Aroma molecules

S of large and small molecules ia several polymers. A low D and a high S mean that lo ss of flavor/aroma molecules into a polymer package wall can be ... 

As a thickener (as opposed to a gel), it is amylose that has the main function. The long water-soluble chains increase the viscosity, which doesn t change much with temperature. Amylose chains tend to curl up into helixes (spirals) with the hydrophobic parts inside. This allows them to trap oils, fats, and aroma molecules inside the helix. 

The second point is related to the simultaneous presence of odorants at g/L levels and of others that can be active at levels as low as ng/L. This means that although it makes sense to use a general screening procedure for detecting by olfactometry the potentially most relevant aroma molecules, it will not be possible to use a single isolation or preconcentration scheme to identify and further quantify the different aroma molecules. Rather, it will be necessary to have an array of chemical isolation and quantification procedures if a comprehensive aroma analysis is our objective. 

In conclusion, the study of the wine aroma chemicals and the understanding of the role they play in the different wine aroma nuances have to be structured into a numbers of steps strongly constrained by the previous considerations. Such steps will be the subject of thischapter. The first step is about the screening of aroma molecules, which will be carried out by using gas chromatography-olfactometry. The second will be the isolation and identification of odorants. The third is the quantitative determination, for which only a very brief outline will be given, and the fourth is about the sensory tools used to assess the sensory role played by the different odorants. 

Since all aroma molecules are more or less volatile, the technique that a priori is best suited to screen the odor active molecules from the rest of molecules is Gas Chromatography-Olfactometry (GC-O). This technique makes use of the human nose as detector for the compounds eluting out of the chromatographic column, typically a fused silica capillary column (Acree et al. 1984). There are several different approaches for GC-O differing in the way in which the olfactometric signals are... 

Aroma perception of a food, e.g. wine, is strongly influenced by the way indigenous aroma molecules distribute between the gas and liquid phases. This distribution... 

Barrier plastics, used in food and beverage packaging applications, which have high resistance to permeation of gas and flavor-aroma molecules. 

Second, the flavor and aroma molecules of the food may leave by permeation through the package or by simple sorption by the package. The flavor profile may be made unacceptable by broad diminution or by selective removal of a few components. 

The permeability is useful for describing the transport rate at steady state. The solubility coefficient is useful for describing the amount of aroma that will be absorbed by the package wall. The diffusion coefficient is useful for describing how quickly the permeant aroma molecules move in the film and how much time is required to reach steady state. 

Fat and water are solvents for aroma chemicals, proteins, and carbohydrates. They can absorb, make complexes, and bind to aroma chemicals. A fat-soluble aroma chemical can be solubilized in a water and gum emulsion or in oil. However, the aromatic compound will be perceived more intense in the water-gum blend due to the higher vapor pressure in the headspace. On the other hand, aroma molecules surrounded by oil molecules will not volatilize (thus a reduction in the perceived intensity), resulting in a lower vapor pressure [75]. 

Very often, aroma molecules are hydrophobic oils. Their characteristic taste or smell may be pleasant, strong (if pure), or not, and may need to be modified, masked, and diluted. The aroma will be used in association with other substances, in an environment which may be a liquid, a paste, a solid, a gas, submitted to different usage conditions (temperature, pH), according to the final... 

Some examples of encapsulation studies are given, using simple model aroma molecules that are more or less volatile and soluble in water. 

One example of study used aroma molecules as models with different MW and volatility (diacetyl (DA) and vanillin (VA), citral, linalyl acetate) and different supports such as maltodextrin, sucrose, skim, and whole milk (Senoussi et al., 1994,1995). 

It was observed higher retention of VA compared to DA (MW VA > DA volatility VA < DA) and better retention with whole milk (due to fat phase) compared to skim milk. The partial replacement of maltodextrin by sucrose (smaller MW) is favorable to departure of aroma molecules with water during spray-drying. 

The properties o/aroma molecules sudi as solubility in water, size and shape of molecules, volatility, MW, and polarity. And the importance of matrix choice, especially in relation with glass transition temperature/crystallization, which can be the source of possible modification of powder structure. Also comparing volatiles and nonvolatiles (o-hmonene, fish oil), the snrface oil content of nonvolatile encapsulated powders was much higher volatile compounds can be evaporated and removed during spray-drying (Jafari et al., 2007b). 

The molecule of cyclodextrin (CD) (usually p) is a cut cone made of seven glucopyranose units the external part is hydrophilic and the internal part is hydrophobic (MW 1145 solubility 1.85 g/100 ml. water (25°C)(a-CD 12.7 g/100 mL y-CD 25.6 g/100 mL). The internal cavity (diameter 5-8 A) is nonpolar, and may accept a nonpolar host molecule of similar size as aroma molecules (6%-15% w/w). This is a selection by the host molecule configuration. If formed, the aroma/cyclodextrin complexes are very stable to evaporation, oxidation, light, heat, with good protection of aroma profile. 

There seems to be a lack of examples of (say) aroma molecules that are a short distance (say, <4) Ifom PLA, where barrier properties would be expected to be limited. As a stimulus to research, a glance at HSP of some typical aroma chemicals suggests that PLA would not be a good barrier for cinnamon-flavored goods. The distance between PLA and ciimamaldehyde is <3. 

Volatile aromatic compounds give coffee its characteristic rich aroma. Molecules responsible for the odor of a substance have distinctive shapes, which enables them to stimulate our sense of smell. 

The sorption characteristics of various proteins for several volatile compounds are presented in Fig. 5.36. Ethanol is bound to the greatest extent, probably with the aid of hydrogen bonds. The binding of the nonpolar aroma compounds probably occurs on the hydrophobic protein surface regions. A proposal for the evaluation of data on the sorption of aroma volatiles on a biopolymer (protein, polysaccharide) is based on the law of mass action. When a biopolymer, B, has a group which attracts and binds the aroma molecule, A, then the following equation is valid ... 

To calculate the average number of aroma molecules bound to a biopolymer, the specific binding capacity, r, has to be introduced ... 

While the oxidation state is temperature dependent, the O negative species occurs at about 400C. In the presence of an aroma molecule, the chemisorbed oxygen species reacts irreversibly and reaction products are formed (typically CO2 and water). 

The resistance of the sensor is thus decreased, the magnitude being dependent upon the type of sensor and the aroma molecule. This change in resistance is the sensor output sent to the computer. The response time of the sensor depends on the reaction kinetics, the headspace and the volume of the measured headspace. This generally takes about 10 to 120 sec (29). Metal oxide sensors are claimed to offer good sensitivities to a broad range of organic molecules (ppm to ppb). 

B. D. Mookheijee and R. W. Trenkle, Sun-scents The production of aroma molecules by the action of sunhght on the essential oil of cotton, Proc. 11 Intern. Congr. Essent. Oils, Fragrances and Flavours, New Delhi, Vol. 2, 1989, p. 69. 

Yongsawatdigul and Gunasekaran (1996) showed that color and texture of microwave-vacuum-dried cranberries were better than those of air-dried samples. If we look specifically at the retention of aroma, it becomes necessary to distinguish between two basic cases. In most foods the aroma molecules are present in very small amounts, so that they are likely to be dissolved in the water phase. In this situation, the volatility of the aroma molecule in water is essential. 

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