Rheological and functional properties of oat β-glucan with different molecular weight

Journal Pre-proof Rheological and functional properties of oat β-glucan with different molecular weight Tao Sun, Jinran Li, Yingying Qin, Jing Xie, Bin Xue, Xiaohui Li, Jianhong Gan, Xiaojun Bian, ZeHuai Shao PII:

S0022-2860(20)30269-6

DOI:

https://doi.org/10.1016/j.molstruc.2020.127944

Reference:

MOLSTR 127944

To appear in:

Journal of Molecular Structure

Received Date: 18 December 2019 Revised Date:

18 February 2020

Accepted Date: 19 February 2020

Please cite this article as: T. Sun, J. Li, Y. Qin, J. Xie, B. Xue, X. Li, J. Gan, X. Bian, Z. Shao, Rheological and functional properties of oat β-glucan with different molecular weight, Journal of Molecular Structure (2020), doi: https://doi.org/10.1016/j.molstruc.2020.127944. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier B.V.

Credit author statement

Tao Sun: Writing- Original draft preparation, Writing- Reviewing and Editing. Jinran Li: Investigation, Software. Yingying Qin: Data Curation. Jing Xie: Funding acquisition. Bin Xue: Resources. Xiaohui Li: Validation. Jianhong Gan: Formal analysis. Xiaojun Bian: Visualization. ZeHuai Shao: Supervision.

10-1 βG-H βG-M βG-L

10

10

0.808

-2

Absorbance

Viscosity (Pa.s)

0.8

-3

10-5

1

0.524

0.4 0.367

β-glucan βG-H βG-M βG-L

10-4

0.6

0.2

10 Shear rate (1/s)

100

0.0 0

2

4

6

8

10

Concentration (mg/mL)

Swelling power g/g

Fat binding capacity (g/g)

Bile acid binding capacity (%)

Glucose availability mmol/L

β-glucan

10.8±0.05 b

1.97±0.14 b

15.87 c

29.92 b

βG-L

-

6.30±0.05 a

50.24 a

29.33 b

βG-M

-

5.04±0.14 a

26.70 b

20.69 a

βG-H

-

1.83±0.05 b

8.35 d

19.91 a

Viscosity decreased with the decreasing of molecular weight of oat β-glucan after degradation. Functionalities of oat β-glucan related to viscosity were enhanced or decreased after degradation. Acid degradation endow oat β-glucan with remarkable antioxidant and antibacterial activities. The functionalities and bioactivities of oat β-glucan were related to its viscosity and molecular weights.

1

Rheological and functional properties of oat β-glucan with different

2

molecular weight

3 4

Tao Suna,b*, Jinran Lia,b, Yingying Qina,b, Jing Xiea,b, Bin Xuea,b, Xiaohui Lia,b, Jianhong Gana,b, Xiaojun Biana,b,

5

ZeHuai Shaoa,b

（ 7

a

b

College of Food Science & Technology, Shanghai Ocean University, Shanghai, 201306, China

Shanghai Engineering Research Center of Aquatic-Product Processing & Preservation, Shanghai 201306, China

8 9

Abstract: Three kinds of oat β-glucan oligosaccharides (βG-L, βG-M, and βG-H) with

10

different molecular weights (1.83×103 Da, 4.55×103 Da, and 2.75×104 Da) were

11

prepared through acid degradation of oat β-glucan. The structure analysis implied that

12

the characteristic absorptions of oat β-glucan were not changed during acid

13

degradation. Viscosity decreased obviously with the decreasing of the molecular

14

weight of oat β-glucan oligosaccharides, and viscoelastic property varied during acid

15

degradation of β-glucan. The functionalities oat β-glucan related to its viscosity were

1（

enhanced or decreased after acid degradation. The swelling power of oat β-glucan was

17

disappeared after acid degradation. Fat binding capacity and bile acid binding

18

capacity of oat β-glucan increased or decreased after acid degradation. Glucose

19

availability of three kinds of oat β-glucan oligosaccharides decreased, which implied

20

the hypoglycemic effect increased after acid degradation. Acid degradation endowed

21

oat β-glucan with antioxidant and antibacterial properties. The antioxidant activities

22

increased with the increasing of molecular weight of oat β-glucan oligosaccharides in 1

23

the experimental. βG-M possessed the best antibacterial activity against

24

Staphylococcus aureus and Escherichia coli (except 5% concentration). The results

25

indicated that the functionalities and bioactivities of oat β-glucan were related to its

2（

viscosity and molecular weights.

