Influence of xanthan gum on the short- and long-term retrogradation of potato starches of various amylose content

Journal Pre-proof Influence of xanthan gum on the short- and long-term retrogradation of potato starches of various amylose content Anna Dobosz, Marek Sikora, Magdalena Krystyjan, Radosław Lach, Barbara Borczak PII:

S0268-005X(19)31323-2

DOI:

https://doi.org/10.1016/j.foodhyd.2019.105618

Reference:

FOOHYD 105618

To appear in:

Food Hydrocolloids

Received Date: 16 June 2019 Revised Date:

30 November 2019

Accepted Date: 22 December 2019

Please cite this article as: Dobosz, A., Sikora, M., Krystyjan, M., Lach, Radosł., Borczak, B., Influence of xanthan gum on the short- and long-term retrogradation of potato starches of various amylose content, Food Hydrocolloids (2020), doi: https://doi.org/10.1016/j.foodhyd.2019.105618. 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. © 2019 Published by Elsevier Ltd.

CRediT author statement Anna Dobosz: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - Original Draft, Writing - Review & Editing, Visualization, Funding acquisition Marek Sikora: Conceptualization, Methodology, Resources, Writing - Original Draft, Writing - Review & Editing, Supervision, Project administration, Funding acquisition Magdalena Krystyjan: Conceptualization, Methodology, Formal analysis, Investigation, Resources, Writing - Original Draft, Writing - Review & Editing Radosław Lach: Methodology, Formal analysis, Investigation, Resources Barbara Borczak: Formal analysis, Investigation, Resources

1

INFLUENCE OF XANTHAN GUM ON THE SHORT- AND LONG-

2

TERM RETROGRADATION OF POTATO STARCHES OF VARIOUS

3

AMYLOSE CONTENT

4

Anna Dobosz1*, Marek Sikora1, Magdalena Krystyjan1, Radosław Lach2, Barbara Borczak3

5 6

1 – University of Agriculture in Krakow, Faculty of Food Technology, Department of Carbohydrates

7

Technology, Balicka Street 122, 30-149 Krakow, Poland; 2– University of Science and Technology, Faculty of

8

Materials Science and Ceramics, Mickiewicza Street 30, 30-059 Krakow, Poland, 3 – University of Agriculture

9

in Krakow, Faculty of Food Technology, Department of Human Nutrition, Balicka Street 122, 30-149 Krakow,

10

Poland.

11 12

(*) Corresponding author: Anna Dobosz; email address: [email protected], [email protected],

13

tel.: +4812 662 47 74.

14 15

Abstract: Effect of the 0.05 and 0.20% (w/w) admixture of xanthan gum (XG) upon short and long-

16

term retrogradation of 4, 5 and 6% potato starch gels was studied in relation to the

17

amylose/amylopectin ratio in the starches. Recorded pasting characteristics, mechanical spectra, gel

18

texture, syneresis, resistant starch content and x-ray patterns of the normal and waxy potato starch gels

19

revealed that XG promoted the formation of a three-dimensional gel network independently on the

20

amylose/amylopectin ratio. It meant that XG favored the short-term retrogradation after samples

21

preparation. Simultaneously, the presence of XG in admixture with potato starch hindered and

22

promoted long-term retrogradation of the gels of normal and waxy starch gels, respectively.

23 24

Key words: gel network, resistant starch, storage stability, syneresis, viscoelasticity.

25 26

Abbreviation list:

27 28 29 30 31 32 33 34

NPS1 – normal potato starch (29.93 wt.% of amylose), NPS2 – normal potato starch (26.72 wt.% of amylose), WPS – waxy potato starch (9.27 wt.% of amylose), XG – xanthan gum, NPH – non-starchy polysaccharide hydrocolloids, RS – resistant starch, DoC – degree of crystallinity.

35

1. Introduction

36

Heating aqueous starch suspensions over temperature of beginning of their pasting

37

provides pastes that can be considered as a composite of swollen starch granules dispersed in

1

38

a continuous amylose phase (Chang, Lim, & Yoo, 2004; Miles, Morris, & Ring, 1985;

39

Morris, 1990, 1991). Retrogradation is a process characteristic for aqueous starch systems. It

40

is a reorganization of starch components after their thermal treatment. It is considered a

41

crystallization phenomenon, involving both amylose and amylopectin, during which a return

42

to partially ordered form takes place (Ottenhof & Farhat, 2004; Ronda & Roos, 2008).

43

Retrogradation proceeds in two steps – a short- and a long-term retrogradation

44

(Funami et al., 2005; Miles et al., 1985; Ronda & Roos, 2008). Short-term retrogradation is

45

based on turning amylose helices into linear species which order into compact micelles. This

46

arrangement allows the formation of intermolecular hydrogen bonds between the chains of

47

amylose and contributes to its crystallization (Chang et al., 2004; Kim, Lee, & Yoo, 2006).

48

The retrogradation process (including mainly short-term retrogradation) of starch begins

49

already during the cooling of starch pastes (BeMiller & Whistler, 2009). Retrogradation of

50

amylose occurs the fastest in the initial period from the moment of starch pasting (Funami et

51

al., 2005; Miles et al., 1985). On the other hand during the long-term retrogradation outer

52

branches of amylopectin are involved in crystallization. In this case, the double helix of

53

amylopectin is usually formed between adjacent chains of the same molecule, rarely between

54

the sequences of different molecules, forming a continuous network, which is largely

55

associated with the aggregation process (Chang et al., 2004; Kim, Lee, & Yoo, 2006). This

56

kind of retrogradation is considerably slower compared to the retrogradation of amylose

57

(Chang et al., 2004; Funami i in. et al., 2005 a; Krystyjan, Adamczyk, Sikora, & Tomasik,

58

2013; Miles et al., 1985; Ronda & Roos, 2008).

