Changes of amygdalin and volatile components of apricot kernels during the ultrasonically-accelerated debitterizing

Article abstract of DOI:10.1016/j.ultsonch.2019.104614

Ultrasound has been regarded as an efficient novel technique for debitterizing of the apricot kernels, but its influence is severely concerned on the possible epimerization of D-amygdalin to the L-amygdalin, a more potentially toxigenic compound. Consider

Full text of DOI:10.1016/j.ultsonch.2019.104614

Accepted Manuscript
Changes of Amygdalin and Volatile Components of Apricot Kernels during the
Ultrasonically-Accelerated Debitterizing
Ning Zhang, Qing-An Zhang, Jian-Li Yao, Xin-Yun Zhang
PII:
S1350-4177(19)30126-9
https://doi.org/10.1016/j.ultsonch.2019.104614
104614
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ULTSON 104614
Ultrasonics Sonochemistry
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28 May 2019
Please cite this article as: N. Zhang, Q-A. Zhang, J-L. Yao, X-Y. Zhang, Changes of Amygdalin and Volatile
Components of Apricot Kernels during the Ultrasonically-Accelerated Debitterizing, Ultrasonics Sonochemistry
(2019), doi: https://doi.org/10.1016/j.ultsonch.2019.104614
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Changes of Amygdalin and Volatile Components of Apricot Kernels
during the Ultrasonically-Accelerated Debitterizing
Ning Zhang, Qing-An Zhang, Jian-Li Yao, Xin-Yun Zhang
Institute of Food & Physical Field Processing, School of Food Engineering and
Nutrition Sciences, Shaanxi Normal University, Xi’an, 710062 Shaanxi Province, PR
China
Corresponding Author: Tel.: +86 29 85310517.
E-mail address: qinganzhang@snnu.edu.cn (Q.-A. Zhang).

ABSTRACT
Ultrasound has been regarded as an efficient novel technique for debitterizing of
the apricot kernels, but its influence is severely concerned on the possible
epimerization of D-amygdalin to the L-amygdalin, a more potentially toxigenic
compound. Considering this, the experiments were conducted to investigate the
epimerization of D-amygdalin and the volatile components in the debitterizing water,
which were separated and identified by the high performance liquid chromatography
(HPLC) and gas chromatography with a mass spectrometer (GC-MS), respectively.
The results indicate that the ultrasonically-debitterizing did not cause the
epimerization of D-amygdalin to the L-amygdalin, while the procedure can be greatly
accelerated due to the rapid mass transfer and degradation of D-amygdalin induced by
ultrasound irradiation. In addition, the water from the ultrasonically-debitterizing of
apricot kernels exerted more aromas compared with that of the conventional
debitterizing, which might have more applications about this kind of water. In a word,
ultrasound can be safely applied in the debitterizing industry of apricot kernels.
KEYWORDS: apricot kernels; debitterizing; amygdalin; epimerization; volatile
components

1 INTRODUCTION
Apricot, Prunus armeniaca L., the genus prunus of the subfamily Prunoideae in
the family Rosaceae [1], mainly distributes throughout the Central Asia, West Asia,
Mediterranean region and Western China, which is an internationally popular crop,
with the global production reaching 4.1 million tons [2]. As the nut seed, apricot
kernels contain abundant compounds like carbohydrates, protein, polyphenols,
flavonoids and amygdalin [3, 4]. Among them, the amygdalin is very distinctive and
determines the healthy function of the apricot kernel to some extent, which has a
content of 2-5 g/100g apricot kernels [4]. According to the chemical structure, the
amygdalin, ever called vitamin B17 or Nitrilosides, is composed of two molecules of
glucose, one benzaldehyde and one hydrogen cyanide [5]. Generally, the amygdalin
itself is considered to be nontoxic, while its metabolic product like HCN has the
potential toxicity, and its lethal dose for human is 0.5-3.5 mg/kg body weight [6].
Therefore, the amygdalin is widely regarded as a potentially toxigenic compound [7,
8], and its occurring has been as an obstacle to the utilization and commercialization
of the apricot kernels for human or animal nutrition. Considering this situation, the
detoxification has become an indispensable operation unit in the processing of apricot
kernels, by which the amygdalin can be lowered to the safe content, simultaneously
removing the bitterness and potential toxicity of the apricot kernels.
The commonly employed methods of detoxifying the apricot kernels include two
categories: conventional and novel methods, the former comprises the cold water

