Analysis of volatile flavour compounds and acrylamide in roasted ...

Analysis of volatile flavour compounds and acrylamide in roasted Malaysian
tropical almond (Terminalia catappa) nuts using supercritical fluid extraction
Ola Lasekan *, Kassim Abbas
Department of Food Technology, Universiti Putra Malaysia, 43400 UPM Serdang, Selangor, Malaysia
article info
Article history:
Received 19 February 2010
Accepted 17 May 2010
Keywords:
Tropical almond nut
SFE
Roasting
Volatile compounds
Acrylamide
1. Introduction
abstract
Tropical almond (Terminalia catappa L.) belongs to the family
Combretaceae and is used commonly as folk medicine in South East
Asia (Mau et al., 2003) and grown for shade and ornament in Africa
(Sosulski et al., 1988). The leaves of T. catappa contains many
hydrolysable tannins such as punicalgin, punicalin, terflavins A
and B, tergallagin, tercatain, chebulagic acid, geramin, granatin B,
and corilagin (Tanaka et al., 1986). Recent, study in our laboratory
revealed that hexadecanoic acid and (Z)-9-octadecenal were the
predominant compounds in steamed tropical almond nuts
(Lasekan and Katib, unpublished). The dried raw nuts of the tropical
almond are highly relished by children in India, Malaysia and
Nigeria (Sosulski et al., 1988; Ezeokonkwo, 2007). The roasted or
boiled edible nuts have been used as snacks at tea time in Jamaica
and India (Morton, 1985). Some tribes in Malaysia, sprinkles the
roasted or steamed nuts over cereal or yogurt for breakfast.
While many studies has been carried out on the medicinal and
antioxidant activities of the leave extracts of tropical almond (Liu
et al., 1996; Chen et al., 2000), there is little or no information on
the aroma and acrylamide content of the snack items prepared
from this edible nut. Recent study (Vivanti et al., 2006) have reported
that potentially toxic acrylamide found in foods was largely
formed by heat-induced Maillard-type reactions between the amino
group of the free amino acid asparagines and the carbonyl group
of the reducing sugars such as glucose and fructose during baking
* Corresponding author. Tel.: +60 3 8946 8535; fax: +60 3 8942 3552.
E-mail address: lasekan@food.upm.edu.my (O. Lasekan).
0278-6915/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.fct.2010.05.050
Food and Chemical Toxicology 48 (2010) 2212–2216
Contents lists available at ScienceDirect
Food and Chemical Toxicology
journal homepage: www.elsevier.com/locate/foodchemtox
Considering the importance of tropical almond nuts as a snack item, a study was conducted to identify
the flavour volatiles and acrylamide generated during the roasting of the nuts. The supercritical fluid
extracted flavour components revealed 74 aroma active compounds made up of 27 hydrocarbons, 12
aldehydes, 11 ketones, 7 acids, 4 esters, 3 alcohols, 5 furan derivatives a pyrazine, and 2 unknown compounds.
While low levels of acrylamide (8–86 lg/kg) were obtained in the roasted nuts, significant
(P < 0.05) increases occurred in concentration with increased roasting temperature and time. Carboxylic
acids were the most abundant volatiles in the roasted almond nuts and less significant (P > 0.05) concentration
of acrylamide was generated with mild roasting and shorter roasting period.
Ó 2010 Elsevier Ltd. All rights reserved.
and frying. Moreover, acrylamide has not been detected in unheated
control or boiled foods, it is therefore considered to be
formed during heating at high temperatures (Tareke et al., 2002).
Conventionally, aroma constituents from processed foods are
recovered by solvent extraction. However, this technique has its
drawback. For example, substantial amounts of artefacts are generated
during the aroma extraction process from extraction solvents
and extraction assembly. Supercritical fluid extraction (SFE) which
uses carbon dioxide as the extractant has been suggested as an
alternative to organic solvent (Saito, 1995). SFE is done at shorter
time periods and the possibility of artefact generation is negligible
(Bhattacharjee et al., 2003). The aim of this study was to identify
and evaluate the volatile constituents and the acrylamide concentration
of roasted tropical almond nuts.
2. Materials and methods
2.1. Samples
Freshly harvested tropical almond fruits were obtained from the Department of
Forestry, Universiti Putra Malaysia. Intact almonds (approximately 250 g for each
treatment) were manually slit with a sharp knife and the nuts were roasted at
(100, 150 and 200 °C) in a roaster (Model Duetl-M, Probat and Emmerich, Germany)
for 5, 15 and 25 min, respectively. Samples were allowed to cool to room temperature
(28 ± 2 °C) before milling in a household food processor (Kenwood Model FP
730).
