Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic)

Food Hydrocolloids xxx (2016) 1e7

Contents lists available at ScienceDirect

Food Hydrocolloids journal homepage: www.elsevier.com/locate/foodhyd

Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic) Yan Shi a, *, Cui Li a, Lu Zhang b, Tao Huang a, Da Ma a, Zong-cai Tu a, b, **, Hui Wang a, Huan Xie a, Nan-hai Zhang a, Bai-ling Ouyang a a

State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, Jiangxi, 330047, China Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Life Science, Jiangxi Normal University, Nanchang, Jiangxi, 330022, China

b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 19 July 2016 Received in revised form 1 October 2016 Accepted 14 October 2016 Available online xxx

This study aimed to investigate the structure characterization and emulsifying properties of esterified Acacia seyal gum (gum arabic) with various octenyl succinate anhydride (OSA) contents (0, 1%, 2%, and 3% based on the weight of Acacia seyal gum) at different OSA incorporates (%OS, 0, 0.64, 1.09, 1.80). Fourier transform infrared spectroscopy and 1H NMR spectroscopy revealed that OSA groups were introduced into the Acacia seyal gum (AS) molecular structure and possibly substituted the rhamnopyranosyl of AS. Static light scattering analysis showed that the molecular weight of OSA-modified AS (OS-AS) significantly increased. Meanwhile, the crystallinity of AS and OS-AS demonstrated no significant difference. In addition, rheological results revealed that the apparent viscosity of OS-AS was higher than that of AS and increased with increasing %OS. The emulsion activity of OS-AS increased nearly twice those of the original AS and its emulsion stability were also significantly improved. Results indicate that the OS-AS have potential applications for microencapsulation and emulsions that require long-term stability. © 2016 Elsevier Ltd. All rights reserved.

Keywords: Gum arabic Acacia seyal gum Octenyl succinate anhydride Structure characterization Emulsifying properties

1. Introduction Gum arabic (GA) is an exudate from trunks and branches of acacia trees, namely Acacia senegal gum and Acacia seyal gum (AS), and is a branched, neutral or slightly acidic, complex polysaccharide together with a small amount of structural protein (Randall, Phillips, & Williams, 1988; Renard, Garnier, Lapp, Schmitt, & Sanchez, 2012). In general, the polysaccharides and proteins present in GA are consisted of three mainly fractions, including arabinogalactan (AG), arabinogalactan protein (AGP), and glycoprotein (GP), which differ from their molecular weight and chemical composition (Desplanques, Renou, Grisel, & Malhiac, 2012). The AG fraction which represents about 88% (in weight) of the total gum has a low molecular weight (Mw, ~300 KDa) and associated little protein content of below 1%. The AGP fraction (~10% of the total

* Corresponding author. State Key Laboratory of Food Science and Technology, Nanchang University, Nanchang, Jiangxi, 330047, China. ** Corresponding author.Key Laboratory of Functional Small Organic Molecule, Ministry of Education and College of Life Science, Jiangxi Normal University, Nanchang, Jiangxi, 330022, China. E-mail addresses: [email protected] (Y. Shi), [email protected] (Z.-c. Tu).

gum) has a high molecular weight (Mw) (~1500 KDa) and protein content (~10%). The GP fraction (<2% of the total gum) has the lowest molecular weight (Mw, ~250 KDa) and the highest protein content (~20%e50%) (Mahendran, Williams, Phillips, Al-Assaf, & Baldwin, 2008; Randall, Phillips, & Williams, 1989). Among these fractions, AGP is the most interfacially active component (Castellani, Al-Assaf, Axelos, Phillips, & Anton, 2010; Ray, Bird, Iacobucci, & Clark, 1995), and is primarily responsible for the emulsifying properties of GA (Al-Assaf, Phillips, Aoki, & Sasaki, 2007; Randall et al., 1988). This fraction can be adsorbed on the oil-water interface to form a visco-elastic film and reduce the interfacial tension between oil and water because of its amphiphilic characteristics, which is conferred by the hydrophobic protein chains combined to the hydrophilic polysaccharide fragments (Castellani, Al-Assaf et al., 2010; Castellani, Guibert et al., 2010). Currently, GA has been widely used in the food industry as an emulsifiers (Patel & Goyal, 2015). However, GA is generally required a high concentration of approximately 15%e25% (w/w) to achieve a stable 20% (w/w) oil in-water emulsions since the AG fraction, which represents the bulk of the gum, is not involved in the emulsification process (Leroux, Langendorff, Schick, Vaishnav, & Mazoyer, 2003; Randall et al., 1988, 1989). In addition, the natural

