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The Correlation between 2-Acetyl-1-pyrroline Content, Biological

Compounds and Molecular Characterization to the Aroma Intensities of Thai
Local Rice

Article in Journal of Oleo Science · June 2018

DOI: 10.5650/jos.ess17238

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Journal of Oleo Science
Copyright ©2018 by Japan Oil Chemists’ Society
doi : 10.5650/jos.ess17238
J. Oleo Sci. 67, (7) 893-904 (2018)

The Correlation between 2-Acetyl-1-pyrroline

Content, Biological Compounds and Molecular
Characterization to the Aroma Intensities of
Thai Local Rice
Sompong Sansenya1,＊ , Yanling Hua2, and Saowapa Chumanee3
1
Department of Chemistry, Faculty of Science and Technology, Rajamangala University of Technology Thanyaburi, Pathum Thani 12110,
THAILAND
2
The Center for Scientific and Technological Equipment, Suranaree University of Technology, Nakhon Ratchasima 30000, THAILAND
3
Division of Chemistry, Faculty of Science and Technology, Phetchabun Rajabhat University, Mueang, Phetchabun 67000, THAILAND

Abstract: Aroma intensities of rice are correlated with the mixture of aroma compounds it contains.
2-acetyl-1-pyrroline (2AP) has been reported as a major aroma compound and as a characteristic compound
in fragrant rice. In this study, Thai local cultivars were classified into fragrant and non-fragrant rice based
on the 2AP content and molecular characterization. Local rice cultivars were also examined for their proline
content and volatile compounds profile, which are important factors in determining aroma. The results
suggested that 43 Thai local rice cultivars were classified into 25 fragrant rice cultivars and 18 non-fragrant
cultivars. The type of fragrant rice cultivars included 16 non-colored and 9 colored rice cultivars, while the
type of non-fragrant rice cultivars included 14 non-colored and 4 colored rice cultivars. The proline content
of local rice cultivars was determined and showed no correlation with the 2AP content; however, the proline
level appears to be associated with the environmental stress in the rice cultivation area. One hundred and
forty volatile compounds were identified from local rice cultivars. Among the detected compounds, 18
volatile compounds, including hexanal 1-pentanol octanal (E)-2-heptenal 6-methyl-5-hepten-2-one 1-hexanol
nonanal 2-butoxy-ethanol (E)-2-octenal 1-tetradecene 1-octen-3-ol decanal benzaldehyde (E)-2-nonenal
1-nonanol benzyl alcohol isovanillin and vanillin contributed to the aroma intensities of both fragrant and
non-fragrant rice. Aroma compounds were more abundant in fragrant than in non-fragrant rice. Moreover,
the levels of aroma compounds recorded in non-colored cultivars were higher than those in colored rice
cultivars. In contrast, the 2AP content of colored rice cultivars was higher than that in non-colored rice
cultivars. Our findings may assist rice breeding programs in producing a new aromatic genotype rice with
high potential aroma intensities.

Key words: 2-acetyl-1-pyrroline, aroma compound, local rice cultivars, proline content

1 Introduction on this study, a method was developed for the analysis of

The aroma intensities in rice are due to a mixture of fragrant and non-fragrant rice genotypes by electrophores-
aroma compounds15 . The characteristic compound in fra- ing the products of specific allele amplifications on an
grant rice is 2-acetyl-1-pyrroline 2AP 59 . This compound agarose gel and identifying the genotypes by their different
is synthesized via L-proline metabolism by the protein molecular sizes, with the upper size identified as the non-
encoded by the betain aldehyde dehydrogenase gene fragrant genotype and the lower size identified as the fra-
badh2 , located on chromosome 810, 11 . An 8-base pair grant rice genotype12 .
bp deletion has been reported in exon 7 of badh2 gene, In plants, proline is one of the amino acids whose levels
which encodes the inactive betaine aldehyde dehydroge- vary in response to environmental stresses, such as high
nase enzyme and is only found in fragrant rice10, 12 . Based salt levels and drought1317 . Proline is the first precursor

＊
Correspondence to: Sompong Sansenya, Department of Chemistry, Faculty of Science and Technology, Rajamangala University of
Technology Thanyaburi, Pathum Thani 12110, THAILAND
E-mail: sompong_s@rmutt.ac.th
Accepted February 7, 2018 (received for review November 3, 2017)
Journal of Oleo Science ISSN 1345-8957 print / ISSN 1347-3352 online
http://www.jstage.jst.go.jp/browse/jos/ http://mc.manusriptcentral.com/jjocs

893
 S. Sansenya, Y. Hua and S. Chumanee

molecule in the 2AP synthesis biochemical pathway4, 10, 18 . for rice production in 2017 United States Department of
Previous reports suggest that the level of 2AP is related to Agriculture USDA. The rice cultivated in Thailand can
the level of proline. Mo et al.19 found that a decrease in be classified into two types the lowland rice cultivars and
solar intensity shade treatment leads to an increased the upland rice cultivars. Among these rice cultivars, the
proline content and 2AP content in rice. The 2AP content most well-known is Thai jasmine rice KDML 105 , due to
was also correlated with the proline content of Aychade its characteristic aroma. Although Thai jasmine rice is
rice under salt condition20 . known worldwide, another local rice cultivar, Thai local
The aroma of rice is due to a mixture of volatile com- rice, has similar characteristics, especially with respect to
pounds. Buttery et al.21 identified nine compounds, namely, the aroma. This rice has been cultivated in areas which are
2AP; E,E -2,4-decadienal; nonanal; hexanal; E -2- suitable only for this particular cultivar, and many cultivars
nonenal; octanal; decanal; 4-vinylguaiacol; and 4-vinylphe- have not been evaluated till date. Therefore, in the present
nol which are classified as major contributors to the aroma study, the 43 Thai local rice cultivars were classified as fra-
intensities of cooked rice. It is well known that 2AP is the grant or non-fragrant, based on the content of active com-
characteristic compound for fragrant rice, while octanal is pounds associated with aroma intensities; the active com-
also associated with aroma intensities; these compounds pound content of these cultivars was also compared with
have been studied extensively in rice19, 21, 22 . Hinge et al.23 , that of Thai jasmine rice.
characterized the volatile compounds of scented and non-
scented rice and found that 26 volatile compounds can be
classified as major volatile compounds. Among these, 14
volatile compounds, including, 2AP; 1-octanol; 1-octen- 2 EXPERIMENTAL
3-ol; E -3-octen-2-one; octanal; E -2-nonenal; nonanal; 2.1 Plant material
heptanal; hexanal; decanal; E -2-octenal; 2-pentylfuran; Grains of 43 Thai local rice cultivars 13 colored and 30
phenylacetaldehyde and pentanal were identified to be as- non-colored rice cultivars, the local rice names of which
sociated with the odor activity value of aroma intensity of are shown in Fig. 1 were obtained from rice fields in
rice. Northeastern Thailand during the harvest season Decem-
Thailand was ranked sixth among the top ten countries ber–February 2015 . KDML 105 grains were used as the

