Structures, properties, modifications, and uses of oat starch

Accepted Manuscript Structures, properties, modifications, and uses of oat starch Fan Zhu PII: DOI: Reference:

S0308-8146(17)30263-7 http://dx.doi.org/10.1016/j.foodchem.2017.02.064 FOCH 20617

To appear in:

Food Chemistry

Received Date: Revised Date: Accepted Date:

14 September 2016 4 February 2017 13 February 2017

Please cite this article as: Zhu, F., Structures, properties, modifications, and uses of oat starch, Food Chemistry (2017), doi: http://dx.doi.org/10.1016/j.foodchem.2017.02.064

This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. 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.

1

2

Structures, properties, modifications, and uses of oat starch

3

4

Fan Zhu*

5

School of Chemical Sciences, University of Auckland, Private Bag 92019, Auckland 1142,

6

New Zealand

7

* Correspondence, email: [email protected]

8 9

Abstract

10

There is increasing interest to utilise oats and their components to formulate healthy food

11

products. Starch is the major component of oat kernels and may account up to 60% of the dry

12

weight. Starch properties may greatly determine the product quality. Starch, as a by-product

13

of oat processing and fractionation, may also be utilised for food and non-food applications.

14

This mini-review updates the recent advances in the isolation, chemical and granular

15

structures, physicochemical properties, chemical and physical modifications, and food and

16

non-food uses of oat starch.

17 18

Keywords: oat starch; structure; property; modification; use

19

Running title: oat starch updates

1

20

1. Introduction

21

Oats (Avena spp.) belong to the grass family Poaceae and are mostly cultivated in cool

22

climate. The most common species of oats is A. sativa, while others with agricultural/local

23

significance include A. nuda (naked oats), A. strigose, A. byzantina, and A. abyssinica (Zwer,

24

2016). The world production of oats reached over 22 million tonnes in 2014. The major

25

producers are Russia, Canada, Poland, Australia, Finland, and USA (FAOSTAT, 2016).

26

Starch is the major component of oats and may amount up to 60% of the dry weight

27

(Doehlert et al., 2013). Whole grain oats contain a range of bioactive components (Rasane et

28

al., 2015; Zwer, 2016). The protein content of oats ranges from ~9 to 15% with a higher

29

lysine concentration than wheat and maize. The content of β-glucans as dietary fiber ranges

30

from ~2−8%. The lipid content of oats is ~3−11% which is higher than most other cereals.

31

The majority of the oat lipids are unsaturated fatty acids. Oats contain vitamin E with α-

32

tocotrienol and α-tocopherol being the major ones (up to 90%). Other minor vitamins of oats

33

include thiamine, riboflavin, and niacin. Whole grain oats are a good source of polyphenols.

34

The major phenolic acids are ferulic, p-coumaric, caffeic, vanillic acids, and hydroxybenzoic

35

acid and their derivatives. Small amounts of flavonoids, including glycosylvitexin, apigenin,

36

tricin, isovitexin, and vitexin, are also present in oats. Avenanthramides, as phenolic alkaloids,

37

are present in oats, being unique among cereals and pseudocereals (Rasane et al., 2015; Zwer,

38

2016). Due to the presence of the above-mentioned chemical constitutes such as β-glucans,

39

oats possess a range of health effects such as cholesterol-lowering and anticancer properties

40

(Rasane et al., 2015; Zwer, 2016).

41

Oats have been commonly used as livestock feed. They are suitable as feed for dairy and beef

42

cattle, horses, and sheep. They have also been gaining importance as human foods in light of

43

the above-mentioned bioactive components and health effects (Rasane et al., 2015; Zwer,

2

44

2016). Oats have been processed and formulated into a range of food products such as bread,

45

biscuits and cookies, breakfast cereals, granola bars and cereals, infant foods, non-dairy milk,

46

and yoghurt (Rasane et al., 2015; Zwer, 2016). Since starch can be the major component of

47

these products, the properties of starch may be critical to their eating and nutritional quality.

48

For example, the total starch content of oats is positively linked with slippery and less

49

uniformed sensation of oatmeal (Lapveteläinen et al., 2001). Furthermore, there has been

50

increasing interest in the unitization of oat components such as bran and β-glucans as dietary

51

fiber for healthy food formulation. Starch becomes a by-product after the extraction and

52

fractionation of oats (Gangopadhyay et al., 2015). Oat starch can be used in a range of

53

products such as fat replacers, cardboard and brown paper products, coating agents for tablet

54

formulation, and cosmetic and cleanser products (Autio & Eliasson, 2009; Zwer, 2016).

55

Therefore, understanding the composition, properties and structures of the starch could

56

provide a basis to better utilise oat starch for human benefits, and to develop oats as a

57

sustainable crop.

58

Previous reviews of oat starch focused on the literatures from roughly two decades ago (Zhou

59

et al., 1998; Autio & Eliasson, 2009; Sayar & White, 2011). Since then, there has been great

60

advance in oat starch research due to assessing more genetic resources and the conceptual

61

breakthroughs. The present mini-review focuses on the recent advance in our understanding

62

in the isolation, composition, structures, properties, modifications, and uses of oat starch. The

63

readers are strongly encouraged to refer to the previous reviews (Zhou et al., 1998; Autio &

64

Eliasson, 2009; Sayar & White, 2011) to gain background information of oat starch, and to

65

better understand the present updates.

66 67

2. Isolation

3

68

Autio and Eliasson (2009) reviewed the starch isolation from oat kernels on both industrial

69

and laboratory scales. In the laboratory, oat flour is soaked in a solution containing NaOH

70

(0.1 to 0.01 M) before centrifugation and filtration for starch purification. Sometimes,

71

protease can be also added to facilitate the starch isolation process. In industry, oat groats are

72

dry-milled and soaked in a cellulase and hemicellulase-containing solution. This process

73

produces protein and fiber fractions beside starch (Autio & Eliasson, 2009).

74

Al-Hakkak and Al-Hakkak (2007) reported a novel gluten-based starch isolation method.

75

Briefly, wheat gluten was added to the oat flour in a ratio of 18% (w/w, gluten/flour). Salt

76

(3%) was also added to facilitate the isolation process. Upon hydration, wheat gluten network

77

forms through kneading. Oat protein also involves in the network through protein-protein

78

interactions. The dough is proved for 1 h before washing. The starch fraction is then

79

separated by bolt cloth before recovering by centrifugation. The starch yield was 60% of the

80

flour weight and was 84.6% of the theoretical total starch content in the flour. The starch

81

purity was also high with the protein and fat contents being less than 0.3%. Pentosans and β-

82

glucans were not detected in the isolated oat starch. No chemicals were involved in the

83

process which is also compatible with industrial wheat starch manufacturing. This non-

84

destructive gluten-based starch isolation can be extended to include a range of other plant

85

sources such as barley and rye, chickpeas and lentils, and amaranth (Al-Hakkak & Al-

86

Hakkak, 2007). This isolation method has been a US patent (Al-Hakkak, 2006). This method,

87

however, remains to be better develop to simultaneously isolate other oat components such as

88

protein and β-glucans which may possess higher market values than the starch.

89 90

3. Composition

4

91

Previous reports showed that the total starch content of oats of various genotypes could

92

amount up to 60% of the dry weight (Zhou et al., 1998). Recent literatures continue to report

93

the total starch contents from more genetic sources and mutants of oats (Doehlert et al., 2013;

94

Verhoeven et al., 2004). The starch contents of oat kernels of 18 genotypes grown in 6

95

locations (North Dakota) varied from 51−59% (Doehlert et al., 2013). Mean values of starch

96

contents of oats of 5 genotypes grown in 6 locations (Manitoba, Canada) varied from 61−65%

97

(Rhymer et al., 2005). The starch content depended on both the genotype and the

98

environment (Rhymer et al., 2005). For example, the mean values of total starch content of

99

the variety (Silverton 1999) harvested in 1998 and 1999 were 61.1% and 63.7%, respectively

100

(Rhymer et al., 2005). In North Dakota, warmer temperatures and less precipitation in the

101

growing seasons such as in April and August gave a higher starch content in oat groats

102

(Doehlert et al., 2001). Mutant of A. strigose (lam-1) had a reduced starch content from 6.61

103

to 5.98 mg/grain, while the sga-1 mutant had no starch but contained water-insoluble (3.88

104

mg/grain) and soluble (0.61 mg/grain) α-glucans (Verhoeven et al., 2004). Therefore, this

105

mutant of A. strigose resembled the sugary-1 mutants of other cereals such as maize.