2.2. Chemical standard and reagents
Acrylonitrile-d 3 (99.5 atom% D) and Raney copper were purchased from Sigma–
Aldrich Co. (St. Louis, MO, USA). All other chemicals were of analytical grade except
for methanol, which was HPLC grade. Volatile compound standards such as: 1-oct-

anol, decanal, octanal, nonanal, hept-2-enal, (E, E)-2,4-nonadienal, (E, E)-2,4-decadienal,
hexadecanoic acid, octadecanoic acid, decanoic acid, octanoic acid, heptanone,
furfuryl octanoate were obtained from (Aldrich, Steinheim, Germany).
Gamma-dodecalactone and 2-ethyl-3,6-dimethylpyrazine were obtained from (Acros,
Organics, New Jersey, USA).
Stock standard solutions of 10 3 or 10 4 mg L 1 of each component was prepared
by dissolving the pure standard in 40% (v/v) ethanol. The samples were stored at
4 °C. Working standard solutions were prepared daily by mixing an aliquot of each
individual solution and diluting with ultra pure water (Millipore Co., Bedford, USA)
to obtain a final ethanol content of 10% (v/v).
2.3. Synthesis of acrylamide-d 3 as an internal standard
Acrylonitrile-d 3 (1 g) was dissolved in water (30 ml) and added to Raney copper
(5 g) in a flask. The mixture was stirred at 80 °C for 3 h under nitrogen atmosphere.
Acrylamide-d3 was obtained as a colourless solid (957 mg) after suction filtration
and lyophilisation. The material was purified by sublimation before use.
2.4. Extraction procedure for aroma analysis
A laboratory-scale SFE system (Thar Model 500, Thar Technologies Inc., and
Pittsburgh, PA, USA) was used in this study. The 500 ml extraction cell was made
of stainless steel (Type 316), with a stainless-steel frit. The ground almond nuts
were mixed with glass wool in the ratio of 25:1 (w/w), packed in a sample cartridge.
The filled cartridge was inserted into the thermal-controlled extraction cell. Liquefied
CO 2 was introduced into the sample cartridge through a piston pump with a
cooling jacket. Both the pressure and temperature of the cartridge were automatically
reached and maintained by a control unit according to settings. After the desired
pressure and temperature were reached, the cell was placed in the oven cavity
and connected to the manifold and the restrictors. The system was held for 30 min
under the desired conditions, and then carbon dioxide was allowed to flow continuously
through the extractor for 3 h. The flow rate of CO2 was regulated by both the
pressure-releasing valve and a thermal-controlled restrictor and monitored by a
flow metre. Extracts were finally separated from CO 2 phase and collected in a collector
at ambient temperature and atmospheric pressure. The nut residue was further
extracted with small amount of methanol added as a modifier to CO 2 in a ratio
of 1:9 (methanol:CO 2). The extracts were pooled together and stored at 18 °C for
5h.
Table 1
Characteristics of the calibration curves.
2.5. Concentration of aroma extracts
The aroma extracts obtained from the SFE, were spiked with 15 ll decanal
(internal standard) and stirred for 30 min for equilibration. The aroma extracts
were later dried over a bed of anhydrous Na2SO4 and finally concentrated to
100 ll by slowly purging nitrogen gas (commercial grade) over the sample. Samples
were stored in screw-capped glass (wrapped with Teflon tape) at 18 °C prior to
analysis.
2.6. Extraction procedure for acrylamide
Finely ground samples of tropical almond nuts (50 g) were each weighed into
an Erlenmeyer flask (500 ml) with a plug and acrylamide-d 3 solution was added
with constant shaking for 5 min. This was followed by the addition of 300 ml of
water. The mixture was homogenised at high speed for 3 min using an Ultra Turrax
(OpticsPlanet, Inc., Northbrook, IL, USA). The extract was poured into centrifuge
tubes (50 ml) and centrifuged at 20,000 rpm (48,000 g) for 20 min at 2 °C. The aqueous
phase of the supernatant was poured into plastic tubes (2 ml) and stored at
30 °C. The frozen extracts were thawed in water bath at room temperature and
centrifuged at 15,000 rpm (21,700 g) for 10 min. Each resulting supernatant was
subjected to a solid-phase extraction cartridge (I solute Multimode, 500 mg; International
Sorbent Technology, Hengoed, Glamorgan, UK), which had been conditioned
with methanol (1 ml) and water (2 ml), and eluted with water. After
discarding the first 1 ml of the eluate, 2 ml eluate were collected and used for the
LC–MS analysis of acrylamide.