Fig. 1 2AP content of 43 local rice cultivars and KDML105. The figure showed 30 non-colored local rice cultivars and 13
colored local rice cultivars. Among non-colored local rice cultivars, 16 rice cultivars were classified as fragrant rice,
while 14 rice cultivars were classified as non-fragrant rice. While, in the group of colored local rice cultivars, 9 rice
cultivars were classified as fragrant rice, while 4 rice cultivars were classified as non-fragrant rice. The error bars
indicate the standard deviation of means n3 ; the same letters indicate no significant difference Duncan, p
0.05 .
894
J. Oleo Sci. 67, (7) 893-904 (2018)
 The Aroma Intensities of Thai Local Rice

standard fragrant rice; this was harvested during the same Quantification was performed by measuring the peak area
season as the other local rice. Approximately 50 g of all of ions at m/z 83. The amount of 2AP was calculated from
local rice and KDML 105 rice grains were sterilized by the calibration curve, y14.51x9.88 R 20.999 .
soaking in 0.1 NaClO for 30 min. The grains were then
rinsed with distilled water and dried in a hot air oven 2.3 Volatile compounds determination
60 to reduce the moisture content to less than 13 . Volatile compounds were analyzed by gas chromatogra-
The sterilized rice grains were homogenized to fine pieces phy-mass spectrometry using the same capillary column
using a CryoMill Retsch, Germany with liquid nitrogen DB-Wax 60 m0.25 mm i.d.0.25 μm film thickness, J
cooling. The homogenized samples were stored at 4 for &W Scientific, Folsom, CA according to our previously de-
the analysis of 2AP, proline, and aroma compound content. scribed protocol Sansenya et al.25 . Identification of volatile
compounds was performed by comparing the mass spectra
2.2 2-acetyl-1-pyrroline determination with mass spectral libraries of the National Institute of
The 2AP content was determined using our previous Standards and TechnologyNIST, 2011 version . The vola-
protocolSansenya et al.24 and with some modifications to tile compound content was calculated from the peak areas.
the method. 2AP with a purity of 95 was purchased from
BOC Sciences New York, USA . A 5 mg/mL stock solution 2.4 Proline determination
was prepared by adding 2 mL of methanol-toluene 1:1 to The proline content was determined using the modified
10 mg of 2AP; this was then diluted to 0.01, 0.05, 0.1, 0.5, method of Mo et al.19 . Homogenized rice grain 3 g was
1.0, and 2.5 mg/mL with ethanol. One local white rice homogenized in 3 sulfosalicylic acid for 15 min followed
without 2AP detected was used as blank for 2AP analysis. by centrifugation at 10,000 rpm for 15 min and sample fil-
The calibration standards were prepared by adding 1.25, tration using a syringe filter 0.45 μm .
2.5, 5.0, 10.0, 25.0, 50.0, and 100.0 μg of the 2AP standard A mixture of 2 mL of the sample, 3 mL of ninhydrin solu-
to a 20 mL headspace vial containing 1 g of rice blank. The tion, and 2 mL of glacial acetic acid was boiled for 20 min.
rice samples were prepared by weighing about 1 g of The reaction mixture was extracted with 4 mL of toluene
powder samples into 20 mL headspace vials and capped followed by centrifugation at 4000 rpm for 15 min. The ex-
immediately. tracted solution was measured at 520 nm, and the amount
The rice samples were analyzed using a headspace tech- of proline was quantified by comparing the value of absorp-
nique. The GC Autosampler 120 from Agilent CA, USA tion with the standard curve of proline: y 0.413x-0.014
was used. Rice samples were incubated at 120 for 15 min R 20.999 .
with shaking, and then 1 mL of gas was withdrawn with a
gas tight syringe2.5 mL and injected into the GC injector 2.5 Fragrant gene determination
port. Separation of the volatile compounds was achieved Primers were designed using PrimerXhttp://www.bioin -
by gas chromatography–mass spectrometryAgilent 7890A formatics.org/primerx/cgi-bin/DNA_1.cgi , as follows:
GC-7000 Mass Triple Quad using equipment fitted with a forward, 5 TCCTCTCAATACATGGTTTATG- 3 and
capillary column DB-Wax 60 m0.25 mm i.d.0.25 μm reverse, 5 TTGGAAACAAACCTTAACCATAG 3 . The nu-
film thickness, J & W Scientific, Folsom, CA and a quadru- cleotide sequence of the badh2 gene used for designing
pole mass detector. The injector was set at 240, and the the primers was obtained from NCBI, GenBank Accession
split mode was applied with a split ratio of 5:1. Helium gas Number AJ746297.
was used as the carrier gas at a constant flow rate of 1.5 The polymerase chain reaction PCR was performed
mL/min. The following oven temperature program was using the following program: denaturationat 95 for 5
used: the column temperature was isothermally maintained min, 35 cycles of 95 for 1 min, 53 for 1 min, and 72
at 40 for 2 min, programmed at a rate of 10 /min to for 1 min, with a final extension step at 72 for 5 min. The
100 , then at a rate of 5 /min to 150 ; and finally at a PCR products were analyzed by horizontal electrophoresis
rate of 30 /min to 250 , and the column temperature on 2.5 agarose gel and stained with 1.0 μg/mL of ethid-
was then maintained isothermally at 250 for 15 min. The ium bromide. The estimated size of the PCR product for
mass spectrometer was used in the electron ionization fragrant rice is 110 bp and 124 bp for non-fragrant rice.
mode with the ion source temperature set at 230 and
ionization energy set at 70 eV. The multi reaction monitor- 2.6 Statistic analysis
ing MRM mode was used to analyze the 2AP content. Data were analyzed using the Statistical Package for the
Helium gas was used as the quenching gas at a flow rate of Social Sciences SPSS 22.0 software for Windows. Quanti-
2.35 mL/min. Nitrogen gas was used as the collision gas at tative data are presented as mean values with standard de-
a flow rate of 1.5 mL/min. The precursor ion m/z 111 and viation values obtained from three replicates. All analyses
the product ion m/z 83 were selected for 2AP with a colli- were processed by one-way analysis of variance ANOVA .
sion energy of 5 v. The MS detection dwell time was 30 ms. A Duncan s multiple range test was used to determine sig-
895
J. Oleo Sci. 67, (7) 893-904 (2018)
 S. Sansenya, Y. Hua and S. Chumanee