59

The temperature of the storage of samples/products containing pasted starch is one of

60

the factors on which retrogradation (short- and long-term) depends (Eliasson &

61

Gudmundsson, 2006; Funami, 2009; Ottenhof & Farhat, 2004; Silverio, Fredriksson,

62

Andersson, Eliasson, & Aman, 2000; Swinkels, 1985). The retrogradation process is

63

particularly favored by a low temperature (however above freezing point) (Funami, 2009;

64

Swinkels, 1985). In turn, the decrease in the rate of this phenomenon is observed at

65

temperatures above 32-40° C (Eliasson & Gudmundsson, 2006). This dependence of the

66

retrogradation rate on the storage temperature of the samples is attached to a large extent to

67

the effect of temperature on the nucleation and on the growth of the amylose and amylopectin

68

crystals (Ottenhof & Farhat, 2004; Silverio et al., 2000).

69

Various starch modifications such as chemical, physical and enzymatic modifications,

70

extend the range of applicability of starches. However, as the component of foodstuffs,

71

modified starches (especially those chemically modified) frequently do not meet acceptance 2

72

of consumers (Kulicke, Eidam, Kath, Kix, Kull, 1996; Sikora et al., 2017). In addition,

73

chemically modified starches, in order to be used in food production (as food additives), have

74

to meet the conditions specified in the relevant legal regulations. Above all, they are required

75

to be non-toxic (Codex Alimentarius, 2018, FAO/WHO, 2015). Since a mixture of non-

76

starchy polysaccharide hydrocolloids (NPH) controls the course of the pasting and viscosity

77

of corresponding pastes and gels (Alloncle & Doublier, 1989; Baranowska, Sikora, Kowalski,

78

& Tomasik, 2008; Kowalski, Sikora, Tomasik, & Krystyjan, 2008; Kulicke et al., 1996;

79

Sikora & Kowalski, 2003), it is (highly) probable that properties of potato starch systems

80

could also be modified in such manner.

81

Short-term retrogradation studies of potato starch gels were mainly carried out for

82

samples without the addition of NPH. Short-term retrogradation of potato starch – XG mixed

83

gels was studied by oscillation (Krystyjan, Sikora, & Adamczyk, 2011) and x-ray

84

measurements (Kowalski et al., 2008; Krystyjan et al., 2011). While the influence of XG on

85

long-term retrogradation of potato starch gels was only examined by texture measurements,

86

oscillating tests (Krystyjan et al., 2013), 1H NMR (Baranowska, Sikora, Krystyjan, &

87

Tomasik, 2012) as well as x-ray measurements (Krystyjan et al., 2011). It should also be

88

noted that retrogradation of normal potato starch (a starch with a standard amylose content,

89

i.e. about 25-30%) gels, at one concentration of starch and NPH was usually tested.

90

Additionally various research materials and only some of the possible retrogradation

91

measurement techniques were used and the tests lasted usually for few days after the samples`

92

preparation.

93

The potential applications of XG-potato starch blends are numerous, e.g. for: caramel

94

sauces (Krystyjan, Sikora, Adamczyk,& Tomasik, 2012), cocoa syrups (Sikora, Juszczak,

95

Sady, & Krawontka, 2003), dessert sauces (Sikora, Kowalski, Tomasik, & Sady, 2006), sweet

96

and sauer sauces (Gibiński et al., 2006, Sikora, Sady, Krawontka, Ptaszek, & Kowalski,

97

2004a, 2004b) etc. Therefore, it is important to reduce the susceptibility to starch

98

retrogradation in these systems, e.g. by choosing the concentration and materials with

99

appropriate properties. The influence of XG concentration in potato starch mixed gels upon short- and long-

100 101

term

retrogradation

was

extensively

studied,

102

amylose/amylopectin ratio in the starches (normal and waxy) and starch concentrations in the

103

gels stored up to 90 days.

104 105

2. Materials and methods 3

included

the

significance

of

the

106 107

2.1. Materials The following materials were used:

108

- normal potato starch (NPS1) (86.48 wt.% – dry matter, 29.93 wt.% – amylose, 0.104 wt.%

109

d.m.– total phosphorus and 0.24 wt.% – fat) isolated from "Tajfun” potatoes collected in

110

2013 in Stacja Doświadczalna Oceny Odmian (Węgrzce, Poland). At 75, 85 and 95o C its

111

aqueous solubility reached 31.16, 52.33 and 61.48 wt.%, and its water binding capacity was

112

15.97, 20.82 and 21.94 g/1 g d.m. of starch, respectively (Dobosz et al., 2019),

113

- normal potato starch (NPS2) (79.47 wt.% – dry matter, 26.72 wt.% – amylose, 0.140 wt.% –

114

total phosphorus, 0.17 wt.% – fat) purchased from Przedsiębiorstwo Przemysłu

115

Ziemniaczanego Bronisław Sp. z o.o. (Strzelno, Poland). At 75, 85 and 95o C its aqueous

116

solubility reached 40.04, 55.81 and 62.53 wt.% at, and its water binding capacity values

117

were 18.61, 19.01 and 19.39 g/1 g d.m. of starch, respectively (Dobosz et al., 2019),

118

- waxy potato starch (WPS) „Eliane 100” (81.90 wt.% – dry matter, 9.27 wt.% – amylose,

119

0.099 wt.% dm – total phosphorus, 0.07 wt.% – fat) purchased from AVEBE FOOD

120

(Veendam, The Netherlands). At 75, 85 and 95o C its aqueous solubility was 52.96, 60.84

121

and 63.36 wt.%, and its water binding capacity was 19.50, 10.42 and 7.01 g/1 g d.m. of

122

starch, respectively (Dobosz et al., 2019),

123

- xanthan gum (XG) was purchased from Sigma Aldrich (St. Louis, USA).

124 125 126

2.2. Methods 2.2.1. Pasting characteristics

127

Pasting characteristics for samples containing 4-6% (w/w) of each starch without and

128

with 0.05 and 0.20% of XG were recorded with Micro Visco-Amylo-Graph (Brabender,

129

Duisburg, Germany) viscometer. The following pasting regime was followed at rotor velocity

130

of 250 rpm: (1) increase and/or decrease in temperature - 4.5° C/min, (2) temperature profile

131

involved heating from 30° to 96° C, maintaining that temperature for 10 min then cooling to

132

50° C and maintaining that temperature for 1 min. The measurements were performed in the

133

range of a torque of 23 mN/m. Experiments were duplicated and viscosity was reported in

134

Brabender units.

