Aroma CHARM analysis

Ethyl 2-methylbutanoate, 2-methylbutyl acetate and hexyl acetate contribute most to the characteristic aroma of Fuji apples [49]. In Red Delicious apples, ethyl butanoate, ethyl 2-methylbutanoate, propyl 2-methylbutanoate and hexyl acetate contribute to the characteristic aroma as determined by Charm-Analysis and/or AEDA [50, 51]. In a comparative study of 40 apple cultivars, the highest odour potency or Charm value was found for -damascenone [52]. This compound usually occurs in a glycosidically bound form and is present primarily in processed products owing to hydrolysis of the glycoside bond after crushing fruit cells [53]. -Damascenone has a very low odour threshold with a sweet, fruity, perfumery odour and is not typical of apple aroma in gen-... 

However, a single GC-O run only is usually insufficient to distinguish between the potent odorants that most likely contribute strongly to an aroma and those odorants that are only components of the background aroma. Therefore, to improve the results, two methods, combined hedonic aroma response measurements (CHARM) analysis [4] and aroma extract dilution analysis (AEDA) [5, 6] have been developed. As discussed in Sect. 16.4 in both methods serial dilutions of food extract are analysed by GC-O. 

Gas chromatography/olfactometry (GCO) methods have been developed as screening procedures to detect potent odorants in food extracts. The FD-factors or CHARM values determined in food extracts are not consequently an exact measure for the contribution of a single odorant to the overall food flavor for the following reasons. During GCO the complete amount of every odorant present in the extract is volatilized. However, the amount of an odorant present in the headspace above the food depends on its volatility from the food matrix. Furthermore, by AEDA or CHARM analysis the odorants are ranked according to their odor thresholds in air, whereas in a food the relative contribution of an odorant is strongly affected by its odor threshold in the food matrix. The importance of odor thresholds in aroma research has been recently emphazised by Teranishi et al. [58],... 

Many aroma compounds have been identified in crackers but which ones are the most important has still not been established. Further studies of these extracts should involve the use of odor assays to sort out to aroma important compounds in crackers from the unimportant aroma compounds present. For example, the method used by Shieberle Grosch (33) to describe the odor-active components in bread in terms of their flavor dilution values and the technique called charm analysis (43, 44) both concentrate chemical investigations at retention indices with odor activity. 

With regard to a glucose-proline system, Roberts and Acree277 have examined the sensory aspects in much more detail by applying Charm analysis (see the Olfactory Threshold section above). Four compounds provided most of the aroma 2-acetyl-3,4,5,6-tetrahydro-l//-pyridine (burnt, caramel 63%), 2-acetyl-1-pyrroline (popcorn 19%), 2-acetyl-l,4,5,6-tetrahydro-l//-pyridine (burnt, caramel 12%), and UDMF (cotton candy 4%). All Maillard systems of interest need to be submitted to similarly detailed analyses. 

Odor-active components in cheese flavor, many of which are derived from milk lipids, can be detected using GC-olfactometry (GC-O). GC-0 is defined as a collection of techniques that combine olfactometry, or the use of the human nose, as a detector to assess odor activity in a defined air stream post-separation using a GC (Friedich and Acree, 1988). The data generated by GC-0 are evaluated primarily by aroma extract dilution analysis or Charm analysis. Both involve evaluating the odor activity of individual compounds by sniffing the GC outlet of a series of dilutions of the original aroma extract and therefore both methods are based on the odor detection threshold of compounds. The key odourants in dairy products and in various types of cheese have been reviewed by Friedich and Acree (1988) and Curioni and Bosset (2002). 

Based on determination of threshold concentration Aroma Extract Dilution Analysis (AEDA) (Schieberle and Grosch 1987 Ullrich and Grosch 1987), and Charm analysis (Acree et al. 1984)... 

The knowledge that not all of the volatiles (e.g. more than 800 in roasted coffee) [5] that occur in a food contribute to its aroma was the rationale for changing the methodology of analysis. Since 1984, when the procedure for charm analysis was published [4], techniques have been developed that focus on the identification of compounds contributing to the aroma with higher OAV. 

After the preparation of an aroma concentrate as detailed in [11], dilution experiments are performed (Table 6.23). As reviewed by Acree [8] and Grosch [11], two techniques - charm analysis and aroma extract dilution analysis (AEDA) - are used to screen the potent, medium and lower volatile odorants on which the identification experiments are then focused. In both procedures, an extract obtained from the food is diluted, and each dilution is analysed by GCO. This procedure is performed until no odorants are perceivable by GCO. 

Charm analysis constructs chromatographic peaks, the areas of which are proportional to the amount of the odorant in the aroma concentrate [4], The difference between the two methods is that charm analysis measures the dilution value over the entire time the compounds elute, whereas AEDA simply determines the maximum dilution value [8],... 

