroma caused the intensity to decline to 60% of initial perception. A minimum of 60% was also reached when both the acid and the volatile were turned off together. These three curves were considerably different from the rest. In runs in which the aroma was removed, but sucrose... 

The aroma of fmit, the taste of candy, and the texture of bread are examples of flavor perception. In each case, physical and chemical stmctures ia these foods stimulate receptors ia the nose and mouth. Impulses from these receptors are then processed iato perceptions of flavor by the brain. Attention, emotion, memory, cognition, and other brain functions combine with these perceptions to cause behavior, eg, a sense of pleasure, a memory, an idea, a fantasy, a purchase. These are psychological processes and as such have all the complexities of the human mind. Flavor characterization attempts to define what causes flavor and to determine if human response to flavor can be predicted. The ways ia which simple flavor active substances, flavorants, produce perceptions are described both ia terms of the physiology, ie, transduction, and psychophysics, ie, dose-response relationships, of flavor (1,2). Progress has been made ia understanding how perceptions of simple flavorants are processed iato hedonic behavior, ie, degree of liking, or concept formation, eg, crispy or umami (savory) (3,4). However, it is unclear how complex mixtures of flavorants are perceived or what behavior they cause. Flavor characterization involves the chemical measurement of iadividual flavorants and the use of sensory tests to determine their impact on behavior. 

Concentration and Aroma Recovery. Concentration of juice from deciduous fmit is best carried out using an evaporator that causes as httle thermal degradation as possible and that permits recovery of volatile materials important to the aroma of the fresh fmit, ie, essence. Evaporators that use a high temperature for a short time and operate under a vacuum, such as the APV Crepaco falling film plate evaporator or the Alfa Laval centrifugal... 

The denomination of odors was schematically related to two separate domains, both related to the memory stimulus of an event concomitant with the perception of the odor. One domain was based on an actual reference point that contains the odor vectors the other was associated with an odor stimulus based on imagination, ie, what image is evoked by the stimulus. With such a system, the final descriptive terminology used would more often than not be expressed in esoteric language, causing confusion and even communication breakdown. The work of Jaubert (1) was the origin of a more standardized descriptive system in the field of aroma description. 

Be mindful of all the cautions about using elder bark and roots (see page 7981) however, if you decide that you still want to harvest this part of the elder, collect in the fall of the second to fourth years. When the elder material is dry, store in a glass jar, protected from light and heat. Dampness will cause the blossoms to get musty and lose their aroma. Use within a year. Nature will provide more the next year. 

However, ozone may have some undesirable effects. There have been a few reports of changes in aroma and surface colour of some fruits and vegetables (Kim etal., 1999 Perez etal., 1999). Ozone can also be hazardous to humans. A concentration above 0.1 ppm in air has a strong odour that causes irritation of the nose, throat and skin (Sharma, 2005). In addition, long-term exposure to the gas may lead to mutagenic effects and even death. 

Microbial spoilage appears to be one of the major causes of quality loss of fresh fruits and vegetables by formation of off-flavors, fermented aromas, and tissue decay. The shelf-life of many food products may be accurately predicted by quantifying the population of microbes present on the food product (Zhuang and others 2003). The... 

Multiple senses, including taste, contribute to our total perception of food. Our perception of the flavor of food is a complex experience based upon multiple senses taste per se, which includes sweet, sour, salty and bitter olfaction, which includes aromas touch, also termed mouth feel , that is, texture and fat content and thermoreception and nociception caused by pungent spices and irritants. Taste proper is commonly divided into four categories of primary stimuli sweet, sour, salty and bitter. One other primary taste quality, termed umami (the taste of L-glutamate), is still somewhat controversial. Mixtures of these primaries can mimic the tastes of more complex foods. 

Although most consumers appreciate the fieriness of chile, capsaicinoids are not perceived through odor or taste receptors but through the nociceptive pain receptors described earlier. The compounds in chile fruit that create the flavor and aroma are produced in the fruit wall. Buttery et al. [90] generated vacuum steam distilled oil from green bell pepper macerate, with well over 40 peaks on subsequent GC/MS analysis. Of these peaks, the major flavor compound associated with bell pepper aroma was 2-methoxy-3-isobutylpyrazine (Fig. 8.1). They also reported several monoterpenoids in abundance, limonene, trans- 3-ocimene, and linalool as well as other aliphatic aldehydes and ketones. The flavor composition of dried red bell pepper powder (sweet paprika) extracted with ether identified 44 key peaks by GC/MS [91]. In these dried samples the key compounds were P-ionone and several furanones. The post-harvest processing and the different fruit maturities as well as possible varietal differences are all causes for the different aromatic profiles. 

