Odor quality, aroma substance

This procedure allows the differentiation of odor active compounds from odorless substances within a complex mixture of volatiles. For decades this procedure has been successfully applied for aroma analyses of foods (Grosch, 1993). The mixture of volatile compounds either collected in a purified organic solvent extract or in a defined headspace volume is separated into its different components by means of GC and the effluent gas flow at the end of the GC capillary column is split between a FID and an experienced test person s nose. By sniffing the column effluent, the human nose is able to perceive the odor active compounds contained in a complex mixture and the test person can mark the corresponding spot in the FID chromatogram recorded in parallel and attribute a certain odor quality. A sample GC—O chromatogram of a solvent extracted material is shown in Figure 8.7. 

In the case of chiral aroma substances, elucidation of the absolute configuration and determination of the enantiomeric ratio, which is usually given as the enantiomeric excess (ee), are of especial interest because the enantiomers of a compound can differ considerably in their odor quality and threshold. The compound 3a,4,5,7a-... 

Aroma substance Odor quality Odor intensity l%fat 5% fat 20% fat... 

The aroma substances that comprise flavors are found in nature as complex mixtures of volatile compounds. A vast majority of volatile chemicals that have been isolated from natural flavor extracts do not provide aroma contributions that are reminiscent of the flavor substance. For instance, n-hexanal is a component of natural apple flavor (1) however, when smelled in isolation, its odor is reminiscent of green, painty, rancid oil. Similarly, ethyl butyrate has a nondescript fruity aroma although it is found in strawberries, raspberries, and pears, it does not uniquely describe the aroma quality of any of these individual fruits. It has long been the goal of flavor chemists to elucidate the identity of pure aroma chemicals that have the distinct character impact of the natural fruit, vegetable, meat, cheese, or spice that they were derived from. Often, these are referred to as character impact compounds (2). 

Many nitrogen- and sulfur-containing heterocycles have been identified in the aroma fractions of foods [214]. In roasted products (e.g., coffee) and heat-treated foods (e.g., baked bread or fried meat), these heterocycles are formed from reducing sugars and simple or sulfur-containing amino acids by means of Maillard reactions [215, 216]. Their odor threshold values are often extremely low and even minute amounts may significantly contribute to the aroma quality of many products [217, 218]. Therefore, N- and N,S-heterocyclic fragrance and flavor substances are produced in far smaller quantities than most of the products previously described. 

Characteristic aroma components in foods and off-flavor substances in processed foods are called character impact compounds. It would be desirable to develop methods for finding such compounds with sensory methods because such information is useful in the food industry. A compilation of odor and taste threshold values was edited by Fazzalari (7). Olfactory-trigeminal response to odorants was measured using rabbits (2). However, aroma quality can be evaluated only by human sense. In spite of this fact, olfactory judgment by humans can not give constant data like... 

OAV = (odor threshold / concentration)matrix] this substance has a positive impact on aroma of barrel stored wines close to 10 years-old (OAV > 1) while in bottle-aged Ports this is only observed after 20 years or more. These results are in close agreement with the empirical observation in the Port wine industry upon which the rancio aroma constitutes a quality factor for wines aged in barrels for more than 10 years, while it is not considered a major attribute of the total aroma of Vintage types. 

Food additives have been used for centuries to improve food quality. Smoke, alcohols, and spices have been extensively used for the last 10,000 years as additives for food preservation. The above-mentioned additives as well as a restricted number of additives comprised the main food additives until the Industrial Revolution. The Industrial Revolution brought so many changes in foods and asked for improved quality as well as quantity of the manufactured foods. For this reason many chemical substances were developed either for preservation or for color and/or odor enhancement. In the 1960s, over 2500 different chemical substances were used toward food manufacturing. In the United States over 2500 different additives were used to manufacture over 15,000 different foods. The desire for nutritional, functional, and tasty foods is an ongoing process. An additive is used to improve the shape, color, aroma, and extend the shelf life of a food. The following categories of additives are described ... 

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