106

The minor components of oat starch such as lipids (0.7−2.5%) and proteins (0.02−1%) have

107

been well documented in a previous review (Autio & Eliasson, 2009). Amylose is a major

108

component of starch. Previous studies showed the amylose contents of oat starch varied from

109

2 to 34%, depending on the genotype and measuring method (Zhou et al., 1998; Autio &

110

Eliasson, 2009). Amylose content has been the most studied compositional parameter in

111

recent reports (Zheng et al., 2015; Simsek et al., 2013; Stevenson et al., 2007; Verhoeven et

112

al., 2004) (Table 1). There is a wide variation in amylose contents (0−38%) among these

113

reports, which can be attributed to the genetic and environmental variation of the crop as well

114

as the measuring method. Analysis of the mutants of A. strigose (lam-1 and lam-2) revealed

115

two waxy genotypes with very little amylose (Verhoeven et al., 2004). These two mutants 5

116

had much reduced activity of granule-bound starch synthase (GBSS) and GBSS1 content in

117

the endosperm. Indeed, GBSS is responsible for the synthesis of amylose in plants (Mason-

118

Gamer et al., 1998). The amylose content is rather sensitive to the analytical method used

119

(Stevenson et al., 2007; Simsek et al., 2013). Stevenson et al. (2007) showed that the average

120

apparent amylose content of oat starch samples (1 genotype and 3 milling fractions) was

121

~37%, while the absolute amylose content, calculated by subtracting the interference of

122

amylopectin, was ~30%. Simsek et al. (2013) showed that the amylose content of oat starch

123

(1 genotype) was 22.7% and 20.5% as measured by concanavalin A-based precipitation and

124

high-performance size exclusion chromatography (HPSEC) of whole starch, respectively

125

(Simsek et al., 2013). Therefore, the quantification method for amylose content should be

126

noted when comparing data from different studies. There is a diversity in molecular size of

127

amylose chains. Gel-permeation chromatography (Sepharose CL 6B) of debranched oat

128

starch showed that the amounts of long and short amylose unit chains were 19.1 and 8%,

129

respectively (Figure 1a) (Bertoft et al., 2008). Short amylose chains from debranching may

130

reflect that amylose is slight branched (Bertoft et al., 2008).

131

The effects of developing endosperm and pin milling on the amylose contents of oats have

132

been investigated (Stevenson et al., 2007; Zheng et al., 2015). The amylose content in oat

133

starch of developing endosperm was followed by iodine-binding-spectrophotometer-based

134

method (Zheng et al., 2015). The average amylose content of oat starches (3 varieties)

135

increased from 12% at 15 days after anthesis (DAA) to 22% at 33 DAA (Zheng et al., 2015).

136

Pin milling of oat kernels decreased the apparent amylose content of oat starch from 40 to 37%

137

(Stevenson et al., 2007). This may be due to the extensive depolymerisation of the amylose

138

component (Stevenson et al., 2007). Among fractions with different size, the one of 300–850

139

µm had a lower amylose content than those of 150–300 µm and <150 µm (Stevenson et al.,

6

140

2007). These results further testified that it is feasible to employ the knowledge of plant

141

growth and food processing techniques to alter the starch composition.

142 143

4. Structures

144

4.1.Chemical structure

145

4.1.1. Molecular size of amylose and amylopectin

146

The weight-averaged molecular weight of oat amylose was 1.68×105 which was similar to

147

that of maize (1.56 ×10 5) and rice (1.63 ×105) amyloses (Simsek et al., 2013). The molecular

148

weight was analysed by HPSEC with commercial dextrans as molecular standards. HPSEC

149

analysis of starch revealed two fractions of amylopectin differing in molecular weight

150

(Simsek et al., 2013). The percentages of the amylopectin fraction with higher molecular

151

weight were 51.7%, 47.4%, and 56.7% for oat, maize, and rice starches, respectively (Simsek

152

et al., 2013). The weight-averaged molecular weights of oat amylopectin fractions were

153

1.36×107 (larger fraction) and 3.19×10 6 (smaller fraction), respectively, which were larger

154

than those of a range of other starches (maize, rice, barley, buckwheat, rye, and durum wheat)

155

(Simsek et al., 2013). It should be noted that the type of standards (e.g., dextrans and

156

pullulans) can influence the molecular weight of starch and should be noted when comparing

157

data from different studies. Indeed, the results of amylose size reported by Simsek et al.

158

(2013) differed from those of previous reports as summarised by Autio & Eliasson (2009).

159

Pin-milling of oat kernels greatly decreased the molecular weight (weight-based) (from 8.37

160

× 108 to 4.32 × 108 g/mol), polydispersity (M w/Mn) (ratio of weight-based to number-based

161

molecular weights) (from 2.6 to 2.15), and gyration radius (Rz) of oat amylopectin (from 431

162

to 302 nm) (Stevenson et al., 2007). The average unit chain length of amylopectin was also

163

decreased from 24.9 to 23 glucosyl residues (Stevenson et al., 2007). This could be readily 7

164

attributed to the depolymerisation of starch by pin-milling. Amylopectin of the milling

165

fraction with the size range of 300–850 µm had a smaller molecular weight (4.17× 108 g/mol),

166

polydispersity (M w/Mn) (1.42), and gyration radius (Rz) (287 nm) than those of the fractions

167

with size ranges of 150–300 µm and <150 µm (Stevenson et al., 2007). Therefore,

168

manipulating the milling and sieving conditions can alter the molecular size of oat starch.

169 170

4.1.2. Unit chain length distribution of amylopectin

171

A typical unit chain length profile of oat amylopectin is presented (Figure 1b) (Bertoft et al.,

172

2008). The weight percentages of oat amylopectin unit chains with DP 6−12, DP 13−24, DP

173

25−36, and DP > 36 were 21.1, 44.3, 14.5, and 19.8%, respectively, as revealed by high-

174

performance anion-exchange chromatography (Stevenson et al., 2007). The unit chain length

175

distribution of oat amylopectins (3 varieties) of developing endosperm was followed by a

176

capillary electrophoresis method (Zheng et al., 2015). In developing endosperms, the amount

177

of short unit chains (DP 6 to 9) decreased (by 2−3%, weight basis), while that of long unit

178

chains (DP > 36) increased (by 1−2%, weight basis) from day 15 to 33 after anthesis (Zheng

179

et al., 2015). Kalinga et al. (2014) analysed the average unit chain length (CL) of

180

amylopectins from developing wheat endosperms and found that CL remained similar (~18

181

glucosyl residues) from 7 to 35 days after anthesis (unit chain length distribution not given).

182

Therefore, how the developing endosperm affects the unit chain length profile of amylopectin

183

in different starches remains to be conclusively studied.

184

Genetic mutations of starch-related biosynthetic enzymes can affect the amylopectin structure

185

of oat starch. The sga-1 mutant of A. strigose produced no starch but water soluble α-glucans

186

with the unit chain length distribution being similar to that of phytoglycogen (Verhoeven et

187

al., 2004). Processing can influence the unit chain profile of amylopectin. Pin-milling 8

188

increased the amounts of short unit chains with DP of 6 to 12 by 2.5% and decreased that of

189

unit chains with DP of > 37 by 2.6% (Stevenson et al., 2007). This could be attributed to the

190

degradation of starch molecules by milling. Amylopectins from milling fractions differing in

191

size (150–300 µm, <150 µm, and 300–850 µm) had similar unit chain length distribution.

192 193

4.1.3. Internal unit chain composition of amylopectin

194

The external parts of amylopectin unit chains can be removed by using phosphorylase a

195

and/or β-amylase to obtain the internal parts in the form of φ, β-limit dextrins (LDs) or β-LDs

196

(Bertoft et al., 2008). Bertoft et al. (2008) analysed the internal unit chain length distribution

197

of oat amylopectin in comparison with that of amylopectins from a range of botanical sources.

198

Based on the internal unit chain composition, amylopectins were categorised into 4 groups.

199

Group 1 has the highest amount of short unit chains and the lowest amount of long unit

200

chains, while group 4 has the opposite composition. Groups 2 and 3 are in between groups 1

201

and 4 (Figure 1c). Oat starch, together with rice, barley, and Andean yam bean (Pachyrhizus

202

ahipa) starches belonged to the group 1, whereas potato and lesser yam (Dioscorea esculenta)

203

starches were of group 4. This pattern follows that of amylopectin unit chain length

204

distribution. The classification of amylopectins also in general agreed with that of starch

205

polymorphism revealed by wide-angle X-ray diffraction (Bertoft et al., 2008).

206

A-chain of amylopectin unit chains carries only one other chain (Peat, Whelan, & Thomas,

207

1952). The molar amount of A-chains of oat amylopectin was 50% as all the A-chains appear

208

as maltose in φ, β-LDs. The molar amounts of Bfp (B-fingerprint chains) (DP 3−7) and B1-

209

chains (DP 3−26) were 15.9% and 45.0%, respectively. The average unit chain length of φ,β-

210

LDs was 7.8 glucosyl residues, which is shorter than that of amylopectins from B-type

211

starches (9−10 glucosyl residues) (Bertoft et al., 2008). The external (ECL) and internal chain 9

212

(ICL) lengths of oat amylopectin were 10.7 and 5.3 glucosyl residues, respectively, both of

213

which are shorter than those of amylopectins from B-type starches (Bertoft et al., 2008).

214

4.1.4. Building block structure of amylopectin

215

The branches of amylopectin are clustered as described in the building block backbone model

216

of amylopectin (Figure 1d, 1e, and 1f) (Bertoft et al., 2012a and 2012b). These clusters can

217

be isolated by enzymatic hydrolysis with α-amylase of Bacillus amyloliquefaciens (Bertoft et

218

al., 2012a). The branches in clusters form the smaller and basic structural units termed

219

“building block” (Figure 1d) (Bertoft et al., 2012a). Building blocks can be isolated by

220

hydrolysing the clusters with a concentrated solution of α-amylase of B. amyloliquefaciens

221

(Bertoft et al., 2012a). The building block concept of amylopectin and many related

222

nomenclatures have been systematically reviewed by Bertoft (2013). These nomenclatures

223

are also employed to explain the structural basis of physicochemical properties of starch as

224

described in the section 5. Therefore, readers who are unfamiliar with the building block

225

concept must refer to previous publications to gain the necessary background knowledge to

226

understand the current content related to oat starch.