debitterizing [9], hot water debitterizing [10, 11], acid solution debitterizing [12] and
acid-base alternate debitterizing, while the latter contains the vacuum debitterizing
[13], ultrasound debitterizing and microwave debitterizing [7], etc. To the
conventional methods, the main disadvantages are high energy consumption (water
and electricity), time waste (from 6-7 hours to 6-7 days), labour-intensive, high
pollution and high loss of compounds in apricot kernels. The contents of protein,
carbohydrates, phenols, flavanoids and amygdalin have been detected in the
debitterizing water concentrate (DWC) from the conventionally industrial
debitterizing. Among them, the amygdalin has the highest content of 23.89 ± 0.03
(g/100 g dry base weight) in the DWC, and the total loss of weight is about 17% of
the apricot kernels after the debitterizing [14]. In comparison, the novel techniques are
relatively low-cost, eco-friendly, rapid and easy-industrialization. As a non-thermal
processing technology, ultrasound is regarded as the most promising technique for
accelerating the debitterizing of apricot kernels. With this method, the debitterizing
time can be reduced to about two hours and the water consumption can also be greatly
decreased by ultrasound irradiation [11], while the safety is severely considered about
the transformation of configuration (epimer) and the products available generated
from the amygdalin during exposure to ultrasound irradiation.
Regarding the amygdalin, it has two epimers of L-amygdalin and D-amygdalin
(Figure 1), the former does not exist in nature, but it can be epimerized from the D-
amygdalin during the decoction, particularly under basic conditions, because of the
weakly acidic character of the benzylic proton [15, 16]. That is to say, the amygdalin

coexisted in D- and L- amygdalin forms at neutral or basic conditions, while the D-
isomer only exists under acid conditions. This phenomenon suggests that the
dominant amygdalin epimer might be easily changed during the debitterizing or
sample pretreatment. Furthermore, the D-amygdalin tastes bitter, while the L-
amygdalin has no bitterness and different physiological properties, so special
concerns should be focused on this case during the debitterizing of apricot kernels,
since both D- and L- amygdalin can be degraded into the HCN causing toxicity
available by the gastric acid or enzymes in the digestive tract of human body. In other
words, if the bitter D-amygdalin only converted into the non-bitter L-amygdalin
during the debitterizing of ultrasound irradiation, its danger will be greater for the
consumers eating this kind of debitterized apricot kernels.
In a word, ultrasound irradiation does greatly shorten the debitterizing time of
apricot kernels and has the promising application in the apricot kernels processing
industry, while its influencing mechanism on the amygdalin should not be neglected.
In the meantime, the debitterizing water, containing abundant components especially
volatile compounds, can also be as the main ingredients of some oral liquid (cough
syrup). In pharmaceutical industry, the water soaked with the apricot kernels (namely
aqua armeniacae) is the dominant constitute for cough syrup to treat the symptom of
asthma, bronchitis, emphysema and cough in China. So special interests were
centered on the available utilization of the debitterizing water in pharmaceutical
industry by our group. Before considering the re-utilization of the debitterizing water,
some investigations should be conducted about the effect of ultrasound irradiation on