135 136

2.2.2. Pastes preparation

137

Aqueous suspensions containing 4, 5 and 6% (w/w) of starch with 0, 0.05 and 0.20%

138

(w/w) of XG (in dry basis) were prepared. The starch and XG were weighed (± 0.0001 g) into 4

139

a beaker per 100 cm3 and 5 cm3 of 0.4% aqueous solution of sodium azide (NaN3) was added

140

to protect samples from microorganisms during storage. Distilled water was finally admixed

141

to achieve 100 g samples. The final concentration of NaN3 in the mixture was 0.02 wt.%. The

142

samples were stirred mechanically (RW20 D, Ika Works, Inc., Wilmington, USA), at 25±2o C

143

for 10 min using 400 rpm stirring speed, followed by 30 min pasting in a water bath of 95º C,

144

using 400 rpm stirring speed (mechanical stirrer – RW20 D, Ika Works, Inc., Wilmington,

145

USA).

146 147

2.2.3. Mechanical spectra

148

Freshly prepared pastes (p. 2.2.2) (4 cm3) were transferred with help of a syringe into

149

disposable aluminum plates (looking the same as reusable titanium plates, delivered by

150

Thermo Scientific, Karlsruhe, Germany) to receive a cylindrical shape. The plates with the

151

samples were placed in non-ventilated polystyrene Petri dishes and maintained therein at

152

25±2o C for 2 h. So equilibrated samples were then placed at 6o C. Oscillation measurements

153

were performed with RheoStress RS 6000 (Thermo Scientific, Karlsruhe, Germany) rotary

154

rheometer equipped with a plate – plate P 35 Ti geometry. In order to adjust the gap the

155

distance between them was reduced with the 0.15 mm/s rate until the normal force reached

156

0.2 N. The spectra were taken for freshly prepared samples (for the gels after 1 and 2 h) and

157

then after 1, 2, 10, 30, 60 and 90 days of storage at 6o C. The oscillation measurements

158

included running mechanical spectra in the range of 0.1-10 Hz at 25o C and 0.3% deformation

159

fitting the range of linear viscoelasticity. The measurements were run in duplicates.

160 161

2.2.4. Textural properties

162

The measurements were performed following modified method reported by Krystyjan

163

et al. (2013) and Dobosz et al. (2019). Freshly prepared pastes (45 cm3) were initially stored

164

for 2 h at 25±2o C in 60 cm3 tightly closed cylindrical polypropylene containers (with a

165

diameter of 39 mm and a height of 63 mm, a height of the gels was 45 mm), then refrigerated

166

at 6o C. Measurements of the hardness of the gels with Texture Analyzer TA.XT plus (Stable

167

MicroSystems Ltd., Godalming, Great Britain) were performed for freshly prepared samples

168

(for the gels after 1 and 2 h ageing) and after their storage for 1, 2, 10, 30, 60 and 90 days.

169

The penetration test involved P/0.5 cylinder (12 mm in diameter and 40 mm length) taken as a

170

measurement probe. It was immersed 10 mm deep and its velocity was 1.00 mm/s. The

171

measurements were run in triplicates.

5

172 173

2.2.5. Syneresis

174

The samples were prepared as described in the section 2.2.4. but additionally the

175

weights of cylindrical polypropylene containers (39 mm – a diameter, 63 mm - a height of the

176

container, 45 mm – a height of the gels), before and after their filling with samples had to be

177

established. Syneresis was determined as a difference of the weights of original samples and

178

those from which water separated on their surfaces was evacuated with a polyethylene Pasteur

179

pipette followed by drying their surface and containers with a tissue. The water loss, X, (in %)

180

was calculated from Eq. (1): (1)

181 182

where:

183

a –the weight (in g) of empty container with its cap,

184

b – the weight (in g) of container with its cap after filling it with a sample,

185

c – the weight (in g) of container with its cap and sample after the separated water was

186

removed. The estimations were performed in triplicates.

187 188

The samples were prepared in cylindrical containers with a diameter of 39 mm and a height of

189

63 mm. The height of the gels was 45 mm.

190 191 192

2.2.6. Resistant starch (RS) content

193

The pastes containing 5% (w/w) of starch without and with 0.20% (w/w) of XG were

194

prepared (see 2.2.4). RS content was determined after 2 h, 1, 30 and 90 days of storage

195

employing a Resistant Starch Assay Kit K-RSTAR (Megazyme International Ireland Ltd.,

196

Wicklow, Ireland) following attached instruction fitting the AOAC 2002.02 and AACC 32-40

197

methods. The RS content was calculated employing the Mega-CalcTM Resistant starch (K-

198

RSTAR) – determination. Operations were duplicated.

199 200

2.2.7. X-ray diffractometry

201

The pastes containing 5% (w/w) of starch without and with 0.20% (w/w) of XG were

202

prepared as described in 2.2.4. The measurements were performed following our former paper

203

(Dobosz et al. 2019). Briefly, after 2 h, 1, 30 and 90 days of storage the samples were frozen

204

for 12 h at -20o C and lyophilized in a FreeZone 6 Liter Benchtop Freeze Dry System 6

205

(Labconco, Kansas City, USA) lyophilizator. Lyophilized samples were powdered in a coffee

206

grinder.

207

The content of the crystalline phase in the samples was recognized with an Empyrean

208

(PANalytical, Almelo, The Netherland) x-ray diffractometer. The degree of crystallinity was

209

calculated following the method of Nara and Komiya (1983). The base line in the range of 5-

210

50o 2θ and the line of separation was determined by the use of X’PertHighScore Plus

211

software. The degree of crystallinity (DoC), expressed in %, was calculated from Eq. (2):

212 213

I C − I amorf

DoC =

IC

⋅ 100% (2)

214

where:

215

IC – intensity of the radiation of the crystalline and amorphous phases, Iamorf – intensity of the

216

radiation of the amorphous phase.

