Aroma, AEDA

In the majority of the studies on the composition of food aromas, AEDA is used for the determination of the relative odour potency of the compounds detected by GC-O (reviewed in [1]). The odour potency is proportional to the odour activity value (OAV) of the compound in air. The OAV is defined as the ratio of the concentration of a compound to its odour threshold [3]. 

Aroma compounds, 11 517 Aroma extract dilution analysis (AEDA), 11 519-520... 

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-... 

Wild and cultivated blackberries have been used as food and medicine for hundreds of years [106]. Approximately 150 volatiles have been reported from blackberries [107]. The aroma profile is complex, as no single volatile is described as characteristic for blackberry [108, 109]. Several compounds have been suggested as prominent volatiles in blackberries using AEDA, e.g. ethyl hexanoate, ethyl 2-methylbutanoate, ethyl 2-methylpropanoate, 2-heptanone, 2-undecanone, 2-heptanol, 2-methylbutanal, 3-methylbutanal, hexanal, ( )-2-hexenal, furaneol, thiophene, dimethyl sulfide, dimethyl disulfide, dimethyl trisulfide, 2-methylthiophene, methional, a-pinene, limonene, linalool, sabinene. 

Twenty-nine odour-active compounds were detected by using aroma extract dilution analysis (AEDA) [60]. The results of AEDA together with GC-MS analysis showed ethyl 2-methylbutanoate (described as fruity flavour), followed by methyl 2-methylbutanoate and 3-methylbutanoate (fruity, apple-like), 4-hydroxy-2,5-dimethyl-3(2H)-furanone (sweet, pineapple-like, caramel-like), d-decalactone (sweet, coconut-like), l-( ,Z)-3,5-undecatriene (fresh, pineapple-like), and a unknown compound (fruity, pineapple-like) as the most odour-active compounds. 

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. 

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. 

As reported in the previous section, AEDA is performed with a concentrated aroma extract. However, concentration of the volatile fraction might lead to losses of odorants, e.g. by evaporation and by enhanced side reactions in the concentrated extract. Consequently, the odour potency of these odorants can be underestimated in comparison to those whose levels are not reduced during concentration. To clarify this point, aroma extract concentration analysis (AECA) [56] should check the results of AEDA. AECA starts with GC-O of the original extract from which the non-volatile components have been removed. The extract is then concentrated stepwise by distilling olf the solvent, and after each step an aliquot is analysed by GC-O [56]. 

In the case of boiled beef the results of AEDA were compared with those of AECA. Table 16.4 indicates that they agreed except in three cases. The odour potencies of 4-hydroxy-2,5-dimethyl-3(2H)-furanone, 3-mercapto-2-pentanone and methional were more than one dilution step higher in AECA than in AEDA [56]. Most likely, portions of these odorants had been lost during concentration of the extract for AEDA. AECA was also used in studies on the aroma of pepper [55], coffee [57] and Camembert cheese [58]. 

Table 16.4 Potent odorants of boiled beef—comparison (AECA) with AEDA [56] of aroma extract concentration analysis...

The influence of the sensitivity of the assessors on AEDA has been studied [11], with the result that the differences in the FD factors determined by a group of six panellists amount to not more than two dilution steps (e.g. 64 and 256), implying that the key odorants in a given extract will undoubtedly be detected. However, to avoid falsification of the result by anosmia, AEDA of a sample should be independently performed by at least two assessors. As detailed in [6], odour threshold values of odorants can be determined by AEDA using a sensory internal standard, e.g. ( )-2-decenal. However, as shown in Table 16.6 these odour threshold values may vary by several orders of magnitude [8] owing to different properties of the stationary phases. Consequently, such effects will also influence the results of dilution experiments. Indeed, different FD factors were determined for 2-methyl-3-furanthiol on the stationary phases SE-54 and FFAP 2 and 2 , respectively. In contrast, 5-ethyl-3-hydroxy-4-methyl-2(5H)-furanone showed higher FD factors on FFAP than on SE-54 2 and 2, respectively. Consequently, FD factors should be determined on suitable GC capillaries [8]. However, the best method to overcome the limitations of GC-O and the dilution experiment is a sensory study of aroma models (Sect. 16.6.3). 

Grosch, W. 1994. Determination of potent odorants in foods by aroma extract dilution analysis (AEDA) and calculation of odor activity values (OAVs). Flavour Fragrance J. 9 147-158. 

At a meeting in Germany in 1983, the idea of using repeated sniffs of sequentially diluted samples, now generally called dilution analysis, was proposed (Acree and Barnard, 1984). This led to the publication of CharmAnalysis in 1984 and Aroma Extract Dilution Analysis (AEDA) in 1987, both of which were based on the idea of quantifying potency by dilution to threshold. Potency here is similar to the concept of titer or the amount of dilution necessary to... 

ACS American Chemical Society AED atomic emission detection AEDA aroma extract dilution analysis AMC 7-amido-4-methylcoumarin ANS anilinonapththalene sulfonate AOAC Association of Official Analytical Chemists... 

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],... 