2.7. GC–MS analysis
The extracts were analyzed using a Shimadzu (Kyoto, Japan) QP-5050A GC–MS
instrument equipped with a GC-17A Ver. 3 gas chromatograph with a flame ionization
detector (FID). The column was a non-polar BP X 5 (5% phenylpolysilphenylenesiloxane)
capillary columns (30 m 0.25 mm id., film thickness
0.25 lm Scientific Instrument Services, Inc., NJ, USA). Helium was used as carrier
gas at a flow rate of 1.5 ml/min, injection temperature, 280 °C; detector temperature,
320 °C; temperature program commenced at 50 °C and held for 3 min, then
raised to 280 °C at a rate of 15 °C/min, held for 10 min and then increased to
320 °C at a rate of 10 °C/min, with a final hold time of 5 min. The effluent from
the capillary column was split into 2:1 (by volume) onto two uncoated but deactivated
fused silica capillaries (50 cm 0.32 mm) leading to a FID and a sniffing port.
Compound Linear range (mg/l) Regression coefficient Linearity (LOL, %) Slope ± SD Intercept ± SD
(Z)-Hept-2-enal 0.024–3.6 0.999 99.2 0.16 ± 0.00 0.013 ± 0.00
Octanal 0.007–0.61 0.997 99.4 4.40 ± 0.07 0.123 ± 0.02
Nonanal 0.006–1.0 0.996 98.6 0.89 ± 0.01 0.021 ± 0.00
Octanoic acid 0.027–1.5 0.999 99.0 1.46 ± 0.02 0.080 ± 0.01
Decanal 0.042–11.0 0.999 99.1 0.49 ± 0.01 0.013 ± 0.02
(E,E)-2,4-Nonedienal 0.019–3.3 0.997 98.2 3.72 ± 0.06 0.39 ± 0.05
(E,E)-2,4-Decadienal 0.002–0.32 1.00 99.5 2.21 ± 0.01 0.11 ± 0.00
2-Ethyl-3,6-dimethylpyrazine 0.002–0.09 0.998 98.1 5.36 ± 0.10. 06 ± 0.00
Decanoic acid 0.002–0.30 0.996 98.8 18.72 ± 0.33 0.073 ± 0.05
Gamma dodecalactone 0.003–0.065 0.995 97.8 18.39 ± 0.01 0.09 ± 0.01
Furfuryl octanoate 0.003–0.065 0.997 98.3 43.73 ± 0.74 0.25 ± 0.03
Hexadecanoic acid 0.054–2.0 0.994 97.9 0.389 ± 0.02 0.05 ± 0.07
Table 2
Performance characteristics of the calibration curves.
O. Lasekan, K. Abbas / Food and Chemical Toxicology 48 (2010) 2212–2216 2213
Compound Analytical sensitivity Detection limit (LOD, mg/l) Quantitation limit (LOQ, mg/l) Recovery (%)
(Z)-Hept-2-enal 0.038 0.100 0.355 93.3
Octanal 0.004 0.011 0.035 90.2
Nonanal 0.022 0.063 0.209 99.7
Octanoic acid 0.021 0.059 0.185 90.6
Decanal 0.133 0.382 1.270 93.1
(E,E)-2,4-Nonedienal 0.027 0.076 0.245 90.1
(E,E)-2,4-Decadienal 0.002 0.006 0.020 93.1
2-Ethyl-3,6-dimethylpyrazine 0.002 0.007 0.023 90.6
Decanoic acid 0.004 0.010 0.038 89.7
Gamma-dodecalactone 0.002 0.005 0.018 99.1
Furfuryl octanoate 0.002 0.004 0.014 91.9
Hexadecanoic acid 0.028 0.076 0.274 90.1

2214 O. Lasekan, K. Abbas / Food and Chemical Toxicology 48 (2010) 2212–2216
Table 3
Volatile constituents of roasted (200 °C) tropical almond nuts.