217 218

2.2.8. Statistics

219

Statistical analysis was performed with the Statistica 12.5 (StatSoft, Tulsa, OK., USA)

220

software. Mono- and bifactorial analysis of variance as well as the Duncan’s test were

221

employed for checking significance of the differences at α = 0.05.

222 223

3. Results and discussion

224

3.1. Pasting characteristics

225

Table 1

226 227

Our studies (Table 1) confirm earlier results of Gularte and Rosell (2011) who found

228

that XG in admixture with potato starch decreased setback values. The decrease in the setback

229

values for the samples of anionic tapioca starch with Arabic gum was observed also by Chen,

230

Ren, Zhang, Tong, & Rashed (2015). The addition of Arabic gum did not affect the setback

231

values in cationic tapioca starch samples. However, the results (Table 1) for binary 6% NPS1

232

+ 0.05% XG gel indicated a slight but significant increase in the setback value. A decrease in

233

the setback values (Table 1) suggest that the addition of GX XG hindered the gel formation

234

and short-term retrogradation of the samples after their cooling to 50o C. However it is very

235

likely that this These effect could result from a competition between starch and XG for water

236

required for swelling starch granules. Inhibition of swelling and stabilization of starch 7

237

granules led to a smaller decrease in viscosity of the system during heating (Cai, Hong, Gu, &

238

Zhang, 2011; Tang, Hong, Gu, Zhang, & Cai, 2013). Additionally, Hence, a decrease in the

239

setback values could be associated not only with lower susceptibility of potato amylose to

240

retrogradation after cooling of the samples to 50o C but also with a relatively small difference

241

between minimum and maximum viscosity (breakdown – results not shown) of the gels

242

(Chantaro, Pongsawatmanit, & Nishinari, 2013). Therefore, the setback value is not sufficient

243

to assess the effect of XG on starch retrogradation. Especially because both the phenomenon

244

of short- and long-term retrogradation take longer than during the cooling of the samples.

245 246

3.2. Mechanical spectra

247

A susceptibility of the gels to retrogradation could be controlled by a competition

248

between the amylose – XG and amylose – amylose interactions (Ferrero, Martino, & Zaritzky,

249

1994).

250

It has been found in our studies that within the first hour after preparation of samples,

251

a tendency to increase in G’ value and, simultaneously, a decrease in tg (G"/G') values were

252

observed after XG addition (Figs. 1 and 2). Thus, it could be assumed that XG facilitated

253

formation of a more rigid three-dimensional structure of the gels and probably progressing in

254

such manner short-term retrogradation after preparation of the samples. Such results differ

255

from those obtained on the basis of the setback values (Table 1). Obtaining different results,

256

as mentioned earlier (see section 3.1.), is most probably connected with a relatively small

257

difference between minimum and maximum viscosity (breakdown – results not shown) of the

258

gels (Chantaro et al., 2013). It may also be related to the influence of temperature on the

259

retrogradation phenomenon described in the introduction section. Furthermore, it confirms

260

that the setback values do not allow to characterize unambiguously the susceptibility of starch

261

to short-term retrogradation.

262

The increase in short-term retrogradation after samples preparation could be associated

263

with an increase in the amylose concentration in the continuous phase (Choi & Yoo, 2009) or

264

lowered mobility of the amylose molecules, which favored local interactions between the

265

chains of this polymer (Choi & Yoo 2009; Eidam, Kulicke, Kuhn, & Stute, 1995). It is

266

known, that retrogradation is caused by a decrease in kinetic energy and Brownian motions of

267

amylose and water molecules, leading to shrinkage of the polymer molecules. As a result of

268

this phenomenon, intra- and intermolecular hydrogen bonds are formed between hemiacetal

269

oxygen atoms and adjacent hydroxyl groups at the C6 atom of glucose residues, as well as

8

270

between hemiacetal oxygen atoms and adjacent hydroxyl groups at the C2 of different glucose

271

residues (Tako, Tamaki, Teruya, & Takeda, 2014). Referring to our recent work (Baranowska

272

et al., 2019), it can be concluded that upon the early stages of gelation (2 h) only in the

273

samples of NPS1 (with the greatest amylose content) with XG water molecules was

274

substantially limited and considerable number of water molecules participated in the network

275

formation and hydrogen bonds built nodes of the networks. While the changes of relaxation

276

times in the mixed samples of WPS suggested that this starch did not interact with XG

277

(Baranowska et al., 2019).

278

The effect of XG on G" values taken after 1 h preparation was irregular. In some cases

279

a slight, usually statistically insignificant, decrease in G" was observed, and in some cases it

280

increased, compared to gels without the gum. It could be associated with changes in the gel

281

viscosity influenced by turning sol into gel on cooling. According to Hansen, Hoseney, &

282

Faubion (1991) during the sol-gel transition beyond the G' increase, a decrease in the value of

283

G" can be observed. This phenomenon may be associated with the change of the fluid nature

284

of the samples to a more constant one.

285

On storage, retrogradation progressed. Similarly as in case of potato starch gels

286

without the XG (Dobosz et al., 2019) it was manifested as a tendency to an increase in G' and

287

G" values. The tg (G"/G') values changed irregularly with the storage time.

288

G' and G" values of almost all binary NPS1 – XG gels exceeded these recorded for

289

NPS1 gels without XG (Fig. 1). Thus, the reinforcing of the three-dimensional structure of the

290

gels continuously progressed.

291

When 0.20% XG was added the effect could be observed already on the 10th day of

292

storage. In the binary 5% NPS1-XG gel that effect was more pronounced (Figs. 1 and 2), than

293

at 4% starch concentration (results not shown). In contrast, in 6% of NPS1 samples, the

294

addition of XG contributed to the strengthening of their structure so that measurements (in

295

terms of linear viscoelasticity) could be made after 60 and 90 days. It was impossible in the

296

case of the gels without XG, because the structure of the samples collapsed and the range of

297

linear viscoelasticity could not be determined (results not shown).

