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Keywords:

  • volatile compounds;
  • flavour chemistry;
  • cashew apple;
  • Anacardium occidentale;
  • dynamic headspace;
  • gas chromatography/olfactometry;
  • gas chromatography/mass spectrometry

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

The headspace volatile components of the juice of cashew apples from a commercial Brazilian dwarf genotype were separated by high-resolution gas chromatography and identified by GC/MS. Five judges evaluated the GC effluents using the Osme technique in order to determine the importance of each compound to the characteristic cashew aroma. Esters methyl 3-methyl butanoate, ethyl 3-methyl butanoate, methyl butanoate, ethyl butanoate, ethyl trans-2-butenoate and methyl 3-methyl pentanoate were important to the sweet, fruity and cashew-like aroma. Cis-3-hexenol, hexanal and 2-methyl-2-pentenal presented different green notes. In spite of the flame ionisation detector being unable to detect sulphur compounds, the olfactometric analysis revealed chromatographic regions where sulphur-like odours were perceived by the Osme sensory panel. The most intense unpleasant odour was due to 2-methyl butanoic acid, which was described as very stinky. The sensory panel showed good olfactory sensitivity and reproducibility. Sensory and instrumental data correlation allowed a greater understanding of the role of several volatile compounds in the sensory quality of the juice. Copyright © 2003 Society of Chemical Industry


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

The cashew tree (Anacardium occidentale L) is a tropical plant of special nutritional interest. The nut (the true fruit) has excellent sensory properties and is widely consumed all over the world, while the stalk (pseudofruit), also called cashew ‘apple’, has a high vitamin C content, averaging three to six times that of orange juice.1, 2 Despite its high level of astringency, cashew apple can be consumed raw and also shows good characteristics for industrialisation owing to its fleshy pulp, soft peel, lack of seeds, high sugar content and strong exotic flavour.

The first study published on the volatile aroma compounds of cashew apple was by MacLeod and Troconis.3 Using a modified simultaneous distillation/extraction (SDE) technique, they detected 46 volatile compounds in fresh material cultivated in Venezuela. Terpene hydrocarbons were the major group of compounds (38%), and car-3-ene was the major constituent (24.3%). Five aldehydes comprised together 26% of the essence. Based on the aroma description of each compound and their concentrations, hexanal, car-3-ene, limonene, trans-2-hexenal and benzaldehyde were considered important contributors to the total aroma.

Analysing the volatile composition of Brazilian cashew apple juices using a dynamic headspace technique, Maciel et al4 obtained quite different results. Esters were the main chemical class, and aldehydes and terpenes were detected in low numbers and concentrations. Sulphur-containing compounds such as dimethyl sulphide, dimethyl disulphide and dimethyl trisulphide were also detected. By sniffing the chromatographic effluents, the authors associated methyl butanoate, ethyl butanoate and ethyl isovalerate (ethyl 3-methyl butanoate) with the sickly sweet and fruit flavours, whilst isovaleric and isobutyric acids were associated with the pungent/sour odour of cashew apple.

In order to clarify whether the chemical differences between the cashew apple volatiles from the Venezuelan/SDE extract3 and those from the Brazilian/headspace extract4 were due to the methodology employed or to species variation, Bicalho et al5 analysed an SDE extract of Brazilian material to provide comparative data. They characterised and quantified 62 free volatile compounds: esters (40%), terpenes (20%), hydrocarbons (14%), fatty acids (9%), aldehydes (8%), alcohols, lactones, ketones and phenols. No car-3-ene was detected in the Brazilian/SDE extract, supporting the authors' conclusion that the differences found in the literature between Brazilian and Venezuelan cashew apple volatiles depend more on genetic variability than on the method of extraction.

However, Bicalho et al5 did not carry out olfactometric analysis to determine the sensory quality of the compounds. In fact, none of the previous authors who used the sniffing technique were able to make positive deductions about the individual contribution of each compound to the characteristic cashew apple flavour, because sniffing data are qualitative, providing only a description of a compound's odour and not its intensity.

