Effects of Planting and Processing Modes on the Degradation of

Subscriber access provided by READING UNIV

Article

Effects of Planting and Processing Modes on the Degradation of Dithianon and Pyraclostrobin in Chinese Yam (Dioscorea spp.) Kaiwei Shi, Xujin Wu, Jingwei Ma, Junfeng Zhang, Ling Zhou, Hong Wang, and Li Li J. Agric. Food Chem., Just Accepted Manuscript • DOI: 10.1021/acs.jafc.7b03916 • Publication Date (Web): 13 Nov 2017 Downloaded from http://pubs.acs.org on November 14, 2017

Just Accepted “Just Accepted” manuscripts have been peer-reviewed and accepted for publication. They are posted online prior to technical editing, formatting for publication and author proofing. The American Chemical Society provides “Just Accepted” as a free service to the research community to expedite the dissemination of scientific material as soon as possible after acceptance. “Just Accepted” manuscripts appear in full in PDF format accompanied by an HTML abstract. “Just Accepted” manuscripts have been fully peer reviewed, but should not be considered the official version of record. They are accessible to all readers and citable by the Digital Object Identifier (DOI®). “Just Accepted” is an optional service offered to authors. Therefore, the “Just Accepted” Web site may not include all articles that will be published in the journal. After a manuscript is technically edited and formatted, it will be removed from the “Just Accepted” Web site and published as an ASAP article. Note that technical editing may introduce minor changes to the manuscript text and/or graphics which could affect content, and all legal disclaimers and ethical guidelines that apply to the journal pertain. ACS cannot be held responsible for errors or consequences arising from the use of information contained in these “Just Accepted” manuscripts.

Journal of Agricultural and Food Chemistry is published by the American Chemical Society. 1155 Sixteenth Street N.W., Washington, DC 20036 Published by American Chemical Society. Copyright © American Chemical Society. However, no copyright claim is made to original U.S. Government works, or works produced by employees of any Commonwealth realm Crown government in the course of their duties.

Page 1 of 30

Journal of Agricultural and Food Chemistry

1

Effects of Planting and Processing Modes on the Degradation of Dithianon and

2

Pyraclostrobin in Chinese Yam (Dioscorea spp.)

3

(Running Title: The Degradation of Dithianon and Pyraclostrobin in Yam)

4

Kaiwei Shib, Xujin Wua,∗, Jingwei Maa, Junfeng Zhanga, Ling Zhoua, Hong Wanga, Li

5

Lib,∗

6

a

7

Academy of Agricultural Sciences /Henan Key Laboratory of Grain Quality and

8

Safety and Testing/ Laboratory of Quality Safety Risk Assessment for Agro-products

9

(Zhengzhou), Ministry of Agriculture, Zhengzhou 450002, China

Institute of Quality Standard and Testing Technology for Agro-products, Henan

b

10

State Key Laboratory of Integrated Management of Pest Insects and Rodents, Institute of Zoology, Chinese Academy of Sciences, Beijing 100101, China

11

12

13

14

15

16

∗

Corresponding author: Xujin Wu, phone: 86-135-9803-0746. E-mail address:[email protected]

∗

Co-corresponding author: Li Li, phone: 86-138-1043-6839. E-mail address: [email protected] 1

ACS Paragon Plus Environment


17

ABSTRACT

18

The yam (Dioscorea spp.) is widely cultivated in China. The degradation of dithianon

19

and pyraclostrobin in yams with different planting and processing treatments were

20

investigated in this paper. An analytical method for two pesticides in yam and yam

21

plant was developed, and recoveries were between 77% and 93%, with relative

22

standard deviations from 0.8% to 7.4%, respectively. Based on this method, half-lives

23

for plants grown on stakes versus plants grown without stakes were compared. The

24

results indicated that the half-life for pesticides residues for plants grown on stakes

25

versus plants grown without stakes differed as 6.7 versus 3.1 days for dithianon and

26

5.4 versus 5.2 days for pyraclostrobin. Dithianon was significantly influenced by

27

planting mode due to its low stability under sunlight. The processing factors of

28

various processing treatments (hot-air-drying, vacuum-freeze-drying, microwave-

29

vacuum-drying, infrared-drying, steaming and boiling) were all less than 1, indicating

30

that those process can reduce residues of two pesticides at different level. Significant

31

amounts of residues were removed during the boiling treatment, whereas the others

32

showed less effect.

33

KEYWORDS: degradation; dithianon; pyraclostrobin; planting mode; processing

34

factor; yam

35

2


Page 2 of 30

Page 3 of 30


36

37

INTRODUCTION Yam (Dioscorea spp.) is the fourth major root crop in the world after cassava,

38

potatoes and sweet potatoes.1 In China, different yam species are not only a common

39

food, but also a traditional Chinese medicine that have also been widely used for the

40

treatment of diabetes, diarrhoea, asthma and other ailments.2-6 Yams are cultivated

41

either on mounds or on ridges, and the growing plants can be staked or spread on the

42

ground without stakes. Staked yams are more productive, however, the cost of stakes

43

and labor to place them may render the practice uneconomical.7 Ground yams without

44

stakes is still widely cultivated in rural areas in China.