27 28

Keywords: acid degradation of oat β-glucan; molecular weight; functional properties

29 30

Introduction

31

Oat β-glucan is a non-starch polysaccharide consisting of β-D-glucopyranosyl units,

32

which are joined by β-(1→4) and β-(1→3) linkages. It is the main soluble dietary

33

fibre components that exist on the endosperm cell wall of oat [1]. Oat β-glucan has

34

gained great interest due to its potential use as a functional food ingredient. It can

35

regulate postprandial blood glucose and insulin level for diabetes [2], reduce serum

3（

cholesterol levels for coronary heart disease [3], and beneficially modulate appetite

37

with increased feelings of fullness and satiety [4]. The nutritional and health

38

functionalities are often related to the physicochemical properties of β-glucan to form

39

and increase the viscosity of digestion [5]. Thus, the viscosity-associated healthy

40

benefits of oat β-glucan are directly dependent on its molecular weights and its

41

concentration in solution [6]. The molecular weights of cereal β-glucan were

42

depended on the genotype and environmental condition during growth [7]. Meanwhile,

43

the variation in molecular weights and structural modifications resulting from

44

processing and storage of cereal food, had a direct influence on the viscosity of 2

45

β-glucan, and further resulted in some effect on its functionalities related to viscosity

4（

[8-10]. The decrease in molecular weight of barley β-glucan after gamma irradiation

47

resulted in enhanced antioxidant and antiproliferative activities [11]. Scission of the

48

polymeric chain and glycosidic linkages of β-glucan caused by microwave

49

modification endowed β-glucan with antioxidant potential [12].

50

Since the molecular weight of oat β-glucan is an important factor to change viscosity,

51

the degradation of β-glucan caused by acid, oxidative and enzymatic hydrolysis

52

during processing and storage had attracted attention of many researchers [13, 14].

53

After enzymatic hydrolysis, decrease in the molecular weight reduced the viscosity

54

and swelling power of oat β-glucan [15]. Carbonyl and carboxyl groups are formed

55

during oxidation hydrolysis of oat β-glucan, and could affect the properties of

5（

β-glucan, such as the cholic acid binding capacity and the available glucose [16]. The

57

antioxidant, anticancer and hypoglycemic activities of oat β-glucan were enhanced

58

after radiation degradation [17]. However, detailed relationship between the

59

molecular weights of β-glucan after acid degradation and its biological properties has

（0

been hardly found in the literature. The aim of the work is to find out the relationship

（1

between molecular weight of oat β-glucan and its structure and properties. The

（2

rheological and functional properties of oat β-glucan oligosaccharide with three

（3

different molecular weighs were studied. The results will provide some interesting

（4

information to understand the influence of the molecular weight on the function of oat

（5

β-glucan.

（（ 3

（7

2 Materials and methods

（8

2.1 Material

（9

Oat β-glucan was purchased from Hubei Yuancheng Technology Co., Ltd. (Mw: 134

70

KDa). Glucose assay kit (Enzymic method) was purchased from Shanghai Rongsheng

71

Biological Pharmaceutical Co., Ltd. Soybean lecithin, 2-thiobarbituric acid and cholic

72

acid were purchased from Sangon Biotech Co., Ltd (Shanghai, China). DPPH and

73

Ferrozine were purchased from Sigma-Aldrich (Shanghai, China). Escherichia coli

74

and Staphylococcus aureus were provided by microbiology laboratory, Shanghai

75

Ocean University. All other reagents were of analytical grade.