Peak no. Retention time (min) Compound Odour description a
Conc. mg/kg % Total Identification methods
1 5.76 3-Ethyl-2-methyl-1-heptene 3.68 0.49 MS
2 5.82 3-Acetyl-2,5-dimethylfuran Musty-nutty 4.85 0.65 MS, odour
3 6.21 3,4,4-Trimethyl-2-hexene Fresh citrus 2.25 0.30 MS, odour
4 6.52 (Z)-Hept-2-enal Almond-like 24.05 3.21 MS, Rt, odour
5 6.90 2-Pentylfuran Beany-like 13.95 1.86 MS, odour
6 7.13 Octanal Citrus-like 3.75 0.05 MS, Rt, odour
7 7.51 Eucalyptol Camphoraceous 2.63 0.35 MS, odour
8 7.56 1-Chloro-2,3-dihydro-1H-indene 1.95 0.26 MS
9 7.82 n-Butylbenzene Sweet pungent 1.20 0.16 MS, odour
10 7.86 (E)-2-Octenal Fresh cucumber 3.98 0.53 MS, odour
11 7.94 2, 4-Dimethylheptane 2.78 0.37 MS
12 8.09 Hexachloroethane 2.63 0.35 MS
13 8.18 4-Methyl-3-heptanone 2.48 0.33 MS
14 8.28 (Z)-4-Tridecene Waxy 14.70 1.96 MS, odour
15 8.37 Nonanal Tallow fruity 18.08 2.41 MS, Rt, odour
16 8.51 1,4-Dimethyl-5-oxabicyclo [2, 1, 0] pentane 1.80 0.24 MS
17 8.88 (E)-2-Nonenal Fatty tallow 7.35 0.98 MS, odour
18 8.98 Pentylbenzene Sweet balsam 1.43 0.19 MS, odour
19 9.03 (E)-2-Decenal Orange-sweaty 2.03 0.27 MS, odour
20 9.12 Octanoic acid Sweaty 1.05 0.14 MS, Rt, odour
21 9.29 n-Udecane 1.73 0.23 MS
22 9.49 Decanal Green soapy 2.93 0.39 MS, Rt, odour
23 9.69 (E, E)-2,4-Nonadienal Fatty 1.35 0.18 MS, Rt, odour
24 9.87 1-Hexylcyclopentene 1.80 0.24 MS
25 9.95 2-Chloro-octane 1.88 0.25 MS
26 10.01 1-Undecyne Vinegar-like 4.28 0.57 MS, odour
27 10.03 Dodecamethyl-cyclo hexasiloxane 4.50 0.60 MS
28 10.10 (Z)-2-Decenal Green 32.18 4.29 MS, odour
29 10.32 Tridecane Waxy 1.88 0.25 MS, odour
30 10.45 (E, E)-2,4-Decadienal Fatty, waxy 41.55 5.54 MS, Rt, odour
31 10.71 2-Ethyl-3,6-dimethylpyrazine Chocolate 115.43 15.39 MS, Rt, odour
32 10.94 8-Methyl-1-decene 1.13 0.15 MS
33 10.98 3-Nonen-2-one Fruity 5.33 0.71 MS, odour
34 11.05 n-Decanoic acid Sweaty 13.5 1.80 MS, Rt, odour
35 11.09 (E)-2-Dodecen-1-al Citrus-metallic 15.65 2.09 MS, odour
36 11.18 Gamma Dodecalactone Fruity 0.83 0.11 MS, Rt, odour
37 11.21 1-Dodecanol Fatty,Coconut 0.98 0.13 MS, odour
38 11.24 2,3-Nonadiene 1.05 0.14 MS
39 11.27 2,4,6-Trimethyl-decane 1.05 0.14 MS
40 11.31 4-Heptenal Cream-like 5.78 0.77 MS, odour
41 11.56 11-Dodecamethyl-hexasiloxane 8.93 1.19 MS
42 11.61 Vanillin Vanilla-like 6.90 0.92 MS, Rt, odour
43 12.06 (Z)-3-Nonen-1-ol Waxy-green 0.68 0.09 MS, odour
44 12.17 Pentadecane Woody 8.03 1.09 MS, odour
45 12.20 4-Hexyl-2,5-dihydro-2,5dioxo-3-furanacetic
acid 3.08 0.41 MS
46 12.92 2,4-Bis[(trimethylsily)oxy] benzoic acid 6.90 0.92 MS
47 12.98 3,8-Dihydroxy-3,4-dihydronaphthalen-1-(2H)-one 1.28 0.17 MS
48 13.03 Unknown Solvent-like 2.48 0.33 MS, odour
49 13.83 Heptadecane Fresh green 4.13 0.33 MS, odour
50 13.90 2-Tridecanone Slightly citrus 1.95 0.26 MS, odour
51 14.03 2,6-Dimethyl-2-octene 1.95 0.26 MS
52 14.08 Unknown 4.65 0.62 MS
53 14.48 Furfuryl octanoate Fruity 3.30 0.44 MS, Rt, odour
54 14.59 2,7,19-Trimethyldodecane 2.33 0.31 MS