45

Fresh yams are consumed in different ways, such as boiled, steamed or baked

46

products. However, fresh yams are perishable during storage. Consequently, the

47

processed yam products occupy a considerable part for daily consumption. Drying is

48

one of the most important preservation processes for yams to extend their storage life

49

and improve the taste, including air-drying, freeze-drying, far-infrared radiation-

50

assisted freeze-drying, and vacuum-drying.8-12

51

During the growth cycle of yam, the crops are exposed to a wide range of pests

52

and diseases. Yam anthracnose is the most important diseases and is caused by

53

Colletotrichum gloeosporioides (Popoolaet al.2013; Raj et al. 2013; Katoh et al.2016),

54

which can be effectively controlled by dithianon and pyraclostrobin.13-17 Dithianon

55

(CAS 3347-22-6, Figure 1 (A)), 5, 10-dihydro-5, 10-dioxonaphtho-(2, 3-b)-1, 4-

56

dithiin-2, 3-dicarbonitrile, is a non-systemic fungicide used against a variety of foliar

57

diseases.16 Pyraclostrobin (CAS 175013-18-0, Figure 1 (B)), methyl 2-[1-(4-

58

chlorophenyl)pyrazol-3-yloxymethyl]-N-methoxycarbanilate, is a broad-spectrum

59

foliar fungicide in the strobilurin chemical class.18 The combination of these two 3



60

pesticides shows higher fungicidal activity and longer lifetimes than either alone.19 In

61

previous studies, dithianon and pyraclostrobin have been determined in various fruits,

62

vegetables and grain by high-performance liquid chromatography coupled with

63

ultraviolet detector (HPLC-UV), high-performance liquid chromatography coupled

64

with tandem mass spectrometry (HPLC-MS/MS) and gas chromatography coupled

65

with time-of-flight mass spectrometry (GC-TOFMS).20-25

66

Pesticide in yams might be concentrated or converted to more toxic metabolites

67

during processing. The processing factors (PFs) are the ratio of residue levels in

68

processed products and their respective raw products, which are important when

69

evaluating the risk associated with intake of pesticide residues.26 The Joint

70

FAO/WHO Meeting on Pesticide Residues (JMPR) evaluated food processing data on

71

dithianon and pyraclostrobin residue behaviors where significant residues occur in

72

plant or plant products that are processed into food.27 To the best of our knowledge,

73

few papers have reported the degradation of dithianon and pyraclostrobin and PFs in

74

yams during different processing procedure.

75

Therefore, the objectives of this work were as follows: (1) to develop an

76

analytical method for determining the residues of dithianon and pyraclostrobin in yam;

77

(2) to assess the influence of different plant modes (ground and staked) on the

78

dissipation of dithianon and pyraclostrobin in Chinese yam; and (3) to evaluate the

79

degradation of dithianon and pyraclostrobin regarding PFs during different processing

80

treatments, including hot-air-drying (HAD), vacuum-freeze-drying (VFD),

81

microwave-vacuum-drying (MVD), infrared-drying (ID), steaming and boiling.

82

MATERIALS AND METHODS

83

Chemicals and Reagents 4


Page 4 of 30

Page 5 of 30


84

Certified reference standards of dithianon (99.0%) and pyraclostrobin (99.0%)

85

were provided by Dr.EhrenstorferGmbh (Augsburg, German). Water dispersible

86

granules (WDGs) containing 12% dithianon and 4% pyraclostrobin was used.

87

Acetonitrile, methanol, acetone and chloroform were of chromatography purity and

88

purchased from Thermo Fisher Scientific Inc. (Waltham, USA). Hydrochloric acid

89

and sodium chloride were of analytical grade and purchased from Beijing Chemical

90

Reagent Co., Ltd. (Beijing, China). Primary secondary amine (PSA) was purchased

91

from Bonna-Agela Technologies, Ltd. (Tianjin, China).

92

Apparatus

93

Several dryers used in this study are as follows: DHG-9070A dryer (Shanghai

94

Keelrein Instruments Co., Ltd., Shanghai, China) for HAD; VirTis lyophilizer

95

(Sentry2.0, SP Industries, Inc., PA, USA) for VFD; HWZ-2B drier (Hongyuan

96

microwave equipment manufacturing Co., Ltd., Shanghai, China) for MVD; WS70-1

97

drier (GongyiYuhua Instrument Co., Ltd., Zhengzhou, China) for ID. Extraction and

98

purification of pretreatment were performed using XW-80A vortexer (Haimen

99

QilinBei'erInstrument Manufacturing Co., Ltd., Jiangsu, China) and H-1650

100

centrifuge (Xiangyi centrifuge instrument Co., Ltd, Hunan, China).