the compositions of the debitterizing water, especially the typical flavor compounds.
However, to the best of our knowledge, little information is available in this field.
The main purpose of this paper was to investigate the effects of ultrasound
irradiation on the amygdalin of apricot kernels and the volatile components in
debitterizing water during the accelerated debitterizing process, so as to evaluate the
safety of the novel debitterizing technique and the re-utilization of the debitterizing
water, finally reducing the pollution of environment and promoting the added-value in
the processing industry of apricot kernels.
2 MATERIALS AND METHODS
2.1 Materials and Reagents
The apricot kernels (harvested in June 2017) were purchased from the Northwest
Herb Market of Xi’an, Shaanxi province, China. The water content of the apricot
kernels is about 4.84 g water/100 g seeds, and the single weight is about 0.53±0.05 g
for each seed.
Standard of D-amygdalin was obtained from Chengdu Manst Biotechnology Co.,
Ltd. Amygdalin was purchased from the Chengdu Perferred Bio-Technology Co. Ltd
(Sichuan Province, China). HPLC-grade methanol and acetonitrile were bought from
the Fisher Scientific (USA). The dichloromethane (CH2Cl2), aether [(C2H5)2O], n-
hexane (C6H14), anhydrous sodium sulfate (Na2SO4), sodium hydroxide (NaOH),
hydrochloric acid (HCl), phosphoric acid (H3PO4), sodium dihydrogen phosphate
(NaH2PO4) were purchased from Tianjin Tianli Reagent Co., Ltd. All other chemicals
were of analytical grade. Ultra-pure water was prepared using a Millipore Milli-Q

purification system.
2.2. Preparation of L-amygdalin
There is no commercial L-amygdalin available in the market, so it was made from
the standard of D-amygdalin according to the literature [17, 18]. To be specific, the
standard solution of D-amygdalin (0.5 mg/mL), prepared by accurately weighing the
D-amygdalin and dissolving in the NaOH solution (pH=11), was set for 2 h in the
dark to make the isomerization of D-amygdalin equilibrium. Then, the mixture
solution with both D- and L- amygdalin was adjusted to pH=7 with HCl solution and
stored at 4 °C before determination by HPLC.
2.3. Optimization of the simultaneous determination conditions of the D- and L-
amygdalin by HPLC
Generally, it is difficult to detect the epimers with the common conditions of HPLC,
so some different operation parameters were optimized to obtain a good separation
and sensitivity of the D- and L- amygdalin by the HPLC, which was considered to be
simple, rapid, accurate [19]. The HPLC system (Dalian Elite Analytical Instruments
Co., Ltd., Liaoning, China) consists of two P230II pumps, a UV230II ultraviolet
visible detector and a ZW230II column oven. The column type, mobile phase, oven
temperature, flow rate and detection wavelength employed were listed in Table 1. For
all the operations, the injection volume was 20 μL. The resolution, sensitivity and
signal intensity of the peaks were used to evaluate the suitable conditions of HPLC for
the simultaneous analysis of the D- and L- amygdalin.
2.4. Pretreatment of apricot kernels and effects of ultrasound irradiation on the

amygdalin during debitterizing
Apricot kernels with removing the impurities were immersed in water of 15 °C for
5 h to peel the skin. Afterwards, one part of the peeled apricot kernels was put in the
boiling water for 10 min to inactivate the beta-glucosidase activity [20], and the
remaining was as the sample of non-inactivated beta-glucosidase. Then the boiled
water for inactivating the beta-glucosidase was collected and filtered through a 0.45
μm membrane to investigate the effect of inactivation pretreatment on the
epimerization of D-amygdalin, which was detected by the HPLC according to the
above-optimized conditions.
Additionally, in order to investigate the effects of ultrasound irradiation on the
amygdalin of apricot kernels during the ultrasonically-accelerated debitterizing, the
experiments were conducted in an ultrasonic bath (SB-500DTY, Ningbo Xinzhi
Biotechnology Co. Ltd., Ningbo City, Zhejiang Province, China) in this study, which
can work at the frequencies of 25, 28, 40 and 59 kHz and with the variable powers
(≤900 W). According to the results obtained in our previous studies [7, 11, 14], the
ultrasonically-accelerated debitterizing parameters were designed as follows: the
peeled apricot kernels of the beta-glucosidase inactivated and non-inactivated were
placed in a container with the sample-to-liquid of 1:12 (g/mL) which was fixed in a
designated position of the ultrasound bath, and the ultrasound parameters were of 55
oC (temperature), 300 W (power), 59 kHz (frequency) and 2 h (irradiation time) [21,
22]. In order to avoid the temperature increasing caused by the ultrasound irradiation,
an in-water pipe was added to the opposite of the ultrasonic cleaner’s out-water pipe,