In an effort to overcome the limitations of the sniffing technique, other gas chromatography/olfactometry (GCO) techniques have been developed, eg charm analysis,6 aroma extraction dilution analysis (AEDA)7 and Osme.8 Charm and AEDA are dilution methods based on thresholds rather than on the psychophysical estimation of individual odour intensities and have been criticised for this.9 According to Piggot,10 Osme is a more satisfactory GCO approach. With Osme, judges directly record the odour intensity and duration time of each odour-active compound in a time–intensity device, while describing its odour quality. The plot of retention index versus odour intensity, called an Osmegram, represents the significance of each compound in the food aroma, with a higher peak and a larger area under the peak suggesting greater importance.

The purpose of this work was to study the volatile composition of the cashew apple juice headspace and determine which compounds were important to the formation of its characteristic aroma by means of Osme principles and novel techniques of computerised data collection.

EXPERIMENTAL

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

Raw material

Cashew apples from an irrigated dwarf CCP 76 cashew clone were harvested in Paraipaba-Ceará State, Brazil early in the 1999 harvest season and transported by air to Campinas, São Paulo. Three batches of 5 kg each were received at the laboratory in consecutive weeks. After removing the nut, the juice was prepared in a blender and filtered using a cotton cloth.

Isolation of volatile compounds

The volatile compounds from the headspace of the cashew apple juice were swept by vacuum (70 mm Hg) to a Porapak Q trap for 2 h and then eluted with 300µl of acetone, according to the general methodology described by Franco and Rodriguez-Amaya11 and adapted to cashew wine and cashew juice.12 The acetone employed was pure, chromatographic grade (Em Science, Merck, Darmstadt, Germany). The Porapak Q polymer (80–100 mesh) was obtained from Waters Associates Inc (Milford, MA, USA). Prior to use in the experiment, the polymer was heated at 170 °C for 48 h in a flow of pure nitrogen at 30 ml min−1. After the addition of 30% w/w NaCl to a 300 g juice aliquot, the solution was put into the collecting apparatus. The salt was previously heated at 200 °C for 2 h. Three samples were prepared for each lot, which were either analysed immediately or kept in sealed flasks under refrigeration (−18 °C).

Gas chromatographic analysis

Compounds were separated on a VA-Wax (Varian, Walnut Creek, CA, USA) bonded phase (PEG 20M), fused silica capillary column (30 m length, 0.25 mm id, 0.25 µm film thickness) in a Varian model 3800 gas chromatograph. The splitless mode injector was maintained at 200 °C and the flame ionisation detector (FID) at 250 °C. Hydrogen was the carrier gas at a flow rate of 1.5 ml min−1. The oven temperature was set at 50 °C, held for 8 min, programmed to 110 °C (4 °C min−1) and then to 200 °C (16 °C min−1). The injected volume was 2 µl.

Gas chromatography/mass spectrometry

The volatile compounds were identified in a Shimadzu model 17-A gas chromatograph (Kyoto, Japan) coupled to a Shimadzu model QP-5000 mass spectrometer (GC/MS) at an MS ionisation voltage of 70 eV and 1 scan s−1 MS scan range. Column and oven conditions were the same as those used for the chromatographic analysis. Helium was the carrier gas at a flow rate of 1.5 ml min−1.

Retention indices

A standard mixture of paraffin homologues C9–C19 (Polyscience 211C kit, Chicago, IL, USA) was prepared using hexane as solvent. Co-injection of sample and standard mixture provided retention indices under the same chromatographic conditions.

Identification of compounds

Identification was made by matching the computerised library provided with the equipment or published mass spectra with those of the unknowns, and also by comparison of experimental and theoretical Kováts retention indices.13, 14 Identification was considered tentative when it was based only on mass spectral data. Compounds that had their identities confirmed by a match of retention indices and mass spectra of authentic chemicals purchased from commercial sources were considered positively identified.

Gas chromatography/olfactometry

The odour evaluation of cashew juice volatile compounds was achieved by Osme.8, 15 For the sensory evaluation of the GC effluents the Varian chromatograph was modified so that the column was moved from the FID to another detector base, but without the flame. A sniffer consisting of a 60 cm × 1 cm silanised glass tube (with Sylon CT, Supelco) was set on top of this detector base. Humidified, heated (28 °C) and charcoal-filtered air flowing through the tube at 41 min−1 collected the GC effluents continuously emerging from the column and delivered them to the judges for evaluation. The chromatographic conditions were the same as those described above.