nificant differences. The level of significance was set at p tion in18 non-fragrant rice cultivars is in the range of 0.09
0.05. 0.016 μg/g to 0.540.042 μg/g. The difference between
the highest 2AP content0.540.042 μg/g of non-fragrant
rice and the lowest 2AP content 2.790.560 μg/g of fra-
grant rice is approximately 5.16-fold. A similar result was
3 RESULTS AND DISCUSSION observed for the 2AP content of 56 rice cultivars from Lao
3.1 2AP content of 43 local rice cultivars PDR, with the highest 2AP content 0.074 μg/g of non-fra-
The 2AP content of 43 local rice cultivars 13 colored grant rice measuring approximately 5.40-fold less than the
and 30 non-colored rice cultivars and Thai jasmine rice lowest 2AP content 0.405 μg/g of fragrant rice31 . Prior
KDML 105 are shown in Fig. 1. The 2AP content of studies have shown that the 2AP content of 13 Indian local
KDML 105 was 17.600.90 μg/g, while the 2AP content of rice cultivars differed approximately by 1.92-fold between
local rice cultivars was in the range of 0.090.019 μg/g to non-fragrant and fragrant rice34 . Furthermore, in two local
13.471.050 μg/g. KDML 105 is well known as a fragrant rice cultivars, Khao Luang Pra-Tan and Khao Hom Nin,
rice variety with a high 2AP content2630 . Our results show both classified as non-fragrant rice, the 2AP content could
that the 2AP content of each of the 43 local rice cultivars not be detected. Previously published studies have report-
was lower than that of KDML 105. The highest and lowest ed that the 2AP content cannot be detected in some other
2AP content were obtained for the Khao Jao 15 and Khao types of non-fragrant rice, such as IR-64 rice23 . In addition,
Pan Tai Bai local rice cultivars, respectively. The 2AP Grimm et al. reported that the 2AP content could not be
content of these rice cultivars was lower than that of detected in 6 non-fragrant rice cultivars, including Drew,
KDML 105 by approximately 1.30-fold and 195.50-fold, re- Giant Embryo, Watermaid, Uncle Ben s, Bhutanese Red,
spectively. It was previously reported that the 2AP content and Himalayan Red32. Rice has been classified as fragrant
of 56 local rice cultivars from Lao People s Democratic or non-fragrant, based on the presence of the recessive
Republic PDR was found to be in the range of 0.074 to badh2 allele, as first reported by Bradbury et al.12 . In this
0.688 μg/g31 . Our results showed that the 2AP content in study, KDML 105 rice was used as the standard fragrant
the Thai cultivars was higher than that in Lao PDR local rice cultivar, and the PCR product or the recessive badh2
rice by approximately 1.2- to 19.5-fold. The disparity in the gene of this rice was approximately 110 base pairs bp
calculated2AP content might be due to the various quanti- Fig. 2 . Khao Gor Dieow exhibited a 2AP content of 0.54
fication methods used, the nature of the different rice cul- 0.042 μg/g, and a PCR product measuring approximately
tivars, and differences in the cultivation regions. 124 bp. The PCR productsfor Khao Gor Kor 6, Khao
2AP has been reported as a major contributor to the Pathum Thani 1, and Khao Nieow Gam were also approxi-
characteristic aroma compounds of colored rice22 . In this mately 110 bp, which was comparable to that for KDML
study, we have identified the 2AP content of 13 colored 105 Fig. 2 . Based on the 2AP content of Khao Gor Dieow,
local rice cultivars Fig. 1 and found that the 2AP concen- which was the highest compared to that of other local rice
tration was in the range of 0.110.015 to 10.410.920 μg/ cultivars including Khao Hang Yee 1, Khao In-Bplaeng,
g. The 2AP content for colored cultivars was relatively Khao Hang Yee 2, Khao Nieow Kieow-Ngoo, Khoa Leuang
lower than that for non-colored cultivars Fig. 1 . Our find- On, Khao Kao Yai, Khao Gam, Khao Yai, Khao Puan Glang,
ings agree with those from a study by Grimm et al.32 , who Khao Gam 101, Khao Rak Pai, Khao Jao Kao, Khao Pan Tai
reported that the 2AP content of non-colored rice was Bai, Khao Hom Surin, Khao Hom Nin, Khao Luang Pra-Tan
higher than that of colored rice. For example, cultivars, 0.090.016 μg/g to 0.540.042 μg/g . Thus, the local
such as Sierra rice and Dellrose rice, showed a higher 2AP rice cultivars with a 2AP content lower than that of Khao
content than Black forbidden rice and IAC600 rice, which Gor Dieow might be expected to show a PCR product
are colored rice cultivars. similar in size to that of Khao Gor Dieow. On the other
hand, All three local rice cultivars Khao Gor Kor 6, Khao
3.2 Fragrant and non-fragrant rice classification Pathum Thani 1, and Khao Nieow Gam had a 2AP content
2AP has been reported in both fragrant and non-fragrant in the range for fragrant rice cultivars2.790.560 μg/g to
rice cultivars, but is only found in small amounts in non- 13.471.050 μg/g . Therefore, other local rice cultivars
fragrant rice8, 31, 33, 34 . 2AP is formed during L-proline me- with a 2AP concentration in this range could be expected
tabolism, which is associated with the recessive from of the to have a PCR product similar in size to that of KDML 105.
badh2 gene10, 12, 35 . We have classified 43 fragrant and non- Our findings are in agreement with those in the report of
fragrant local rice cultivars based on the 2AP content and Bounphanousay et al.31 , who showed that the different
presence or absence of this recessive badh2 allele. Our sizes of the recessive badh2 gene products could be used
results indicate that the 25 local rice cultivars classified as to classify the local rice cultivars from Lao PDR. The
fragrant rice have a 2AP content in the range of 2.79 authors found that the molecular analysis results for all
0.560 μg/g to 13.471.050 μg/g, while the 2AP concentra- local rice cultivars correlated with the 2AP content, with
896
J. Oleo Sci. 67, (7) 893-904 (2018)
 The Aroma Intensities of Thai Local Rice

was similar in size to the PCR product of non-fragrant rice,

while the smaller product approximated the PCR product
size of fragrant rice.