298

Thus, likely XG promoted retrogradation of amylose (short-term retrogradation) and

299

stabilized the gel structure on longer storage hindering in such manner long-term

300

retrogradation. In addition, the effect of XG was greater with increasing concentration of both

301

polysaccharides. High storage stability and low susceptibility to long-term retrogradation of

302

NPS1 gels with XG may be evidenced by small changes of relaxation times T1 and T2 during

303

storage of the samples (Baranowska et al. 2019). Higher storage stability of normal potato 9

304

starch gels with XG was formerly observed by Krystyjan et al. (2013) in the samples stored

305

for 30 days on cooling. Krystyjan et al. (2013) also stated that storage stability of normal

306

potato starch with guar gum was enhanced. In turn, the promotion of amylose retrogradation

307

upon an addition of guar gum to tapioca starch was observed by Chaisawang & Suphantarika

308

(2005, 2006) and the same was stated by He, Zhang, Hong, & Gu (2015) in the gels of corn

309

starch with guar gum.

310

Stored samples of NPS2 containing 0.05% XG had G' values comparable with these found for

311

corresponding gels without XG. The differences between the G' values were bigger with

312

longer storage periods. There was a tendency to decrease G" and increase tg(G"/G') of the

313

stored gels by adding 0.05% XG. Probably a smaller amount of XG hindered the long-term

314

retrogradation of NPS2, while not affecting the development of a stronger gel structure during

315

further storage. In comparison with the NPS2 gels without XG, the samples with 0.20% XG

316

had higher G' and G" values, and up to a certain time of storage, they had stronger structure

317

(than gels without XG) as deduced based on lower tg(G"/G') values. However, their structure

318

weakened in the final period of the storage. The changes in viscoelastic properties of mixed

319

gels containing 4% NPS2 and 0.20% XG were so big (collapsed structure, syneresis,

320

shrinkage etc.) that no measurements were possible after 90 days of storage, and in the case of

321

5 (Table 2) and 6% of NPS2 samples – also after 60 days (results not shown).

322 323

Fig. 1

324

Fig. 2

325 326

Up to 10th day G' and G" values for the 4% WPS – XG binary gels were higher and the

327

tg(G"/G') values (results not shown) were lower than corresponding values taken for the gels

328

without XG. However, within 30 days, the tg(G"/G') value rose and the G' and G" values

329

declined (Figs. 1 and 2). Binary WPS of the higher, 5 and 6% concentration up to 30 days had

330

higher G' and G" values and tg(G"/G') values decreased. Already after 60 and 90 days the

331

structure of the gels was ruined to a such extent that their linear viscoelastic properties could

332

not be measured. One could assume that admixture of XG promoted long-term retrogradation

333

proportionally to the concentration of WPS and XG. WPS-XG mixed gels showed a rapid

334

increase of the mean correlation times during storage, which could indicate successive

335

formation of solid state structures. However, after 90 days of storage, a decrease in the value

336

of the mean correlation times was observed. This may evidence of the weakening the structure

337

as a result of significant progress of the retrogradation phenomenon. It is possible that in this 10

338

case the progressive retrogradation of amylose led to crystallization, large amounts of water

339

bound to solubilized amylose chains were released, increasing the volume of the bulk

340

available for xanthan chains. This could explain the increase in G” upon long storage time.

341

Then, the released water could have been bound by XG, as evidenced by the small changes in

342

T1 and T2 values upon storage observed in our previous paper (Baranowska et al. 2019) and

343

the small syneresis (see section 3.4.).

344 345

3.3. Texture

346

Hardness of binary potato starch - XG gels measured after 1 and 2 h since their

347

preparation did not change in any statistically significant manner. Similarly to the gels

348

without XG (Dobosz et al., 2019), mixed systems had similar hardness (Fig. 3, only selected

349

results are shown). A significant increase in gel hardness occurred after 1 day and between 30

350

and 90 days of storage.

351

Independently of the concentration of XG added, initially hardness of the NPS1-XG

352

gels remained almost not changed on storage (Fig. 3). Small hardness changes of the gels was

353

reported also by He et al. (2015), after 24 h storage of the gels of corn starch upon an addition

354

of guar gum. From the 2nd day of storage hardness of the binary NPS1-XG gels was lower

355

than that of corresponding gels without XG. Solely, 4% NPS1 gels with XG and 5% NPS1

356

gels with 0.05% XG manifested after 30 days a slightly higher hardness than the samples

357

without the gum addition. One could suppose that in these cases a considerable progress in

358

retrogradation of 4 and 5% NPS1 gels resulted in their lower rupture strength (Dobosz et al.,

359

2019). It should be underlined that hardness of the NPS1 – XG binary gels after 60 and 90

360

days was higher than that of gels without XG. The 0.20% admixture of XG considerably

361

increased the hardness. Such effect was also observed by Mandala, Palogou, & Kostaropoulos

362

(2002) after 30 and 45 days of storage of the potato starch gels. However, according to

363

Krystyjan et al (2013) in 3% potato starch gels stored at 5o C for 30 days, XG affected solely

364

brittleness and strength of those gels. The obtained results (Figs. 3a, not all the results are

365

presented) suggest that XG increased the durability of the starch gels with the highest amylose

366

content (NPS1) with a longer storage time of the samples, which could be associated with a

367

decrease in their susceptibility to long-term retrogradation. It could be associated with

368

decreased susceptibility of the samples to long-term retrogradation. In addition, the influence

369

of XG was greater the higher its concentration. These results are consistent with those

370

obtained on the basis of oscillatory measurements (Figs. 1 and 2).

11

371 372

Fig. 3

373 374

Effect of XG upon hardness of the NPS2-XG gels (Fig, 3b, only selected values are

375

quoted) resembled that observed for the NPS1-XG gels (Fig. 3a). Upon storage, binary gels of

376

that starch were almost always less hard than these without XG. More concentrated gels and

377

these with a higher XG content when stored for over 30 days behaved exceptionally. They

378

were harder than these without XG. Storing the binary gels for up to the 30 day did not evoke

379

any essential changes in their hardness. Solely in 6% NPS2-0.05% XG gels hardness

380

distinctly decreased. In 4 and 5% NPS2-0.05% XG binary gels such effect could be observed

381

just after 60 days of storage. In turn, after 90 days, regardless of the starch concentration, the

382

hardness of the gels decreased as the amount of added gum increased.