7（

2.2 Acid degradation of oat β-glucan

77

Oat β-glucan (5 g) was dissolved in hot distilled water (100 mL, 90 °C) and stirred for

78

1 h, then HCl solution (10%) was added to get its concentration of 0.5 mol/L. The

79

reaction continued for 5 h at 90 °C, then it was cooled by tapping water. The pH of

80

the resulting solution was adjusted to 7.0 with NaOH solution (1.0 mol/L), and then

81

was filtered through a 4.5 µm syringe filter. The solution was dialyzed by using

82

dialysis bag (3500, 7000 and 14000 Da) against deionized water for 3 d, and further

83

freeze dried to get β-glucan oligosaccharides, and named as βG-L, βG-M, and βG-H,

84

respectively.

85

2.3 Characterization of oat β-glucan oligosaccharides

8（

2.3.1 Fourier transform infrared spectroscopy

87

The structures of oat β-glucan oligosaccharides were confirmed by an Agilent ATR

88

Fourier transform infrared spectroscopy (FT-IR) at room temperature in the 4

89

wavelength region between 4000 and 500 cm-1 with a resolution of 2 cm-1.

90

2.3.2 Determination of molecular weights

91

Gel permeation chromatography (GPC) was used to determine the molecular weights

92

of β-glucan oligosaccharides. The GPC was carried out on a Waters-515

93

Chromatograph equipped with Waters 2410 refractive index detector and

94

Ultrahydrogel 500 and 120. Na2SO4 (0.07%) solution was used as mobile phase at a

95

flow rate of 0.5 mL/min. The temperatures of the column and detector were both

9（

maintained at 40 ℃ during the determination process. The reference standard was

97

glucan (molecular weight: 188,000 Da, 76,900 Da, 473,000 Da, 43,200 Da, 10,500 Da,

98

and 4000 Da, respectively).

99

2.4 Rheological properties

100

Rheological

101

instruments-Waters LLC) using cone and plate geometry (1.0 mm distance, 40/40

102

mm). β-glucan and its oligosaccharides were dissolved in distilled hot water (70 ℃)

103

and stirred for 60 min, and then cooled in refrigerator at 4 ℃ for 12 h. The rheometer

104

was used to conduct viscosity and oscillatory measurement. Each sample was

105

measured in duplicate.

10（

2.5 Functional properties of β-glucan

107

2.5.1 Swelling power

108

The swelling power was determined according to the following methods [15]. A

109

sample (0.3 g) was added into distilled water (70 ℃, 10.0 mL) and stirred for 10 min.

110

Then the tubes placed in a boiling water for 10 min, then the tubes were cooled with

analyzes

were

performed

5

on

a

rheometer

(DHR-3,

TA

111

tap water for 5 min and centrifuged at 2000 rpm for 5 min. Swelling power was

112

expressed as the ratio of wet sediment weight and dry sample weight.

113

2.5.2 Fat binding capacity

114

The fat binding capacity was determined according to the method with some

115

modifications [16]. A sample (0.2 g) was added in soy oil (10.0 mL) with continuous

11（

stirring for 5 min, then kept at room temperature for 1 h, with successive agitation

117

every 15 min, and centrifuged at 2000 rpm for 15 min. Fat binding capacity was

118

expressed as the ratio between the wet weight and dry weight of the sediment sample.

119

2.5.3 Bile acid binding capacity

120

The bile acid binding capacity of β-glucan oligosaccharides was determined

121

according to the method described by Doubilet [18]. The bile acid solution was

122

prepared using cholic acid (200 mg) and NaOH (0.1 mol/L, 4.7 mL), and distilled

123

water was added to make a volume of 200 mL. The sample (25 mg) was added into a

124

test tube, and then 10 mL of cholic acid solution was added. The mixture was stirred

125

at 37°C for 2 h and filtered through a syringe filter (0.2 µm). The resulting solution

12（

(1.0 mL) was treated with alcoholic furfural solution (1.0 mL, 0.9%) and sulphuric

127

acid (5.0 mL, 16 mol/L) and kept in an ice bath for 5 min, followed by a water bath

128

(70 °C) for 8 min, then 3 min in an ice bath. The absorbance was read at 490 nm.