http://dx.doi.org/10.1016/j.foodhyd.2016.10.043 0268-005X/© 2016 Elsevier Ltd. All rights reserved.

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

2

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

variability (geography, soil, age of the tree, and on both species) of GA has became a barrier to complete industrial acceptance (AlAssaf et al., 2007). Currently, about one-quarters of GA comes from the species AS. But AS is generally less valued than Acacia senegal gum due to its poor emulsifying properties (Dickinson, 2003; Fauconnier et al., 2000; Flindt, Al-Assaf, Phillips, & Williams, 2005), it then can neither be used in emulsions that need long term stability (Elmanan, Al-Assaf, Phillips, & Williams, 2008; Siddig, Osman, Al-Assaf, Phillips, & Williams, 2005), nor be used as encapsulating agent for some monoterpenes alone (Bertolini, Siani, & Grosso, 2001). Therefore, improving the emulsifying properties of GA by modification, and researching effects of structure on emulsifying properties of modified gum, especially AS, is urgently needed. Recently, there has been increasing interest in chemical modification of GA to enhance its emulsifying properties, and this involved esterification using octenyl succinate anhydride (OSA) and dodecenyl succinic anhydride (DSA). Pan, Yang, and Qiu (2015), Sarkar, Gupta, Variyar, Sharma, and Singhal (2013) and Sarkar and Singhal (2011) showed the optimum condition for synthesis of modified GA using OSA, and found that OSA-modified GA had improved performance compared to the original GA. Wang, Williams, and Senan (2014) demonstrated the modified GA (Acacia senegal gum) can be readily synthesized in aqueous solutions using DSA, and the modified GA had superior emulsifying properties to GA. However, the structure characterization, emulsifying properties and effects of OSA incorporation (%OS) on functionalities and applications of OSA-modified AS (OS-AS) have not yet been reported. The present study aimed to enhance the emulsifying properties of AS through chemical modification using different concentrations of OSA. Effects of %OS on the apparent viscosity and emulsifying properties of AS were evaluated. Fourier transform infrared (FT-IR), 1 H NMR spectroscopy, static light scattering spectrometer (SLS) and X-ray diffraction (XRD) were employed to compare the influence of OSA-modification on the structure of AS, and to elucidate the possible relationship between the structure and emulsification. 2. Materials and methods

process was repeated for 5 times. The final solid portion was ovendried at 40
C for 24 h. The products are referred to as AS0, AS1, AS2 and AS3 corresponding to 0, 1%, 2% and 3% OSA (Wt % based on the weight of dry AS), respectively.

2.3. Fourier-transform infrared spectroscopy (FT-IR) The changes in chemical structure of AS and OS-AS were qualitatively analyzed using FT-IR (Nicolet 380, Thermo Nicolet, USA). Samples were prepared by grinding the finely powdered samples with potassium bromide (KBr). The spectrum was recorded over the wave number range of 400e4000 cm1. The samples were dried at 105
C for 12 h before analysis to avoid the interference of moisture.