and the flux ratio between in-water and out-water was regulated to keep the solution
temperature stable in this experiment. Once finishing the debitterizing, the water was
collected for determining the changes of the amygdalin mediated by ultrasound, and
the quantitative was calculated according to the constructed working curve of
amygdalin standard, and the formula is y=8421.6x +210.06 (R2=0.9996).
2.5. Effects of ultrasound irradiation on the volatile components in the
debitterizing water of apricot kernels
2.5.1 Preparation of the volatile components from the debitterizing water
The debitterizing water mentioned in the section of 2.4 (the peeled apricot kernels
were treated by the boiling water to inactivate the beta-glucosidase, then the apricot
kernels were ultrasonically or non-ultrasonically debitterized and the waters were
collected for the analysis) was also used for the analysis of volatile components by
using a Shimadzu GC-MS QP-2010 Ultra gas chromatography coupled with a mass
spectrometer (GC-MS). Regarding the sample pretreatment, the water (300 mL) was
extracted 3 times with the solvent of diethyl ether (90 mL, 60 mL and 60 mL), and
each extraction operation was for 8 h. Next, the collected extraction solutions were
o
added with the nanhydrous sodium sulfate and placed at 4 C overnight. Finally, the
supernatant was condensed to 1 mL by a glass KD concentrator under the conditions
o
of vacuum and 35 C. Before use, it was diluted to 500 folds with the n-hexane. As
the blank sample, the procedure was the same as the ultrasonically-accelerated
debitterizing besides the ultrasound irradiation.
2.5.2 GC-MS determination of the volatile components

The volatile components were separated by GC-MS according to methods with a
slight modification [23, 24], and were identified by retrieving the mass spectrometry
data in a NIST14 library. The working parameters of GC were as follows: a Rtx-5MS-
o
1 column (30 m×0.25 mm×0.25 μm, Restek), inlet temperature of 250 C, injection
volume of 1 μL and carrier gas of Helium. The programmed temperature was:
maintaining 40 oC for 3 min, with an increase from 40 oC to 120 oC at the flow rate of
o
o
o
5 C/min, then up to 230 C with the flow rate of 10 C/min and keeping for 5 min.
The MS working parameters were as follow: Electron energy 70 eV; EI source; ion
source temperature 200 oC; 40-550 amu scanning range; full spectrum scanning mode.
3 RESULTS AND DISCUSSION
3.1 Simultaneous determination of the D- and L- amygdalin by
HPLC
Regarding the determination of D- and L- amygdalin, although some methods such
as high-performance liquid chromatography (HPLC) [25], carbon-13 nuclear
magnetic resonance (13CNMR) spectroscopy [26], chemical ionization mass
spectrometry [27] and gas chromatography with flame ionization detection (GC-FID)
[28] have been employed for the identification and quantitative determination of the
amygdalin epimers, yet these methods required some time-consuming complicated
procedures to prepare the sample. In the meantime, considering the possible
epimerization from D- to L- amygdalin, and the latter’s potential safety, it is very
necessary to have a simple, rapid and sensitive method which can simultaneously
detect the epimers of D- and L- amygdalin during the processing of apricot kernels.