227

The internal part of clusters in the form of φ, β-LDs can be quantified and compared with that

228

of other starches (Bertoft et al., 2012a). The average DP of the clusters of oat amylopectin

229

was 72.4. The number of chains per cluster (NC) was 11.8, and the average and internal chain

230

lengths of a cluster was 6.1 and 4.1 glucosyl residues, respectively (Bertoft et al., 2012a). The

231

cluster structural parameters of oat amylopectin were similar to those of rice amylopectin, but

232

the size and NC of oat clusters were larger than those of edible canna (Canna edulis) and

233

lesser yam (D. esculenta) clusters. The difference in the structure of clusters of different

234

amylopectins follows the pattern of the internal unit chain composition of amylopectins as

235

well as that of the polymorph type of starch (Bertoft et al., 2012a and 2008).

10

236

The weight percentage of branched building blocks of oat amylopectin was 86.7%, which is

237

‘similar to that of rice and Andean yam bean amylopectins, and higher than that of clusters

238

from B-type starches (Bertoft et al., 2012a). It appeared that the structures of building blocks

239

from the clusters of different botanical sources were similar (Bertoft et al., 2012a). The inter-

240

block chain-length (IB-CL) of oat clusters was 5.7 glucosyl residues, which is similar to that

241

of rice and Andean yam bean amylopectins and is shorter than that of clusters from B-type

242

starches. The number of building blocks per cluster for oat was 5.7, which is similar to that of

243

rice amylopectin and is higher than that of clusters from B-type starches. Building blocks can

244

be classified by the number of chains per block. Oat clusters contained a higher amount of

245

singly branched building block (55%) and a lower amount of multiply-branched blocks (1.7%)

246

than those of clusters from B-type starches (Bertoft et al., 2012a). Structural analysis of

247

isolated building block fractions showed that blocks of oat amylopectin, like those of some

248

other cereals (rice, rye, and waxy maize), have a higher A-to-B-chain ratio than those of

249

starches from other non-cereal sources (Bertoft et al., 2012b). This indicates a higher

250

proportion of Haworth conformation than Staudinger conformation in the clusters from

251

cereals (Bertoft et al., 2012b). Therefore, the building block composition of clusters and

252

amylopectins are linked to the polymorph type of starch. The compositional and structural

253

profiles of clusters and building block of oat amylopectin are of the starches with A-type

254

polymorph.

255

4.2.Granular structure (polymorphism and morphology)

256

Previous studies revealed that oat starch has the A-type polymorph (Zhou et al., 1998; Autio

257

& Eliasson, 2009). Recent studies continue to confirm that oat starch has the A-type

258

polymorph (Tian et al., 2016; Bertoft et al., 2008). The relative degree of crystallinity of oat

259

starch was 23.3% which is similar to that of barley and rye starches (Bertoft et al., 2008).

260

This value is lower than that of a previous report as summarised previously (Autio & 11

261

Eliasson, 2009). It should be noted that the relative degree of crystallinity greatly depends on

262

the analytical and calculation method. Germination (16 oC, up to 144 h) of oat kernels had no

263

effect on the polymorph type (Tian et al., 2016).

264

Numerous studies have probed the morphology of oat starch as summarised by Autio &

265

Eliasson (2009). The shape is irregularly polygonal. The granule size of oat starch is mostly ~

266

10−15 mm (Verhoeven et al., 2004). No pores were found on the surface of oat starch,

267

whereas pores were commonly noted on the surface of maize, sorghum, and millet starches

268

(Fannon et al., 1992). The effects of developing endosperm, genetic mutation, and

269

germination on the morphology of oat starch were studied (Verhoeven et al., 2004; Zheng et

270

al., 2015; Tian et al., 2016). Starches of the mutants of A. strigose, including waxy (lam-1

271

and lam-2) and sga-1 mutants, had similar granule size distribution to the wild type

272

(Verhoeven et al., 2004). The morphological change of starch in the developing oat

273

endosperm was followed by scanning electron microscopy (SEM) (Zheng et al., 2015).

274

Compound granules were noted at 10 days after anthesis (DAA). These compound granules

275

became polygonal or irregular after 12 DAA. The granule shape was not affected by the

276

germination (16 oC, up to 144 h) of oat kernels. Toward the end of germination, surface

277

fissures were found in the granules probably due to amylolysis (Tian et al., 2016). Particle

278

size analysis showed that the germination gradually decreased the granule size.

279 280

5. Physicochemical properties

281

5.1.Swelling and solubility

282

Genetic diversity in swelling and solubility of oat starch has been observed (Šubarić et al.,

283

2011). For example, the swelling power (SP) and solubility of oat starches from 3 varieties

284

cultivated in Czech Republic ranged from 12.8 to 31.1 g/g and from 7 to 35% at 85 oC, 12

285

respectively (Šubarić et al., 2011). Mean values of swelling volume of the starches from oats

286

(5 varieties grown in 6 locations) were 5.17−6.44 cm3. The results showed that the swelling

287

of oat starch depended not only on the genotype but also the growing environment (Rhymer

288

et al., 2005). In a comparative study between oat and barley starches (3 varieties each), the

289

former showed higher SP values (e.g., SP = 24−31.5 g/g at 95 oC) than the latter (e.g., SP =

290

20.8−21.8 g/g at 95 oC) (Šubarić et al., 2011). Factors affecting the swelling and solubility

291

include the amylose content, amylose and amylopectin structures, and granular organization,

292

as well as the presence of minor components such as protein and lipids (Vamadevan &

293

Bertoft, 2015; Srichuwong & Jane, 2007).

294

The ghost structure after the starch gelatinization was obtained by heating a diluted starch

295

suspension without shearing (Obanni & BeMiller, 1996). After cooking, oat starch retained

296

less granular structure than wheat and barley starches. Like the other starches, the remaining

297

starch granules of oats after cooking were stained reddish brown with iodine solution. It

298

would be interesting to study the molecular structure of the starch ghost which may play an

299

important role in starch properties during shearing (Obanni & BeMiller, 1996). The leached

300

material of oat starch during heating and swelling was studied (Shamekh et al., 1999). The

301

amount of leached material increased from 6.1 to 37.4% with increasing temperature from 85

302

to 97 oC (Shamekh et al., 1999). Lysophospholipids were present in both the solubilised

303

material and starch residues. Fractionation analysis of dispersed starch solution (95 °C) by

304

centrifugation revealed the composition of the leached material. The majority of the

305

solubilised material (70%) was amylose. Re-centrifugation revealed an insoluble fraction that

306

had a high amylose-to-lipid ratio (Shamekh et al., 1999). Compared with barley starch, the

307

solubilised material of oat starch was higher in the molecular weight (Shamekh et al., 1999).

308

13

309

5.2.Gelatinization by differential scanning calorimetry (DSC)

310

DSC gelatinization parameters of oat starch from the recent reports agreed well with the

311

previous studies as reviewed (Zhou et al., 1998; Autio & Eliasson, 2009) (Table 2). More

312

genetic resources and genotype-environment interactions on oat starch gelatinisation were

313

investigated (Šubarić et al., 2011; Rhymer et al., 2005). Šubarić et al. (2011) showed that oat

314

starches from 3 varieties grown in Czech Republic had ∆H (enthalpy change) of 7.88−10.15

315

J/g. Rhymer et al. (2005) analysed oat starches from 5 varieties grown in 6 locations

316

(Manitoba, Canada) and revealed that mean values of Tp (peak temperature) varied from

317

57.72 to 60.32 oC and ∆H from 8.74−9.48 J/g, which was affected by both genotype and

318

environment. Compared with barley starches (3 varieties), only Tc (conclusion temperature)

319

of oat starches (3 varieties) appeared to be higher, while the other DSC parameters (To, Tp,

320

and ∆H) were similar (Šubarić et al., 2011). Vamadevan et al. (2013a) compared the

321

gelatinization profile of oat starch with 16 other starches from various botanical sources. Oat

322

starch, like the other starches of group 1 (based on the internal unit chain composition of

323

amylopectin) (Bertoft et al., 2008), was among those with the lowest gelatinization

324

temperatures and ∆H. The gelatinization properties of starch were correlated with the cluster

325

structure of amylopectin (Vamadevan et al., 2013a). To was negatively correlated with the

326

number of building block per cluster and positively correlated with IB-CL, while ∆H was

327

positively correlated with ECL of amylopectin. A structural model of amylopectin was

328

proposed to explain the differences in the thermal properties of starch (Figure 1e)

329

(Vamadevan et al., 2013a). Group 1 starches (including oat starch and other A-type starches),

330

with shorter IB-CL and larger numbers of blocks per cluster, have lower flexibility for

331

conformational packing and increased chances to develop non-parallel double helices during

332

biosynthesis. Group 4 starches (including B-type starches) with longer IB-CL and smaller

333

numbers of blocks per cluster have higher conformational flexibility and increased chances to 14

334

develop parallel double helices (Vamadevan et al., 2013a). The importance of amylopectin

335

internal structure in determining the physicochemical properties of starch has been reviewed

336

recently (Vamadevan & Bertoft, 2015).