2.4. Determination of bound %OS content The bound OS content was determined according to Qiu, Bai, and Shi (2012) with some modifications. Exactly, 0.5000 g dry samples were immersed in 10 mL of 4 M NaOH, and stirred overnight. The alkali treated solutions (2 mL) were transferred into a 25 mL volumetric flask, mixed with 18 mL of 1 M HCl and made volume to 25 mL with acetonitrile. The solutions were then analyzed using an HPLC system (D-2000 HSM, HITACHI, Tokyo, Japan) with a Nova-Pak® C18 column (4 mm, 3.9  150 mm, Waters, CA, USA), using a mixture of acetonitrile and water containing 0.1% formic acid (35:65, v/v) as the mobile phase. 10 mL of solution was injected after filtered through 0.45 mm membrane, the UV spectra was recorded at 200 nm. The OS content was calculated from the standard curve (y¼19.3690.0662) of OSA plotted using OSA concentration (mg/mL) vs total peak area. The bound %OS of OS-AS were calculated by using following equation:

%OS ¼

12500Wt W

where W is the dry weight (g) of OS-AS, Wt is the OS content calculated from standard curve, 12,500 is dilution factors.

2.1. Materials 2.5. Acacia seyal gum (gum Arabic) was obtained from Nexira (Shanghai, China). Octenyl succinate anhydride (OSA) (99.9% purity) was purchased from Vertellus (Shenzhen, China). Evening primrose oil was obtained from Tianjin Baoxin International Oil Bio Co., Ltd. Chromatographic pure acetonitrile and methanol were purchased from TEDIA (Shanghai, China). Spectroscopic pure potassium bromide was obtained from Solarbio (Beijing, China). All other chemicals were analytical reagents and used as received.

1

H NMR experiment

1 H NMR experiment of AS and OS-AS was carried out according to Nie et al. (2013) with slight modifications. Both samples were dissolved in 0.5 mL deuterium oxide (D2O) (~2%, w/v), and deuterium exchanged by successive freeze-drying steps. The samples were kept in D2O at room temperature for 3 h before NMR analysis. 1 H NMR spectrum was recorded on NMR spectrometer (Avance 600 MHz, Brucker, Rheinstetten, Germany) at 25
C.

2.2. Preparation of OS-AS 2.6. Determination of molecular weight Preparation was carried out according to the method of Pan et al. (2015) with some modification. Dry weight AS (30.00 g) was dispersed in deionized water to prepare a 30% (w/v) solution. The pH was adjusted to 8.00 using 0.5 M NaOH solution. Four reactions were performed using 0, 1%, 2%, 3% OSA (Wt % based on the weight of dry AS) respectively, which were diluted with ethanol and added at 25
C. The mixtures were allowed to reaction at 40
C for 1.5 h with pH maintained at 8.00. Following, the reactions were ceased by adjusting the pH to 6.00 using 0.1 M HCl solution. OS-AS was obtained by spray drying. Then the product was dispersed in deionized water to prepare a 10% (w/v) solution following by washing with absolute ethanol to remove the residue of OSA. This

Molecular weight of AS and OS-AS was determined using an laser light scattering spectrometer (BI-200SM, Brookhaven Instruments, New York, USA) with He-Ne laser (633 nm) as the light source according to Wang, Burchard, Cui, Huang, and Phillips (2008) and Wang, Huang, Nakamura, Burchard, and Hallett (2005) with slight modifications. Static light scattering measurements of the samples were performed at 25
C. The stock gum solutions (5 mg/mL) used for molecular weight measurement were prepared with 0.2 M NaCl. The scattering angles detected ranged from 20
to 150
in steps of 10
. A specific refractive index increment was set at 0.141 mL/g.

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

3

2.7. X-ray diffraction

3.2. Structural characterization of OS-AS

X-ray diffraction analysis of AS and OS-AS was carried out on an X-ray powder diffractometer (D1 system, Bede, UK) with Cu Ka radiation operated at 40 kV and 40 mA. Diffractograms were obtained from 5
(2q) to 60
(2q) in 0.02
step. The samples were dried at 40
C for 24 h prior to detection.