Osme data acquisition

Five judges (four women and one man) ranging in age from 25 to 40 years responded to the intensity of the stimulus by using a time–intensity device with a 10 cm unstructured scale ranging from none to extreme, which was manipulated by the mouse of a personal computer. Time and intensity values were registered and stored in a data collection software system named SCDTI (Sistema de Coleta de Dados Tempo-Intensidade) developed at UNICAMP, Campinas, Brazil. At the same time the researchers collected verbal descriptions of the quality of each odorant. Each sample was repeated three times by each judge, each replicate representing a different GC run. The sniffing time for each run was 30 min. Linalool was added in every run as an internal odour standard in order to monitor the sensory panel and help in locating the perceived odours in the chromatogram.

Judge selection and training procedure

Judges were selected from among students of the Food Science and Food Technology Departments at UNICAMP on the basis of availability, interest and ability in discriminating the intensity of cashew apple juice aroma.16 Cashew apple juice samples were served at different dilutions in three replications. Subjects were asked to rate the intensity of cashew aroma using an unstructured 10 cm scale. Selected judges showed statistical significance at p < 0.15 for samples and showed no significance for repetitions (p > 0.05). More details of this procedure are given by Franco et al.12 The training procedure consisted of three Osme sessions prior to data collection, enabling judges to become familiar with the time–intensity device, the unstructured scale and the sensory properties of the compounds to be evaluated.

Osme data analysis

For each odorant in each run the software provided: (a) the odour peak, by plotting the retention time vs the odour intensity value; (b) the odour duration time; (c) the maximum odour intensity (Imax); and (d) the area under the odour peak. The combination of all this information across the peaks provided the sample Osmegram, which was the individual aromagram of each isolate, as assessed by the use of the Osme technique, by each judge. The retention times (time corresponding to Imax) of odour-active peaks were converted to indices.

The Osme data analysis as described by Sanchez et al17 was modified. In the present study, to summarise the Osme panel results in a ‘consensus Osmegram’, all odour peaks detected at least once by a judge were computed as actual peaks. The values for time, intensity and area under the peak were averaged for the 15 analyses (five judges, three replications). When a judge could not detect a certain compound, the intensity and area under the peak were considered as zero ratings in the averaging process. As a consequence, all peaks reported during the analysis sessions are present in the aromagram.

Reproducibility of sensory panel

Reproducibility for each compound was estimated by assessing the standard deviation of the initial and final times, time of maximum odour intensity, duration time, maximum odour intensity rating and area under the odour peak.

RESULTS AND DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

FID chromatogram response

The volatile composition of cashew apple juice is shown in Table 1. Fifty-eight compounds were detected in the cashew apple juice samples by high-resolution gas chromatography. The volatile compounds of the cashew apple clone CCP 76 were predominantly esters (42% of total compounds, corresponding to ∼50% of the total area), followed by aldehydes (14%, corresponding to ∼32% of the total area). Similar results were found by Maciel et al4 and Bicalho et al,5 who detected a great variety of ethyl and methyl esters in Brazilian cashew apples.

Table 1. Odour-active and non-active compounds in cashew apple juice detected by FID and Osme, with retention index, odour descriptors, maximum odour intensity (Imax) and relative area percentage of both chromatogram and Osmegram peaks
PeakCompoundRetention indexOdour descriptorsImax% area Osme% area FID
  • NI, not identified.

  • a

    Compound tentatively identified.

  • b

    Compound identified by MS and retention index.

  • c

    Compound positively identified (pure standard).

