Effect of gamma-radiation on major aroma compounds and vanillin glucoside of cured vanilla beans (Vanilla planifolia)

Article abstract of DOI:10.1016/j.foodchem.2010.03.006

Cured vanilla beans were irradiated (5, 10, 15, 20 and 30 kGy) for a possible enhancement of vanillin content by radiolysis of vanillin glucoside. The vanillin content of control and irradiated (30 kGy) samples were 26.6 ± 0.85 and 26.9 ± 0.70 mg/g (dw), respectively, while vanillin glucoside were 7.74 ± 0.2 and 7.35 ± 0.35 mg/g (dw). Radiation caused no significant changes (p ≤ 0.05) in aroma constituents. In a pulse radiolysis experiment, vanillin glucoside on reacting with ^{{radical dot}}OH radical gave transients with absorption peaks at 360 nm and 410 nm. The species absorbing at 410 nm has been interpreted to be a hydroxyl radical adduct. It decayed at the same rate in the presence of oxygen, while the absorption at 360 nm did not. Results obtained revealed that the more stable one absorbing at 360 nm is aldehydic radical. Hence the highly stable oxygen-carbon linkage between vanillin and glucose limits the possible enhancement of aroma quality of irradiated beans.

Full text of DOI:10.1016/j.foodchem.2010.03.006

Food Chemistry 122 (2010) 841–845
Contents lists available at ScienceDirect
Food Chemistry
journal homepage: www.elsevier.com/locate/foodchem
Short communication
Effect of gamma-radiation on major aroma compounds and vanillin glucoside
of cured vanilla beans (Vanilla planifolia)
a
c
b
b
K. Kishor Kumar a, A. Arul AnanthaKumar b, , R. Ahmad , S. Adhikari , P.S. Variyar , A. Sharma
*
a Department of Applied Botany, Mangalore University, Mangalore, India
b Food Technology Division, Bhaba Atomic Research Center, Mumbai, India
c Radiation and Photochemistry Division, Bhaba Atomic Research Center, Mumbai, India
a r t i c l e i n f o
a b s t r a c t
Article history:
Cured vanilla beans were irradiated (5, 10, 15, 20 and 30 kGy) for a possible enhancement of vanillin con-
tent by radiolysis of vanillin glucoside. The vanillin content of control and irradiated (30 kGy) samples
were 26.6 0.85 and 26.9 0.70 mg/g (dw), respectively, while vanillin glucoside were 7.74 0.2 and
7.35 0.35 mg/g (dw). Radiation caused no significant changes (p 6 0.05) in aroma constituents. In a
pulse radiolysis experiment, vanillin glucoside on reacting with ꢀOH radical gave transients with absorp-
tion peaks at 360 nm and 410 nm. The species absorbing at 410 nm has been interpreted to be a hydroxyl
radical adduct. It decayed at the same rate in the presence of oxygen, while the absorption at 360 nm did
not. Results obtained revealed that the more stable one absorbing at 360 nm is aldehydic radical. Hence
the highly stable oxygen–carbon linkage between vanillin and glucose limits the possible enhancement
of aroma quality of irradiated beans.
Received 7 September 2009
Received in revised form 11 February 2010
Accepted 2 March 2010
Keywords:
Vanilla planifolia Andrews
Vanillin
Vanillin glucoside
Moulds
Ó 2010 Elsevier Ltd. All rights reserved.
Gamma-irradiation
Microbial decontamination
Aroma glycosides
Pulse radiolysis
1. Introduction
of cured vanilla beans by fungal species belonging to the genera
Aspergillus and Penicillium.