3.2.1. FT-IR analysis Succinylation can cause esterification between the hydroxyl groups in polysaccharide molecules and the carbonyl groups in OSA. The ester bond of hydroxyl groups into carbonyl groups could be verified by FT-IR (Marcazzan, Vianello, Scarpa, & Rigo, 1999). The FT-IR spectra of AS and OS-AS with different %OS values are shown in Fig. 2a, b. An extremely broad band that appeared at 3423 cm1 resulted from the vibration of O-H or N-H (Wang et al., 2014). The bands at 2930 and 1611 cm1 corresponded to C-H stretching vibration or N-H plan bending vibration (Wang et al., 2014). In the fingerprint region of the samples, five characteristic peaks were observed at 1300 - 670 cm1, which were mainly attributed to C-O bond stretching (Miao et al., 2014). No distinct difference was observed between the spectra of AS and AS0. Compared with AS and AS0, however, the spectra of AS1, AS2 and AS3 showed a new peak at 1721 cm1, which indicated the formation of ester carbonyl groups (Wang et al., 2014; Xu et al., 2012). For AS3, the peak was most obvious than those of AS1 and AS2 because of the highest %OS.

2.8. Determination of apparent viscosity Solutions of AS and OS-AS were prepared at 30% (w/v) by dissolving samples in deionized water under gentle stirring at 60 ± 1
C for 30 min and then cooled to room temperature. Experiments at imposed shear stress were performed on a Rheometer (PaarePhysica MCR 302, 104 Anton Paar, Austria), fitted with a parallel plate geometry (50 mm diameter, 0.1 mm gap). Temperature control (25 ± 0.1
C) was achieved with a Peltier system in the bottom plate. 2.9. Evaluation of emulsifying properties 2.9.1. Emulsions preparation Solutions of AS and OS-AS were prepared by dissolving 0.60 g of samples in 7.40 g deionized water, and the dispersions were heat with agitation at 60
C for 10 min. After cooling to room temperature, 2.00 g evening primrose oil was added for each gradually, and homogenized (T18, IKA, Germany) set at 2,4000 r/min for 3 min. 2.9.2. Emulsification properties The emulsion activity (EA) of AS and OS-AS was investigated according to Chikamai, Banks, Anderson, and Weiping (1996) with some modification. The absorption at 500 nm given by a 30 mL freshly prepared emulsions diluted in 25 mL 1% SDS solution is quoted as emulsion activity (EA). Freshly prepared emulsions were sealed in 10 mL tubes (height: 52 mm, internal diameter: 11 mm) with a small headspace to minimize evaporation, and stored quiescently at ambient temperature. The emulsion stability (ES) of samples investigated at 24 h and 7 days according to Huang, Kakuda, and Cui (2001), respectively. The average particle size and distribution of dispersed oil in emulsion at 0 h, 24 h and 7 days were determined by Nicomp 380/ ZLS Zeta potential/Particle sizer (Nicomp 380/ZLS, PPS, Santa Barbara, USA) based on dynamic light scattering (DLS). The emulsions were diluted approximately 2000 times with deionized water before determination, and all measurements were carried out at 25
C (Liu et al., 2011). 2.10. Statistical analysis Analyses of variance were performed. The results were expressed as mean ± standard deviations and compared by the Duncan's multiple range test at 5% confidence level, using SPSS (version 17.0, Chicago, USA). All figures were plotted with Origin (Origin Lab Co., Pro.8.6, USA).