The results of simultaneously determining the D- and L- amygdalin by HPLC were
shown in Fig. 2, which is corresponded to the conditions in Table 1. As shown in Fig.
2a, the D and L- amygdalin were not separated at the retention time of 17-20 min with
the first working condition of HPLC, and the resolution of two peaks was very small.
In comparison, the signal intensity of the peaks in Fig. 2b was stronger than that in
Fig. 2a, when the detection wavelength was set at 210 nm, although the 214 nm was
the optimal wavelength for determining the D-amygdalin. Therefore, the 210 nm was
used as the optimum detection wavelength for the mixture of L-, D- amygdalin in the
following studies, which is also in accordance with the results by Liu [29].
It could be seen from Fig. 2c that the changing of the column temperature still
could not achieve a better separation between the D- and L- amygdalin. Generally, the
mass transfer resistance decreases with the increase of temperature from the
perspective of chromatographic thermodynamics, so the column efficiency increases
and the peak shape becomes sharp, which is also favorable for the separation. The
increase of temperature makes the retention factor and the solute’s relative retention
value smaller, which is not conducive to the separation [30]. Therefore, the detection
was carried out using a column temperature of 8 oC.
Generally, the mobile phase composition has an important influence on the
separation [31]. As shown in Fig. 2d and 2e, the resolution of the two peaks was
significantly lowered, and the retention time was also shortened when the ratio of
organic phase to acetonitrile was at 10%, while the retention time was increased to 25
min when the ratio of acetonitrile was reduced to the 7%. In Fig. 2f and Fig. 2g, the

compounds of D and L- amygdalin were well separated, but the signal was relative
weak. Meanwhile, the mobile phase contained a high proportion of phosphate buffer
not suitable for the equipment of the HPLC. In comparison, Fig. 2h demonstrated a
good resolution and sensitivity about the separation of D- and L- amygdalin, which
was therefore employed in this research.
3.2 Effect of ultrasonically-accelerated debitterizing on the
epimerization of D-amygdalin
As shown in Fig. 3, the D-amygdalin could be epimerized into the L-amygdalin by
the treatment of inactivating the beta-glucosidase in the peeled apricot kernels, which
demonstrates that the processing does influence the existing form of the amygdalin.
Furthermore, the epimerization rate of D-amygdalin was 34.29% with the peeled
apricot kernels treated by the boiling water for 10 min. That is to say, high
temperature treatment can cause the epimerization of the D-amygdalin, and the safety
should be concerned about the water generated from inactivating the beta-glucosidase
of apricot kernels.
Fig. 4 illustrated the chromatograms about the amygdalin transferred to the water
from the apricot kernels during the ultrasonically-accelerated debitterizing. Obviously,
no L-amygdalin was separated and detected using the same conditions of HPLC as in
the above section of 3.1 (Fig. 2h). However, the D-amygdalin occurred in the
debitterizing water, which suggests that the ultrasonically-accelerated debitterizing
technique did not cause the epimerization of D-amygdalin under the employed
conditions whether the beta-glucosidase of the apricot kernels inactivated or not. In

other words, the epimerization of D-amygdalin was not caused by the ultrasound
irradiation and the beta-glucosidase, and the ultrasonic debitterizing can not induce
the secondary problem of safety.
Furthermore, the signal intensity of the D-amygdalin in the ultrasonically-
debitterizing water with the beta-glucosidase inactivated of the apricot kernels was
stronger than that of the beta-glucosidase non-inactivated (in Fig. 4A and 4B),
indicating that the beta-glucosidase did promote the degradation of D-amygdalin
during the debitterizing of apricot kernels. Moreover, the beta-glucosidase activity can
also be activated with an increase of 34.67% by the ultrasound irradiation, which
explains the reason why the time can be greatly shortened during the debitterizing of
apricot kernels exposed to ultrasound irradiation [22]. Considering the potential
application and recycling of the D-amygdalin, it is better to inactivate the beta-
glucosidase of the apricot kernels when using the ultrasonically-accelerated
debitterizing technique so as to reduce the degradation of amygdalin and make more
amygdalins transferred into the debitterizing water.
3.3 Changes of D-amygdalin with different pretreatments on the
beta-glucosidase of apricot kernels during debitterizing
Table 2 shows the changes of D-amygdalin with different pretreatments on the
beta-glucosidase of apricot kernels during debitterizing. The content of D-amygdalin
was 64.68 mg/g in the peeled apricot kernels (Untreated), and the residual content was
24.85 mg/g, when the peeled apricot kernels with the beta-glucosidase denatured were
debitterized with the water of 55 oC for 2 h, and the leaching rate was 61.58%, which