3.3 Correlation between proline content and 2-acetyl-

1-pyrroline content
The proline content was determined for grains of fra-
grant and non-fragrant local rice cultivars Table 1 . The
proline content ranged from 1.520.09 to 4.640.34 μg/g.
Proline is the precursor for the 2AP synthesis pathway4, 10, 18 .
Our results indicate that the 2AP content was not correlat-
ed with the proline content of the grains of local rice. For
example, Khao In-Bplaeng was classified as non-fragrant
rice and has a high proline content, while KDML 105 was
the standard fragrant rice but showed a low proline
content. Thus, our results indicate that the accumulation
of proline might not affect the accumulation of 2AP in
grains of local rice. Previously published work has reported
the association between proline content and 2AP content
in rice. Poonlaphdecha et al.20 found that the 2AP content
Fig. 2 The 2.5 agarose gel of 5 rice cultivars. Lane 3; increases and is correlated with the proline content under
corresponding to standard fragrant rice cultivars salt stress. Recently, Mo et al.19 reported that an increased
KDML 105 with the PCR product approximately 2AP content in grains is correlated with a higher proline
110 bp. Lane 2; the PCR product of Khao Gor concentration under low light intensity conditions.
Dieow with the PCR product approximately 124 bp 2AP is formed in rice grains by two mechanisms. 2AP
and this rice cultivars was classified as non-fragrant can be synthesized from other parts of rice and can be
rice. Lane 4, 5 and 6; the PCR product of three rice translocated to the grain during grain formation. 2AP syn-
cultivars including of Khao Gor Kor 6, Khao thesis can occur inrice grains after translocation of the
Pathum Thani 1 and Khao Nieow Gam and all three proline precursor from another part of the rice into the
rice cultivars were classified as fragrant rice. Lane grains19, 20, 23, 37 . 2AP accumulation may be affected by envi-
7; indicated the negative control. ronmental factors. Yoshihashi et al.28 reported that during
grain formation ina drought-affected area, the 2AP content
fragrant rice yielding smaller PCR products. The fragrant of rice grains was higher than that in areas not affected by
rice cultivars analyzed in this study showed a 2AP content drought. Proline content in rice can also be affected by en-
similar to that of the standard fragrant rice. In contrast, vironmental factors. In rice grains, proline accumulation
non-fragrant rice yielded larger PCR products and had a depends on the stress factors in different areas of rice cul-
2AP content lower than that of standard fragrant rice. To tivation 17, 38 . Moreover, Aspinall et al. 13 reported that
investigate this further, the two sizes of PCR products for during grain formation, the proline content was maintained
Khao Gor Kor 6 were analyzed, and the smaller product by its incorporation into proteins. The 2AP and proline
was found to be similar to that of KDML 105, while the content in grains of the 43 local rice cultivars analyzed in
larger product was similar in size to the PCR product of this study were obtained during the same harvest season
Khao Gor Dieow Fig. 2 . Khao Gor Kor 6 rice is generated but from different cultivation areas. The lack of a correla-
from KDML 105 by mutations induced on exposure to tion between the contents of the two compounds in rice
gamma irradiation. The mutations in Khao Gor Kor 6 may grains analyzed in this study may be explained by the dif-
affect the badh2 gene, yielding a PCR product similar in ferential accumulation of 2AP and proline in grains de-
size to those from non-fragrant rice Fig. 2 . The PCR pending on environmental conditions in each cultivation
product size for Khao Gor Kor 6 was correlated with its area; in addition, during grain formation the proline resi-
2AP content, and a decreased 2AP content of Khao Gor dues were incorporated into proteins.
Kor 6 was observed when compared to the 2AP content of
KDML 105 Fig. 1 . Our results are concordant with those 3.4 Aroma compounds of fragrant and non-fragrant rice
reported by Ahmadikhah et al. 36 , who showed that the The volatile compounds present in 14 local rice cultivars
PCR products of badh2 in mutant rice the mutant rice 9 fragrant rice and 5 non-fragrant rice were identified
were generated by crossing fragrant and non-fragrant gen- and are listed in Table 2. One hundred forty volatile com-
otype rice were of two different sizes. The larger product pounds were identified. The number of volatile compounds
897
J. Oleo Sci. 67, (7) 893-904 (2018)
 S. Sansenya, Y. Hua and S. Chumanee

Table 1 Proline content obtained from the grains of fragrant F and

non-fragrantN local rice cultivars.
Rice cultivar Genotype Proline content (μg/g)
Khao In-Bplaeng N 4.64±0.34a
Khao Jao Hom Tung F 3.91±0.18b
Khao Nieow E-Dtia F 3.83±0.33bc
Khao Nieow Laao F 3.68±0.14bcd
Khao Bplaa Chiw F 3.65±0.06bcdf
Khao Hang Yee 1 N 3.59±0.24cdf
Khao Nieow Kieow-Ngoo N 3.45±0.07dfg
Khao Jao 15 F 3.39±0.23fgh
Khao Puan Glang N 3.27±0.10gh
Khao Sin Lek F 3.13±0.17hi
Khao Jao Kao N 2.97±0.16ij
Khao Piw Tong F 2.91±0.20ijk
Khao Hang Yee 2 N 2.88±0.12ijk
Khao Jao Daeng F 2.78±0.08jk
Khao Bpraa Jeen F 2.66±0.10kl
Khao Hom U-Dom F 2.65±0.24kl
Khao Man Bpoo F 2.64±0.08klm
Khao Pa-Maa Leuang F 2.45±0.06lmn
Khao Pathum Thani 1 F 2.44±0.29lmn
Khao Leuang Noi F 2.39±0.08lmno
Khao Gor Kor 6 F 2.35±0.09mno
Khao Gor Dieow N 2.31±0.10nop
Khao Leum Pua F 2.11±0.11opq
Khao Pan Tai Bai N 2.07±0.07pq
Khao Wan F 2.06±0.20pq
Khoa Leuang On N 1.98±0.08qr
Khao Luang Pra-Tan N 1.95±0.07qr
KDML 105 F 1.92±0.04qr
Khao Yai N 1.85±0.08rs
Khao Rak Pai N 1.76±0.14rs
Khao Soh Maalee F 1.75±0.07rs
Khao Kao Yai N 1.52±0.09s
Values are means±standard deviation (n=3). Values in the same column
with the same superscript letter are not significantly different (Duncan, p >
0.05). F, means fragrant rice and N, means non- fragrant rice.