Freeze concentration involves the concentration of an aqueous solution by partial freezing and subsequent separation of the resulting ice crystals. It is considered to be one of the most advantageous concentration processes because of the many positive characteristics related with its application. Concentration processes such as evaporation or distillation usually result in removal of volatiles responsible for arom in addition the heat addition in these processes causes a breakdown in the chemical structure that affects flavor characteristics and nutritive properties. In contrast freeze concentration is capable of concentrating various comestible liquids without appreciable change in flavor, aroma, color or nutritive value (1.2.3) The concentrate contains almost all the original amounts of solutes present in the liquid food. 

The a-keto adds and their metabolic byproducts are excreted in urine, and these compounds cause the characteristic sweet, "maple syrup"aroma. 

It is used in a large number of blossom fragrances. However, its use in perfumes for soap and cosmetics is limited because it causes discoloration. It is used in aroma compositions (e.g., in grape and citrus flavors). 

Semivolatile and non-volatile compounds of wood change the colour of the distillate and contribute to an up-rounded flavour. The wooden barrels which are permeable allow air to pass in and cause ethanol to evaporate thus, the ethanol content decreases and the aroma gets more intense, complex, and concentrated. Also harsher aroma constituents are removed and the spirit changes to mellow. The period of maturation depends on the size of the casks used, the alcoholic strength, as well as the temperature and humidity in the warehouse which leads to a smoother flavour. For production of neutral highly rectified distilled spirits like vodka, grain spirit, or white rum, the quality of water is of utmost importance to the flavour. In vodka production different treatments of water like de-... 

The aroma of foods is caused by volatile compounds which are perceived by the human nose. Many studies (reviews in [1, 2]) have indicated that only a small fraction of the hundreds of volatiles occurring in a food sample contribute to its aroma. To detect these compounds, a method proposed by Fuller et al. [3] is used. In this procedure, which is designated gas chromatography-olfactometry (GC-O), the effluent from a gas chromatography column is sniffed by an expert who marks in the chromatogram each position at which an odour impression is perceived. 

Reviews published by Acree and Teranishi [7], Blank [8], Grosch [1, 2, 9], Mistry et al. [10] and Schieberle [11] agree that GC-O was the starting point for the development of a systematic approach for the identification of the compounds causing food aromas. The aim of this chapter is to discuss the potential and the limitations of GC-O. 

Odorants that cause aroma changes, e.g. olf-flavours, may be detected by a comparative AEDA of fresh and deteriorated samples. Studies on storage defects of soybean oil [22, 51], buttermilk [52], boiled cod [53], dry parsley [54] and black and white pepper [55] are examples. 

These porous structures may hinder the transport of solutes away from the membrane downstream surface, causing a local increase of the solute partial pressure and hence a decrease of the driving force (19.1). Eventually, solute condensation may occur if the solutes local partial pressure surmounts its saturation vapour pressure. This problem becomes particularly relevant when dealing with high-boiling aroma compounds [14] and when pressure drop in the downstream circuit increases owing to poor module design. 

Similarly, in potato Solanum tuberosum), silencing LOX-Hl caused a severe decrease in the amount of volatiles produced by the leaves and in the intensity of their aroma, while the depletion of HPL increased the content of C5 (2-pente-nal, pentanal, l-penten-3-ol and ds-2-pentenol) volatiles [27]. These examples clearly demonstrate that the fatty acid metabolism involved in aroma biosynthesis is not as simple as initially supposed. 

On the positive side, thermization and minimum pasteurization should not cause the formation of undesirable flavours and aromas and should, in fact, result in improved flavour by reducing bacterial growth and enzymatic activity, e.g. lipolysis. If accompanied by vacuum treatment (vacreation), pasteurization removes indigenous off-flavours, i.e. those arising from the cow s metabolism or from feed, thereby improving the organoleptic qualities of milk. 

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