3.2.2. 1H NMR analysis Comparison of 1H NMR of AS and its derivatives also clearly demonstrated the grafting of OSA onto AS. The spectra of AS and OS-AS with different %OS values are presented in Fig. 3. The 1H spectrum of AS allowed peaks obtained in the 2.00e2.30 ppm spectral region due to acetyl groups (Meng, Zheng, Wang, Liang, & Zhong, 2014; Nie et al., 2013) that were not found in FT-IR probably because of its low levels in AS. In the 1H spectra of OS-AS, the protons on the acetyl groups could also be readily identified close to 2.10 ppm, and the peak intensities had no distinct difference. This result indicated acetyl groups were not cleaved during the modification of AS, and the spectra of AS and AS0 showed no obvious difference. However, compared with AS and AS0, AS1, AS2 and AS3 had several additional signals at 5.4e5.6 ppm and 0.7e3.0 ppm, which stemmed from the OS group (Bai & Shi, 2011). The multiplet peaks at 5.4e5.6 ppm and 0.8e1.0 ppm corresponded to the double bond proton and the terminal methyl protons of the OS group, respectively (Bai, Shi, Herrera, & Prakash, 2011). The multiplet peaks at 1.30 ppm corresponded to the methylene protons on the octenyl chain of the grafted OS groups (Eenschooten, Guillaumie, Kontogeorgis, Stenby, & Schwach-Abdellaoui, 2010). Moreover, the intensities of the above-mentioned signals increased with increasing %OS. These findings indicated the grafting of OSA onto AS molecules, which is consistent with the results obtained by FTIR. 1 H spectra were also helpful in determining the position of OS substitution on AS. The 1H spectra of OS-AS revealed the possible substituted positions of the OS groups in rhamnopyranosyl (Rhap). This phenomenon occurred because the peak of OS-AS (%OS ¼ 0.64, 1.09 and 1.80) at 1.20 ppm that corresponded to the proton of CH3Rhap (Nie et al., 2013) became broader than those of AS and AS0. It is consistent with the report of Bai et al. (2011), who attributed the peak broadening at 5.38 ppm (H-1 of 1,4-linked repeated units) to the substitution of OS at the O-2 position. Simultaneously, Rhap was mainly distributed in the outer surface of AS molecular, suggesting that OSA is more readily reacts with Rhap.

3. Results and discussion 3.1. Preparation of OS-AS The OS-AS was obtained from the esterification reaction between AS and OSA (Fig. 1). %OS of OS-AS was determined through HPLC. The %OS values of OS-AS were 0, 0.64, 1.09 and 1.80 when the reactions were performed using 0, 1%, 2%, and 3% OSA, respectively.

3.2.3. Determination of Mw The Mw values of AS and OS-AS with different %OS values are presented in Table 1. Compared with AS and AS0, OS-AS (% OS ¼ 0.64, 1.09 and 1.80) had significantly higher Mw values (9.28  105, 9.06  105, and 1.19  106, respectively). In general, the Mw of OS-AS increased with increasing %OS. This result may indicated that AS was undegraded during the modification but was also

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

4

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

Fig. 1. Schematic representation of the esterification reaction between AS and OSA.

Fig. 3. 1H NMR spectra of AS and esterified AS. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

Table 1 Mw of AS and esterified AS measured by SLS. Sample 5

Mw  10 (g/mol)

AS

AS0

AS1

AS2

AS3

7.79

8.02

9.28

9.06

11.93

Note: AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

Fig. 2. (a) FT-IR spectra of AS and esterified AS. (b) FT-IR spectra of AS and esterified AS. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

incorporated into OS groups, which is consistent with the results obtained by FT-IR and 1H NMR. Additionally, the critical aggregation concentration of OSA esterified gum was decreased with increasing hydrophobe incorporation (Wang et al., 2014). Then, the

increased Mw of OS-AS might also be attributed to molecular aggregation induced by the hydrophobic association of molecules through the alkyl chains of OSA. Moreover, the Mw value of AS0 was higher than that of AS, indicating that AS might undergo “maturation” during the modification without OSA. This is consistent with many previous researchers, who indicated that “maturation” could increase the Mw of gum (Al-Assaf et al., 2007; Aoki, Al-Assaf, Katayama, & Phillips, 2007). Therefore, two reactions of “maturation” and esterification may occurred simultaneously in the modification process. 3.2.4. X-ray diffraction In order to illuminate the effect of OSA modification on the physical state of AS molecular, AS and OS-AS were examined by X-