Vanilla (Vanilla planifolia) is a commercial crop widely culti-
vated as a source of natural vanillin. The compound is obtained
from cured vanilla beans and is extensively used in flavouring food,
beverages and confectionery (Ranadive, 1994). Worldwide total
demand for vanillin is more than 10,000 tons per year, of which
less than 0.5% is met out by vanillin isolated from vanilla beans
(Priefert, Rabenhorst, & Steinbuchel, 2001). The rest is produced
synthetically, mostly from petrochemicals, such as guaiacol and
lignin (Clark, 1990). The price of natural vanillin extracted from
beans is between US$1200/kg and US$4000/kg, while that of syn-
thetic vanillin is less than US$15/kg (Serra et al., 2005). Thus there
is a need for improving the yield of natural vanillin obtained from
vanilla beans for economic reasons.
Radiation processing of food materials by gamma-radiation is a
well established method for microbial decontamination and insect
disinfestation. Irradiation of spices at doses ranging from 10 to
30 kGy has been reported to result in complete elimination of
microorganisms with negligible changes in the flavour quality
(Farag, Aziz, & Attia, 1995). The effect of gamma-radiation on micro
flora and vanillin content of cured vanilla beans in the dose range
of 5–50 kGy has been investigated by Bachman, Pietka, and Zegota
(1995), but its effect on other major aroma compounds and vanillin
glucoside (vanillin aroma precursor) remaining after curing have
not been studied so far.
Recent studies have demonstrated the role of radiation process-
ing in improving the sensory quality of spices, such as saffron
Cured vanilla beans have moisture content in the range of 25–
30%. They are generally kept in cartons or wooden boxes for
conditioning (3–6 month’s period) and subsequent storage. The
conditions prevailing in these boxes are conducive for fungal
growth. Thomas and Bindumol (2005) reported microbial spoilage
(Zareena, Variyar, Gholap, & Bongirwar, 2001) and nutmeg
(Ananthakumar, Variyar, & Sharma, 2006). Radiolytic breakdown
of glycosidic precursors of aroma constituents and consequent re-
lease of free aroma was shown to result in the enhancement of ar-
oma quality of these products. Since a considerable amount of
vanillin exists as its glycosidic precursor (7.74 0.20 mg/g) in
cured vanilla pods, a possible enhancement in yield of vanillin by
radiation processing is thus expected. Results with enzymatic
preparations have demonstrated that as much as half of the
* Corresponding author. Tel.: +91 22 22590560; fax: +91 22 25590565.
E-mail address: aakgen1@gmail.com (A.A. AnanthaKumar).
0308-8146/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved.
doi:10.1016/j.foodchem.2010.03.006

842
K.K. Kumar et al. / Food Chemistry 122 (2010) 841–845
amount of vanillin sequestered in the complex cellulose matrix is
in either free or bound glycosidic forms, and can be liberated by
enzyme assisted procedures (Ovando, Waliszewski, & Pardio,
2005; Ruiz-Teran, Perez-Amador, & Lopez-Munguia, 2001).
Hence, the present work was aimed to study the effect of gam-
ma-radiation processing on the major aroma compounds of cured
vanilla beans and also to investigate possible enhancement in van-
illin content by the radiolytic breakdown of vanillin glucoside pres-
ent already.
completely and the resultant aqueous portion was suitably diluted
with distilled water. Total glycosides from this aliquot were sepa-
rated using an XAD-16 (Sigma) column (13 cm bead ꢀ 3 cm ID),
following standard procedures (Gunata, Bayonove, Bumes, & Cord-
oinnier, 1985). The methanol fraction (100 ml) eluting from the
XAD-16 column was evaporated to dryness under vacuum and
the residue was dissolved in an appropriate volume of methanol
to obtain a final concentration of 10 mg/ml. Individual glycosides
from this extract were separated by preparative TLC, using ethyl
acetate:isopropanol:water (65:30:15) as the mobile phase. Vanillin
glucoside, the most abundant glycoside reported (Odoux, 2006) in
vanilla beans, visualised after exposure of plates to iodine vapours
(Rf = 0.7) was scraped from TLC plates and eluted with methanol.
