Aroma extract concentration analysis

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]. 

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

Grosch, W., Kerscher, R., Kubickova, J., JageUa, T. (2001) Aroma extract dilution analysis versus aroma extract concentration analysis. In Leland, J.V., Schieberle, R, Buettner, A., Acree, T. (eds.) Gas Chromatography Olfactometry The State of the Art. ACS Symposium Series 782, pp. 138-147... 

The aroma extract dilution analysis of concentrates prepared from the crusts of wheat and rye breads revealed fourty-three odorants in rye and thirty-two in wheat extracts (37). 

If more exact data are desired, the results obtained by aroma extract dilution analysis must be complemented by quantitative measurements. Quantification of odorants is a difficult task, since the concentration of the odorants showing high FD-factors can be extraordinarily low. 

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)... 

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. 

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. 

It is well known that the aroma extract dilution analysis (AEDA) is a nsefnl method for the recognition of the odor quality and odor intensity of each component." Especially the AEDA is a useful method for the identification of trace amonnts of the component that significantly affects the flavor of tea drinks. The odor intensity of the flavor component is expressed by the flavor dilution (ED) factor, that is, the ratio of the concentration of the flavor component in the initial extract to its concentration in the most dilnte extract in which odor was detected by gas chromatography-olfactometry (GC-0). Therefore, hereafter, from the viewpoint of sensory evalnation, the change in the flavor of tea drink dnring heat processing by AEDA will be mainly discnssed. Furthermore, in order to inhibit flavor deterioration of tea drink, the stndy of flavor precnrsor in a variety of foods, including tea drinks, will be proposed. 

Another powerful technique known as aroma extract dilution analysis is used to determine the most significant odor and flavor compounds in a complex mixture in a food product. This method determines the odor activity of volatile compounds in an extract eluted from a high-resolution capillary GC-SP column (see Table 11.9). The odor activity or impact of a compound is expressed as the flavor dilution factor (FD), which is the ratio of its concentration in the initial extract to its concentration in the most dilute extract in which the odor can be detected by GC-SP. However, the information from this technique may be of limited practical value, because it ignores the significant effect of food matrices on flavor and odor perception of mixtures of flavor and odor compounds. Advanced instrumental techniques have been developed for flavor analysis during food consumption. These techniques permitting direct mass spectrometry at atmospheric pressure are discussed in Chapter 6. 

Two techniques based on dilution have been developed CharmAnalysis by Acree and coworkers (6,12,13) and aroma extract dilution analysis (AEDA) by Grosch and his group (7,14,15). Both evaluate the odor activity of individual compounds by sniffing the GC effluent of a series of dilutions of the original aroma extract. Both methods are based on the odor-detection threshold. The dilution value obtained for each compound is proportional to its OAV in air, i.e., its concentration. Several injections are required to reach a dilution of the aroma extract in which odorous regions are no longer detected. 

Aroma analysis is most often performed utilizing GC-MS. This demands separation of volatile constituents from nonvolatile matrices. Additionally, higher concentrations of analytes are favorable to allow detection of trace key compounds.16,64,65 82 Therefore, various preparation methods derived from aroma extract production were developed. The composition of the concentrate may differ depending on the method used and thus selected to accommodate the aim. 

In the early 90s, a new technique called solid-phase-micro extraction (SPME), was developed (Arthur and Pawliszyn, 1990). The key-part component of the SPME device is a fused silica fiber coated with an adsorbent material such as polydimethylsiloxane (PDMS), polyacrylate (PA) and carbowax (CW), or mixed phases such as polydimethylsiloxane-divinylbenzene (PDMS-DVB), carboxen-polydimethylsiloxane (CAR-PDMS) and carboxen-polydimethyl-siloxane-divinylbenzene (CAR-PDMS-DVB). The sampling can be made either in the headspace (Vas et al., 1998) or in the liquid phase (De la Calle et al., 1996) of the samples. The headspace sampling in wine analyses is mainly useful for quantifying trace compounds with a particular affinity to the fiber phase, not easily measurable with other techniques. Exhaustive overviews on materials used for the extraction-concentration of aroma compounds were published by Ferreira et al. (1996), Eberler (2001), Cabredo-Pinillos et al. (2004) and Nongonierma et al. (2006). Analysis of the volatile compounds is usually performed by gas chromatography (GC) coupled with either a flame ionization (FID) or mass spectrometry (MS) detector. 

Kerscher, R., Grosch, W. (1997) Comparative evaluation of boiled beef aroma by aroma extract dilution and concentration analysis. Z. Lebensm. Unters. Forsch. 204. 3-6... 

Identified by Viani et al. (1965), the structure was confirmed by IR-spectroscopy comparison with a commercially available sample found also by Gianturco et al. (1966), Stoffelsma et al. (1968) and by Silwar et al. (1987) in the analysis of a coffee-aroma extract obtained by distillation-extraction and concentration (2.0 5.0 ppm in coffee). Procida et al. (1987) detected this ketoester in a roasted arabica but in none of the green coffees that they studied. Ramos et al. (1998) found it in a brew only after liquid-liquid extraction with pentane or methylene chloride. 

Fig. 5.13. Enantioselective gas chromatographic analysis of trans-a-ionone in aroma extracts of different raspberry fruit juice concentrates (according to Werkhoff et al., 1990) a and b samples with nature identical aroma, c natural aroma...

Later, the chemical characterisation of the volatiles from yellow passion fruit essence and from the juice of the fruit was done by GC-MS and GC-olfactom-etry (GC-O) [27]. Esters were the components found in the largest concentrations in passion fruit juice and essence extracted with methylene chloride. Analysis by GC-O yielded a total of 66 components which appeared to contribute to the aroma of passion fruit juice and its aqueous essence. Forty-eight compounds were identified in the pulp of Brazilian yellow passion fruits (Passiflora edulis f. flavicarpa) [48]. The predominant volatile compounds belonged to the classes of esters (59%), aldehydes (15%), ketones (11%), and alcohols (6%). 

The highest OAVs were found for 4-hydroxy-2,5-dimethyl-3(2H)-fura-none, followed by ethyl 2-methylpropanoate, ethyl 2-methylbutanoate, methyl 2-methylbutanoate and ( ,Z)-l,3,5-undecatriene. It is assumed that these odorants contribute strongly to the aroma of pineapples [50]. However, FD factors and OAVs are functions of the odorants concentrations in the extract, and are not psychophysical measures for perceived odour intensity [71,72]. To take this criticism into account, aroma models are prepared on the basis of the results of the quantitative analysis (reviewed in [9]) and in addition omission experiments are performed [9]. 

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