means that the hot water can promote the transferring of D-amygdalin to the contacted
water resulting in the removal of bitterness. In comparison, the ultrasonically-
debitterizing could promote the leaching rates of the amygdalin from 61.58% to
85.42% and 95.70%, respectively. An increase of 23.84% was mainly attributed to the
ultrasound when the beta-glucosidase was inactivated during ultrasonically-
debitterizing, and the beta-glucosidase contributed an increase of 10.28% to the
leaching rate of D-amygdalin. The reason that the beta-glucosidase promoted the
removal of bitterness might be the synergistic action of temperature and ultrasound on
o
the enzyme, i.e. the temperature of 55 C is suitable for activating the beta-
glucosidase, in the meantime, the activity of beta-glucosidase can also be triggered by
the cavitation of ultrasound irradiation [22] which resulted in the degradation of of D-
amygdalin, and then the rapid transferring from the apricot kernels. As a consequence,
the residuals of D-amygdalin were decreased to 9.43 mg/g and 2.78 mg/g compared
with the results of non-ultrasonically debitterizing, indicating that the ultrasound
technology could improve the debitterizing efficiency of apricot kernels by
accelerating the leaching rate of D-amygdalin. In a word, it is not necessary to
inactivate the beta-glucosidase when the ultrasound was employed to rapidly remove
the bitterness of apricot kernels.
3.4 Effects of ultrasonically-accelerated debitterizing on the volatile
components in the debitterizing water of apricot kernels
In order to explore the re-utilization of the debitterizing water, the volatile
components were analyzed and identified by the GC-MS according to the matching of

their recorded mass spectra with those of NIST14 (National Institute of Standards and
Technology) libraries data provided by the software of GC-MS system, and the results
were shown in Fig. 5, Table 3 and Table 4, respectively. Table 3 shows that a total of
44 kinds of volatile compounds were detected and identified in the debitterizing water
of apricot kernels, including phenols, acids, aldehydes, esters, ketones and
hydrocarbons. Among them, the benzaldehyde was the main compound with a
relative content of 94.41%, followed by the benzyl alcohol and di-tert-butyl-p-
methylphenol, and their contents were of 1.50% and 1.56%, respectively. To the main
components of benzaldehyde and benzyl alcohol, they are considered to be originated
from the degradation of the D-amygdalin due to contacting with the hot water during
the debitterizing.
In comparison, 57 kinds of volatile compounds were detected and identified in the
water from the ultrasonically-debitterized apricot kernels in Table 4, including
aldehydes, ketones, esters, alcohols, acids, ethers and hydrocarbons, which was more
than those in the debitterizing water without ultrasound irradiation on the apricot
kernels during the debitterizing. Furthermore, the benzaldehyde was still the dominant
volatile compound, accounting for 74.86%, followed by the benzyl alcohol with a
relative content of 21.81%, which was much higher than that in the debitterizing
water without ultrasound irradiation on the apricot kernels, and these results may be
attributed to the degradation of amygdalin induced by the cavitation of ultrasound,
which was also corresponded to the results of the amygdalin residual in the apricot
kernels. In other words, ultrasound did have a great influence on the volatile

components in the debitterizing water of the apricot kernels. Furthermore, considering
the preservative, flavor-adding and healthy function of the benzyl alcohol and
benzaldehyde, it is necessary to recycle these compounds from the water or to develop
some novel healthy drinks with this water as the main raw material. From the
viewpoint of the flavor, the water from the ultrasonically-debitterized apricot kernels
was better than that of the water from the non-ultrasonically debitterized apricot
kernels. To some extent, the so-called wastewater from the debitterizing can not only
be re-utilized, but also decrease the discharge and the environment pollution,
consequently resulting in the added value of the apricot kernels in the industrial
processing.
4 Conclusions
In summary, ultrasound irradiation can accelerate the debitterizing of apricot
kernels by promoting the mass transfer and degradation of the D-amygdalin.
Moreover, it can not cause the epimerization of the D-amygdalin to the L-amygdalin,
which means that this novel ultrasonically-debitterizing technique has the same
mechanism as the conventional debitterizing of hot water, i.e. there is no novel safety
issue occurred in the ultrasonically-debitterizing based on the changes of D-
amygdalin, while the procedure can be greatly accelerated due to the cavitation of
ultrasound irradiation. In addition, the water from the ultrasonically-debitterizing of
apricot kernels exerted more aromas compared with that of the conventional
debitterizing, which suggests that there are more possible applications about this kind
of water in the beverage drinks, cosmetics and pharmaceutical industry. However, the