in non-fragrant rice cultivars was greater than that in fra- results contradict data from prior studies, such as the
grant rice cultivars Fig. 3 . The highest number of volatile study by Hinge et al.23 , who found that the number of vola-
compounds was obtained from Khao Mali Daeng, Khao tile compounds present in fragrant rice was higher than
Gam, and Khao Hom Nin rice cultivars, all 3 of which that in non-fragrant rice. In addition, Bryant et al.39 report-
contain 53 compounds and are classified as non-fragrant ed that the number of volatile compounds in non-fragrant
rice. In contrast, the lowest number of volatile compounds rice Cocodrie was similar to that in fragrant rice Dell-
43 was obtained from Khao Jao 15 fragrant rice . Our rose . Previously published studies and our results indicate
898
J. Oleo Sci. 67, (7) 893-904 (2018)
 The Aroma Intensities of Thai Local Rice

Table 2 Volatile compounds of fragrant and non-fragrant rice cultivars which analyzed from rice grain.
Peak Area (%)2
Retention
Rice genotype
No. Compounds time
I II III IV V VI VII VIII IX X XI XII XIII XIV
(min)
F F F F F F F F F N N N N N
1 2-Pentanone 14.615 1.6 3 － － － － － － － － － － － －
2 Pentanal 14.656 － － － － － 1.12 － － － 1.17 － － － －
3 Acetonitrile 16.047 2.5 1.5 － － 1.15 － － － － － 1.28 － 1.35 1.26
4 Trichloromethane 17.426 6.5 － 4.24 2.75 3.87 2.28 3.46 3.66 5.33 1.83 15.73 2.98 15.07 15.55
5 Toluene 18.286 3.5 1.5 1.60 1.11 2.45 － 0.95 0.87 3.06 0.93 1.75 2.01 1.38 1.28
6 Hexanal 21.113 4.4 10.0 11.7 7.79 10.35 14.02 14.68 12.28 7.34 12.56 3.58 11.19 1.75 1.95
7 4-methyl-2-hexanone 23.396 0.9 4.8 － 1.79 2.16 0.87 0.94 － 2.47 － 0.93 0.53 － －
8 Ethylbenzene 23.571 － － － － － － － － － － 1.01 － 1.03 0.83
9 2-Pentanol 24.052 5.1 － － － － － － － － － － － － －
10 (R)-(-)-2-Pentanol 24.054 － － － － － － － 0.67 － － － － － －
11 2-n-Butyl furan 24.163 － 1.0 － － 1.15 0.73 0.80 0.56 － － － 0.92 － －
12 1-Methoxy-2-propanol 24.200 0.9 － － － － － － － － － － － － －
13 o-Xylene 24.371 － － － － － － － － － － － － － 0.69
14 1,3-Dimethyl-benzene 24.402 － － － － － － － － － － 0.75 － 0.77 －
15 2-Heptanone 27.047 0.7 0.9 0.94 0.86 1.88 1.74 1.11 1.28 2.97 2.37 － 1.51 － －
16 Heptanal 27.163 1.2 1.5 2.18 1.56 1.55 1.54 2.54 1.77 1.60 1.91 1.14 1.59 0.83 0.57
17 Dodecane 28.021 1.0 0.8 0.67 0.87 0.73 0.77 1.01 0.46 1.05 0.72 2.00 0.69 1.69 1.54
18 2-Pentyl-furan 29.691 4.9 9.0 6.57 5.23 7.23 7.74 5.88 6.61 4.71 3.47 3.00 8.62 2.47 2.14
19 2,7,10-Trimethyl-dodecane 30.385 － － － － － － － － 0.67 － － － 0.77 0.76
20 Styrene 30.916 6.1 3.0 0.89 0.85 1.94 0.96 1.01 0.82 3.28 0.62 12.81 1.58 16.34 16.54
21 1-Pentanethiol 30.987 － 1.7 1.57 2.01 － － 1.67 1.22 1.60 － － 1.84 － －
22 1-Pentanol 30.998 － － － － 1.94 1.79 － － － 2.02 － － － －
23 2-Octanone 32.503 － － － 0.52 0.60 － － － － － － 0.50 － －
24 4-Methyl-2-hexanol 32.496 － 0.9 － － － － － － － － － － － －
25 Octanal 32.669 1.7 2.1 3.40 3.08 2.63 2.65 3.61 4.17 2.17 3.15 1.40 2.76 1.22 0.86
26 2,6,11-Trimethyl-dodecane 33.097 － － － － － － － － － － － － 0.63 0.44
27 Tridecane 33.194 1.8 1.4 0.85 1.38 0.85 0.81 1.10 0.76 1.16 0.66 5.49 0.94 5.16 4.48
28 (Z)-2-Heptenal 34.379 － 2.2 1.83 1.94 1.56 1.96 2.32 2.25 1.19 1.98 1.02 1.73 － 0.70
29 (E)-2-Heptenal 34.387 1.3 － － － － － － － － － － － － －