129

2.5.4 Chemical digestion and glucose availability

130

The chemical digestion and glucose availability were measured according to an

131

artificial stomach-duodenum model [19]. The sample (0.3 g), glucose (0.3 g) and

132

distilled water (10 mL) were stirred and mixed in a shaker, heated to 70 °C for 10 min, （

133

and cooled with tap water. Further, 0.1 mol/L HCl was added to adjust the pH value of

134

the mixture to 1.0-2.0, and then the bath was rehydrated at 37 °C for 1 h to reproduce

135

the gastric environment. Formed mixes were taken from an acidic medium to a pH

13（

6.8-7.2 using NaHCO3 (15 g/L), and then the mixture was maintained at 37°C for 30

137

min to reproduce the duodenal environment. The digestion was left to rest for 15 min

138

until phases separation took place. Sample to determine glucose concentration was

139

taken from the supernatant and glucose content was measured using the glucose assay

140

kit.

141

2.6 Antioxidant activity assays

142

2.6.1 DPPH radical scavenging activity

143

The DPPH scavenging activity was determined according to the modified method

144

[20]. 2.0 mL of ethanol solution of DPPH (0.1 mmol/L) was incubated with test

145

sample (2.0 mL) at varying concentrations. The reaction mixture was shaken well and

14（

incubated for 30 min in the darkness, and then the absorbance of the resulting solution

147

was measured at 517 nm against a blank. The DPPH scavenging activity was

148

measured as a decrease in the absorbance of DPPH and calculated by the following

149

equation: scavenging effect (%) = (1- Asample/Acontrol) ℃ 100%.

150

2.6.2 Reducing power

151

The reducing power was evaluated according to the method of Oyaizu [21]. 2.5 mL of

152

sample at different concentrations was mixed with 2.5 mL of sodium phosphate buffer

153

(pH = 6.60, 0.2 mol/L) and potassium ferricyanide (2.5 mL, 1%), respectively. The

154

mixture was kept at 50 °C for 20 min. After addition of trichloroacetic acid (2.5 mL, 7

155

10%), the mixture was centrifuged at 1900 r/min for 20 min. 2.0 mL the supernatant

15（

solution was mixed with 2.0 mL distilled water and 0.4 mL ferric chloride (0.1%), the

157

mixture was kept for 10 min. Absorbance at 700 nm of the solution was read to

158

evaluate the reducing power.

159

2.6.3 Inhibition of lipid peroxidation

1（0

The lipid peroxidation was evaluated according to the following steps of Tang [22].

1（1

Briefly, soybean lecithin (0.2 g) was dissected and homogenized in ice-cold phosphate

1（2

buffer saline (pH = 7.40, 200 mL). 4.0 mL sample solution at different concentrations

1（3

was added to each test tube, respectively. 3.6 mL of lecithin solution, 0.4 mL of

1（4

FeSO4 solution (10 mmol/L) and 0.4 mL of VC solution (10 mmol/L) were added in

1（5

turn. The mixture was kept at 37 °C for 60 min and was cooled with tap water. The

1（（

reaction was stopped by the addition of trichloroacetic acid (1.0 mL, 20%, w/v) and

1（7

thiobarbituric acid (1.0 mL, 0.8%, w/v) in succession, and all tubes were placed in a

1（8

boiling water for 15 min. The tubes were centrifuged at 3000 rpm for 20 min, and the

1（9

absorbance at 535 nm of the sample was measured against a blank. The inhibition

170

ability of lipid peroxidation was calculated as the following formula: inhibition ability

171

(%) = (1- Asample/Acontrol) ℃ 100%.

172

2.7 Antibacterial activities

173

The antibacterial activity was determined using the agar diffusion method. Bacterial

174

suspension (106 CFU/mL, 150 µL) was spread onto agar plates before holes (diameter

175

of 6.00 mm) containing test solution were punched on agar plates. Inhibition zones

17（

were evaluated after incubation of the bacterial at 37 ºC for 8 h. Potassium sorbate 8

177

was used as positive control and sterile water was used as blank control.