  • nq, not quantified owing to being mixed with the solvent peak in some runs; nd, not detected by FID; tr, detected in trace amounts (<0.1%).

a <900Chlorine solution, dried cashew1.180.26nd
1Ethyl acetateb <900Dried cashew, wet cloth, solvent4.883.12nq
2Ethyl propanoateb  950Sweet1.230.27nd–0.35
3NI  965Sweet, nail polish, plastic, fruity5.322.670.27
4Methyl butanoateb  974Sweet, fruity, caramel, overripe fruit3.721.392.05
b 1005Plastic, sweet, pineapple, irritating3.481.95nd
5NI 1016Sweet, fruity, nail polish, strawberry3.822.291.92
6Methyl 3-methyl butanoateb 1025Cashew, sweet, plastic, stinky5.203.689.72
7NI 1035Plastic, stinky, rotten fruit, sweet3.161.51tr
8Ethyl butanoateb 1042Sweet, cashew apple, fruity, ester4.793.358.47
9Ethyl 2-methylbutanoateb 1057Cashew, sweet, floral, fruity, apple4.411.770.93
10NI 1059Not detected by Osme0.34
11Ethyl 3-methyl butanoatec 1073Cashew, sweet, fruity, ripe fruit5.134.3416.70
12Hexanalb 1085Green, grassy, herbal6.544.467.68
13Methyl 2-butenoateb 1103Not detected by Osme0.36
14Isoamyl acetatec 1111Plastic, unpleasant, solvent, green3.522.900.69
15Methyl 3-methyl pentanoateb 1130Sweet, cashew, fruity3.421.400.40
16Ethyl pentanoatec 1140equation image5.043.110.51
17NI 11430.45
182-Methyl-2-pentenala 1149Green, grassy, herbal, green cashew5.034.839.27
191-Butanolb 1157Not detected by Osmetr
20Ethyl trans-2-butenoatec 1169Cashew, sweet, ripe fruit, fruity4.582.641.31
21Ethyl 3-methyl pentanoatea 1181Cashew, sour, unpleasant1.791.520.33
22N-Amyl acetateb 1183Sweet0.500.150.19
23Methyl hexanoateb 1188Cashew, sweet, eucalyptus1.751.100.88
24Methyl 2-methylene butanoatea 1190Not detected by Osme1.52
253-Hexanolb 1197Not detected by Osme0.95
26Trans-2-hexenalb 1214Pentatomidae bug, nutty, sweet, floral4.542.9514.27
27Ethyl hexanoatec 1222Fruity, sweet, cashew, minty2.401.021.44
28Ethyl 2-methyl-2-butenoateb 1229Cashew, sweet, fruity, minty, pineapple cake3.621.662.62
292-Hexanolb 1232Not detected by Osmend–tr
303-Methyl-1-butanolb 1237Smokey, overripe cashew, unpleasant1.930.593.23
31Methyl 2-hexenoatea 1272Not detected by Osmetr–0.12
32Octanalb 1278Eucalyptus, citric, nut oil, minty, green3.001.46tr
331-Pentanolc 1260Not detected by Osmetr–0.14
34Ethyl trans-3-hexenoateb 1287Green1.601.030.23
35NI 1295Glue, mould, wet cloth, cashew2.941.81tr
363-Hydroxy-2-butanoneb 1296Sweet0.270.070.46
376-Methyl 5-hepten-2-oneb 1325Not detected by Osmetr–0.16
38Ethyl trans-2-hexenoateb 1328Sweet0.320.08tr–0.12
c 1359Sulphury, unpleasant, butane gas, rotten fruit4.552.01nd
391-Hexanolc 1362Not detected by Osmend–0.14
40Cis-3-hexenolb 1370Green, fruity, acid, citric6.265.060.65
41Nonanalc 1380Sweet, perfume, nut oil, plastic3.291.87tr
422-Butoxy-ethanolb 1391Reminds of cashew0.620.693.35
43NI 1417Plastic, Pentatomidae bug1.470.57nd–tr
44Ethyl octanoatec 1429Fruity, coconut, floral2.501.710.12
d 1438Woody, floral, fruity0.980.26nd
45Acetic acidb 1447Acetic, acid, fermented fruit2.091.150.89
e 1457Plastic, wet cloth1.962.65nd
46Benzaldehydec 1498Plastic, green, fruity, cashew2.920.910.41
f 1528Waxy, woody1.930.63nd
47Ethyl 2-hydroxy-4-methyl pentanoateb 1547Not detected by Osme0.17
SLinalool (internal standard) 1559Papaya, perfume, lily6.45
481-Octanolc 1567Not detected by Osmend–tr
49aNI 1583Floral, perfume, green, citric4.85equation image 
49bNI 1592Spicy, bell pepper, green0.802.92
49cNI 1605Cashew, fruity, floral, fresh7.72 
50Acetophenoneb 1637Overripe cashew, unpleasant0.570.200.12
51Ethyl benzoateb 1653Not detected by Osmend–tr
523-Methyl butanoic acidb 1666Not detected by Osme0.15
532-Methyl butanoic acidc 1674Stinky, sweaty, dirty socks, dried cashew7.899.033.01
54NI 1692Pentatomidae bug, plastic0.950.28tr–0.24
554-Ethyl benzaldehydec 1731Unpleasant0.970.92tr
56γ-Hexalactoneb 1750Waxy, green, acid0.660.880.30
g 1839Cashew, acid, unpleasant0.730.56nd
57NI>1900Not detected by Osme1.28
58δ-Octalactoneb>1900Green0.961.430.15
h>1900Green, green fruit1.020.20nd