337

Effects of developing endosperm and pin-milling on thermal properties of oat starch were

338

studied by DSC (Zheng et al., 2015; Stevenson et al., 2007). Gelatinization temperatures and

339

∆H of oat starch increased by ~4 oC and ~2 J/g, respectively, from day 15 to 33 after anthesis

340

(Zheng et al., 2015). The increased gelatinization parameters may partially be attributed to an

341

increased amylose content and a decreased amount of short amylopectin unit chains (DP

342

6−12) (Zheng et al., 2015; Srichuwong & Jane, 2007). Pin-milling had little effect on the

343

starch gelatinization, and starches from the milling fractions differing in size (150–300 µm,

344

<150 µm, and 300–850 µm) had similar gelatinization parameters (Stevenson et al., 2007). It

345

may be expected that increasing milling time and energy input can lead to decreased DSC

346

gelatinization parameters.

347

5.3.Amylose-lipid inclusion complex

348

Oat starch contains a small amount of endogenous lipids (0.7−2.5%) which can complex with

349

the amylose to form inclusion complexes (Autio & Eliasson, 2009). Mean values of peak

350

temperature of melting amylose-lipid complexes from oats (5 varieties grown in 6 locations)

351

ranged from 101.48−104.71 oC (Rhymer et al., 2005). Starches from milling fractions

352

differing in size (150–300 µm, <150 µm, and 300–850 µm) had somewhat similar

353

gelatinization parameters of amylose-lipid inclusion complexes as measured by DSC (Tp =

354

~101 oC, ∆H = ~1−2 J/g) (Stevenson et al., 2007). These results generally agreed with

355

previous reports on oat starch (Autio & Eliasson, 2009).

356

5.4.Rheological properties

357

5.4.1. Pasting 15

358

The pasting properties of starch are rather sensitive to the analytical methods and

359

experimental conditions (Zhu, 2016). Recent reports on the pasting of oat starch used

360

different instruments [RVA (Rapid Visco-Analysis), BV (Brabender Viscograph), and

361

BMVA (Brabender Micro Visco-Analyser)], different starch concentrations (3, 7, 8, and

362

9.1%), and different heating-cooling programmes (Rhymer et al., 2005; Šubarić et al., 2011;

363

Sikora et al., 2008; Stevenson et al., 2007). Therefore, the results from different studies are

364

regretfully impossible for direct comparison (Table 3).

365

More oat genotypes have been assessed. Šubarić et al. (2011) showed that PV (peak

366

viscosity), BD (breakdown), and SB (setback) of oat starches from 3 varieties ranged from

367

787−910 BU, 105−570 BU, and 386−1410 BU, respectively. Rhymer et al. (2005) showed

368

that the mean values of PV and CPV of oat starches from 5 varieties grown in 6 locations

369

ranged from 150−192 and 187−289 RVU, which were affected by both the genetics and

370

environments (Rhymer et al., 2005).

371

Effect of pin-milling on starch pasting properties was studied (Stevenson et al., 2007).

372

Starches from pin-milling fractions differing in size (150–300 µm, <150 µm, and 300–850

373

µm) had similar pasting temperatures (Stevenson et al., 2007). Starch from the fraction of

374

150–300 µm had lower PV, CPV, and SB of pasting than that from the other two fractions

375

(Stevenson et al., 2007). This suggests that milling and sieving can be used to modify the

376

pasting property of oat starch (Stevenson et al., 2007).

377

Pasting properties of oat starch were compared with those of other starches (Sikora et al.,

378

2008; Šubarić et al., 2011). Pasting properties of oat starches (3 varieties) were compared

379

with those of barley starches (3 varieties) (Šubarić et al., 2011). The onset pasting

380

temperatures of oat starches were lower than those of barley starches (71.9−77.6 oC). PV,

381

CPV and BD of oat starches were higher than those of barley starches (PV = 432− 568; CPV

16

382

= 645−861; BD = 3−18) (Šubarić et al., 2011). Pasting properties of oat starch (1 variety)

383

were also compared with those of cassava, maize, and potato starches (Sikora et al., 2008).

384

Oat starch had a higher onset pasting temperature (85 oC) than the others (62−83.5 oC). The

385

PV of oat starch was lower than that of potato (2305 BU) and cassava (215 BU) starches and

386

higher than that of maize starch (10 BU). Previous studies on oat starch discussed the factors

387

affecting the pasting behaviours (Zhou et al., 1998). These factors include granule size,

388

composition and structures of amylose and amylopectin, granular architecture, and the

389

presence of minor components (e.g., lipids and proteins) (Srichuwong & Jane, 2007;

390

Vamadevan & Bertoft, 2015).

391 392

5.4.2. Flow

393

Flow curve of oat starch paste (3% starch concentration) was modelled by the Herschel–

394

Bulkley equation (1) and compared with that of cassava, maize, and potato starches (Sikora et

395

al., 2008).

396

τ = τo + K⋅γn

397

Yield stress (τo), consistency coefficient (K), and flow behavior index (n) of starch paste were

398

obtained from the equation (1) (Sikora et al., 2008). τo of oat starch (7.6 Pa) was higher than

399

that of maize (1.8 Pa), cassava (0.53 Pa), and potato (1.39 Pa) starches (Sikora et al., 2008).

400

This may suggest that the granular ghost of oat starch after gelatinization had a higher

401

mechanical strength than that of the other starches (Obanni & BeMiller, 1996). K of oat

402

starch (2.3 Pa · n-1) was higher than that of maize (1.8 Pa · n-1), cassava (0.06 Pa · n-1), and

403

potato 0.40 Pa · n-1) starches (Sikora et al., 2008). n of oat starch (0.286) was lower than that

404

of maize (0.702), cassava (0.985), and potato (1.011) starches, indicating that oat starch paste

405

had a stronger shear-thinning behaviour. A previous study also showed that the oat starch

(1)

17

406

paste was more thixotropic than that of wheat and maize starches (Doublier et al., 1987).

407

Factors affecting the flow properties of starch pastes are solid concentration, starch type

408

(composition and structure), temperature, and gel preparation method (Doublier, 1981;

409

Nguyen et al., 1998). There is a lack of investigation on the structural basis of flow

410

behaviours of oat starch.

411

5.5.Retrogradation

412

Recent studies reported the effects of developing endosperm and pin-milling on oat starch

413

retrogradation as revealed by DSC (Zheng et al., 2015; Stevenson et al., 2007). The

414

retrogradation rate of gelatinized oat starches (stored at 4 oC for 1 month) of developing

415

endosperms from day 15 to 33 after anthesis increased by ~10−20% (Zheng et al., 2015). The

416

increased retrogradation rate may be at least attributed to the decreased amounts of short

417

amylopectin unit chains and increased amylose content (Zheng et al., 2015). Pin-milling of

418

kernel had a very slight influence on the retrogradation property of oat starch, and starches

419

from the milling fractions differing in size (150–300 µm, <150 µm, and 300–850 µm) had

420

rather similar retrogradation behaviours (gelatinized starch stored at 4 oC for 7 days)

421

(Stevenson et al., 2007). Compared with barley starches (3 varieties), oat starches (3 varieties)

422

had lower degrees of retrogradation after 7 and 14 days upon gelatinization (4 °C), though the

423

melting temperatures were similar (Šubarić et al., 2011). The lower retrogradation of oat

424

starch could be partially due to a higher amount of endogenous lipids as stated in a previous

425

oat starch review (Autio & Eliasson, 2009).

426 427

5.6.Enzyme susceptibility

428

A systematic study of 28 different starches from various botanical sources showed that oat

429

starch (un-cooked) had one of the highest enzyme susceptibility to porcine pancreatic α18

430

amylase (Jane et al., 2003). A-type starches tend to have higher enzyme susceptibility than B-

431

type starches. This is mostly due to the higher amount of short amylopectin unit chains of the

432

former which causes the structural defects within the crystallites of the granules (Jane et al.,

433

2003). Furthermore, oat starch has a relatively small granule size which facilities the starch-

434

enzyme interactions. Konsula & Liakopoulou-Kyriakides (2004) showed that native and

435

gelatinized oat starches had similar susceptibility to an α-amylase from Bacillus subtilis,

436

probably due to starch retrogradation and amylose-lipid inclusion complex formation.

437

However, whole grain oats tend to have low enzyme susceptibility and glycaemic index (GI)

438

than the refined cereals (Ballance et al., 2013). The digestion of oat starch in complex food

439

systems largely depends on the food structure and composition (Ballance et al., 2013). For

440

example, the in vitro GI of oat flour and extruded oat flakes were 92 and 105, respectively

441

(Ballance et al., 2013). The time to reach the peak level of glucose in the blood were 59 and

442

39 min, for the former and the latter, respectively (Ballance et al., 2013). Non-starch

443

components such as non-starch polysaccharides and polyphenols in whole grain cereal

444

products can greatly impact the enzyme susceptibility of starch (Kim & White, 2013; Zhu,

445

2015). β-Glucans in oats tend to decreased the enzyme susceptibility of starch to porcine

446

pancreatin. The extents of decreasing were positively correlated with the increasing

447

molecular weight and viscosity and the decreasing solubility of β-glucans (Kim & White,

448

2013). There is a great variation in in vitro digestibility of starch in whole grain oat products

449

(Mishra & Monro, 2009). Therefore, selecting suitable oat varieties can be employed to target

450

the desired GI.