178

2.8 Statistical analysis

179

All the figures were obtained from Origin Pro 9. The analysis of data was performed

180

by SPSS 21 (USA) when appropriate (n=3, p<0.05).

181 182

3 Results and discussion

183

3.1 FT-IR spectroscopy and molecular weights

βG-H

Transmittance (%)

βG-M

4000

βG-L

β-glucan

3500

3000

2500

2000

1500

1000

-1

Wavenumber (cm )

184 185

Fig. 1. The FT-IR of oat β-glucan and its oligosaccharides.

18（

FT-IR spectroscopy confirmed the chemical structure of oat β-glucan and its

187

oligosaccharides (Fig. 1). Oat β-glucan and its three kinds of oligosaccharides have

188

the same strong absorptions around 1015 cm-1 that originated from the glycosidic

189

linkage C-O-C stretching vibration. This structure belonged to the different units of

190

(1→3) and (1→4) in oat β-glucan [23]. The typical C=O and –CHO stretching

191

vibration are around 1643 cm-1 [24], which were founded in oat β-glucan and its three

192

kinds of oligosaccharides. The weak band around 897 cm-1 indicated the presence of 9

193

β-linked-D-glucopyranose residues [25]. The result indicated that the structures of the

194

main chain of oat β-glucan were not changed during acid degradation.

195

Gel permeation chromatography results indicated that the average molecular weights

19（

of oat β-glucan, βG-L, βG-M and βG-H were 1.34×105 Da, 1.83×103Da, 4.55×103Da,

197

and 2.75×104 Da, respectively.

198

3.2 Rheological properties

199

3.2.1Viscosity

Viscosity (Pa.s)

10-1

10-2

10-3 β-glucan βG-H βG-M βG-L

10-4

10-5

200

1

10 Shear rate (1/s)

100

201

Fig. 2. The viscosity of oat β-glucan and its oligosaccharides at various shear rate (5 ℃, 10%).

202

Oat β-glucan and its oligosaccharides exhibited Newtonian behavior during

203

experimental shear rate (Fig. 2). Researches showed that the viscosity of oat β-glucan

204

depends on its molecular weights and concentration [26]. Oat β-glucan exhibited

205

pseudoplastic behavior at high molecular weights and concentrations, whereas

20（

Newtonian behavior was observed at lower molecular weights and concentrations

207

[27]. The viscosity of β-glucan decreased sharply after acid degradation resulting

208

from the decrease in the molecular weights, and the viscosity of oat β-glucan 10

209

oligosaccharides decreased with the decreasing of the molecular weight. The healthy

210

benefits of β-glucan are related to its viscosity, which slowed down the intestinal

211

transit and the absorption of glucose and sterols [28, 29]. Therefore, the decreasing in

212

viscosity of β-glucan after degradation implied the decline of its functional property.

213

3.2.2 Viscoelastic properties 101

β-glucan

βG-H

103

G',G'' (Pa)

G',G'' (Pa)

100

102

10-1

10-2

101

1

10

10-3

100

1

10 Angular frequency (rad/s)

Angular frequency (rad/s)

214

100

100

βG-L

βG-M

10

-1

G',G'' (Pa)

G',G'' (Pa)

10

100

-2

10

-1

10-2 10-3

10

215

10-3

-4

1

10

100

Angular frequency (rad/s)

1

10

100

Angular frequency (rad/s)

21（ 217

Fig. 3. Frequency dependence of storage (G′) and loss (G″) modulus of β-glucan and its oligosaccharides: G′ (solid symbols) and G″ (open symbols) (5 ℃, 10%).

218

The variation of storage modulus (G') and loss modulus (G") as a function of the

219

angular frequency (ω) for β-glucan and its oligosaccharides was shown in Figure 3. G′

220

values of β-glucan and βG-H were higher than G″ values through the experimental

221

range. These observations implied that both oat β-glucan and βG-H possessed a

222

typical biopolymer gel network. This phenomenon was similar to the behavior of oat

223

β-glucan reported by Shah [30]. The viscoelastic property of β-glucan was affected by 11

224

its molecular weights. The G″ of β-glucan with lower molecular weights (βG-M and

225

βG-L) was higher than G′ in the low frequency region in this experimental, which

22（

indicated the liquid-like behavior of β-glucan with lower molecular weights. The

227

sol-gel transition point (G′ = G″) was observed in βG-M and βG-L, which showed the

228

transition from solation to gelation.