The eluate was dried under vacuum and made up to a 1% solution
in methanol. A part of this solution was subjected to acid hydroly-
sis (2N HCl, 1 h, 100 °C) and extracted with diethyl ether. The
remaining aqueous portion was neutralised with 1N KOH, dried
under vacuum and the residue was dissolved in methanol. This
methanol solution along with standard glucose was subjected to
TLC (isopropanol:acetone:water, in ratio of 45:30:25, as mobile
phase) and the spots were detected by 10% sulphuric acid spray,
followed by heating at 110 °C for 15 min, in order to identify the
sugar moiety.
2. Materials and methods
Cured and fresh green vanilla beans were procured from a cur-
ing centre in South Canara district of Karnataka State, India. Beans
were stored at 4 °C until analysis. Standard compounds were pro-
cured from Sigma–Aldrich Chemical Company, St. Louis, MO. All
solvents including HPLC grade were purchased from E. Merck India
Ltd., Mumbai. Solvents were distilled before use. Other chemicals
and reagents of AR grade were obtained from Thomas Baker,
Mumbai.
2.1. Moisture content and water activity
The vanillin glucoside thus isolated in pure form was used as
authentic standard for quantitative estimation of vanillin glucoside
by HPLC. The diethyl ether extract was washed free of acid with
distilled water and then dried over sodium sulphate. The organic
layer was concentrated by passing over it a mild stream of nitrogen
gas and then analysed by GC–MS.
Moisture content of the samples was determined using a mois-
ture metre (Sartorius MA100, Goettingen, Germany). Water activ-
ity (aw) of samples was measured at fixed temperature
(27 1 °C), using an Aqualab water activity metre (Model Series
3 TE, Decagon Devices, Pullman, WA) with temperature control.
2.2. Irradiation of the vanilla beans
2.5. GC/MS analysis
Ten different doses (0, 1, 2, 3, 4, 5, 10, 15, 20 and 30 kGy) of
gamma-radiation were given to cured vanilla beans samples of
250 g each. All the treatments were performed in triplicate. Irradi-
ation was carried out on a GC5000 Gamma irradiator (BRIT, Mum-
bai) using 60Co as source, with dose rate of 7.881 kGy/h.
GC/MS analysis was carried out on a Shimadzu GC/MS instru-
ment (Shimadzu, Kyoto, Japan) equipped with a GC-17A gas chro-
matograph and provided with a DB-5 (J&W Scientific, Folsom, CA)
capillary column (length, 30 m; i.d., 0.25 mm and film thickness,
0.25 lm). The operating conditions were: column temperature
programmed from 60 to 200 °C at the rate of 4 °C/min, held at ini-
tial temperature and at 200 °C for 5 min and further to 280 °C at
the rate of 10 °C/min, held at final temperature for 20 min; injector
and interface temperatures, 210 and 230 °C, respectively; carrier
gas helium (flow rate, 0.9 ml/min); ionisation voltage, 70 eV; elec-
2.3. Isolation of free aroma constituents
The procedure developed by Ranadive (1992) was followed
with some modifications. Cured vanilla bean samples (25 g) from
each treatment were ground using a pestle and mortar with liquid
nitrogen. The resultant powder was made into a slurry by mixing it
thoroughly with 100 ml of 45% ethanol and kept overnight at room
temperature. Before filtering, the slurry was stirred using an Omni
Mixer (2–3 min; Omni International, Kennesaw, GA) and then fil-
tered under suction using a Buchner funnel. The residual cake
was again extracted (100 ml ꢀ 2) as above and the extracts were
pooled and centrifuged at 8500g for 45 min at room temperature
to remove any suspended particles. Exactly 50 ml of the superna-
tant were taken and dried completely under vacuum and the resi-
due was made up as a 10% solution in 45% ethanol. These solutions
were analysed by HPLC for qualitative and quantitative changes in
aroma profile of cured vanilla beans.
tron multiplier voltage, 1 kV. Samples (0.5 ll) were injected in
splitless mode. Peaks were identified by comparing their mass
fragmentation pattern with that of standard compounds as well
as with the data available in the spectral library (Wiley/NIST Li-
braries) of the instrument.