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

3.3. Determination of apparent viscosity Chemical changes in polysaccharides may change their functional properties, and hydrophobically modified polysaccharides, such as alkylated hyaluronic acid and alkylated pectin (Creuzet, Kadi,
ly-Velty, 2006; Liang, Wang, Chen, Liu, & Liu, 2015), Rinaudo, & Auze are generally efficient rheology modifiers. Viscosity is an important property of AS, and highly branched structures result in lowviscosity solutions compared with other polysaccharides with similar Mw (Al-Assaf et al., 2007). Fig. 5 shows the apparent viscosity of AS and OS-AS. All solutions of OS-AS exhibited an enhanced apparent viscosity. In general, the apparent viscosity of OS-AS (% OS ¼ 0.64, 1.09, and 1.80) increased with increasing %OS owe to the formation of multimolecular cluster caused by intermolecular association of hydrophobic segments (Dulong, Mocanu, & Le Cerf, 2007; Liang et al., 2015). The apparent viscosity of AS0 was also obviously higher than that of AS, which may be explained by the increase in Mw or change in molecular dimensions of AS0 compared with AS (Al-Assaf et al., 2007). In addition, the rheological behavior of OS-AS was similar to AS, indicating a shear thinning at lower shear rates, and a Newtonian behavior at higher shear rates (Li et al., 2009). It also suggested that esterification did not cause changes in rheological behavior of AS in 30% (w/v) aqueous solution. 3.4. Emulsification properties Emulisfying activity (EA) and emulsion stability (ES) are common emulsifying properties of surfactants. EA and ES refer to the abilities of surfactants to facilitate the formation of emulsions and

0.08

AS3 AS2

Apparent Viscosity [Pa.s]

ray diffraction. As indicated in Fig. 4 AS and OS-AS exhibited fairly similar diffraction patterns. The diffuse and large peaks appeared at approximately 19
, revealing the amorphous natural of AS and OSAS. This result suggested that esterification has no significant effect on the amorphous state of AS, that is, the ordered state of AS molecular would not be formed during the process of esterification. In addition, the esterification reaction of AS with OSA may more easily to execute than the polysaccharides having complete or partial crystalline structure because esterification occurred primarily in amorphous regions (Meng et al., 2014; Wang & Wang, 2002).

5

0.07

AS1 AS0

0.06

0.05

AS 0.04 0

200

400

600

800

1000

Shear Rate [1/s] Fig. 5. Apparent viscosities of AS and esterified AS. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

stabilize fine droplets during and after emulsification, respectively (Liang et al., 2015). The EAs of AS and OS-AS are shown in Fig. 6. The EA of AS was significantly lower than that of AS0. This might be attributed to the occurred “maturation” during modification process without OSA. “Maturation” is a process which associates AG and the GP at lower molecular weight to give more and higher molecular weight AGP, which is considered to be a main ingredient of AS to emulsification (Al-Assaf et al., 2007). As compared to AS0, the EAs of OSA derivatives were significantly improved with increasing %OS. A higher %OS indicates a better substitution of OS group in the gum (Figs. 2 and 3), the short octenyl succinate side chains and carboxyl group are more easily contacted with oil and water, eliciting a positive effect on the emulsifying properties of AS. This result differed from that of Sarkar and Singhal (2011), who found that an increased substitution degree of GA could not improve EA. This difference could be that the highest %OS detected in the present study was not enough to make the octenyl chain fold itself toward the central region of the AS granule and could not decrease the interaction between the oil phase and the hydrophobic part of the chain (Viswanathan, 1999).