383

Comparing the obtained results of hardness (Fig. 3) with the results of oscillatory

384

measurements (Figs. 1 and 2, only selected results are shown), one can assume that a smaller

385

amount of XG hindered the long-term retrogradation of the gels, but only up to a certain

386

point, which could be associated with the formation of a weaker gel structure at the beginning

387

of the storage period. In addition, at the beginning of the storage period, the differences

388

between the hardness of samples without and with 0.05% XG were so small that for gels

389

containing 4 and 5% NPS2 they were not captured in the hardness measurement. In contrast,

390

the higher hardness of NPS2 gels with 0.20% XG, compared to samples with 0.05% XG at the

391

beginning of the storage period, could have been the result not of a greater starch

392

retrogradation, but rather of a stronger structure. However, this structure was weakened

393

(probably around the 30th day of storage), which resulted in lower hardness of these gels after

394

60 and 90 days.

395

Compared to gels of both normal potato starches, the effect of XG upon the hardness

396

of WPS gels was much smaller (Fig. 3, only selected results are shown). Up to 30 days of

397

storage the 4% binary WPS – XG gels (results not shown) were only subtly less hard than gels

398

without XG of that starch. After addition of 0.05% XG such effect lasted for 60 days storage.

399

Although hardness of the 4% WPS-0.20% XG gel (results not shown) was closely identical

400

after such long storage, after 90 days it increased twice compared to that of gel without XG.

401

XG had the least effect on the hardness of the 5% WPS gels. Only after 30 days of

402

storage, 5% WPS with 0.20% XG had a much higher hardness than samples without XG. This

403

suggest their greater susceptibility to long-term retrogradation (Fig. 3c).

12

404

Behavior of the 6% binary WPS-XG gels resembled that of the 4% WPS gels, wherein

405

the similar hardness of the gels with and without 0.20% XG was observed after 30 days of

406

storage. On extending storage to 60 and 90 days, an admixture of XG provided a drop in the

407

gel hardness (results not shown).

408

Comparison of hardness of those gels with results from mechanical spectra (Figs. 1

409

and 2) revealed that XG could promote long-term retrogradation of the WPS gels and that

410

effect was favored by higher concentrations of XG and starch. Observed declining of hardness

411

of the binary 5 and 6% WPS-XG gels after 60 and 90 days of storage could be associated

412

solely with a reduction in the repture strength of the mixed gels instead of less starch

413

retrogradation in these samples.

414 415

3.4. Syneresis

416

A considerable increase in syneresis of the gels could be observed just between 30th

417

and 90th day of storage (Fig. 4, only selected data are presented). There was a tendency to

418

increase syneresis with increasing storage period. However, as in oscillatory measurements

419

(Figs. 1 and 2) and the ones of gel hardness (Fig. 3), this was not a rule.

420

The most irregular effect of XG upon syneresis was observed for NPS1 gels after 30

421

days of storage. After that time the 0.05% admixture of XG to 5% NPS1 gel had no effect

422

upon syneresis but the 0.20% admixture of that hydrocolloid significantly suppressed it.

423

Syneresis of 4% NPS1-XG mixed gels stored for 30 days was only slightly higher than that of

424

the corresponding gels without XG. Syneresis in 6% NPS2-XG gels stored for 30 days

425

decreased with an increase in the concentration of XG added. After 60 and 90 days of storage

426

the NPS2-XG mixed gels exhibited lower syneresis than corresponding gels without XG

427

(results not shown). Such decrease depended on the XG concentration. According to Ferrero

428

et al. (1994) the decrease in syneresis of starch gels as a result of the addition of XG was most

429

likely related to the effect of this polysaccharide not as much to reduce the retrogradation of

430

amylopectin as to reduce the retrogradation of amylose. While, Sea-kang and Suphantarika

431

(2006) explained the reduction of syneresis by phase separation between the added non-

432

starchy polysaccharide hydrocolloid and starch polysaccharides, especially amylose. Such

433

results of our study, compared to oscillation (Figs. 1a and 2a) and hardness (Fig. 3a)

434

measurements confirmed that XG either reduced the susceptibility of the NPS1 gels to long-

435

term retrogradation or suppressed non-beneficial changes of physico-chemical phenomena

436

evoked by that phenomenon. That phenomenon was supported by an increase in the XG

13

437

concentration. Most likely, such effect was associated with binding by XG water molecules

438

released from starch as a result of retrogradation/crystallization, decreasing syneresis as

439

compared to samples without XG. This assumption was confirmed by 1H NMR results, that is

440

for all starches XG reduced the mobility of water molecules (Baranowska et al., 2019).

441

XG only slightly influenced syneresis of the NPS2-XG gels up to 60 or 90 days of

442

storage (Fig. 4b). After 60 days only 4% NPS-XG binary gels showed syneresis which

443

exceeded that of the gels without XG. In the 5 and 6% NPS2 gels the addition of XG reduced

444

syneresis and that effect rose with increasing the XG concentration. After 90 days of storage,

445

in binary 4 and 5% NPS2-XG gels syneresis decreased with an increase in the XG

446

concentration. On the other hand, the gels containing 6% of the starch exhibited smaller

447

syneresis only when the addition of XG was 0.20%.

448 449

Fig. 4

450 451

These observations jointly with results of former measurements (Figs. 1, 2 and 3) suggested

452

that increased syneresis of gels containing 4% NPS2 and XG as well as a decrease in

453

syneresis in gels of 5 and 6% NPS2, especially with a larger gum addition, were the result of a

454

significant progress in retrogradation. Deetae et al. (2008) and Ye et al. (2016) assumed that

455

decrease in syneresis resulted from re-adsorption of water in porous structure of the developed

456

gels.