101

Preparation of Standard Solutions

102

Individual stock standard solutions (1000 mg L-1) were prepared by exact

103

weighing of the solid pesticide and dissolved in 25 mL of acetonitrile. To determine

104

the linearity a 100 mg L-1 stock solution was also prepared and working standard

105

solutions (0.10, 0.25, 0.50, 1.00, 2.00, 5.00 mg L-1 for dithianon, 0.05, 0.10, 0.25, 0.50,

106

1.00, 2.00 mg L-1 for pyraclostrobin) were prepared by diluting the stock solutions

107

with acetonitrile. All standard solutions were stored at -10 °C before use. 5



108

109

Field Trials The field trial was conducted in 2014 at Jiaozuo City, Henan Province, China.

110

Each treatment consisted of three replicate plots and a control plot. The area of each

111

plot was 30 m2. A buffer area was also employed to separate each plot, according to

112

“Guidelines on Pesticide Residue Trials”.28 The fields in this study were previously

113

investigated and determined to be free of the pesticide.

114

To investigate the dissipation of dithianon and pyraclostrobin in Chinese yam

115

with or without stakes, the WDGs were sprayed once at 800 g a. i. ha-1(two times of

116

the recommended dosage) on the surface of yam plant. Representative yam samples

117

(about 1 kg) were collected at 2 hours and 1, 2, 3, 5, 7, 10, 14, 21, 28 and 35 days

118

after the application. All samples were homogenized and stored at -20 °C for further

119

analysis.

120

The physicochemical properties of the soil are as follows: the soil type was lu

121

soil; organic matter 1.2-1.6%; pH 6.5-7.5. The average annul precipitation was 552

122

mm. The average annual temperature was 14.3 °C.

123

Sample Preparation and Processing

124

Pretreatments before Processing

125

The whole tubers of yams sampled from the control plot were soaked in water

126

with WDGs at dosage of 1.76 g a. i. L-1 for 30 min, then dried in the open air. For

127

HAD, VFD, MVD and ID, the tubers were cut into slices 5 mm in thickness. For

128

steaming and boiling, the tubers were cut into pieces (20 cm long). In this study, the

129

samples in different processing steps were collected to determine the residue. The

130

detailed processing procedures are as follows. 6


Page 6 of 30

Page 7 of 30


131

Hot-air-drying (HAD)

132

A DHG-9070A dryer was first allowed to run for an hour to stabilize at the

133

desired temperature (35 °C) at constant air velocity (1 m s-1).The yam samples were

134

then transferred into the drier and dried for 24 hours to constant weight.

135

Vacuum-freeze-drying (VFD)

136

The yam samples were previously spread on a plate and placed at -80 °C for 24

137

hours, then freeze-dried with a VirTis lyophilizer. The pressure was set to 32 Pa. The

138

temperature of the cold trap was -80 °C. The primary and secondary

139

drying temperatures were 20 °C and 35 °C, respectively. The yam samples were dried

140

for 12 hours to constant weight.

141

Microwave vacuum-drying (MVD)

142

The yam slices were spread in one layer on the tray of an HWZ-2B drier. The

143

vacuum degree, drying temperature and power density were set at 0.95 MPa, 50 °C

144

and 1.3 W g-1, respectively. The yam samples were dried for 10 hours to constant

145

weight.

146

Infrared-drying (ID)

147

The yam slices were spread in one layer on the tray of a WS70-1 drier. The

148

power was set at 500 W. The yam samples were dried for 24 hours to constant weight.

149

Steaming and Boiling

150

151

The yam pieces were steamed or boiled at 100 °C for 10 min. Extraction and Cleanup 7



152

153

Extraction and Cleanup for Dithianon The homogenized yam sample (5.00 ± 0.01g) was weighed into a 50-mL

154

centrifuge tube (Corning Inc., NY, USA). Next, 1 mL hydrochloric acid (37.2%, w/w),

155

5 mL of water and 10 mL of acetonitrile were added in that order. The tube was

156

vortexed vigorously for 1 min with vortexer. After the addition of 5 g sodium chloride,

157

the tube was vortexed vigorously for another 0.5 min, allowed to stand for 20 min at

158

room temperature, and finally centrifuged for 5 min at 5000 rpm. Subsequently, 2 mL

159

of supernatant was transferred into a 2.5mL centrifuge tube containing sorbent (100

160

mg anhydrous MgSO4 and 50 mg PSA). The tube was vortexed for 1 min, then

161

centrifuged for 5 min at 4500 rpm with centrifuge. The resulting supernatant was

162

filtered using a 0.22µm nylon syringe filter into a colored auto-sampler vial for

163

analysis.