specific forming mechanism should be further conducted about the volatile
compounds induced by the ultrasound irradiation.
ACKNOWLEDGMENTS
This study was funded by National Natural Science Foundation of China [No.
31101324], Natural Science Foundation of Shaanxi Province, China [No.
2015JM3097], Technology Transfer Promotion Project of Xi’an, Shaanxi Province,
China [No.2017071CG/RC034(SXSF003)], Key Research Development Program of
Shaanxi Province, China [No.2017NY-167, 2018ZDXM-NY-086] and the
Fundamental Research Funds for the Central Universities of China [No.
GK201602005, GK201802012].
CONFLICT OF INTEREST
No potential conflict of interest was reported by the authors.
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FIGURE CAPTIONS:
Figure 1 Chemical structures of D- and L- amygdalin
Figure 2 Chromatograms of the D- and L- amygdalin with different conditions of
HPLC
Figure 3 Chromatogram of the D- and L- amygdalin in the water from the
inactivating of the beta-glucosidase in apricot kernels
Figure 4 Chromatograms of D-amygdalin in the debitterizing water with the beta-
glucosidase of apricot kernels inactivated and non-inactivated
Figure 5 Total ion chromatograms of the volatile components in the debitterizing
water and the ultrasonically-debitterized water of the apricot kernels by GC-MS

Tables
Table 1 Conditions for the separation of D- and L-amygdalin by high performance
liquid chromatography
Table. 2 Changes of D-amygdalin with different pretreatments on the β-glucosidase of
apricot kernels during debitterizing
Table 3 The volatile components in the non-ultrasonically debitterizing water of
apricot kernels
Table 4 The volatile components in the ultrasonically debitterizing water of apricot
kernels
Figure 1

Figure 2
b
a
100
80
60
40
20
0
100
80
60
40
20
0
Condition 2
Condition 1
D-
L-
L- D-
0
0
0
5
10
15
20
25
30
30
35
0
5
10
15
20
25
30
Time(min)
Time(min)
d
c
100
80
60
40
20
0
100
80
60
40
20
0
Condition 4
Condition 3
D-
L-
D-
L-
10
20
0
5
10
15
20
25
30
Time(min)
Time(min)
e
f
100
80
60
40
20
0
100
80
60
40
20
0
Condition 5
Condition 6
L-
25
D-
L-
D-
5
10
15
20
30
0
5
10
15
20
25
30
Time(min)
Time(min)
h
g
100
80
60
40
20
0
100
80
60
40
20
0
Condition 8
L-
Condition 7
D-
L-
D-
0
5
10
15
Time(min)
20
25
0
5
10
15
Time(min)
20
25
30

Figure 3
2000
1500
1000
500
0
D-
L-
0
5
10
15
20
Time(min)

Figure 4
1500
1200
900
600
300
0
800
600
400
200
0
Beta-glucosidase non-inactivated
Beta-glucosidase inactivated
A
B
0
3
6
9
12
15
0
5
10
15
20
25
Time (min)
Time (min)