Major compounds were ethyl 3-methyl butanoate (16.70%), trans-2-hexenal (14.27%), methyl 3-methyl butanoate (9.72%), 2-methyl-2-pentenal (9.27%), ethyl butanoate (8.47%), hexanal (7.68%), 2-butoxy-ethanol (3.35%), 3-methyl-1-butanol (3.23%) and 2-methyl butanoic acid (3.01%).

Osme response

Fig 1 shows the consensus Osmegram compared with the FID chromatogram of the cashew apple isolate. There were basically three areas of the Osmegram with significant odour importance. There was a large concentration of odour-active peaks at the beginning of the chromatogram, ie the region corresponding to compounds of higher volatility; two compounds of high odour impact in the central part of the chromatogram; and another odour-active area in the retention index region between 1500 and 1700.

thumbnail image

Figure 1. (a) Gas chromatogram and (b) consensus Osmegram of cashew apple isolate. A, acetone; S, internal Osme standard; I, impurity of solvent. Compounds identified by small letters were not detected by FID.

Download figure to PowerPoint

Some of the compounds that showed a significant relative area in the chromatogram also showed an intense odour. However, the Osmegram revealed a different profile as compared with the gas chromatogram. Most of the odour-active compounds perceived in cashew apple by the GCO panel as having moderate and high odour intensities were present in the chromatogram in very low relative areas. Almost 50% of the total Osmegram area corresponded to peaks where little (traces to 1%) or no response was noted by the FID. Compounds perceived by the panel but not detected by the FID are labelled with small letters. On the contrary, compounds such as 3-methyl-1-butanol and 2-butoxy-ethanol with high relative areas in the chromatogram showed low or no odoriferous importance.

In Osme analysis the odour intensity and the area under the odour peak of each compound in the GC effluent are associated with its odorant potency. High Imax and/or large area are indicative of an important compound in the aroma isolate, while low odour intensity and/or small peak area are indicative of a minor flavour contributor in the given sample.

Since peaks 53 (identified as 2-methyl butanoic acid and described as stinky, sweaty, dirty socks), 40 (cis-3-hexenol described as green, fruity), 12 (hexanal described as green, grassy, herbal) and 49c (described as cashew, fruity, floral) showed the highest Imax values, rating between 6 and 8 on the 10 cm scale, they may represent the major contributors to the overall aroma and flavour of cashew.

In Osme runs, judges perceived three odour-active peaks (49a, 49b and 49c) with distinct odour characteristics in the chromatogram region corresponding to peak 49 (retention index around 1600), indicating that this peak is a non-resolved mixture of compounds. Mass spectral data of peak 49 were indicative of the presence of sesquiterpene hydrocarbons.

A great part of the odour-active peaks of the cashew apple isolate imparted moderate odour intensities, as was the case of the methyl and ethyl esters at the beginning of the chromatogram. Compounds methyl 3-methyl butanoate (peak 6), ethyl 3-methyl butanoate (peak 11), ethyl butanoate (peak 8), ethyl trans-2-butenoate (peak 20), ethyl 2-methyl butanoate (peak 9), methyl butanoate (peak 4), methyl 3-methyl pentanoate (peak 15) and ethyl 2-methyl-2-butenoate (peak 28) were described as ‘cashew’, ‘sweet’, ‘floral’ and ‘fruity’. Ethyl pentanoate (peak 16) was perceived together with peak 17 (not identified) as showing green, herbal and grassy notes.