451

6. Modifications

452

6.1.Chemical modifications

453

Oat starch has been subjected to oxidation (Berski et al., 2011), cross-linking (Woo & Seib,

454

2002; Mirmoghtadaie et al., 2009), phosphorylation (Berski et al., 2011), and acetylation 19

455

(Berski et al., 2011; Mirmoghtadaie et al., 2009) to obtain the altered properties (Figure 1g)

456

(Table 4). Oxidation introduced the carboxyl groups onto the starch and decreased the

457

molecular size as well as the granule size (Berski et al., 2011). Oxidation increased the water

458

binding capacity and solubility, decreased the viscosity during pasting events, and the yield

459

stress and consistency coefficient of flow property (Figure 1g) (Berski et al., 2011). Cross-

460

linking of oat starch were conducted by using sodium trimetaphosphate plus sodium

461

tripolyphosphate- or POCl3-based methods (Woo & Seib, 2002; Mirmoghtadaie et al., 2009).

462

Cross-linking decreased the granular swelling and the enzyme susceptibility to α-amylase.

463

Cross-linked starch can be used as a type of resistant starch (Woo & Seib, 2002). Woo &

464

Seib (2002) reported that cross-linking increased the temperatures and reduced the ∆H of

465

gelatinization, while Mirmoghtadaie et al. (2009) reported that this modification had little

466

effect on the DSC gelatinization temperatures. Therefore, the gelatinization properties of

467

modified starch depend on the preparation method. Phosphorylation and acetylation

468

(substitution-type modifications) of oat starch had similar outcomes with differences

469

(Mirmoghtadaie et al., 2009; Berski et al., 2011). Both of the modifications decreased the

470

molecular weight of starch, increased the water solubility and water binding capacity, and

471

decreased the DSC gelatinization parameters. Acetylation decreased the viscosity of starch

472

during the pasting events, while phosphorylation increased that (Figure 1g). This could be

473

attributed to the much increased ionic interactions between the starch chains as a result of

474

phosphorylation (Berski et al., 2011). The results of the above-mentioned modifications in

475

general agreed with previous reports on these well-established modifications of other starches

476

(Wurzburg, 1986).

477

6.2.Physical modifications

478

Various hydrothermal treatments such as steaming and roasting are used to dry oats and to

479

deactivate the endogenous enzymes to prolong the shelf life (Ovando-Martínez et al., 2013; 20

480

Hu et al., 2010). These hydrothermal treatments lead to altered starch properties. Steaming

481

and roasting altered the granule shapes and dis-figured the large granules in kernels (Hu et al.,

482

2010). Ovando-Martínez et al.(2013) employed various hydrothermal treatments [ethanol

483

boiling, ethanol boiling and roasting, steaming (106 °C), steaming (106 °C) and roasting,

484

autoclaving with cover (120 or 130 °C), and autoclaving without cover (120 or 130 °C)] to

485

treat oat flour. Structurally, these treatments decreased the molecular size of amylopectin.

486

The decreased molecular weight of oat starch as a result of hydrothermal treatments may be

487

attributed to the action of endogenous amylase (Smith & Bennett, 1974). The treatments

488

altered the properties of starch isolated from the flour to various extents, depending on the

489

treatment type. Uncovered autoclaving greatly decreased the ∆H of gelatinization, while

490

increasing the gelatinization temperatures. Covered autoclaving (120 °C) and steaming

491

significantly retarded the retrogradation. Uncovered autoclaving (120 °C) greatly reduced the

492

viscosity of starch during the pasting events. Uncovered autoclaving reduced the content of

493

resistant starch (Ovando-Martínez et al., 2013). Shah et al. (2016) showed that autoclaving

494

(121 oC, 30 min) plus storage (4 oC, 24 h) of isolated oat starch (20% solid content) increased

495

the resistant starch content by ~10−15%. This combined treatment also decreased the

496

temperatures and ∆H of gelatinisation and the starch viscosity during pasting events (Shah et

497

al., 2016). These above-mentioned hydrothermal treatments facilitate the starch chain

498

interactions within the crystalline and amorphous domains of the granules and/or disrupting

499

the crystalline units (Hoover, 2010). Different treatment conditions influence the properties

500

and structures of starch to different extents (Hoover, 2010).

501

Vamadevan et al. (2013b) compared the impact of annealing on the DSC gelatinization

502

behaviours of starches from diverse botanical origins including oats. As discussed in the

503

section 4.1 (chemical structure of amylopectin), oat starch belonged to the type 1 group

504

according to the internal unit chain composition (Bertoft et al., 2008). Oat starch of type 1 21

505

group showed the most significant changes in the gelatinization temperatures upon annealing,

506

while those of type 4 group showed a great increase in ∆H. This suggests that a longer IB-CL

507

imparted the flexibility and improved the parallel packing of splayed double helices in the

508

granules, and there was a large number of unpacked double helices in type 1 starches

509

including oat starch (Figure 1f) (Vamadevan et al., 2013b). This model is in line with the

510

structural model discussed in section 5.2. (Figure 1e) (Vamadevan et al., 2013a).

511 512

7. Uses

513

Oat starch can used in a range of food and non-food products such as fat replacers,

514

soup/gravie/source/dessert ingredients, paper and cardboard ingredients, coating agents for

515

tablets in cosmetic and bath/soap products as reviewed previously (Autio & Eliasson, 2009;

516

Sayar & White, 2011; Zwer, 2016). Recent studies mostly explored the potential of oat starch

517

for thermoplastic film production due to the relatively high concentration of endogenous

518

lipids (up to 2.5%) (Table 5). The lipids in oat starch can increase the hydrophobicity of the

519

starch film (Galdeano et al., 2009a). Furthermore, these endogenous lipids tend to form

520

inclusion complexes with the amylose component, therefore preventing the phase separation

521

(Galdeano et al., 2009a; 2009b). The structural changes of oat starch films plasticized with

522

glycerol stored for 5 weeks were followed by atomic/friction force microscopy (Kuutti et al.,

523

1998). The flat and homogeneous film surface became rough and heterogeneous during

524

storage. Glycerol diffused onto the film surface and reduced the friction and stickiness of oat

525

starch films, while this was less the case for barley starch film (Kuutti et al., 1998). Forssell

526

et al. (1999) structurally followed the changes of both oat and barley starch films stored at 20

527 528

o

C with a relative humidity of 50% for 8 months. Initially, the crystallization rate of oat starch

film was slower than that of barley starch film. This observation agreed with a comparative

22

529

studies on the retrogradation of oat and barley starches and may be partially attributed to the

530

higher amount of endogenous lipids present in oat starch (section 3) (Šubarić et al., 2011;

531

Autio & Eliasson, 2009). The crystallinity and thermal transition of both starch films became

532

similar towards the end of storage. The failure properties of the films are mostly due to the

533

amylopectin crystallization (Forssell et al., 1999). Galdeano et al. (2009a, 2009b, and 2013)

534

investigated the effect of film production method, the type of plasticizers, and the film

535

thickness on the properties of oat starch films. Oat starch films and sheets were produced by

536

casting and extrusion, respectively, in the presence of urea, glycerol, and sorbitol (Galdeano

537

et al., 2009b). The sheets had a higher water vapor permeability than the films. The type of

538

plasticizers had no effect on the relative humidity (11−90%)−stress/strain at break

539

relationships. However, the glass transition temperature (Tg) and the relative degree of

540

crystallinity of films were much affected by the plasticizer type. Sorbitol gave the highest Tg

541

(59 oC) and urea (5%) gave the lowest relative degree of crystallinity (5%) (Galdeano et al.,

542

2009b). The presence of plasticizers increased the water adsorption capacity and decreased

543

the water vapor permeability as well as the stress at break of casted starch film (Galdeano et

544

al., 2009a). The film with glycerol was the most hygroscopic and that with sucrose was the

545

most fragile (Galdeano et al., 2009a). Thicker films had a higher opacity and a higher

546

elongation. The thickness little affected the water permeability and greatly influenced the

547

puncture force of the films (Galdeano et al., 2013). Therefore, the properties of oat starch

548

films greatly depend on the type of plasticizer, film thickness, and production method.

549

Acetylated oat starch, together with deamidated and succinylated oat proteins, were

550

formulated up to 20% to make oat cake (Mirmoghtadaie et al., 2009). Addition of acetylated

551

oat starch enhanced batter viscosity, whiteness of cake crust, and cake volume. This may be

552

due to that the acetylated oat starch had a higher cool viscosity after pasting than the native

553

starch (Berski et al., 2011). The increased viscosity of the batter may better hold the gas 23

554

during the production process (Mirmoghtadaie et al., 2009). For this kind of applications,

555

comparative studies employing other commonly used starches (e.g., maize, cassava, and

556

potato) at the same time should be conducted. This is to reveal if there is any technical

557

advantages of using oat starch for specific applications.

558 559

8. Conclusions

560

There is great advances in our understanding in the nature of oat starch. Wheat gluten-based

561

isolation method with no chemicals has been developed to isolate oat starch with high purity.