30 (2R,4R)-2,4-Dimethylheptan-1-ol 34.391 － － － － － － － － － － － － 0.95 －
31 2-hexyl-furan 34.732 － － － － － － － 0.68 － － － － － －
32 2,6,10-Trimethyl-dodecane 35.073 － － － － － － － － － － 1.42 － － －
33 2,2,4,4,6,8,8-Heptamethyl-nonane 35.073 － － － － － － － － － － － － 0.92 －
34 6-Methyl-5-hepten-2-one 35.079 1.4 1.7 1.26 1.00 0.83 0.79 0.94 0.61 1.19 0.79 － 0.58 － 0.75
35 5-(2-Methylpropyl)-nonane 35.645 － － － － － － － － － － 0.69 － － －
36 2,6,10-Trimethyl-pentadecane 35.916 － － － － － － － － － － 0.58 － － －
37 2,6,8-Trimethyl-decane 35.916 － － － － － － － － － － － － 0.76 －
38 1-Hexanol 36.011 5.3 6.6 6.48 8.72 7.63 7.56 4.53 3.50 3.12 1.36 － 6.87 2.56 1.93
39 3-Methyl-tridecane 36.384 － － － － － － － － － － 1.40 － 1.14 0.82
40 Carbonic acid, 2-ethoxyethyl 2-methoxyethyl ester 36.805 － － － － － － － － － － － － － 1.08
41 2-Nonanone 37.528 － － － － － － － － － － － 0.48 － －
42 Nonanal 37.711 5.1 5.8 8.19 7.81 5.04 7.12 8.61 8.96 6.38 13.91 5.69 6.49 3.84 2.85
43 2-Methyl-tridecane 37.814 0.8 － － － － － － － － － － － － －
44 3-Methyl-tetradecane 37.818 － － － － － － － － － － － － － 0.57
45 6-Propyl-tridecane 37.821 － － － － － － － － － － － － 0.92 －
46 5,5-Dibutylnonane 37.822 － － － － － － － － － － 1.09 － － －
47 Tetradecane 37.908 1.7 1.5 1.34 1.60 1.34 1.30 1.96 1.21 1.77 － 4.08 1.69 4.63 0.69
48 2-Butoxy-ethanol 38.301 － － － － － － － － － － 0.60 － － －
49 3,5-Octadien-2-ol 38.384 － － － － － 1.26 1.01 － 0.92 0.63 － － － －
50 3-Octen-2-one 38.390 － 1.5 0.99 1.36 0.90 － － 1.25 － － － 1.65 － －
51 2-Decanone 39.024 － － － － 1.06 0.45 － 0.57 － 0.99 － － － －
52 6-Methoxy-2-hexanone 39.031 0.6 － － － － － － － － － － 0.47 － －
53 1-Methyl-4-(1-methylethyl)-cis-cyclohexanol 39.032 － － 0.52 0.94 0.86 0.86 － 0.71 － － － － － －
54 3-Furaldehyde 39.247 － 1.0 － － － － 1.27 － 1.17 － － － － －
55 Furfural 39.249 0.9 － 0.90 0.60 0.57 0.55 － 0.67 － 1.05 0.98 0.84 0.93 0.85
56 (E)-2-Octenal 39.351 － 1.5 1.96 2.18 1.18 2.11 1.93 2.86 1.06 2.29 － 1.57 － －
57 (E)-2-dodecenal 39.353 － － － － － － － － － － － － － 0.90
58 (Z)-3-Hexadecene 39.359 1.0 － － － － － － － － － － － － －
59 (E)-9-Eicosene 39.367 － － － － － － － － － － 0.92 － － －
60 Pentadecane 39.789 － － － － － － － － － － － － 0.88 0.89
61 2-Hexyl-1-decanol 39.916 － － － 0.53 － － － － － － － － 0.58 －
62 1-Tetradecene 39.923 0.8 － － － － 0.55 － － － － － － － －
63 3-Tetradecanol 39.926 － － － － － － － － － － 0.55 － － －
64 Acetic acid 40.262 1.9 2.0 3.64 2.54 2.61 1.34 2.39 1.98 5.22 3.99 2.00 1.40 2.25 4.30
65 1-Octen-3-ol 40.342 2.7 3.4 2.82 3.06 3.78 4.11 3.35 2.84 2.78 2.75 1.79 3.02 1.75 1.42
66 1-Heptanol 40.635 － 1.5 1.32 2.11 1.34 1.62 1.51 1.15 1.05 1.73 － 1.67 － －
67 5-Methyl-1-hexanol 40.639 1.6 － － － － － － － － － － － － －
68 2-Butyl-1-octanol 40.639 － － － － － － － － － － 0.72 － 0.55 －
69 2-Ethyl-1-decanol 40.639 － － － － － － － － － － － － 1.18 －
70 (R,S)-5-Ethyl-6-methyl-3E-hepten-2-one 40.950 0.6 － 0.75 － 0.60 － － － － － － － － －
71 2-Ethyl-1-hexanol 42.102 － － － － － － － 0.68 － － 2.12 － － －
72 Undecyl-cyclopentane, 42.156 0.9 － － － － － － － － － 1.19 － － 1.03
73 1-Hexadecanol 42.159 － － － 0.98 0.93 － － － 1.22 － 1.73 1.06 1.23 1.28
74 Nonyl-cyclopentane 42.160 － － － － － － － － － － － 1.64 －
75 Decanal 42.381 1.2 1.3 1.81 1.53 2.69 2.48 1.80 2.24 － 1.11 0.87 1.59 0.93 0.52