Peaks 3 and 5 could not be identified because their mass spectra were contaminated by the neighbouring peak, but they were distinctly perceived by the Osme panel, being considered to be important to the sweet aroma of cashew apple (moderate intensity but high area under the peak). Both of them were described as ‘sickly sweet’, ‘nail polish’ and ‘fruity’. Peak 5 was also described as a strong ‘artificial strawberry’ flavour.

Some aroma peaks, although imparting a low odour intensity to the GC effluent (rating Imax < 3.5), were perceived for a long period of time, showing a high area under the peak, and were considered as important contributors to the overall cashew aroma. This was the case for peaks 21 (ethyl 3-methyl pentanoate/cashew, sour), 32 (octanal/eucalyptus, citric, minty), 41 (nonanal/sweet, perfume, nut oil) and 44 (ethyl octanoate/fruity, coconut, floral), amongst others.

Cashew apple juice was shown to have several potent flavour compounds which were not detected by the FID but were perceived by the GCO panel (compounds labelled with small letters). Especially important were peaks ‘b’ and ‘c’, which showed moderate odour intensity and significant area.

Several compounds perceived by the sensory panel but not present in the chromatogram were described as having sulphurous notes, suggesting the presence of sulphur compounds in extremely low concentrations (in general, sulphur compounds have very low threshold values). Their detection requires a specific detector, which was not available when this work was carried out. These compounds were not detected by the mass spectrometer either.

There were many other compounds that imparted unpleasant notes to cashew aroma. 2-Methyl butanoic acid showed a very strong and prolonged stinky odour, being the odour peak with the highest odour intensity and largest area under the peak. The aromas of peaks 7, 30, 35, 43, 54 and 55, amongst others, were much lower in intensity, but possible interactions between these odorants, described by terms such as ‘plastic’, ‘stinky’, ‘rotten fruit’, ‘wet cloth’ and ‘bug’, cannot be disregarded as contributors to the cashew apple juice aroma.

The frequency of use of the descriptor ‘cashew’ was high (50–60%) for compounds ethyl 3-methyl butanoate, ethyl trans-2-butenoate and 49c, but it was also used for a number of other individual compounds in a lower frequency percentage. The cashew descriptor appeared along with other terms such as sweet and fruity (peaks 6, 8, 9, 15, 23, 27, 28 and 46), which could represent an inability of individual judges to find other appropriate terms. However, it was observed that judges also used cashew aroma with terms describing unpleasant odours (peaks ‘a’, 1, 6, 21, 35, 53 and ‘g’) that could be due to co-eluted and undetected compounds, possibly sulphur-containing ones. Taking into account that cashew apple aroma has been described, by sensory descriptive analysis,18 basically as ‘pungent’ and ‘sweet’, we can presume that the perception of strong sweet notes together with unpleasant notes was associated with the characteristic natural cashew apple aroma.

Overripe cashew odour was associated with 3-methyl-1-butanol and acetophenone. Cashew apple is a non-climacteric fruit,19 but peduncles travelled from Fortaleza to Campinas (about 3000 km away) and could arrive at the laboratory presenting some incipient fermentation.

A comparison of the present results with those from previous works, where olfactometry consisted only of sniffing the effluents, readily evidences the advantages of the Osme technique. Maciel et al4 could not make a clear correspondence between the identified compounds and sniffing descriptors. They found that esters such as methyl butanoate, ethyl butanoate and ethyl 3-methyl butanoate (ethyl isovalerate) contributed the ‘sickly sweet and fruity’ flavours, similar to the present work, but they also concluded that isovaleric and isobutyric acids contributed the ‘pungent/sour odour, characteristic of acids’. In the current work, 3-methyl butanoic acid was detected in a low concentration, eluting just before 2-methyl butanoic acid. During the olfactometric runs, these two compounds may have been perceived together as a single peak, but the odour quality of isovaleric acid was not described as sour, characteristic of acids, but rather as sweaty and very stinky.