562

More genetic resource has been assessed and the impact of gene-environment interactions on

563

starch structures and properties has been studied. As a result of these exploits, much diversity

564

in amylose content, swelling and solubility, gelatinization, and rheological properties of oat

565

starch has been documented. The diversity provide a basis to understand the variations in the

566

quality of oat-based products, and to support further utilization of the starch. Agricultural and

567

processing factors affecting the characteristics of oat starch include growing environment,

568

developing endosperm, milling, and germination, though some other factors remain to be

569

studied. The internal structure of oat amylopectin has been systematically studied, which is of

570

the A-type starches such as those of cereals. The clusters of oat amylopectin have an average

571

size of DP 72.4 and contain 11.8 chains and 5.7 blocks per cluster, which resembles that of

572

rice amylopectin. The isolated oat starch has high enzyme susceptibility to amylases, and this

573

susceptibility is greatly reduced in whole grain oats due to the food matrix effects. Oat starch

574

has been subjected to various chemical (oxidation, substitution, and cross-linking) and

575

physical (hydrothermal) modifications, and the outcomes well agree with numerous previous

576

results on the modifications of other starches. The most recent application of oat starch has

577

been the thermoplastic films due to the relatively high content of lipids. The properties of the

24

578

films are affected by the type of plasticizers and the production method. However, in general,

579

the quality of starch thermoplastics is much affected by the amylose content, which remains

580

to be better studied. Acetylated oat starch has been used to enhance the quality of cake,

581

though other acetylated starches may have similar functions. Therefore, comparative studies

582

should be conducted to study if commercially important starches from other botanical sources

583

may be replaced by oat starch in specific applications.

584

There has been a great inconsistency in analytical methodology (e.g., for pasting analysis)

585

among different studies. This should be addressed to maximise the efforts of research

586

community. There is a great lack of comparative studies of oat starch, especially in the

587

application side, by employing other commonly used starches (e.g., maize, cassava, and

588

potato). Comparative studies would enable the revelation of any technological advantages of

589

using oat starch over the other commercially available starches. In a broad picture, the

590

knowledge obtained from studying the basics of oat starch (physicochemical properties,

591

structures, and modifications) remain to be applied to develop innovative food and non-food

592

uses.

593 594

The author declares no conflict of interest.

595 596

References

597

Al-Hakkak, J. (2006). Procedure for separating starch from comminutates of plant materials,

598

Patent US7001469.

599

Al-Hakkak, J., & Al-Hakkak, F. (2007). New non-destructive method using gluten to isolate

600

starch from plant materials other than wheat. Starch/Stärke, 59, 117–124.

25

601

Autio, K., & Eliasson, A. C. (2009). Oat Starch. In J. BeMiller, & R. Whistler (Eds.), Starch:

602

Chemistry and technology (Third Edition) (pp. 589−599). Cambridge: Academic Press.

603

Balance, S., Sahlstrøm, S., Lea, P., Nagy, N. E., Andersen, P. V., Dessev, T., Hull, S.,

604

Vardakou, M., & Faulks, R. (2013). Evaluation of gastric processing and duodenal digestion

605

of starch in six cereal meals on the associated glycaemic response using an adult fasted

606

dynamic gastric model. European Journal of Nutrition, 52, 799–812.

607

Berski, W., Ptaszek, A., Ptaszek, P., Ziobro, R., Kowalski, G., Grzesik, M., & Achremowicz,

608

B. (2011). Pasting and rheological properties of oat starch and its derivatives. Carbohydrate

609

Polymers, 83, 665–671.

610

Bertoft, E. (2013). On the building block and backbone concepts of amylopectin structure.

611

Cereal Chemistry, 90, 294–311.

612

Bertoft, E., Koch, K., & Åman, P. (2012a). Building block organisation of clusters in

613

amylopectin from different structural types. International Journal of Biological

614

Macromolecules, 50, 1212–1223.

615

Bertoft, E., Koch, K., & Åman, P. (2012b). Structure of building blocks in amylopectins.

616

Carbohydrate Research, 361, 105–113.

617

Bertoft, E., Piyachomkwan, K., Chatakanonda, P., & Sriroth, K. (2008). Internal unit chain

618

composition in amylopectins. Carbohydrate Polymers, 74, 527–543.

619

Doehlert, D. C., McMullen, M. S., & Hammond, J. J. (2001). Genotypic and environmental

620

effects on grain yield and quality of oat grown in North Dakota. Crop Science, 41, 1066–

621

1072.

26

622

Doehlert, D. C., Simsek, S., Thavarajah, D., Thavarajah, P., & Ohm, J. B. (2013). Detailed

623

composition analyses of diverse oat genotype kernels grown in different environments in

624

North Dakota. Cereal Chemistry, 90, 572–578.

625

Doublier, J. L. (1981). Rheological studies on starch-flow behaviour of wheat starch pastes.

626

Starch/Stärke, 33, 415−420.

627

Doublier, J. L., Paton, D., & Llamas, G. (1987). A rheological investigation of oat starch

628

pastes. Cereal Chemistry, 64, 21−26.

629

FAOSTAT (Statistics division of food and agriculture organization of the United Nations).

630

(2016). http://faostat3.fao.org/browse/Q/*/E

631

Fannon, J. E., Hauber, R. J., & BeMiller, J. N. (1992). Surface pores of starch granules.

632

Cereal Chemistry, 69, 284−288.

633

Forssell, P. M., Hulleman, S. H. D., Myllärinen, P. J., Moates, G. K., & Parker, R. (1999).

634

Ageing of rubbery thermoplastic barley and oat starches. Carbohydrate Polymers, 39, 43–51.

635

Galdeano, M. C., Grossmann, M. V. E., Mali, S., Bello-Perez, L. A., Garcia, M. A., &

636

Zamudio-Flores, P. B. (2009b). Effects of production process and plasticizers on stability of

637

films and sheets of oat starch. Materials Science and Engineering C, 29, 492–498.

638

Galdeano, M. C., Mali, S., Grossmann, M. V. E., Yamashita, F., & García, M. A. (2009a).

639

Effects of plasticizers on the properties of oat starch films. Materials Science and

640

Engineering C, 29, 532–538.

641

Galdeano, M. C., Wilhelm, A. E., Mali, S. & Grossmann, M. V. E. (2013). Influence of

642

thickness on properties of plasticized oat starch films. Brazilian Archives of Biology and

643

Technology, 56, 637−644.

27

644

Gangopadhyay, N., Hossain, M. B., Rai, D. K., & Brunton, N. P. (2015). A review of

645

extraction and analysis of bioactives in oat and barley and scope for use of novel food

646

processing technologies. Molecules, 20, 10884−10909.

647

Hoover, R. (2010). The impact of heat-moisture treatment on molecular structures and

648

properties of starches isolated from different botanical sources. Critical Reviews in Food

649

Science and Nutrition, 50, 835−847.

650

Hu, X., Xing, X., & Ren, C. (2010). The effects of steaming and roasting treatments on β-

651

glucan, lipid and starch in the kernels of naked oat (Avena nuda). Journal of the Science of

652

Food and Agriculture, 90, 690–695.

653

Jane, J. L., Ao, Z., Duvick, S. A., Wiklund, M., Yoo, S. H., Wong, K. S., & Gardner, C.

654

(2003). Structures of amylopectin and starch granules: How are they synthesized? Journal of

655

Applied Glycoscience, 50, 167−172.

656

Kalinga, D. N., Bertoft, E., Tetlow, I., Liu, Q., Yada, R. Y., & Seetharaman, K. (2014).

657

Evolution of amylopectin structure in developing wheat endosperm starch. Carbohydrate

658

Polymers, 112, 316–324.

659

Kim, H. J., & White, P. J. (2013). Impact of the molecular weight, viscosity, and solubility of

660

β-glucan on in vitro oat starch digestibility. Journal of Agricultural and Food Chemistry, 61,

661

3270−3277.

662

Konsula, Z., & Liakopoulou-Kyriakides, M. (2004). Hydrolysis of starches by the action of

663

an α-amylase from Bacillus subtilis. Process Biochemistry, 39, 1745–1749.

664

Kuutti, L., Peltonen, J., Myllärinen, P., Teleman, O., & Forssell. P. (1998). AFM in studies of

665

thermoplastic starches during ageing. Carbohydrate Polymers, 37, 7–12.

28

666

Lapveteläinen, A., Alho-Lehto, P., Sinn, L., Laukkanen, T., Lindman, T., Kallio, H.,

667

Kaitaranta, J., & Katajisto, J. (2001). Relationships of selected physical, chemical, and

668

sensory parameters in oat grain, rolled oats, and cooked oatmeal—a three-year study with

669

eight cultivars. Cereal Chemistry, 78, 322−329.

670

Mason-Gamer, R. J., Weil, C. F., & Kellogg, E. A. (1998). Granule-bound starch synthase:

671

structure, function, and phylogenetic utility. Molecular Biology and Evolution, 15,

672

1658−1673.

673

Mirmoghtadaie, L., Kadivar, M., & Shahedi, M. (2009). Effect of modified oat starch and

674

protein on batter properties and quality of cake. Cereal Chemistry, 86, 685–691.

675

Mishra, S., & Monro, J. A. (2009). Digestibility of starch fractions in wholegrain rolled oats.

676

Journal of Cereal Science, 50, 61–66.

677

Nguyen, Q. D., Jensen, C. T. B., & Kristensen, P. G. (1998). Experimental and modelling

678

studies of the flow properties of maize and waxy maize starch pastes. Chemical Engineering

679

Journal, 70, 165−171.