55 14.96 6,10,14-Trimethyl-2pentadecanone
Celery-like 1.95 0.26 MS
56 15.13 Hexadecamethyl-octasiloxane 4.20 0.56 MS
57 15.22 Butyl-2-ethylhexyl ester Fruity 6.60 0.88 MS, odour
58 15.33 3,6-Dimethyldecane 2.25 0.30 MS
59 15.43 2-Nonadecanone 2.03 0.27 MS
60 15.57 Nonadecanoic acid, methylester Rancid sweaty 1.28 0.17 MS, odour
61 15.74 Tetrahydro-6-tridecyl-2H-pyran-2-one Oily-fruity 1.35 0.18 MS, odour
62 15.88 Hexadecanoic acid Waxy 157.80 21.04 MS, Rt, odour
63 16.82 2-Pentadecanone Fresh jasmine 2.55 0.34 MS, odour
64 16.95 Dihydro-5-tetradecyl-2(3H)-furanone Fruity 4.13 0.55 MS, odour
65 17.07 (Z, Z)-9,12-Octadecadienoic acid Sweaty 19.95 2.66 MS, odour
66 17.09 (E)-9-Octadecenoic acid Sweaty 31.50 4.20 MS, Rt, odour
67 17.18 6-Heptyltetrahydro-2H pyran-2-one Fruity, oily 27.08 3.61 MS, odour
68 17.09 Octadecanoic acid 13.88 1.85 MS, odour
69 19.44 Di-n-octylphthalate 3.98 0.53 MS
70 19.81 Octadecamethyl-cyclonosiloxane 2.93 0.39 MS
71 20.22 11-(1-Ethylpropyl)heneicosane 2.48 0.33 MS

Table 3 (continued)
Peak no. Retention time (min) Compound Odour description a
Conc. mg/kg % Total Identification methods
72 20.88 Squalene Fish-like 15.38 2.05 MS, odour
73 21.22 2,6,10,14-Tetramethyl-hexadecane 5.48 0.73 MS
74 22.41 6-Hydroxy-7-n-pentadecyl-mercapto-5,8-quinolindione 15.65 2.09 MS
a Odour quality perceived at the sniffing port.
The mass spectrometer was operated in electron impact mode with the following
conditions. The source temperature was 320 °C; the quadruple temperature selected
was 280 °C and the relative electron multiplier voltage (EM) applied was
400 V with a resulting voltage of 1553 V. In order to improve the detection limits,
the selected ion monitoring (SIM) mode was used. The data acquisition was carried
out with the HP-Chemstation Software and identified using the National Institute of
Standards and Technology database with mass spectra version NBS75JK.
2.8. Gas chromatography–olfactometry
The samples were applied by the ‘cool’-on-column injection technique at 40 °C.
The odorants were screened in parallel by three panellists who sniffed the effluent.
Sniffing analysis was repeated twice by each panellist. The compounds were tentatively
identified by comparing their retention times with those of the available standards,
odour quality perceived at the sniffing port and by comparison of mass spectra
using National Institute of Standards and Technology database with mass spectra version
NBS75JK (United States National Bureau of Standards, 1986). GC–MS conditions
were as follows: oven temperature was raised at 50–60 °C/min (BP X 5), held for
3 min isothermally, raised at 10–280 °C/min, then raised at 15–320 °C/min and held
for 10 min. The flow rate of the carrier gas helium was 1.5 ml/min.
2.9. Quantification
Semi-quantitative analysis was made by the internal standard method, using
decanal as reference substance without the use of response factors for all compounds.