Figure 5
8.0x107
4.0x107
6.0x107
——Treated sample with ultrasound
——Untreated sample
4.0x107
8.0x106
6.0x106
4.0x106
2.0x106
0.0
8.0x106
6.0x106
4.0x106
2.0x106
0.0
5
10
15
20
25
30
5
10
15
20
25
30
Time(min)
Time(min)
Table 1 Conditions for the separation of D- and L-amygdalin by high
performance liquid chromatography
Detection
Conditions
number
Flow rate
(mL/min)
Column Temperature
(oC)
Column type wavelength
(nm)
Mobile phase (mL: mL)
Eclipse Plus
214
Acetonitrile: Phosphate buffer
(pH 3.1) = 8.5: 91.5
1
2
3
4
5
6
7
1.2
1.2
1.2
1.2
1.2
1.2
1.2
8
8
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) = 8.5: 91.5
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) = 8.5: 91.5
35
8
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) = 10:90
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) = 7:93
8
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) = 5:95
8
C18
Eclipse Plus
210
Acetonitrile: Phosphate buffer
(pH 3.1) =4:96
8
C18

Cosmosil
C18-AR-II
Acetonitrile: 0.1% Phosphate
buffer=7:93
8
210
1.0
25

Table. 2 Changes of D-amygdalin with different pretreatments on the β-glucosidase of
apricot kernels during debitterizing
55 oC water for
Ultrasonic
Ultrasonic
2 h
Untreated
debitterizing with debitterizing with the β-
the β-glucosidase
with the β-
glucosidase
denatured
apricot kernels
glucosidase non-
denatureda
denatured
Residual of amygdalin
64.68±0.69
24.85±0.11
61.58±0.25
9.43±1.08
2.78±0.18
(mg/g)
Leaching rate of amygdalin
(%)
85.42±1.79
95.70±0.35
a: Ultrasound conditions as power of 300 W, time of 2 h, frequency of 59 kHz, temperature of 55
oC and sample-to-liquid of 1:12 (g/mL).

Table 3 The volatile components in the non-ultrasonically debitterizing water of
apricot kernels
Retention time
Relative
n
Component
（min）
5.85
content (%)
0.0654
94.4064
0.0084
0.0168
1.5007
0.0118
0.0716
0.1087
0.1424
0.0211
0.0072
0.1799
0.0527
0.1538
0.0291
0.2534
0.0122
0.0088
0.0214
1
2
Ethylbenzene
Benzaldehyde
9.38
3
10.56
11.48
11.77
12.90
13.46
13.88
14.03
15.87
16.11
17.03
18.16
19.93
20.30
20.84
21.42
21.95
22.11
Decane
4
D-Limonene
5
Benzyl alcohol
6
Diethyl malonate
Benzeneacetonitrile, alpha.-oxo-
Undecane
7
8
Nonanal
9
Acetic acid, phenylmethyl ester
Benzoic acid, ethyl ester
Dodecane
10
11
12
13
14
15
16
17
18
19
2,3-Dimethoxytoluene
Tridecane
Phenylpropanamide
1,3-Dioxolane, 2-(1-phenylethyl)-
2-Dodecenal, (E)-
1-Tetradecene
Tetradecane
1-tert-butyl-2-(1-methyl-2-nitroethyl)
cyclohexanone
20
22.32
0.0067
21
22
23
24
25
26
22.38
22.96
23.01
23.20
23.49
23.66
1-Tetradecene
0.0139
0.0129
0.0057
0.9315
0.0035
0.0246
2-Butanone, 1-bromo-3,3-dimethyl-
1-Hexadecanol
3-tert-Butyl-4-hydroxyanisole
Butane, 1,1'-sulfonylbis-
Heptadecane
Pyrimido[1,2-a]azepine, 2,3,4,6,7,8,9,10-
octahydro-
27
23.71
0.0389
28
29
23.92
24.36
Di-tert-butyl-p-methylphenol
2-Butanone, 1-chloro-3,3-dimethyl-
Spiro[4.5]decan-7-one, 1,8-dimethyl-4-(1-
methylethyl)-
1.5648
0.0705
30
24.49
0.0150
31
33
34
24.81
25.33
25.78
Tetradecane, 1-chloro-
Tetradecane
0.0001
0.0223
0.0078
Benzene, (1-butyloctyl)-