229

3.3 Swelling power, fat binding capacity, bile acid binding capacity, and glucose

230

availability

231

The swelling power (SP), fat binding capacity (FB), bile acid binding capacity (BAB),

232

and glucose availability (GA) of oat β-glucan and three kinds of its oligosaccharides

233

are showed in Table 1. Swelling power (SP) of polysaccharides indicated its ability to

234

reduce cholesterol [31]. Oat β-glucan possessed 10.8 g.g-1 of SP. The swelling power

235

of oat β-glucan decreased sharply after degradation, three kinds of oat β-glucan

23（

oligosaccharides do not exhibit swelling power. The result may be related to the fact

237

that three kinds of oat β-glucan oligosaccharides possess good water solubility after

238

acid degradation. The SP of oat β-glucan decreased after oxidation treatment [32].

239

This phenomenon may be related to the structural disintegration of oat β-glucan after

240

degradation, which further led to a reduction of swelling power. Research showed that

241

molecular weight reduction of oat β-glucan caused by partially degradation leads to

242

reduction of swelling power. This behavior is related to increased breaks of the

243

glycosidic chain, and the break lead to a lower capacity of water retention in the chain

244

[15]. The result implied that SP could decrease in the food processing and storage

245

involved in acid degradation. 12

24（

Fat binding capacity of oat β-glucan implied its hypolipidemic effect [33]. FB of oat

247

β-glucan was 1.97 g.g-1 in this test. FB of oat β-glucan oligosaccharides decreased

248

slightly for βG-H (1.83), but remarkably increased for βG-M (5.04) and βG-L (6.30).

249

βG-L showed the best fat binding capacity. Active hydroxyl groups of oat β-glucan

250

are released after degradation. The active hydroxyl groups could play an important

251

role in fat binding capacity, which resulted in the fact that FB of βG-L is the strongest.

252

The related mechanism needs to be investigated.

253

As an acidic steroid, bile acid is synthesized by cholesterol in the liver. The bile acid

254

binding capacity indicated the ability to reduce cholesterol levels in the body [34].

255

The BAB of βG-M (26.70%) and βG-L (50.24%) increased obviously after acid

25（

degradation in comparison with that of oat β-glucan (15.87%). The phenomenon was

257

similar to the result of Asma [35]. βG-L showed the strongest bile acid binding

258

capacity. Similar to fat binding capacity, BAB of oat β-glucan oligosaccharides

259

decreased and remarkably increased with the decreasing of the molecular weights.

2（0

The glucose availability decreased after acid degradation of oat β-glucan. The GA of

2（1

βG-L was similar with that of oat β-glucan, and βG-H possessed lowest glucose

2（2

availability of 19.91 mmol/L. Research showed that glucose availability of oat

2（3

β-glucan increased after oxidative degradation, which implied the hypoglycemic

2（4

effect of oat β-glucan reduced after oxidative degradation. The result may be related

2（5

to degradation of β-glucan caused by the action of hydrogen peroxide, which

2（（

increases the susceptibility of the molecule, and the chemical action raises

2（7

postprandial glucose [16]. The glucose availability of oat β-glucan decreased after 13

2（8

acid degradation, and the results need to be investigated in the future.

2（9 270

Table 1. Swelling power, fat binding capacity, bile acid binding and glucose availability of oat β-glucan, βG-H, βG-M and βG-H.

Swelling power

Glucose availability

g/g

Fat binding capacity (g/g)

Bile acid binding capacity (%)

β-glucan

10.8±0.05 b

1.97±0.14 b

15.87 c

29.92 b

βG-L

-

6.30±0.05 a

50.24 a

29.33 b

βG-M

-

5.04±0.14 a

26.70 b

20.69 a

βG-H

-

1.83±0.05 b

8.35 d

19.91 a

mmol/L

271 272

Different letters in the same column (a, b, c, d) indicate significant difference among sample at the p < 0.05 level determined with Tukey’s test.