Charm analysis and AEDA both constitute screening procedures, as the results are not corrected for the losses of odorants during the isolation procedure. Furthermore, in GCO, the odorants are completely volatilised and then evaluated by sniffing, whereas the volatility of the aroma compounds in foods depends on their solubility in the aqueous and/or oily phase as well as their binding to non-volatile food constituents. To elucidate which of the compounds revealed in the dilution experiments contribute with high OAV to the aroma, quantification of the odorants with higher FD factors and calculation of their OAVs are the next steps in the analytical procedure. 

DILUTION ANALYSIS CHARM ANALYSIS AND AROMA EXTRACT DILUTION ANALYSIS (AEDA)... 

Gas chromatography, (GC) sniffing, aroma extract dilution analysis (AEDA), and CHARM analysis are well accepted tools to identify the sensory properties of individual molecules in complex mixtures [9-10]. In fact, they are the fastest tool to identify typical character impact molecules and odor off-notes. They require well trained people who are able to keep pace with the fast emerging GC peaks imagine that a small gas balloon of ca. 0.1 mL leaving the sniff port within 3 sec has to be transferred to the... 

In summary, GC-0 techniques should be seen as screening methods to gain an insight into important contributors to a characteristic aroma (7,71). GC-O performed as Charm analysis and Osme have also been claimed as quantitative bioassays (10,77). However, more time is needed for training of assessors and verification using statistical means. 

In recent studies, potent aroma compounds have been identified using various gas chromatography-olfactometry (GCO) techniques, such as Charm Analysis and aroma extract dilution analysis (AEDA) (7,8). The flavor compounds that are identified by these methods are significant contributors to the sensory profile. In some cases, these sensory-directed analytical techniques have enabled the discovery of new character impact compounds. However, in other instances, key aroma chemicals have been identified that, while potent and significant to flavor, do not impart character impact. For example, in dairy products, chocolate, and kiwifmit, these flavor types appear to be produced by a complex blend of noncharacterizing key aroma compounds. 

These methods were developed to quantify and visualize the intensity of aroma as a chromatogram. A specific system named combined hedonic and response measurement (CHARM) was initially developed. Later on, aroma extract dilution analysis (AEDA) (Figure 3), a new method using a conventional GC-O system, was proposed. They share the same strategy aroma extract is diluted to a certain extent and then GC—O methodology is applied. In an AEDA procedure, if such a maximum extent of a dilution that allows the detection of a certain component is times diluted from the original sample, this component is referred to have a flavor dilution (FD) factor of . CHARM value corresponds to FD factor in a CHARM procedure. These values represent the contribution of the volatile the larger these values are, the more important they are considered as key components. 

GC-0 methods are commonly class ed in four categories dilution, time intensity, detection frequency, and posterior intensity methods. Dilution analysis, the most applied method, is based on successive dilutions of an aroma extract until no odor is perceived by the panelists. This procedure, usually performed by a reduced number of assessors, is mainly represented by combined hedonic aroma response method (CHARM) [67], developed by Acree et al., and aroma extraction dilution analysis (AEDA), rst presented by Ullrich and Grosch [68]. The former method has been applied to the investigation of two sweet orange oils from different varieties, one Florida Valencia... 

Another more elaborate variant of the dilution analysis requires, in addition, that the duration of each odor impression is recorded by a computer and CHARM values are calculated (CHARM acronym for combined hedonic response measurement), which are proportional to aroma values. The result of an AEDA can be represented as a diagram The FD factor is plotted against the retention time in the form of the retention index (RI) and the diagram is called a FD chromatogram. 

Aroma activities of volatile compounds obtained by GCO dilution analyses were represented as Charm values, and the relative intensities of component odorants were represented in terms of the odor spectrum value (OSV) [14]. Each Charm value was rounded off to two significant figures in order to reflect the actual resolution of the dilution analysis. Acidic, buttery-oily, green-black currant, green-earthy, nutty-roast, phenolic, smoke-roast, soy sauce, sweet-caramel, and sweet-fruity were the aroma descriptions used in all GCO experiments to describe potent odorants. These descriptions were chosen from the results of a single preliminary free choice GCO analysis using a lexicon of words commonly used for coffee evaluation. 

Principal component analysis (PCA) was carried out by using an SPSS program. Thirty-five odorants with an OSV of 50 or above, calculated by using mean Charm values of each odorant, were selected from the volatile compounds of the aroma released during grinding and categorized into 10 aroma descriptions the total of Charm values of each description was applied to the PCA. 

The aim of GC-0 techniques in food aroma research is to determine the relative odor potency of compounds present in the aroma extract. This method gives the order of priority for identification and thus indicates the chemical origin of olfactory differences (7). The value of the results obtained by GC-O depends directly on the effort invested in sample preparation and analytical conditions. Analysis of an aroma extract by dilution techniques (AEDA, Charm) combined with static headspace GC-O provides a complete characterization of the qualitative aroma composition of a food. However, this is only the first step in understanding the complex aroma of a food. 

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