2.6. HPLC analysis
HPLC separation of compounds was performed using a JASCO
HPLC (Model PU 980; JASCO International Co. Ltd., Tokyo, Japan)
fitted with C18 reverse-phase column (250 mm ꢀ 4.6 mm, Thermo
Hypersil-Keystone; Thermo Fisher Scientific Inc., Waltham, MA)
and 3-cm guard column. Compounds were detected by UV–Vis
detector (UV 975) set at 275 nm and data were interpreted using
Jasco Borwin-PDA Software (Version 1.50). The mobile phase used
was methanol:acetonitrile:acetic acid (50:100:10 ml) finally di-
2.4. Isolation of vanillin glucoside
Vanillin glucoside from vanilla beans (both fresh green and
cured) was isolated following the method described by Dignum,
Kerler, and Verpoorte (2002). In a 100-ml volumetric flask, 65 ml
of acetate buffer (pH 5.0) and 5 g of ground vanilla bean sample
were mixed thoroughly for 5–10 min. Then the suspension was
heated in microwave oven to deactivate enzymes. Finally the vol-
ume was made up to 100 ml using distilled methanol. This whole
extract was concentrated under vacuum to remove methanol
luted to 1 l with filtered (0.45-
lm nylon membrane) deionised
water (Milli-Q), at a flow rate of 1 ml/min (Archer, 1989). Samples
were filtered through 0.45-lm nylon membrane before HPLC
analysis.
Standard solutions of vanillin, vanillin glucoside, vanillic acid, p-
hydroxybenzaldehyde and p-hydroxybenzoic acid were prepared
at appropriate concentrations in methanol and analysed by HPLC.

K.K. Kumar et al. / Food Chemistry 122 (2010) 841–845
843
Standard graphs were prepared by plotting peak area against con-
centration using the above standards.
icant quantitative changes up to a dose of 30 kGy. Hence, gamma-
radiation may be the method of choice for hygienisation of cured
vanilla beans without any significant effect on the aroma profile.
2.7. Pulse radiolysis
3.2. Isolation and identification of vanillin glucoside
Use of pulse radiolysis system (7 MeV electrons) for generation
and studies on the free radical reactions have been described ear-
lier (Adhikari & Mukherjee, 2001). Dosimetry was carried out using
an air-saturated aqueous solution containing 5 ꢀ 10ꢁ2 mol/dm
Earlier studies have shown that the vanillin glucoside content in
green vanilla beans range from 10% to 15% on a dry weight basis
(Odoux, Escoute, & Verdeil, 2006; Ovando et al., 2005). Aroma gly-
cosides separated from aqueous extracts using Amberlite XAD-16
column were further separated by preparative TLC using the proce-
dure outlined in Section 2.4. The major band corresponding to van-
illin glucoside (Rf = 0.7) was isolated by preparative TLC. GC/MS
analysis of the aglycone moiety obtained after acid hydrolysis con-
firmed it to be vanillin [m/z 152 (88%, M+), 151 (100%, M+ꢁH), 137
(6%, MꢁCH3), 123 (88%, MꢁCHO)], and the sugar moiety was iden-
tified to be glucose by TLC. The vanillin glucoside thus obtained
from green vanilla beans [purity >99% on HPLC (Rt 4.3 min)] was
used as a standard for all subsequent analyses.
ꢁ
KSCN, assuming a G-value for (SCN)2 of 23.889 dm3/mol/cm per
100 eV at 500 nm (Buxton & Stuart, 1995). The width of the elec-
tron pulse was 50 ns and the dose per pulse was 15 Gy. The kinetic
spectrophotometric detection system covered the wavelength
range from 250 to 800 nm. High purity (99.9%) N2O, from British
Oxygen Co. (Kolkata, India) was used as per requirement. The fol-
lowing reactions occur after irradiation in the reaction medium
used.
-
.