In turn, MacLeod and Troconis3 reported several odour descriptors similar to those used in the present work, but with the exception of hexanal and cis-3-hexanol (both described as ‘green’) the perceived aromas were associated with different compounds. The authors found it impossible to make any positive deductions concerning which compounds might be important to the characteristic cashew apple flavour. Hence, as only benzaldehyde was described as ‘cashew’, it was considered an important component of the essence.

Judges' performance and reproducibility

The reproducibility of judges was estimated by assessing the standard deviations of individuals. Judges showed excellent reproducibility in recording the time in which they perceived each eluted compound. The individual standard deviations corresponding to the initial time, final time and time corresponding to the odour maximum intensity ranged from 0.3 to 5.0 s. Higher deviations can be associated with variations in the retention times of compounds, commonly observed from one chromatographic run to another.

The lack of reference samples caused a greater variability in maximum odour intensity ratings. The individual standard deviations of this variable ranged from 0.02 to 2.84 on a 10 cm scale. In turn, the standard deviations calculated for the sensory panel (assessed by the mean values for each judge) averaged 1.85. In this case, one can take into account that, when a judge could not perceive a particular compound, the methodology rated it as zero, causing a greater deviation than would be expected if the mean were calculated without the missing points. Besides, it is quite acceptable, even amongst trained judges, that individuals use different portions of the scale to express the same perception.20, 21

Differences in individual olfactory sensitivity were probably the reason for the high standard deviations observed within the sensory panel for the duration time recordings of the same odour-active compound (panel standard deviations reached 11 s). Such variability, together with that observed for the maximum intensity ratings, consequently caused great variability of the areas under the odour peak ratings.

Judges showed good performance in identifying odour quality for the same peak, presenting good olfactory memory and good reproducibility in using descriptive terms in all repetitions. There was also good agreement of judges on descriptor characteristics of GC effluents. It must be emphasised that all judges perceived the internal standard, linalool, in all repetitions, describing it as ‘papaya’ (eight times in the 15 analyses), ‘perfume’ (four times) and ‘lily’ (three times).

Observations made in this work regarding the sensory panel agree with the results reported by Silva et al,15 who concluded that human subjects are reliable ‘instruments’ for reporting odour quality and intensity. According to those authors, it appears possible to estimate the relative significance of odorants present in an aroma extract by directly assessing their odour intensities from the GC effluent through the use of Osme.

CONCLUSIONS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

GC/MS and GCO analyses confirmed that cashew apple juice has a complex aroma profile and that its typical flavour is formed from the contributions of a wide spectrum of compounds. However, Osme analysis could estimate the odoriferous importance of each compound to the overall aroma. The most important cashew volatile compounds, as assessed by Osme, can be summarised into four main categories, based on descriptors:

  • (a)
    esters and other unidentified compounds from the beginning of the chromatogram—ethyl 3-methyl butanoate, methyl 3-methyl butanoate, ethyl butanoate, ethyl trans-2-butenoate, methyl butanoate, methyl 3-methyl pentanoate and peaks 3 and 5—which were related to the descriptors ‘cashew’, ‘sweet’ and ‘fruity’;
  • (b)
    cis-3-hexenol, 2-methyl-2-pentenal and hexanal, responsible for different ‘green’ notes;
  • (c)
    compounds labelled 49a and 49c, probably sesquiterpenes, which showed strong ‘floral’ and ‘cashew’ odours respectively;
  • (d)
    compounds associated with unpleasant odour descriptors–2-methyl butanoic acid (strongly ‘stinky’) and some unidentified or undetected compounds.

Acknowledgements

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES

The authors are grateful to the sensory judges from the Departments of Food Science and Food Technology (UNICAMP) who contributed their time and effort. The authors are also grateful to FAPESP for financial support of this project and to CNPq for a postgraduate scholarship.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. EXPERIMENTAL
  5. RESULTS AND DISCUSSION
  6. CONCLUSIONS
  7. Acknowledgements
  8. REFERENCES
  • 1
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