164

Extraction and Cleanup for Pyraclostrobin

165

The homogenized yam or yam plant sample(20.0 g) was weighed into a 100-mL

166

centrifuge tube (Taizhou Weierkang Medical Supplies Co., Ltd., Jiangsu, China), and

167

5 mL of water and 40 mL of acetonitrile were added. The tube was then shaken in a

168

mechanical shaker for 1 hour. After the addition of 5 g of sodium chloride, the tube

169

was vortexed vigorously for 1 min and centrifuged for 5 min at 4500 rpm.

170

Subsequently, 20 mL of supernatant was evaporated to dryness at 40 °C. For cleanup,

171

the NH2solid-phase extraction (SPE) cartridge was conditioned with 5 mL of

172

acetone/n-hexane (2:3, v/v). The concentrated extracts were dissolved in 5 mL of

173

acetone/n-hexane (2:3, v/v),transferred to the cartridge, and then eluted with 15 mL of

174

acetone/n-hexane (2:3, v/v). The eluent was collected and evaporated to near dryness

8


Page 8 of 30

Page 9 of 30


175

at 40 °C. The extract sample was re-dissolved in 2 mL of acetonitrile and filtered

176

using a 0.22-µm nylon syringe filter into an auto-sampler vial for analysis.

177

Both the blanks and spiked samples were treated the same as the samples

178

throughout the study process. Yam samples cultivated in control plots were used as

179

field blanks. The blank samples were analyzed to ensure the absence of interference

180

with retention times of the analytes. Blanks fortified with working solution mixtures

181

of target pesticides at three concentration levels (0.5, 2 and 5 mg kg-1 for dithianon,

182

0.05, 0.5 and 1 mg kg-1 for pyraclostrobin) were used for the and recovery experiment.

183

All samples were analyzed in quintuplicate.

184

HPLC Analysis

185

HPLC determination was performed using a Waters HPLC system equipped with

186

an E2695 separation module and 2998 photodiode array detector (Waters Corporation,

187

MA, USA). SunFire C18 chromatographic column (4.6 mm×150 mm, 5 µm, Waters

188

Corporation, MA, USA) was used. The injection volume was 20 µL. Mobile phase (A)

189

was acetonitrile. and mobile phase (B) was ultra-pure water.

190

HPLC Conditions for Dithianon

191

The gradient elution program was as follows: 60% (A) from 0 to 10 min, then 80%

192

(A) from 10 to 20 min, then 100% (A) from 20 to 25 min, then 60% (A) from 25 to

193

25.1 min. The flow rate was 0.8 mLmin-1, and the column temperature was 30 °C. The

194

detection wavelength for dithianon was set at 233 nm.

195

HPLC Conditions for Pyraclostrobin

9



196

Page 10 of 30

The mobile phase of the isocratic elution was 70% (A) and 30% (B). The flow

197

rate was 1 mLmin-1, and the column temperature was 25 °C. The detection

198

wavelength for pyraclostrobin was set at 275 nm.

199

Calculations

200

Residue Levels in Fresh Yam

201

The residue in this study was expressed as residue in fresh yam, calculated using

202

the following equations (Eq. (1)-(2)):

203

% =

204

= × (1 − %) (2)

205

where ω is the water content (%), WF is the fresh weight (g), WD is the dry weight (g),

206

CF is the residue in fresh yam (mg kg-1), and CD is the residue in dry yam (mg kg-1).29

207

Processing Factor

208 209

210

× 100%(1)

Based on the effects on residue levels and the disposition of the residues in various processed products, the PFs are calculated as follows (Eq. (3)): ( ! "!#$ )

= %&%'(%())* (

! "!#$ )

(3)

211

The ratios of residue levels in processed products and their respective raw

212

products are called processing factors (PFs). A PF value 1 indicates

214

the concentration effect of processing procedures.30,31

215

Dissipation Kinetics 10


Page 11 of 30


216

The dissipation process follows first-order kinetics. The degradation rate

217

constant and half-life were calculated using first-order kinetics equations as follows

218

(Eq. 4): = + e- (4)

219

220

where Ct is the concentration of pesticide residue (mg kg-1) at the time t (day), C0 is

221

the initial concentration after application (mg kg-1), and k is the degradation rate

222

constant (day-1). The half-life (t1/2) is defined as the time required for the pesticide

223

residue level to fall to half of the initial residue level after application and was

224

calculated from the k value:t1/2=ln 2/k.

225

Statistical Analysis

226

All experiments were performed at least three times. Data were statistically

227

evaluated by one-way ANOVA analysis with SPSS base 20.0 software. When

228

significant differences were found between groups (p

Effects of Planting and Processing Modes on the Degradation of

Recommend Documents