ð1Þ
H2O
eaq , H., OH, H2, H2O2
eꢁaq þ N2O þ H2O ) ꢀOH þ OHꢁ þ N2
ð2Þ
Odoux et al. (2006) reported the presence of about 15 glyco-
sides in green vanilla beans, of which vanillin glucoside was the
most abundant. Fig. 1 shows the HPLC chromatogram of aqueous
extracts of green and cured vanilla beans. The amount of vanillin
glucoside in green beans and cured beans as estimated by HPLC
in the present study was found to be 72.5 0.5 mg/g and
7.74 0.2 mg/g, respectively, on a dry weight basis. So, approxi-
mately 10–15% of vanillin glucoside is still present in the cured
beans, compared to the green beans thanks to incomplete hydroly-
sis of glucovanillin during the curing process. Thus there is scope
for further enhancing the vanillin content of cured beans by an
appropriate technology which can release vanillin from the
remaining glucovanillin.
The bimolecular rate constants were calculated by plotting the
pseudo-first order rates of formation of the transients against the
concerned solute concentrations. The uncertainty in the measure-
ment in bimolecular rate constant is 10%.
2.8. Statistical analysis
All analyses were performed in triplicate. One-way ANOVA was
done to evaluate the differences between treatments at the 5% sig-
nificance level (Sokal & Rohlf, 1987).
3. Results and discussion
3.3. Effect of radiation processing on vanillin glucoside content
3.1. Effect of radiation processing on aroma profile of cured beans
Irradiation has been successfully used for the quality improve-
ment of many agricultural products. Ananthakumar et al. (2006)
reported the radiolytic breakdown of aroma glycosides in nutmeg.
A linear increase in antioxidant isoflavones with radiation dose
resulting from a breakdown of glycosidic precursors, was also
noted in soybean (Variyar, Limaye, & Sharma, 2004). In a recent
Natural vanilla aroma is a mixture of more than 200 volatile
compounds. Among these, four major compounds collectively con-
stitute 97% w/w of the total aroma compounds reported. They in-
clude vanillin (86% w/w), vanillic acid (6% w/w), p-
hydroxybenzaldehyde (4% w/w) and p-hydroxybenzoic acid (1%
w/w) (Perez-Silva et al., 2006). The aqueous ethanol extracts from
treated samples (control, 5, 10, 15, 20 and 30 kGy) were analysed
by HPLC as per the procedure described earlier. Presence of the
above four major compounds was confirmed using authentic stan-
dards. The quantitative distribution of the four major aroma com-
pounds in samples subjected to different radiation doses are
presented in Table 1. Bachman et al. (1995) studied the effect of
gamma-radiation on vanillin content. No change in the vanillin
content was reported, even at a dose of 50 kGy. The results ob-
tained in the present study are also in tandem with the report of
Bachman et al. Besides vanillin, the content of other aroma com-
pounds identified and reported in this study also showed no signif-
work on the stability of phenol-b-D-glucopyranosides in fenugreek,
Chatterjee, Adhikari, Variyar, Gupta, and Sharma (2009) have
demonstrated a radiolytic breakdown of glycosidic linkage, via a
carbon-centred radical using pulse radiolysis studies. Thus car-
bon–oxygen linkages in the glycoside are susceptible to radiolysis.
It was of interest to understand the stability of vanillin glucoside
during radiation processing, with a view to improve the vanillin
content in cured beans. Contents of vanillin and its glycoside as
estimated by HPLC in cured beans samples subjected to various
doses of gamma-radiation, is provided in Table 1. No difference
in either vanillin or glucovanillin content was noted in the samples
subjected to different radiation doses up to 30 kGy. Strong resis-
Table 1
Contents of major aroma compounds and vanillin glucoside of cured vanilla beans irradiated at different doses of gamma-radiation (mg/g).