680

Obanni M., & BeMiller, J. N. (1996). Ghost microstructures of starch from different

681

botanical sources. Cereal Chemistry, 73, 333−337.

682

Ovando-Martínez, M., Whitney, K., Reuhs, B. L., Doehlert, D. C., & Simsek, S. (2013).

683

Effect of hydrothermal treatment on physicochemical and digestibility properties of oat starch.

684

Food Research International, 52, 17–25.

685

Peat, S., Whelan, W. J., & Thomas, G. J. (1952). Evidence of multiple branching in waxy

686

maize starch. Journal of the Chemical Society, Chemical Communications, 1952, 4546–4548.

29

687

Rasane, P., Jha, A., Sabikhi, L., Kumar, A., & Unnikrishnan, V. S. (2015). Nutritional

688

advantages of oats and opportunities for its processing as value added foods - a review.

689

Journal of Food Science and Technology, 52, 662–675.

690

Rhymer, C., Ames, N., Malcolmson, L., Brown, D., & Duguid, S. (2005). Effects of genotype

691

and environment on the starch properties and end-product quality of oats. Cereal Chemistry,

692

82, 197–203.

693

Sayar, S., & White, P. J. (2011). Oat starch: physicochemical properties and functions. In F.

694

H. Webster, & P. J. Wood (Eds.), Oats: Chemistry and Technology (Second Edition). (pp.

695

109−122). Minnesota: AACCI.

696

Shah, A., Masoodi, F. A., Gani, A., & Ashwar, B. A. (2016). In-vitro digestibility, rheology,

697

structure, and functionality of RS3 from oat starch. Food Chemistry, 212, 749–758.

698

Shamekh, S., Forssell, P., Suortti, T., Autio, K., & Poutanen, K. (1999). Fragmentation of oat

699

and barley starch granules during heating. Journal of Cereal Science, 30, 173–182.

700

Sikora, M., Kowalski, S., & Tomasik, P. (2008). Binary hydrocolloids from starches and

701

xanthan gum. Food Hydrocolloids, 22, 943–952.

702

Simsek, S., Whitney, K., & Ohm, J. B. (2013). Analysis of cereal starches by high-

703

performance size exclusion chromatography. Food Analytical Methods, 6, 181–190.

704

Smith, J. B., & Bennett, M. D. (1974). Amylase isozymes of oats (Avena sativa L.). Journal

705

of the Science of Food and Agriculture, 25, 67−71.

706

Srichuwong, S., & Jane, J. L. (2007). Physicochemical properties of starch affected by

707

molecular composition and structures: a review. Food Science and Biotechnology, 16,

708

663−674.

30

709

Stevenson, D. G., Jane, J. L., & Inglett, G. E. (2007). Structure and physicochemical

710

properties of starches from sieve fractions of oat flour compared with whole and pin-milled

711

flour. Cereal Chemistry, 84, 533–539.

712

Šubarić, D., Babić, J., Lalić, A., Ačkar, Đ., & Kopjar, M. (2011). Isolation and

713

characterisation of starch from different barley and oat varieties. Czech Journal of Food

714

Sciences, 29, 354–360.

715

Tian, B., Wang, C., Wang, L., & Xie, B. (2016). Granule size and distribution of raw and

716

germinated oat starch in solid state and ethanol solution. International Journal of Food

717

Properties, 19, 709–719.

718

Vamadevan, V., & Bertoft, E. (2015). Structure-function relationships of starch components.

719

Starch/Stärke, 67, 55–68.

720

Vamadevan, V., Bertoft, E., & Seetharaman, K. (2013a). On the importance of organization

721

of glucan chains on thermal properties of starch. Carbohydrate Polymers, 92, 1653–1659.

722

Vamadevan, V., Bertoft, E., Soldatov, D. V., & Seetharaman, K. (2013b). Impact on

723

molecular organization of amylopectin in starch granules upon annealing. Carbohydrate

724

Polymers, 98, 1045–1055.

725

Verhoeven, T., Fahy, B., Leggett, M., Moates, G., & Denyer, K. (2004). Isolation and

726

characterisation of novel starch mutants of oats. Journal of Cereal Science, 40, 69–79.

727

Woo, K. S., & Seib, P. A. (2002). Cross-linked resistant starch: preparation and properties.

728

Cereal Chemistry, 79, 819–825.

729

Wurzburg, O. B. (Ed.). (1986). Modified starches: Properties and uses. Boca Raton, FL:CRC

730

Press, Inc.

31

731

Zheng, K., Jiang, Q. T., Wei, L., Zhang, X. W., Ma, J., Chen, G. Y., Wei, Y., Jennifer, M. F.,

732

Lu, Z. X., & Zheng, Y. L. (2015). Characterization of starch morphology, composition,

733

physicochemical properties and gene expressions in oat. Journal of Integrative Agriculture,

734

14, 20–28.

735

Zhou, M., Robards, K., Glennie-Holmes, M., & Helliwell, S. (1998). Structure and pasting

736

properties of oat starch. Cereal Chemistry, 75, 273–281.

737

Zhu, F. (2015). Interactions between starch and phenolic compound. Trends in Food Science

738

& Technology, 43, 129–143.

739

Zhu, F. (2016). Structures, properties, and applications of lotus starches. Food Hydrocolloids,

740

in revisions.

741

Zwer, P. K. (2016). Oats: Overview. In C. Wrigley, H. Corke, K. Seetharaman, & J. Faubion

742

(Eds.), Encyclopedia of food grains (Second Edition) (pp.173−183). Oxford: Elsevier.

743

32

744 745 746 747 748

Figure captions

749

Figure 1 Characterisation of oat starch, amylopectin, and clusters. (A) Gel-permeation

750

chromatography (Sepharose CL 6B) of debranched oat starch (OS); LC and SC represent

751

long and short unit chains of amylose; (B) High-performance anion-exchange

752

chromatography of debranched oat amylopectin; OS, oat starch (Bertoft et al., 2008); (C)

753

Internal unit chain length distribution (average) of amylopectins from 4 groups (group 1 ●,

754

group 2 ∆, group 3 ♦, and group 4 □); oat amylopectin belongs to group 1; Bfg, B-fingerprint

755

chains; BSmajor, major fraction of short B-chains; Bfp and BSmajor are the two subgroups of B1

756

(BS) chains, and B2 and B3 chains are the two subgroups of BL chains (Bertoft et al., 2008);

757

(D) Building block and cluster model for amylopectin; IB-S, interblock segments, TIC-S,

758

total internal chain segment; individual building blocks are encircled in grey; bo-chains are

759

involved in structuring individual blocks; b1a- and b1b-chains link two blocks; b2-chains and

760

b3-chains link three and more blocks, respectively (Bertoft et al., 2012a); (E) Illustration of

761

the packing of double helices in granules as affected by the inter-block chain length (IB-CL);

762

a, shorter IB-CL more facilitates the formation of unparalleled packing of double helices; b, a

763

longer IB-CL more facilitates the formation of paralleled packing of double helices; oat

764

starch belongs to the case (a) (Vamadevan et al., 2013a); (F) Illustration of the impact of

765

annealing on the packing of double helices in starches with a short inter-block chain length

766

(IB-CL) (e.g., oat starch); c, crystalline region; annealing greatly improves the order of

767

double helices in the granules (Vamadevan et al., 2013b); (G) pasting properties of native and 33

768

modified oat starches; P_65, phosphorylated starch (Berski et al., 2011). All the figures are

769

reprinted with permissions from Elsevier.

770 771

772 773

(A)

774 775

(B) 34

776

777 778

(C)

779

35

780

(D)

781 782

(E)

783 784

(F)

785 786 36

787 788

(G)

789

Figure 1

790 791

37

792 793 794

Table 1 Amylose contents of oat starch Genotype Amylose content (%)

Amylose quantification method

References

Gel-permeation chromatography

Verhoeven

(Sepharose CL 2B) of whole starch

et al., 2004

no. 1 (A.

0

strigose) 1a

36−38 (apparent amylose Iodine-binding potentiometry-based

Stevenson et

content), 30 (absolute

method

al., 2007

Gel-permeation chromatography

Bertoft et

amylose content) b 1

27.1

(Sepharose CL 6B) of debranched starch al., 2008 1

22.7 (Con A), 20.5

Concanavalin A (Con A)-based

Simsek et

(HPSEC)

precipitation, high-performance size-

al., 2013

exclusion chromatography (HPSEC) of whole starch 3c

12−22%

Iodine-binding spectrophotometer-based

Zheng et al.,

method

2015

795

All the genotypes are from A. sativa except for being noted; no., number; a, 3 milling

796

fractions differing in size: 300–850 µm, 150–300 µm, and <150 µm; b, absolute amylose

797

content derived from the difference in iodine affinity between starch and amylopectin; c,

798

developing endosperms of 3 varieties from 15 to 33 days after anthesis

799

38

800

Table 2 DSC gelatinization properties of oat starch

Genotype Starch-to-water ratio Scanning rate no.