457

In binary and simple WPS gels considerable differences in syneresis were observed

458

between 30 and 60 days of storage (Fig. 4c). Then syneresis of the majority of the binary

459

WPS-XC gels was lower than that of simple WPS gels. After this time, in most cases samples

460

with XG were characterized by smaller syneresis than those without the gum. Only 4% WPS-

461

0.05% XG after 60 and 90 days as well as the 4% gels with 0.20%XG after 90 days showed

462

syneresis higher than the corresponding gels without XG (results not shown). One could

463

suppose that in the least concentrated gels the content of starch was insufficient for building

464

the gel structure sufficiently strong to held water. XG additionally obstructed that building by

465

a competition with amylose and amylopectin for water molecules. This effect was greater

466

with the greater addition of gum. Therefore water is retained within the gel structure via

467

capillary forces, the lower the pore size, the higher is water retention. The results suggests that

468

smaller pores were obtained at higher gelling biopolymer concentrations and/or with high

469

number or cross-links between biopolymers establishing the network. XG could be in fact

470

located within the pores. At higher concentration of starch, XG bound water in WPS samples, 14

471

so that with longer storage the gels had lower hardness than those without the gum (Fig. 3c).

472

Simultaneously the resulting structure was so poor that it was impossible to perform

473

oscillatory measurements (Figs. 1 and 2).

474 475

3.5. Resistant starch content

476

In binary gels as well as in the gels without XG (Dobosz et al., 2019), the content of

477

resistant starch (RS) rose with the storage time (Table 2). Exceptionally, in NPS1-XG binary

478

gels after 30 days of storage, the RS content exceeded that found after the 90 days of storage.

479

The largest differences in RS content occurred after 1-st day and after 30 days of storage. The

480

rate of the RS content increase was the highest within first two hours and in the first day of

481

storage and it positively depended on the amount of amylose in the starch. The subsequent

482

increase in the RS content took place after 30 days. Generally, XG present in the NPS1 and

483

NPS2 gels did not favor formation of RS but in WPS gels an opposite effect was noted. After

484

30 and 90 days of storage the RS content in binary WPS-XG gels was the highest and in the

485

binary NPS2-XG gels it was the lowest. Since the WPS contained only 0.07 wt.% of fat, one

486

can assume that the amount of lipids was too small to have an influence on decrease in

487

number of interactions between water molecules and amylose. Such situation occurs in case

488

of high-amylose starches, wherein starch amylose-lipid complexes (type RS5) are formed

489

(Fuentes-Zaragoza et al., 2011).

490 491

Table 2

492 493

Such results confirm the accelerating role of XG in the formation of the amylose-

494

based three-dimensional gel structure. It was associated with promoting short-term

495

retrogradation. Analysis of the setback values (Table 1) and mechanical spectra (Figs. 1 and

496

2) spoke in favor of such interpretation.

497

The strongest interaction of XG with WPS could favor retrogradation of amylopectin

498

(see Figs. 1 and 2). In addition, as stated in our previous paper (Baranowska et al., 2019),

499

WPS-XG mixed samples showed a rapid increase in the mean correlation times during the

500

storage of the gels. This can mean the gradual formation of solid state structures. However,

501

after 90 days of storage, a decrease in the values of the mean correlation time of these gels

502

was observed, suggesting a weakening of the structure as a result of significant progress of the

15

503

retrogradation phenomenon (Baranowska et al., 2019). In binary NPS1-XG and NPS2 –XG

504

gels XG stabilized the stored samples.

505

No links between RS content and hardness (Fig. 3) and syneresis (Fig. 4) could be observed.

506

It meant that XG promoted retrogradation of amylose and, simultaneously, it controlled some

507

potential non-beneficial changes of physico-chemical properties resulting from long-term

508

retrogradation.

509 510 511

3.5.1. X-ray diffractometry

3.6. X-ray diffractometry It was found that XG was amorphous (random structure – results not shown), which

512 513

was also confirmed by Krystyjan et al. (2011).

514

Diffractograms of potato starch gels (Dobosz et al., 2019) and corresponding binary

515

gels containing XG demonstrate a sharp peak at 2ϴ around 17o and another broad peak

516

around 22-24o 2ϴ. Diffractograms of some samples, particularly samples of WPS with XG,

517

contained a shoulder at 2ϴ around 15o (Fig. 5). These peaks delivered an evidence for

518

reconstruction of the B-type crystalline structure of retrograded starches (Ji et al., 2017; Kim,

519

Kim, & Shin, 1997; Li et al., 2016; Miles et al., 1985; Schwartz et al., 2014).

520

Such peaks could be observed in corresponding diffractograms already after 2 h

521

storage. It meant that in spite of the presence of XG the crystalline structure readily recovered

522

through retrogradation. According to Krystyjan et al. (2011) the ordered structure in the NPS-

523

XG binary gels was recovered within 12 h whereas in corresponding gels without XG

524

amorphous structure remained for at least 72 h. In contrast to that finding Kowalski et al.

525

(2008) did not observe changes in diffractograms of various binary potato starch – non-

526

starchy hydrocolloid gels after 24 storage.

527

Time dependent changes occurring in the diffraction pattern were observed but their

528

character, particularly the intensities of the maxima could not be linked to any parameter

529

characterizing the gel (Fig. 5). Hence, no effect of XG on retrogradation of potato starch

530

based on this approach could be presented in a rational manner.

531 532

Fig. 5

533 534

Similarly, time dependent degree of crystallinity of the binary starch – XG gels varied

535

irregularly (Table 2). The results of DoC for potato starch systems with the addition of XG, in

16

536

contrast to samples without the gum (Dobosz et al., 2019), did not coincide with those found

537

on the basis of the RS determination (Table 2). There was no link between that parameter and

538

the RS content, viscoelastic properties (Figs. 1 and 2), hardness (Fig. 3) and syneresis (Fig. 4)

539

of the samples.