Aroma constituents
Irradiation dose (kGy)
0
5
10
15
20
30
Vanillin
Vanillic acid
p-Hydroxy benzaldehyde
p-Hyroxy benzoic acid
Vanillin glucoside
26.60 0.85a
0.93 0.08b
1.32 0.12c
0.45 0.03d
7.74 0.20a
26.50 0.80a
0.91 0.10b
1.30 0.12c
0.40 0.04d
7.40 0.30a
25.80 0.73a
0.90 0.08b
1.28 0.14c
0.43 0.03d
7.35 0.20a
25.62 0.82a
0.95 0.09b
1.31 0.12c
0.44 0.02d
7.45 0.25a
26.20 0.85a
0.94 0.10b
1.29 0.14c
0.41 0.02d
7.50 0.20a
26.91 0.70a
0.95 0.07b
1.33 0.13c
0.42 0.03d
7.35 0.35a
a–d
Means SD values sharing the same letter are not significantly different (p < 0.05, n = 3).

844
K.K. Kumar et al. / Food Chemistry 122 (2010) 841–845
Fig. 1. HPLC chromatogram of aroma glycosides in green bean and cured bean containing vanillin glucoside.
tance to radiolysis by standard vanillin glucoside exposed directly
to gamma-radiation as high as 60 kGy was also observed during
this study (data not shown). Thus unlike other glycosides reported
above, the carbon–oxygen linkage in glucovanillin appears to be
quite stable. This observation warranted understanding the mech-
anism of stability of vanillin glucoside to radiolytic cleavage, so a
pulse radiolysis experiment on vanillin glucoside was carried out.
3.4. Pulse radiolysis study on vanillin glucoside
ꢀ
In an N2O-saturated aqueous solution, it is the OH radical that
is produced by the passage of electron pulses. Vanillin glucoside
ꢀ
upon reacting with OH radical was found to give a transient with
absorption peaks at 360 nm and 410 nm (Fig. 2). The bimolecular
rate constant for the reaction as determined by following the pseu-
do-first order rate of formation both at 360 nm and 410 nm is
8.0 ꢀ 109 dm3/mol/s. While the absorption at 410 nm decays with
time, absorption at 360 nm does not show a significant decay up to
1 ms (Fig. 3A). From this result it is clear that at least two species
are produced at the initial step with one species being more stable.
Further, the formation of the more stable species has no relation
with the decay of the other species absorbing at 410 nm. However,
both the species decay by first order kinetics, as evident from
experiments carried out at different doses. It is known that a first
order decay process does not depend upon the concentration of
the species decaying. In this case if the concentration of the species
is increased by increasing the dose of the pulse, thereby increasing
the concentration of the radical, there should not be any change in
the decay rate. On the contrary, a second order decay process will
be faster with a proportionate increase in concentration. We have
observed no effect on the decay of both the radicals by increasing
the dose per pulse to 32 Gy from 16 Gy (figure not shown). In an
earlier study on the reaction of hydroxyl radical with vanillin
(Mahal, Badheka, & Mukherjee, 2001), it was reported that,
Fig. 2. Transient absorption spectra obtained from an N2O-saturated aqueous
solution (natural pH) containing 1 ꢀ 10ꢁ4 mol/dm3 vanillin glucoside. (a) 15
ls, (b)
85 1 ls, (c) 150 ls, (d) 300 ls and (e) 850 ls after the electron pulse.
depending upon pH, two types of radicals were formed. At pH 5,
a hydroxyl radical adduct (absorption maximum at 430 nm) is
the predominating species while at pH 9, phenoxyl radical was ob-
served with absorption maximum at 410 nm. In the present case,
formation of phenoxyl radical is unlikely because the phenolic site
is blocked by glycoside linkage. In general, phenoxyl radicals decay
by second order process and become faster with increase in radia-
tion dose, which is not the case in the present study. Thus the spe-
cies absorbing at 410 nm must be a hydroxyl radical adduct. Even
in the presence of oxygen this species decays at the same rate.