To (oC)

Tp (oC)

Tc (oC)

∆H (J/g)

Reference

57.72−60.32 b

8.74−9.48 b

Rhymer et al., 2005

10−11

Stevenson et al., 2007

(°C/min)

5a

2:3

10

1c

1:3

10

61

66

3

7:13

10

59.4−61.4

64.1−64.9

68.7−70.3

7.88−10.15

Šubarić et al., 2011

3

1:2

10

56.2− 63.6 d

62.9−68.6

71.8−77.7

9−11.1

Zheng et al., 2015

801

no., number; To, onset temperature; Tp, peak temperature; Tc, conclusion temperature; ∆H, enthalpy change; a, grown in 6 locations; b, mean

802

values of different plot replicates and environments; c, 3 milling fractions differing in size: 300–850 µm, 150–300 µm, and <150 µm; d,

803

developing endosperms of 3 varieties from 15 to 33 days after anthesis

39

804

Table 3 Pasting properties of oat starch Genotyp e

Starch Instrument concentratio

no.

n (%)

Tonset (oC)

PV

BD

SB

CPV

Referenc e

Rapid

Rhymer 150−19

5a

Visco-

79−135 b

9.1 2b

187−289 et al., b

Analysis

2005

Rapid

Stevenso 101−11 21.4−29. 74.1−108.

1c

Visco-

8

~93−94

153−193 n et al., 6

2

6

Analysis

2007

Brabender 1

Viscograp

100, 3

85

h

130,

745

Sikora et al., 2008

570 d

Brabender Micro3

61−63. 787−91 7

Visco-

941−137 105−570 386−1410

4

0

Šubarić et al.,

4 2011

Analyser 805

no., number; a, grown in 6 locations; b, mean values of different plot replicates and

806

environments; c, 3 milling fractions differing in size: 300–850 µm, 150–300 µm, and <150

807

µm; d, different phases during temperature programme; Tonset, temperature where the

808

viscosity starts to take off; viscosity units for Rapid Visco-Analysis and Brabender

809

instruments are RVU and BU, respectively

810 811

40

812

Table 4 Chemical and physical modifications of oat starch Modification Major findings

type

Reference

Chemical Oxidation of oat starch by sodium hypochlorite introduced carboxyl group (0.25%), decreased the weight-based molecular weight from 9 ×107 to 4 ×10 7 g/mol, and increased the water binding capacity (from 6 to 29 g/g at 95 o

C) and water solubility (from 3 to 39% at 95 oC). Oxidation Berski et al.,

Oxidation decreased the granule size and had little effect on the DSC

2011

gelatinization parameters. Oxidation increased the pasting temperature and decreased the viscosity during the pasting events (Figure 1g). Oxidation decreased the yield stress and consistency coefficient of flow curve of oat starch Compared with native starch, cross-linked starch (sodium trimetaphosphate and sodium tripolyphosphate-based method) had elevated phosphorus content, decreased swelling powers, insolubilities in KOH (1 M) and DMSO Woo & Seib, Cross-linking

(95%) solutions, increased temperatures and decreased ∆H 2002 of gelatinization measured by DSC. Cross-linking decreased the enzyme susceptibility to α-amylase. Manipulating modification conditions could maximise the content of resistant starch

Cross-linking Cross-linking (POCl3-based method) of oat starch decreased Mirmoghtadaie

41

the swelling power, increased the syneresis, while having no

et al., 2009

effect on the DSC gelatinization temperatures Phosphorylation of oat starch by sodium tripolyphosphate and sodium phosphate was conducted to produce mono starch phosphates. Phosphorylation decreased the weightbased molecular weight from 9 ×107 to 5 ×107 g/mol, and increased the water binding capacity (from 6 to 95 g/g at 95 o

C) and water solubility (from 3 to 12% at 95 oC).

Berski et al.,

Phosphorylation decreased the granule size, To and ∆H of

2011

Phosphorylation DSC gelatinization parameters, while greatly increasing the starch viscosity of pasting events (Figure 1g). Phosphorylation increased the yield stress (from 1.5 to 2.8 Pa at 20 oC) and consistency coefficient (from 3.2 to 5.7 Pa sn at 20 oC) of flow curve of oat starch Acetylation

Acetylation of oat starch increased the swelling power and Mirmoghtadaie decreased the syneresis and DSC gelatinization temperatures

et al., 2009

The molecular weight of acetylated starch (number-based molecular weight 3.51×104 g/mol) was lower than that of native starch (number-based molecular weight 8.8 ×10 4 g/mol). Acetylation greatly increased the water binding Acetylation

capacity (from 6 to 38 g/g at 95 oC) and water solubility (from 3 to 48% at 95 oC) and decreased the granule size.

Berski et al., 2011

Acetylation decreased the temperatures and ∆H of

gelatinization, and pasting temperature and peak viscosity of starch during the pasting event (Figure 1g). Acetylation

42

increased the retrogradation (short term) of starch paste during cooling. Acetylated oat starch paste strongly gelled at 20 oC and the flow curve was only obtained at 50 oC Physical Normal pressure steaming, autoclaving, and hot-air/infrared roasting were employed to treat oat kernels. Both steaming Steaming, and roasting altered the granule shapes and dis-figured large Hu et al., 2010 roasting granules in the kernels, while reducing the contact between starch and protein Different types of hydrothermal treatments of oat flour included ethanol boiling, ethanol boiling and roasting, steaming (106 °C), steaming (106 °C) and roasting, autoclaving with cover (120 or 130 °C), and autoclaving without cover (120 or 130 °C). Starch was isolated from the treated flour. Autoclaving with cover increased the granule Hydrothermal treatments

size without affecting the starch composition. The molecular

Ovando-

weight of amylopectin component was decreased by the

Martínez et al.,

hydrothermal treatments. Uncovered autoclaving greatly

2013

decreased the ∆H of gelatinization, while increasing the gelatinization temperatures. Steaming and covered autoclaving (120°C) greatly retarded the retrogradation. Uncovered autoclaving (120°C) significantly reduced the starch viscosity during the pasting events. Uncovered autoclaving much reduced resistant starch content Annealing

Annealing (up to 24 h) increased the temperatures and ∆H, Vamadevan et

43

while reducing the melting range of gelatinization of oat

al., 2013b

starch Oat starch (20% starch content) was subjected to autoclaving at 121 oC for 30 min before storing at 4 oC for 24 h. Enzymatic analysis showed that the treatment increased the content of resistant starch by ~10−15%. FT-IR Autoclaving-

Shah et al., spectroscopic analysis showed that the treatment increased

storage

-1

2016

-1

the ratio of intensity of 1047 cm /1022 cm . DSC analysis showed that the treatment decreased the temperatures and ∆H of gelatinisation. Pasting analysis showed that the treatment decreased the viscosity of the pasting curve 813

Table 5 Applications of oat starch Uses

Form

Major findings

Reference

Thermoplastic Native

The structural changes on the surface of starch

Kuutti et al.,

films

films during aging up to 5 weeks were studied by

1998

atomic force microscopy and friction force microscopy. The film surface initially was flat and homogeneous before becoming rough and heterogeneous during aging. Glycerol appeared to diffuse onto the film surface, resulting in reduced friction and stickiness of oat film

Thermoplastic Native

The structural changes of starch films stored in

films

rubbery state (20 oC, relative humidity of 50%) for 1999

Forssell et al.,

8 months were studied. Crystal structures and

44

crystallization rate of the films at initial stage depended on the starch type (barley vs oat) (changes in barley starch film were faster than oat starch film), while the final crystallinity and thermal transition were similar. Amylopectin crystallization during the storage may be responsible for the altered failure properties

Thermoplastic Native

Oat starch films were made by casting. Sorbitol,

Galdeano et

films

glycerol, glycerol–sorbitol mixture, sucrose and

al., 2009a

urea were used as plasticizers. Plasticizers increased the water adsorption capacity and decreased the water vapor permeability of starch films. Plasticizers decreased the stress at break of the films. At low relative humidity, films with sucrose were the most fragile and films with glycerol were the most hygroscopic

Thermoplastic Native

Oat starch films and sheets with urea, glycerol, and Galdeano et

films

sorbitol incorporation were produced by casting

al., 2009b

and extrusion, respectively. Plasticizers had no impact on relative humidity (11−90%)−stress/strain at break relationships of the films and sheets. Sheets had higher water vapor permeability than films. Tg (glass transition temperature) of films with urea, glycerol, and sorbitol were 36, 50, and 59 oC, respectively.

45

Relative degree of crystallinity of film with urea (5%) was significantly lower than the other films (~23%)

Thermoplastic Native

Effect of thickness (80−120 µm) on properties of

films

oat starch films with plasticizers (sorbitol, glycerol, al., 2013

Galdeano et

glycerol and sorbitol blend, sucrose, and urea) was studied at a range of relative humidity up to 90%. Increasing thickness increased the film opacity. Increasing thickness increased the elongation of the film with glycerol and sorbitol blend. Puncture force of films (except for that with sucrose) greatly depended on the film thickness, whereas the water permeability was little affected by the thickness Cake

Acetylated Acetylated oat starch and deamidated and succinylated oat proteins were used up to 20% of

Mirmoghtadaie et al., 2009

oat flour to formulate oat cake. Acetylated oat starch enhanced batter viscosity, whiteness of cake crust, and cake volume. Addition of both acetylated starch and modified proteins may enhance the quality of cake 814 815

46

816 817 818 819

•

Diversity in physicochemical properties and structures of oat starch recorded

820

•

Amylopectin cluster structure-property relationships of oat starch discussed

821

•

Impact of agricultural practise and processing on oat starch properties summarised

822

•

Potential of oat starch for thermoplastics production explored

823

47