The calibration curves of amount ratios (compound/internal standard) versus
peak area ratio (compound/internal standard) were used to quantify positively
identified compounds. The concentration of a compound in the sample was calculated
as:
amount ratio lg of Decanal
Concentration ðmg=kgÞ ¼
G of sample
2.10. LC–MS analysis
Analysis was performed using Thermo Fisher Scientific (San Jose, CA, USA) System
equipped with a TSQ Quantum Discovery MAX triple stage quadruple mass
spectrometer with an electron spray ionization (ESI) probe (Thermo Fisher, Scientific,
San Jose, CA, USA). The system consists of a binary pump, a degasser, a column
oven, and an auto sampler (Thermo Fisher, Scientific, San Jose, CA, USA). Analysis
was done on a 150 2 mm i.d., 4 lm Symmetry C 18 Column (Waters, Massachusetts,
MA, USA). An aliquot (0.5 ml) of the eluate was centrifuged at 15,000 rpm
(21,700 g) for 10 min and passed through a syringe filter with a hydrophilic membrane
(Fluor pore PTFE, 0.22 lm; Millipore). The filtrate was kept at 20 °C under
dark until analysis. The sample (2 lL) was injected and eluted with 10% methanol
in water isocratically at a flow rate of 0.1 ml/min at 40 °C. The mass spectrometer
conditions were as follow: the ion spray voltage was set at 5200 V, turbo gas temperature
was 450 °C and the flow rate was 6 l/min.
3. Results and discussion
3.1. Calibration, linearity and analytical sensitivity
The range of linearity studied for each aroma compound is
shown in Table 1. The correlation coefficients were good
(r 2 > 0.99). This was followed by an excellent linearity in all cases.
The linearity which is the ‘on-line linearity (LOL) was determined
by the following equation in which RSD is the relative standard
deviation of the slope (expressed as a percentage)
LOLð%Þ ¼100 RSD ð1Þ
The analytical sensitivity, detection, and quantitation limits
were calculated from the curves constructed for each compound.
Analytical sensitivity is defined by the quotient S r/m, in which S r
O. Lasekan, K. Abbas / Food and Chemical Toxicology 48 (2010) 2212–2216 2215
is the residual standard deviation and m is the slope of the calibration
curve. Moreover, the limits of detection (LOD) (3 the relative
standard deviation of the analytical blank values) and quantitation
(LOQ) (10 the relative standard deviation of the analytical blank
values) obtained (Table 2) were low enough to determine the aroma
compounds in the roasted tropical almond nut extract. In addition,
good recoveries of compounds were also obtained (Table 2).
Similarly, standard curves for the LC–MS analysis were produced
by linear regression using the peak area ratios of the analyte
at m/z 55 to the internal standard at m/z 58. Each concentration
was analysed in triplicate to provide a standard deviation (SD).
The LOD and the LOQ were calculated based on the analysis of
1ngml 1 acrylamide standard solution and the obtained LOD value
was 0.1 ng ml 1 while that of the LOQ was 0.9 ng ml 1 . Also,
a high linearity (r 2 = 0.998) was obtained.
3.2. Volatile compounds in roasted tropical almond nut
A total of 74 volatile compounds were identified and quantified
(Table 3). These compounds comprised the following; 27 hydrocarbons,
12 aldehydes, 11 ketones, 7 acids, 4 esters, 3 alcohols, 5 furan
derivatives and a pyrazine. The volatiles with the major peaks
were; 2-ethyl-3,6-dimethylpyrazine, n-hexadecanoic acid, (E)-9octadecenoic
acid, (Z)-2-decenal and (E, E)-2,4-decadienal. Other
volatile compounds with appreciable peaks comprised, (Z)-hept-
2-enal, nonanal, (Z, Z)-9, 12-octadecadienoic acid, 6-heptylterahyro-2H-pyran-2-one.
Quantitatively, the carboxylic acids
were the most abundant volatile compounds. They constituted
approximately 33% of the total compounds.
In general, all the main classes of compounds commonly listed
as thermally generated flavours in oily seeds were identified in the
roasted tropical almond nuts, with the most important from a flavour
standpoint being furans and volatile heterocyclic compounds.
A total of 5 furans and their oxygenated substituents were identified.