The absorption at 360 nm on the other hand is susceptible to
oxygen concentration (Fig. 3B). The carbon-centred radicals react
with dissolved oxygen if present very quickly and the bimolecular
rate constant values are in the range 2–4 ꢀ 109 dm3/mol/s, which

K.K. Kumar et al. / Food Chemistry 122 (2010) 841–845
845
for accelerated curing. But gamma-radiation may be useful in rup-
turing the cellulose matrix of fresh vanilla beans, thereby enhanc-
ing the contact between b-glycosidase enzyme and vanillin
glucoside, which are separately located in the outer fruit wall re-
gion and the placental region, respectively. However, gamma-radi-
ation is the best tool for the complete hygienisation of vanilla
beans from spoilage and toxin-producing microbes without alter-
ing its aroma quality and market value.
References
Adhikari, S., & Mukherjee, T. (2001). Kinetics of free radical reactions of some
biologically important compounds as studied by pulse radiolysis. Progress in
Reaction Kinetics and Mechanisms, 26, 301–336.
Ananthakumar, A., Variyar, P. S.,
& Sharma, A. (2006). Estimation of aroma
glycosides of nutmeg and their changes during radiation processing. Journal of
Chromatography A, 1108, 252–257.
Archer, A. W. (1989). Analysis of vanilla essence by high performance
chromatography. Journal of chromatography A, 462, 461–466.
Bachman, S., Pietka, M., & Zegota, H. (1995). Studies on some microbiological and
chemical aspects of irradiated vanilla beans. Journal of Radio Analytical and
Nuclear Chemistry, 189, 71–76.
Buxton, G. V., & Stuart, C. R. (1995). Re-evaluation of the thiocyanate dosimeter for
pulse radiolysis. Journal of Chemical Society, Faraday Transactions, 91, 279–281.
Chatterjee, S., Adhikari, S., Variyar, P. S., Gupta, S., & Sharma, A. (2009). Estimation of
aroma precursors in radiation processed fenugreek. Food Chemistry, 115(3),
1102–1107.
Clark, G. S. (1990). Vanillin. Perfumer and Flavourist, 15, 45–54.
Cooper, J. W., Cramer, C. J., Martin, N. H., Mezyk, S. P., O’Shea, K. E., & Sonntag, C. V.
(2009). Free radical mechanisms for the treatment of methyl tert-butyl ether
(MTBE) via advanced oxidation/reductive processes in aqueous solutions.
Chemical Reviews, 109, 1302–1345.
Dignum, M. J. W., Kerler, J., & Verpoorte, R. (2002). Vanilla curing under laboratory
conditions. Food Chemistry, 79, 165–171.
Farag, S. E., Aziz, N. H.,
& Attia, E. S. (1995). Effect of irradiation on the
microbiological status and flavouring materials of selected spices. Zeitschrift
fur Lebensmittel-untersuchung und -Forschung, 201, 283–288.
Gunata, Y. Z., Bayonove, C. L., Bumes, R. L., & Cordoinnier, R. E. (1985). Journal of
Chromatography A, 331, 83–90.
Mahal, H. S., Badheka, L. P., & Mukherjee, T. (2001). Radical scavenging properties of
a flavouring agent – Vanillin. Research on Chemical Intermediates, 27, 595–604.
Nlki, H., Maker, P. D., Savage, C. M., & Breitenbach, L. P. (1978). Relative rate
constants for the reaction of hydroxyl radical with aldehydes. The Journal of
Physical Chemistry, 82, 132–134.
Odoux, E. (2006). Glycosylated aroma precursors and glucosidase(s) in vanilla bean
(Vanilla planifolia G Jackson). Fruits, 61(3), 171–184.