540 541

4. Conclusions

542

The most remarkable changes of the physico-chemical properties of the gels,

543

indicating the occurrence of starch retrogradation, took place between 30th and 90th day of

544

storage. Regardless of the amylose content, the addition of XG promoted the formation of a

545

three-dimensional gel network, and thus accelerated short-term retrogradation. While the

546

addition of xanthan gum caused a decrease in susceptibility to the long-term retrogradation of

547

the normal potato starch gels. That effect was favored by the high content of both amylose

548

and xanthan gum. In case of WPS samples, XG addition promoted the long-term

549

retrogradation, and that effect was supported by elevated concentration of both

550

polysaccharides. Whereas, xanthan gum reduced syneresis of the gels on prolonged storage.

551 552

Funding

553

This project was financed from the funds of the National Science Centre of Poland awarded

554

basing on the decision number UMO-2013/11/B/NZ9/01951.

555 556

Conflict of interest

557

The authors declare no conflict of interests.

558 559

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Figure captions

720

Fig 1. Mechanical spectra at frequency of 1 Hz for: a) G' of 5% NPS1 with XG, b) G" of 5% NPS1

721

with XG, c) G' of 5% NPS2 with XG, d) G" of 5% NPS2 with XG, e) G' of 5% WPS with XG, f) G"

722

of 5% WPS with XG.

723

Fig 2. Values of tg (G"/G') at 1 Hz for potato starch pastes and gels without and with

724

admixture of 0.05 and 0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS.

725

Fig. 3. Hardness of potato starch pastes and gels without and with admixture of 0.05 and

726

0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS; after 1 and 2 h since their

727

preparation and, then after 1, 2, 10, 30, 60 and 90 days of storage on cooling.

728

Fig. 4. Syneresis of potato starch pastes and gels without and with the addition of 0.05 and

729

0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS; after 1 and 2 h since their

730

preparation and, then after 1, 2, 10, 30, 60 and 90 days of storage on cooling.

731

Fig. 5. Diffractograms of 5% (w/w) lyophilized starch without and with 0.20% XG admixture

732

taken after 2 h and 1, 30 and 90 days of storage at 6o C: a) NPS1, b) NPS2, c) WPS.

22

Table 1. Setback values of 4, 5 and 6% (w/w/) pastes of potato starches without and with 0.05 and 0.20% (w/w) XG. Setback* [B.U.]

Starch concentration

XG concentration

[%]

[%]

NPS1

NPS2

WPS

0**

303±4e***

163±10e

139±4d

0.05 0.20 0 0.05 0.20 0 0.05 0.20

287±6e 166±4f 453±12c 412±23d 281±4e 579±10b 603±10a 406±6d

186±2e 105±1f 299±2bc 278±3c 217±4d 438±3a 423±2a 314±31b

843±3f 74±1g 188±1a 139±2d 125±4e 188±2a 170±1b 149±5c

4

5

6

* Setback – difference of viscosity between η50ºC and ηmin. ** Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019). .*** Different letters in columns denote statistically significant differences at α = 0.05..

Table 2. Content of RS and degree of crystallinity of 5% (w/w) starch without XG and with 0.20% XG admixture taken after 2 h and 1, 30 and 90 days of storage at 6o C. Sample

Starch*

Starch + 0.20%XG

RS [g/100 g s.m.]

Storage

DoC [%]

time

NPS1

NPS2

WPS

2h

0.30±0.04f**

0.23±0.01f d

1D

2.76±0.00

d a

2.91±0.12

NPS2

WPS

0.18±0.03d

33.03

28.19

32.29

c

31.08

31.37

32.99

b

33.83

35.82

39.16

3.68±0.09

30D

6.16±0.25

90D

6.13±0.17a

5.56±0.33a

6.50±0.13a

34.04

33.50

34.81

1.01±0.14

e

0.63±0.09

e

0.32±0.08

d

34.06

24.12

34.03

1D

4.49±0.04

c

4.50±0.10

c

5.42±0.24

b

35.52

26.00

37.76

30D

5.80±0.33a

4.82±0.03bc

5.79±0.24b

35.65

26.26

34.10

90D

b

b

a

32.49

33.95

32.19

2h

5.15±0.11

5.39±0.16

a

NPS1

4.99±0.03

5.53±0.07

6.66±0.24

* Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019). ** Different letters in columns denote statistically significant differences at α = 0.05.

a)

b)

c)

d)

e)

f)

Fig 1. Mechanical spectra at frequency of 1 Hz for: a) G' of 5% NPS1 with XG, b) G" of 5% NPS1 with XG, c) G' of 5% NPS2 with XG, d) G" of 5% NPS2 with XG, e) G' of 5% WPS with XG, f) G" of 5% WPS with XG.

Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019).

1

a)

b)

c) Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019).

Fig 2. Values of tg (G"/G') at 1 Hz for potato starch pastes and gels without and with admixture of 0.05 and 0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS.

1

a)

b)

c)

Different letters on particular diagrams denote statistically significant differences at α = 0.05. Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019).

Fig. 3. Hardness of potato starch pastes and gels without and with admixture of 0.05 and 0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS; after 1 and 2 h since their preparation and, then after 1, 2, 10, 30, 60 and 90 days of storage on cooling.

a)

b)

c)

Different letters on particular diagrams denote statistically significant differences at α = 0.05. Results for NPS1, NPS2 and WPS without XG were published in our former paper (Dobosz et al., 2019).

Fig. 4. Syneresis of potato starch pastes and gels without and with the addition of 0.05 and 0.20% (w/w) XG: a) 5% NPS1, b) 5% NPS2, c) 5% WPS; after 1 and 2 h since their preparation and, then after 1, 2, 10, 30, 60 and 90 days of storage on cooling.

a)

b)

c) Fig. 5. Diffractograms of 5% (w/w) lyophilized starch without and with 0.20% XG admixture taken after 2 h and 1, 30 and 90 days of storage at 6o C: a) NPS1, b) NPS2, c) WPS.

Highlights

Influence of XG on the short- and long term retrogradation of potato starch was studied. Greatest changes in properties of the gels took place between 30th and 90th day of storage. Addition of XG promoted short-term retrogradation. Xanthan gum promoted long-term retrogradation of waxy potato starch gels. Xanthan gum reduced syneresis of the gels on prolonged storage.

Declarations of interest: none.