AS3

1.80

AS2

1.09

% OS

d

0.64

c

c

AS1

0

b

AS0

AS

0 0.0

0.1

a 0.2

0.3

0.4

0.5

0.6

0.7

Emulisfying activity (EA) Fig. 4. X-ray diffraction pattern of AS and esterified AS. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

Fig. 6. Emulisfying activity of AS and esterified AS. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

6

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

The droplet size and PDI of the emulsions were determined after 24 h and 7 days of storage (Table 2). The droplet size and PDI, which show that the degree of dispersion of the particles, deceased with increasing %OS. Presumably, increasing hydrophobe content facilitates rapid adsorption onto the droplets as they are created under shears, thus leading to reduced droplet aggregation and coalescence (Wang et al., 2014). Moreover, the droplet size and PDI significantly increased with the extension of storage time for the AS-, AS0-, AS1-, and AS2-stabilized emulsions, but these parameters remained almost constant for the emulsion prepared using AS3. The AS1-, AS2-, and AS3-stabilized emulsions had an ESs of 76.82%, 82.10%, and 100% and 72.78%, 79.03%, and 100% after 24 h and 7 days of storage, respectively. Meanwhile, the AS- and AS0stabilized emulsions had ESs of 58.23% and 62.53%, respectively, after 24 h of storage, and ESs of 0 and 0, respectively, after 7 days of storage. As shown in Fig. 7, a serious phenomenon of water stratification occurred in AS- and AS0-stabilized emulsions after 24 h of storage, but the AS3-emulsion was homogenous. After 7 days of storage, complete separation of the oil and water of AS- and AS0stabilized emulsions and significant creaming of the AS1- and AS2-stabilized emulsions occurred. While, the AS3-stabilized emulsion showed no significant changes, which indicated the AS3 had the best emulsifying properties. It has suggested that the major stabilization mechanism of emulsion formed by AS was steric repulsion (Jayme, Dunstan, & Gee, 1999). The high Mw and size of the amphiphilic macromolecule in the continuous phase generally have improved steric repulsion in emulsion (Jayme et al., 1999; Xu, Huang, Fu, & Jane, 2015). That is, the high Mw of AS3 (Table 1) might help stabilize emulsion, which is consist with (Li, Fu, Luo, & Huang, 2013), who found that the high molecular esterified starch would be beneficial to stabilize emulsion. In addition, the stability of emulsion also affected by the apparent viscosity of gum. The apparent viscosity of emulsion, an important characteristic in determining storage stability of emulsion, is generally affected by the apparent viscosity of emulsifier (Doki
c, Doki
c, Dap cevi
c, & Krstonosi
c, 2008; Xu et al., 2015). Generally, the esterified polysaccharides with high apparent viscosity would make emulsion with high viscosity (Doki
c et al., 2008). The increase in viscosity of emulsion could retard free motion and aggregation of the oil droplets, delaying creaming, flocculation, and coalescence (Xu et al., 2015). Thus, the emulsion AS3-stabilized emulsion has the best stability. Given above results, it can be known that suitable modification of Acacia seyal gum with OSA could efficiently produce and stabilize oil-in-water emulsions compared to that without modification. Therefore, OSA esterified gum will have potential applications for microencapsulation and emulsions that require long-term stability for improving their emulsifying properties. 4. Conclusions AS was hydrophobically modified by various OSA contents (0,

Fig. 7. Phase separation profiles of AS- or esterified AS-stabilized 20% (w/w) oil-inwater emulsions during 0 h (A), 24 h (B), and 7 days (C) storage at ambient temperature. AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively.

1%, 2%, and 3%) with different %OS values. The FT-IR and 1H NMR spectra of OS-AS showed that esterification occurred and that most OS substitutions probably occurred at Rhap. The Mw of OS-AS generally increased with increasing %OS. OSA modification caused no significant change in the crystalline pattern of AS. Their apparent viscosities increased with increasing %OS. The increase in %OS also led to a decrease in the size of emulsion droplets and to a stable emulsion. The results of the present study suggest that OS-AS with a %OS of 1.80 is a strong emulsifying agent. We conclude that

Table 2 The oil droplets size, EA and ES of AS- or esterified AS-stabilized 20% (w/w) oil-in-water emulsions during 24 h and 7 days storage. Sample

24 h of storage

7 days of storage

Particle size (mm)

PDI

ES (%)