During AEDA, interactions between the odorants are not taken into consideration, since every odorant is evaluated individually. Therefore, it may be possible that odorants are recognized which are possibly masked in the food flavor by more potent odorants. Furthermore, the odor activity values only partially reflect the situation in the food, since OAVs are mostly calculated on the basis of odor thresholds of single odorants in pure solvents. However, in the food system, the threshold values may be influenced by nonvolatile components such as lipids, sugars or proteins. The following examples will indicate that systematic sensory model studies are important further steps in evaluating the contribution of single odorants to the overall food aroma. 

By AEDA the four odorants shown in Figure 9 were detected with the highest FD-factors in dill herb [33], A mixture of these compounds, dissolved in water at the same concentration ratios occurring in the herb (Table 16) very much resembled the typical odor of the dill herb. If (S)-a-phellandrene or the dill ether (B and A Fig. 9), respectively, were omitted, the mixture lost its typical odor note. On the contrary, omission of myristicin and methyl 3-methylbutanoate (D and C Fig. 9) did not significantly influence the overall dill herb aroma of the model mixture [33, 66], The data indicated that (S)-a-phellandrene and the dill ether are the character impact compounds of the dill herb. Since, on the basis of AEDA or calculation of OAVs further odorants have been shown to contribute to the dill herb flavor [33, 66], the results of the simulation experiments revealed that obviously the two monoterpenes are able to mask the flavor contributions of these compounds. 

In order to evaluate the best temperature and time of baking process, Silva et al. (2008) used an expert panel to analyze seven descriptors, including dried fruit, nutty, baked, oak, mushroom, and brown sugar. The optimal temperature and time of baking process respecting the specificity of Madeira winemaking are considered 45 °C for 4 months. On the basis of aroma extract dilution analysis (AEDA), several Maillard byproducts, such as Sotolon, 2-furfural, 5-methyl-2-furfural, 5-ethoxy-methyl-2-furfural, methional, and phenylacetaldehyde, were identified in both Malvasia and Sercial wines under study which may explain the baked, brown sugar, and nutty odor descriptors. 

The volatiles of fresh leaves, buds, flowers and fruits were isolated by solvent extraction and analysed by capillary gas chromatography-mass spectrometry. Their odour quality was characterized by gas chromatography-olfactometry—mass spectrometry (HRGC-O-MS) and aroma extract dilution analysis (AEDA). In fresh bay leaves, 1,8-cineole was the major component, together with a-terpinyl acetate, sabinene, a-pinene, P-pinene, P-elemene, a-terpineol, linalool and eugenol. Besides 1,8-cineole and the pinenes, the main components in the flowers were a-eudesmol, P-elemene and P-caryophyllene, in the fruits (EJ-P-ocimene and biclyclogermacrene, and... 

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. 

The intensity of aroma compounds found by AEDA and CHARM may be determined with further accuracy by subjecting them to odor unit (also called odor activity value) measurement.71,72 This is done by first measuring the odor threshold of a compound while the concentration of this compound in the specimen is determined using internal standards (for instance, isotopic samples in contemporary approach). Dividing the latter concentration with the odor threshold will give the odor unit value, naturally being higher when a compound better contributes to the total aroma. 

Rice is an important calorie source mainly in Asia and also throughout the world. Some rice cultivars are especially rich in 2-acetyl-1-pyrroline (119) content and are referred to as Kaori-mai (fragrant rice).142 Bread is also recognized to play a major role in the human diet. The aroma of bread differs substantially between the crust and the crumb, and both of them have been analyzed by AEDA method.143,144 Maize145 is respected as the staple food in Mexico and southern Africa and is also consumed in various forms throughout the world (for instance, popcorn) (Table 15). 

The composition of the aroma of coffee is extremely complex with more than 900 compounds determined146,147 (see Chapter 3.25). The aroma of tea is greatly influenced by the degree of fermentation (green tea148 and black tea149 to mention a representative example) (see Chapter 3.23). Research of cacao mass volatiles using AEDA was also conducted (Table 16).150... 

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)... 

Fang, Y, and Qian, M. (2005). Aroma compounds in Oregon Pinot Noir wine determined by aroma extract dilution analysis (AEDA). Flav. Frag. J., 20, 22-29. 

By using aroma extract dilution analysis (AEDA) of the volatile fractions of fresh and stored butter oil, Widder et al. (29) determined diacetyl, butanoic acid, 8-octalactone, skatole, 8-decalactone, cw-6-dodeceno-8-decalactone, l-octen-3-one, and l-hexen-3-one as potent contributors to the flavor of butter oil. The concentration of l-octen-3-one, trani-2-nonenal, and i-l,5-octadien-3-one increased during the storage of the butter oil at room temperature. 

Table 5 shows the sensory evaluation by Schieberle et al. (30) of the different kinds of butter, namely, Irish sour cream (ISC), cultured butter (CB), sour cream (SC), sweet cream (SwC), and farmer sour cream (ESC). It revealed ISC butter and ESC butter with the highest overall odor intensities. Table 5 shows that 19 odor-active compounds were detected by aroma extract dilution analysis (AEDA) in a distillate of the ISC butter. The highest flavor dilution (ED) factors have been found for 5-decalactone, skatole, i-6-dodeceno-y-lactone, and diacetyl followed by trany-2-nonenal, cw,c -3,6-nonadienal, c/i-2-nonenal, and l-octen-3-one. 

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. 

---