Odoux, E., Escoute, J., & Verdeil, J. L. (2006). The relation between glucovanillin, b-
D-
Fig. 3. Kinetic traces recorded from the same solution as for Fig. 2. (A) The decay
traces at 360 and 410 nm. (B) Decay traces at 360 nm in presence and absence of
oxygen.
glucosidase activity and cellular compartmentation during the senescence,
freezing and traditional curing of vanilla beans. Annals of Applied Biology, 149,
43–52.
is slightly below the diffusion controlled limit (Cooper et al., 2009,
and references therein). Thus the decay rate of the carbon-centred
radical becomes faster with increase in oxygen concentration in
the experimental solution. It can be inferred that this absorption
is due to a carbon-centred radical. The aldehydic hydrogen is
weakly bonded to the carbonyl carbon, and should be highly sus-
ceptible to abstraction by ꢀOH radical (Nlki, Maker, Savage, & Brei-
tenbach, 1978). Thus it can be inferred that the more stable radical
absorbing at 360 nm is the aldehydic radical. In comparison to van-
illin the glycoside analogue reacts in a different way. In the case of
vanillin aldehyde radical formation does not occur. Thus the oxy-
gen–carbon linkage between vanillin and glucose is less suscepti-
ble to cleavage. This explains the high stability of glucovanillin to
radiolysis.
Ovando, S. L., Waliszewski, K. N., & Pardio, V. T. (2005). The effect of hydration time
and ethanol concentration on the rate of hydrolysis of extracted vanilla beans
by commercial cellulose preparations. International Journal of Food Science and
Technology, 40, 1011–1018.
Perez-Silva, A., Odoux, E., Brat, P., Ribeyre, F., Rodriguez-Jimenes, G., Robles-Olvera,
V., et al. (2006). GC–MS and GC–Olfactometry analysis of aroma compounds in a
representative organic aroma extract from cured vanilla (Vanilla planifolia G
Jackson) beans. Food Chemistry, 99(4), 728–735.
Priefert, H., Rabenhorst, J., & Steinbuchel, A. (2001). Biotechnological production of
vanillin. Applied Microbiology and Biotechnology, 56, 296–314.
Ranadive, A. S. (1992). Vanillin and related flavour compounds in vanilla extracts
made from beans of various global origins. Journal of Agricultural and Food
Chemistry, 40, 1922–1924.
Ranadive, A. S. (1994). Vanilla-cultivation, curing, chemistry, technology and
commercial products. In Charalambous G, spices, herbs and edible fungi, (pp.
517–577). Amsterdam: Elsevier.
Ruiz-Teran, F., Perez-Amador, I., & Lopez-Munguia, A. (2001). Enzymatic extraction
and transformation of glucovanillin to vanillin from vanilla green pods. Journal
of Agricultural and Food Chemistry, 49, 5207–5209.
Serra, S. et al. (2005). Biocatalytic preparation of natural flavours and fragrances.
Trends in Biotechnology, 23, 193–198.
4. Conclusion
The gamma-radiation processing (up to 30 kGy) did not cause
any significant changes in the aroma profile of cured vanilla beans
both qualitatively and quantitatively. To our knowledge this is the
first report about the effect of gamma-radiation on vanillin gluco-
side and major aroma compounds of cured vanilla beans. This
study showed that, gamma-radiation may not be a useful alternate
to b-glycosidase enzyme for the release of vanillin from its glyco-
side precursor, either for the purpose of aroma enhancement or
Sokal, R. R., & Rohlf, F. J. (1987). Introduction to biostatistics (2nd ed.). New York:
W.H. Freeman and Company. pp. 363.
Thomas, J., & Bindumol, G. P. (2005). Microbial contamination in cured vanilla
beans. Spice India, 6, 8.
Variyar, P. S., Limaye, A., & Sharma, A. (2004). Radiation-induced enhancement of
antioxidant contents of Soybean (Glycine max Merrill). Journal of Agricultural and
Food Chemistry, 52, 3385–3388.
Zareena, A. V., Variyar, P. S., Gholap, A. S., & Bongirwar, D. R. (2001). Chemical
investigation of gamma-irradiated saffron (Crocus sativus L.). Journal of
Agricultural and Food Chemistry, 49, 687–691.