273

3.4 Antioxidant activities

274

3.4.1 DPPH radical scavenging activity

80

Scavenging effect (%)

70

βG-H βG-M βG-L

60 1.08

50

1.36

2.73

40 30 20 10 0 0.0

0.5

1.0

1.5

2.0

2.5

3.0

Concentration (mg/mL)

275 27（

Fig. 4. DPPH scavenging effect of oat β-glucan oligosaccharides.

277

The relatively stable DPPH radical has been widely used to test the ability of a

278

compound as free radical scavenger or hydrogen donor to evaluate the antioxidant

279

activity [36]. Oat β-glucan didn’t show DPPH scavenging ability due to its poor water

280

solubility. The DPPH scavenging ability of its oligosaccharides may be related to the 14

281

breakdown and degradation of β-glucan that leads to the exposure of their active

282

hydroxyl groups and decreasing the intermolecular hydrogen bonding [20].

283

DPPH scavenging activity of β-glucan oligosaccharides increased with the increasing

284

of the concentrations (Fig.4). The 50% inhibitory concentration (IC50) of βG-H, βG-M

285

and βG-L on DPPH was 1.08, 1.36 and 2.73 mg·mL-1, respectively. The result

28（

indicated that DPPH scavenging activity of oat β-glucan oligosaccharides increased

287

with the increasing of the molecular weights in this experiment. The related

288

mechanism needed to be studied further in the future.

289

3.4.2 Reducing power

βG-H βG-M βG-L

Absorbance

0.8

The

0.808

0.6 0.524

0.4 0.367

0.2

0.0 0

290

2

4

6

8

10

Concentration (mg/mL)

291

Fig. 5. Reducing power of oat β-glucan oligosaccharides.

292

Antioxidants with reducing power are electron donors and reduce the oxidised

293

intermediates of lipid peroxidation, as primary and secondary antioxidants [37]. It can

294

be determined by measuring the formation of Perls’ Prussian blue at 700 nm [38]. The

295

reducing power of oat β-glucan oligosaccharides was shown in Figure 5. The

29（

absorbance of βG-H, βG-M and βG-L at the 2.0 mg/mL concentration were 0.808, 15

297

0.524, and 0.367, respectively. Higher absorbance value implied stronger reducing

298

power. This showed the order of the reducing power was as follows: βG-H > βG-M >

299

βG-L. The result indicated that reducing power of oat β-glucan oligosaccharides

300

increased with the increasing of the molecular weights in this experiment. The result

301

has the same trend with the DPPH scavenging activity of oat β-glucan

302

oligosaccharides.

303

3.4.3 Inhibition of lipid peroxidation

70 βG-H βG-M βG-L

Inhibition ability (%)

60 50

3.01

1.31

40 30 20 10 0 0

1

2 Concentration (mg/mL)

3

4

304 305

Fig. 6. Inhibition ability of oat β-glucan oligosaccharides on lipid peroxidation.

30（

The structure and functionality of biomolecules could be destroyed by lipid

307

peroxidation [32]. The inhibitory ability of oat β-glucan oligosaccharides against lipid

308

peroxidation was shown in Figure 6. The 50% inhibitory concentration of βG-H and

309

βG-M was 1.31 and 3.01 mg·mL-1, respectively. βG-L had the worst ability to inhibit

310

lipid peroxidation and its IC50 can’t be read in this experiment. Similar to DPPH

311

scavenging activity and reducing power, the results also indicated the inhibition of

312

lipid peroxidation increased with the increasing of the molecular weights of β-glucan 1（

313

oligosaccharides.

314

3.5 Antibacterial activities

315

The antibacterial activities of β-glucan oligosaccharides are shown in Table 2. Oat

31（

β-glucan didn’t show antibacterial activities due to its poor water solubility, but its

317

oligosaccharides possessed antibacterial activities. The result may be related to the

318

breakdown and degradation of β-glucan that leads to the exposure of their active

319

hydroxyl groups and decreasing the intermolecular hydrogen bonding [37].