899
J. Oleo Sci. 67, (7) 893-904 (2018)
 S. Sansenya, Y. Hua and S. Chumanee

Table 2 Continued.
Peak Area (%)2
Retention
Rice genotype
No. Compounds time
I II III IV V VI VII VIII IX X XI XII XIII XIV
(min)
F F F F F F F F F N N N N N
76 Benzaldehyde 43.403 4.6 7.7 3.55 2.62 3.03 3.54 6.19 5.26 8.51 4.70 3.62 3.26 4.02 4.61
77 4-Methyl-hexadecane 43.910 － － － － － － － － － － 0.45 － － －
78 7-Methyl-pentadecane 43.911 － － － － － － － － － － － － 0.69 －
79 2-Dodecenal 43.967 － － － － － － － － － 0.69 － － － －
80 (E)-2-Nonenal 43.974 0.7 1.2 1.10 1.07 0.58 0.84 0.77 1.41 － － 0.55 0.77 0.43 －
81 3,7-dimethyl-1,6-Octadien-3-ol 44.451 － 2.1 0.60 0.83 0.60 0.78 1.15 3.84 3.68 0.83 － 0.76 － －
82 4-Ethyl-tetradecane 44.454 0.7 － － － － － － － － － 0.73 － 0.57 0.55
83 1-Octanol 44.967 1.8 2.2 2.02 2.94 1.79 2.44 2.21 1.52 1.59 3.85 1.19 2.36 1.70 1.05
84 3-Methyl-pentadecane 45.085 － － － － － － － － － － 0.48 － 0.66 0.60
85 2-Dodecanol 45.773 － － － － 1.49 － － － － － － － － －
86 2,3-Butanediol 45.781 － － － 1.59 － － － － － － － － － －
87 Bornyl acetate 46.173 － － － － － － － － － － － 0.46 － －
88 Isoborneol acetate 46.177 － 0.6 － － － － － － 0.61 － － － － －
89 Isobornyl acetate 46.178 1.0 － － － － － － － － － － － － －
90 2-Methyl-pentadecane 46.301 0.6 0.7 － － － － － － 0.80 － 0.77 0.43 0.92 0.82
91 2-Methyl-heptadecane 46.307 － － － － － － － － － － 0.72 － 0.83 0.75
92 Hexadecane 46.418 － － － － － － － － 0.80 0.66 1.55 － 0.98 0.54
93 n-Nonylcyclohexane 46.734 － － － － － － － － － － － － － 0.57
94 (E)-2-Decenal 48.375 － － 0.81 1.02 － 0.50 － 3.42 － 0.70 － － － －
95 Acetophenone 48.661 － － － － － － － － － － 0.59 － 0.80 0.93
96 2-Ethyl-2-methyl-tridecanol 48.864 － － － － － － － － － － 0.74 － － －
97 1-Nonanol 49.045 1.9 1.5 0.81 2.11 1.25 1.59 1.31 1.00 0.92 1.50 0.81 1.00 1.33 0.81
98 Sulfurous acid, octyl 2-pentyl ester 49.209 1.6 － － － － － － － － － － － － －
99 2-Butyl-2-octenal 49.312 － － － － 2.89 2.49 － 0.76 － － － 1.60 － －
100 (Z)-3,7-Dimethylocta-2,6-dienal 49.871 － 1.2 － － 0.53 － － － 0.82 － － － － －
101 6,10-Dimethyl-2-undecanone 50.057 － － － － － － － － － 0.56 － － － －
102 (E,E)-2,4-Nonadienal 50.624 － 1.4 0.69 0.76 － 0.56 － 0.59 － － － 0.56 － －
103 (Z)-3-Decen-1-ol 50.627 0.7 － － － － － － － － － － － － －
104 2,4-Dodecadienal 50.627 － － － － － － 0.78 － － － － － － －
105 1,2-Dimethoxy-Benzene 51.390 － － － － － － － － － － － 1.81 － －
106 (E)-3,7-Dimethyl-2,6-octadienal 51.779 － 1.4 － － 0.71 － － － 0.93 － 0.61 － － －
107 Pentanoic acid 51.939 － － － － － － － － － 0.54 － － － －
108 Pentanoic acid, 3-hydroxy-2-methyl-, propyl ester 52.099 1.1 － － － － － － － － － － － － －
109 2-Undecenal 52.518 － － 0.53 0.71 － － － 0.73 － － － － － －
110 Methoxy-phenyl-oxime 52.694 1.4 － 1.77 1.37 1.10 1.55 1.86 1.01 2.67 2.23 － 0.89 － －
111 3-Tridecanone 53.333 － － － － － － － － － － 0.60 － － －
112 Hexanoic acid 55.796 1.9 2.3 3.32 4.37 5.05 3.77 3.64 3.11 3.95 5.22 1.93 6.48 1.07 2.14
113 trans-Geranylacetone 56.135 0.6 0.9 0.58 0.48 － 0.57 0.58 0.47 0.75 0.42 0.55 － 0.56 0.58
114 2-methoxy-phenol 56.311 － － － － － － 1.29 － － － － － － －
Propanoic acid, 2-methyl-, 3-hydroxy-2,4,4-
115 56.631 － － 0.96 1.12 0.66 0.77 0.79 0.47 － 0.63 － － － －
trimethylpentyl ester
Propanoic acid, 2-methyl-, 2-ethyl-3-hydroxyhexyl
116 56.631 － － － － － － － － － － － － － 0.96
ester
117 Benzyl alcohol 56.906 1.6 1.3 1.39 1.04 1.91 1.00 0.94 0.70 1.36 1.16 0.91 0.87 1.41 1.84
118 2,2,4-Trimethyl-1,3-pentanediol diisobutyrate 57.222 － － － 0.78 － － － － － － － － － －
Propanoic acid, 2-methyl-, 2,2-dimethyl-1-(2-hydroxy-
119 57.224 － － 0.65 － － 0.49 － － － － － － － 0.67
1-methylethyl)propyl ester
120 2-Methyl-2-pentenoic acid 58.267 0.9 － － － － － － － － － － － － －
121 2,3-Dimethyl-2-pentenoic acid 58.512 4.3 － － － － － － 0.70 － － － － － －
122 Heptanoic acid 59.207 － － － 0.80 0.64 0.54 － － 0.80 0.64 － 0.69 － －
123 1,2-Dimethoxy-4-chloro-benzene 60.361 － － － － － － － － － － － 0.46 － －
124 Dihydro-5-pentyl-2(3H)-furanone 61.614 － － － 1.07 － － － － － － － 0.95 － －
125 Octanoic Acid 62.272 0.7 0.8 0.83 2.09 1.18 0.98 1.02 1.18 1.20 1.58 0.54 1.50 － －
126 6,10,14-trimethyl-2-Pentadecanone 64.010 1.3 1.6 1.01 1.34 1.05 0.86 1.20 0.91 1.80 1.02 0.54 0.48 0.84 0.91
127 Octasiloxane 64.510 － － － － － － － － － 0.47 － － － －
128 Nonanoic acid 65.059 1.6 1.2 1.44 2.69 1.13 1.59 1.67 3.62 3.48 4.38 0.99 1.93 0.99 0.73
129 Hexadecanoic acid, methyl ester 66.296 － － － － － － － － － － － － － 0.58
130 n-Decanoic acid 67.642 － － － － － － － 0.62 0.62 0.48 － － － －
131 2-Ethylhexyl salicylate 68.429 － － － － － － － － － － － － 0.71 －
(R)-4,4,7a-Trimethyl-5,6,7,7a-tetrahydrobenzofuran-
132 69.872 － － 0.61 － － － － － － － － － － －
2(4H)-one
133 Diethyl Phthalate 70.044 － － 0.68 0.61 0.52 1.59 1.96 0.56 2.19 0.59 － 0.50 － －
134 Butyl hexadecanoate 71.248 － 0.4 0.56 0.43 － 0.39 0.53 0.45 － 0.33 － － － －
135 Dodecanoic acid 72.424 0.7 － 0.99 0.60 － 0.83 0.60 － 0.61 － － 0.41 0.39
136 n-Hexadecanoic acid 73.365 － － 5.28 － － 1.96 － － － 2.56 1.97 1.67 2.78
137 Isovanillin 74.703 － － 0.67 － － － － － － － － － － －
138 Vanillin 74.703 － － － 0.54 － － － － － － － － － －
139 (Z,Z)-9,12-Octadecadienoic acid 77.772 － － － － － － － － － 1.26 － － － －
140 Tetradecanoic acid 78.419 － － 0.52 － 0.88 0.86 0.63 － － － 0.81 1.10 － －
Note. Rice cultivars including, I; KDML 105, II; Khao Jao 15, III; Khao Mali Nin, IV; Khao Bpraa Jeen, V; Khao Bplaa Chiw, VI; Khao Gor Kor 6, VII; Khao Jao Hom Nin, VIII; Khao Pathum Thani 1, IX; Khao Sin
Lek, X; Khao Mali Daeng, XI; Khao Gam, XII; Khao Gam 101, XIII; Khao Hom Surin, XIV; Khao Hom Nin. F; Fragrant rice, N; Non-fragrant rice. - ; absence of compounds