These included, the musty-nutty, 3-acetyl-2,5-dimethylfuran,
beany-like, 2-pentylfuran, furfuryl octanoate, dihydro-5-tetradecyl-2(3H)-furanone
and 4-hexyl-2,5-dihydro-2,5-dioxo-3-furanacetic
acid. 2-Pentylfuran was previously identified as a compound
of the volatile decomposition products of slightly autooxidised
soybean and cottonseed oils and those of thermal oxidation of corn
oil and hydrogenated cottonseed oil, respectively (Krishnamurthy
et al., 1967). Furans are products of carbohydrate thermal degradation
and rearrangement (Morini and Maga, 1995). The heating process
catalyses the reaction between amino acids and sugars via the
Maillard reaction which is responsible for the development of colour,
and volatile heterocyclic compounds. Interestingly, only one
pyrazine derivative, 2-ethyl-3,6-dimethylpyrazine was identified
in the roasted nuts. This is probably due to the nut’s low lipid content.
This is in agreement with previous studies which focused on
the interaction of lipid content in the Maillard reaction (Mottram
and Edwards, 1983; Saittagaroon et al., 1984). In an examination
on the contribution of lipids to the development of aroma during
the heating of meat, the phospholipids were shown to be of significant
importance (Mottram and Edwards, 1983). When inter- and
intra-muscular triglycerides were removed from lean meat muscle
using hexane, the aroma after cooking could not be differentiated

2216 O. Lasekan, K. Abbas / Food and Chemical Toxicology 48 (2010) 2212–2216
Table 4
Effect of roasting temperatures on the acrylamide content (lg kg 1 ) of tropical
almond nuts.
Roasting temperature ( o C) Roasting time (min)
5 15 25
100 8 c C 24 b C 45 a C
150 21 c B 42 b B 65 a B
200 49 c A 66 b A 86 a A
A
Different
difference.
capital letters along each column indicate significant (P < 0.05)
a
Different superscript letters along row indicate significant (p < 0.05) difference.
from the untreated material in sensory triangle tests. However,
when a more polar solvent was used to extract all the lipids, phospholipids
as well as triglycerides, a very marked difference in aroma
resulted.
Although, a relatively small number of aldehydes, ketones, and
alcohols were identified in this study (Table 3), they are expected
to play an important role in the aroma of the roasted tropical almond
nuts. Also, most of these volatile compounds have been
identified in some oily seeds. For instance, (Z)-hept-2-enal, (E, E)-
2,4-nonadienal, nonanal and (Z)-2-decenal were reported in
roasted sesame seeds (Nakamura et al., 1989), roasted peanuts
(Leunissen et al., 1996) and as off flavour in tuna fish oil (Roh
et al., 2006). (E, E)-2,4-Decadienal which was the most abundant
aldehyde in the roasted nuts have been reported in the dried leaves
of tropical almond (Mau et al., 2003) and it is formed by the oxidative
degradation of linoleic and linolenic acids (Seo and Baek,
2005). Also, the celery-like, 6,10,14-trimethyl-2-pentadecanone,
was reported to contribute to the characteristic aroma of tropical
almond leaves (Mau et al., 2003).
3.3. Acrylamide concentration in roasted tropical almond nuts
The acrylamide concentrations of nuts roasted at three different
temperatures and times are shown in Table 4. The acrylamide concentrations
of roasted nuts were not very high. However, higher
roasting temperatures and roasting time significantly (P < 0.05) increased
the acrylamide concentration. Mechanism study (Becalski
et al., 2004) on the formation of acrylamide demonstrated that
acrylamide is generated from the Maillard reaction by free asparagines.
The formation mechanism of acrylamide regarding the participation
of asparagines in the Maillard reaction is called
‘asparagine pathway’. Two different reaction pathways that can
both result into the formation of acrylamide has been suggested
(Zyzak et al., 2003): (i) Strecker pathway, in which the Amadori
product is formed via the Amadori rearrangement of Schiff base,
carbonyl-containing products are subsequently formed via dehydration
and deamination. Acrylamide is finally formed via the
Strecker degradation of asparagines in the presence of carbonylcontaining
products; (ii) N-glycoside pathway, in which oxazolidone
is initially formed via the intramolecular cyclization of Schiff
base. The decarboxylated Amadori product is subsequently formed
and acrylamide is finally generated via fragmentation of the ‘C–N’
bond of decarboxylated Amadori product.
In conclusion the carboxylic acids were the most abundant volatile
compounds identified in the roasted almond nuts. Also, significant
number of compounds commonly listed as thermally
generated flavours in oily seeds were identified in the roasted nuts.
While low concentration of acrylamide was obtained in the roasted
nuts, it was observed that the acrylamide concentration was significantly
(P < 0.05) increased with roasting temperature and time.
4. Conflict of Interest
The authors declare that there are no conflicts of interest.
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