320

Antibacterial activities of oat β-glucan oligosaccharides increased with the increasing

321

of the concentration, and the antibacterial activity against Staphylococcus aureus is

322

stronger than that against Escherichia coli. βG-M possessed the best antibacterial

323

activity against Staphylococcus aureus and Escherichia coli (except 5%

324

concentration). βG-H showed the best DPPH scavenging activity, reducing power and

325

inhibition ability of lipid peroxidation in our above antioxidant activities evaluation.

32（

The results implied that there is different mechanism between antioxidant and

327

antibacterial activities of oat β-glucan oligosaccharides.

328

Table 2. Antibacterial abilities of oat β-glucan oligosaccharides.

Escherichia coli (mm) 1% βG-H-L βG-H-M βG-H-H potassium sorbate sterile water 329 330

2%

Staphylococcus aureus (mm) 5%

1%

b

24.95±0.21 25.90±0.14c 24.70±0.42b

a

b

27.75±0.21 30.60±0.57b 28.60±0.57a

33.25±0.35 34.60±0.57b 35.60±0.57a

24.40±0.85a

31.75±1.06b

37.45±0.92c

2% c

5%

34.15±0.07 44.05±0.07d 42.05±2.76b

c

39.45±0.49 50.00±0.28d 46.00±2.83b

46.60±0.57c 57.50±0.71d 51.10±1.27b

6.00±0.00a

16.55±0.64a

21.00±0.28a

6.00±0.00

Different letters in the same column (a, b, c, d) indicate significant difference among sample at the p < 0.05 level determined with Tukey’s test. 17

331

Oat β-glucan with high molecular weight exhibits high viscosity that restricts its

332

applications. Furthermore, water-soluble β-glucan seems to be more beneficial for

333

human health than water-insoluble β-glucan, because the latter often exert health

334

effects only as a dietary fible [1]. Research showed chemical modification could

335

endow material with enhanced bioactivities, such as antibacterial and anticancer

33（

activities [39]. In this work, the functionalities of oat β-glucan were changed, and its

337

antioxidant and antibacterial activities increased after acid degradation.

338 339

Conclusion

340

The structures of the main chain of oat β-glucan were not changed during acid

341

degradation. Viscosity decreased obviously with the decreasing of the molecular

342

weight of oat β-glucan. The functionalities related to the viscosity increased or

343

decreased. The swelling power was disappeared; meanwhile, fat binding capacity and

344

bile acid binding capacity were enhanced or decreased during acid degradation of oat

345

β-glucan. Glucose availability of three kinds of oligosaccharides decreased.

34（

Degradation endow polysaccharides with excellent bioactivities, such as antioxidant

347

and antibacterial activities [40, 41]. Oat β-glucan oligosaccharides possessed

348

remarkable antioxidant and antibacterial activities owing to the breakdown and

349

degradation of β-glucan that leads to the exposure of their active hydroxyl groups and

350

decreasing the intermolecular hydrogen bonding. The results indicated that the

351

functionalities and bioactivities of oat β-glucan were related to its viscosity and

352

molecular weights. The related mechanism needed to be investigated further in the 18

353

future.

354 355

Acknowledgements

35（

This work was financially supported by the Natural Science Foundation of China

357

(grant number: 31571914) and Key Research and Development Plan of National

358

“13th Five-year” (grant number: 2016YFD0400106).

359 3（0

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Highlights 1. Viscosity decreased with the decreasing of molecular weight (Mw) of oat β-glucan. 2. Functionalities related to viscosity were increased/decreased after degradation. 3. Degradation endow β-glucan with good antioxidant and antibacterial activities. 4. The functionalities of oat β-glucan were correlated to its viscosity and Mw.

Conflict of Interest

The authors declared that they have no conflicts of interest to this work. We declare that we do not have any commercial or associative interest that represents a conflict of interest in connection with the work submitted.