900
J. Oleo Sci. 67, (7) 893-904 (2018)
 The Aroma Intensities of Thai Local Rice

Fig. 3 The number of volatile compounds identified from 14 local rice cultivars which includes 9 fragrant rice and 5 non-
fragrant rice.

that the number of volatile compounds might depend on yl-hexadecane; 7-methyl-pentadecane; 2-dodecenal; bornyl
the rice cultivars and area of rice cultivation. As was re- acetate; n-nonylcyclohexane; 2-ethyl-2-methyl-tridecanol;
ported by Liyanaarachchi et al.40 , the volatile compound 6,10-dimethyl-2-undecanone; 1,2-dimethoxy-benzene; pen-
profiles of rice vary with the rice cultivars analyzed. tanoic acid; 3-tridecanone; propanoic acid, 2-methyl-,
Among 140 volatile compounds, 17 compounds were ob- 2-ethyl-3-hydroxyhexyl ester; 1,2-dimethoxy-4-chloro-ben-
served in all rice cultivars, namely, hexanal; heptanal; do- zene; octasiloxane; hexadecanoic acid, methyl ester; 2-eth-
decane; 2-pentyl-furan; styrene; octanal; tridecane; ylhexyl salicylate and Z,Z -9,12-octadecadienoic acid. The
nonanal; acetic acid; 1-octen-3-ol; benzaldehyde; 1-octanol; presence of specific volatile compounds in different rice
1-nonanol; hexanoic acid; benzyl alcohol; 6,10,14-trimeth- cultivars may be related to the odor-active compound of
yl-2-pentadecanone and nonanoic acid. Twenty-three vola- that rice 8, 23, 3941 . Although non-fragrant rice cultivars
tile compounds were observed only in fragrant riceculti- contain a small amount of major aroma compounds, such
vars, including 2-pentanol; R -- -2-pentanol; 1-methoxy- as 2AP, some volatile compounds, such as 2-butoxy-etha-
2-propanol; 4-methyl-2-hexanol; E -2-heptenal; 2-hexyl- nol, are only found in non-fragrant rice and are believed to
furan; Z -3-hexadecene; 5-methyl-1-hexanol; contribute to its aroma intensities40 .
2-dodecanol; 2,3-butanediol; isobornyl acetate; sulfurous
acid, octyl 2-pentyl ester; 2-butyl-2-octenal; Z -3-decen- 3.5 Volatile compound contribution to aroma intensities in
1-ol; 2,4-dodecadienal; pentanoic acid; 3-hydroxy-2-meth- Thai local rice
yl-, propyl ester; 2-methoxy-phenol; 2,2,4-trimethyl-1,3- Among the detected volatile compounds, 2AP is well
pentanediol diisobutyrate; 2-methyl-2-pentenoic acid; R known as a major contributor to aroma intensities8, 21, 23, 39 .
-4,4,7a-trimethyl-5,6,7,7a-tetrahydrobenzofuran-2 4H Our results showed the presence of 2AP in all rice cultivars
-one; isovanillin and vanillin. In contrast, 34 volatile com- except Khao Luang Pra-Tan and Khao Hom Nin. Moreover,
pounds were observed only in non-fragrant rice cultivars, a higher 2AP content was recorded in fragrant than in non-
namely, o-xylene; 2R,4R -2,4-dimethylheptan-1-ol; fragrant rice. Along with 2AP; hexanal; octanal; nonanal;
2,6,10-trimethyl-dodecane; 2,2,4,4,6,8,8-heptamethyl-non- 1-octen-3-ol; benzaldehyde and 1-nonanolwere detected in
ane; 5- 2-methylpropyl -nonane; 2,6,10-trimethyl-pen- all 14 local rice cultivars and were major contributors to
tadecane; 2,6,8-trimethyl-decane; carbonic acid, 2-ethoxy- the aroma intensities of rice grains. Although the major
ethyl 2-methoxyethyl ester; 2-nonanone; 3-methyl- aroma compounds were identified in both fragrant and
2
tetradecane; 6-propyl-tridecane; 5,5-dibutylnonane; non-fragrant rice, a higher content peak area of
2-butoxy-ethanol; E -2-dodecenal; E -9-eicosene; 3-tet- aroma compounds was measured infragrant rice compared
radecanol; 2-ethyl-1-decanol; nonyl-cyclopentane; 4-meth- to non-fragrant rice Table 2 . Mathure et al.42 also report-
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J. Oleo Sci. 67, (7) 893-904 (2018)
 S. Sansenya, Y. Hua and S. Chumanee

ed that octanal and nonanal levels in Basmati rice are Acknowledgements

higher than in non-fragrant rice. Hexanal; octanal; nonanal; This work was supported by the National Research
1-octen-3-ol and benzaldehyde were recorded at higher Council of Thailand Grant 2560A16502120 , and the
levels in fragrant than in non-fragrant rice23 . In addition, Higher Education Research Promotion and National Re-
volatile compounds, which were responsible for aroma in- search University Project of Thailand, Office of the Higher
tensities, were present in greater amounts in colored than Education Commission Grant 2559A16562003 , Rajaman-
in non-colored rice Table 2 . Ajarayasiri et al.43 found that gala University of Technology Thanyaburi and Phetchabun
the level of aroma compounds in black glutinous rice was Rajabhat University. We are also grateful to Sarawut Wong-
higher than that in white glutinous rice. E -2-heptenal; piput for assistance providing plant samples.
isovanillin and vanillin,three other volatile compounds that
contribute to aroma intensities, were only recorded in
KDML 105, Khao Mali Nin, and Khao Bpraa Jeen, respec-
tively. Previously published studies have reported that Conflict of interest
these three compounds contribute to the aroma intensities The authors declare no any conflict of interest.
of fragrant rice21, 34, 41 . Nine aroma compounds,namely,1-
pentanol; 6-methyl-5-hepten-2-one; 1-hexanol; 2-butoxy-
ethanol; E -2-octenal; 1-tetradecene; decanal; E -2-
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