AS AS0 AS1 AS2 AS3

39.21 ± 3.404c 24.40 ± 2.779 0.65 ± 0.003 0.56 ± 0.002 0.47 ± 0.012

10.66 ± 1.477c 5.97 ± 0.469 0.41 ± 0.002 0.41 ± 0.035 0.32 ± 0.011

58.23 ± 62.53 ± 76.82 ± 82.10 ± 100.00e

0.029 0.005 0.009c 0.004d

Particle size (mm)

PDI

ES (%)

e e 0.79 ± 0.001c 0.58 ± 0.027 0.51 ± 0.001

e e 0.88 ± 0.009 0.58 ± 0.059 0.49 ± 0.008

0 0 72.78 ± 0.005 79.03 ± 0.013c 100.00d

Note: AS0, AS1, AS2 and AS3 were esterified AS with various OSA contents (0, 1%, 2%, and 3% based on the weight of AS), respectively. Date are mean ± standard deviation. “e” Means not determination. Values in each column with different letters (a-e) are significantly different (p < 0.05).

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043

Y. Shi et al. / Food Hydrocolloids xxx (2016) 1e7

OSA-modified AS possesses emulsifying properties that are superior to those of original AS and thus has potential applications in microencapsulation and emulsion that need long-term stability. Acknowledgment This research was financially supported by the National Natural Science Foundation of China (No. 31360390), and the Key Research and Development Program in Agricultural Area of Jiangxi Province (20161BBF60097). References Al-Assaf, S., Phillips, G. O., Aoki, H., & Sasaki, Y. (2007). Characterization and properties of Acacia senegal (L.) willd. var. senegal with enhanced properties (Acacia (sen) SUPER GUM™): Part 1dcontrolled maturation of Acacia senegal var. senegal to increase viscoelasticity, produce a hydrogel form and convert a poor into a good emulsifier. Food Hydrocolloids, 21(3), 319e328. Aoki, H., Al-Assaf, S., Katayama, T., & Phillips, G. O. (2007). Characterization and properties of Acacia senegal (L.) willd. var. senegal with enhanced properties (Acacia (sen) SUPER GUM™): Part 2dmechanism of the maturation process. Food Hydrocolloids, 21(3), 329e337. Bai, Y., & Shi, Y.-C. (2011). Structure and preparation of octenyl succinic esters of granular starch, microporous starch and soluble maltodextrin. Carbohydrate Polymers, 83(2), 520e527. Bai, Y., Shi, Y.-C., Herrera, A., & Prakash, O. (2011). Study of octenyl succinic anhydride-modified waxy maize starch by nuclear magnetic resonance spectroscopy. Carbohydrate Polymers, 83(2), 407e413. Bertolini, A., Siani, A., & Grosso, C. (2001). Stability of monoterpenes encapsulated in gum arabic by spray-drying. Journal of Agricultural and Food Chemistry, 49(2), 780e785. Castellani, O., Al-Assaf, S., Axelos, M., Phillips, G. O., & Anton, M. (2010). Hydrocolloids with emulsifying capacity. Part 2eAdsorption properties at the nhexadecaneeWater interface. Food Hydrocolloids, 24(2), 121e130. Castellani, O., Guibert, D., Al-Assaf, S., Axelos, M., Phillips, G. O., & Anton, M. (2010). Hydrocolloids with emulsifying capacity. Part 1eEmulsifying properties and interfacial characteristics of conventional (Acacia senegal (L.) Willd. var. senegal) and matured (Acacia (sen) SUPER GUM™) Acacia senegal. Food Hydrocolloids, 24(2), 193e199. Chikamai, B., Banks, W., Anderson, D., & Weiping, W. (1996). Processing of gum arabic and some new opportunities. Food Hydrocolloids, 10(3), 309e316.
ly-Velty, R. (2006). New associative systems Creuzet, C., Kadi, S., Rinaudo, M., & Auze based on alkylated hyaluronic acid. Synthesis and aqueous solution properties. Polymer, 47(8), 2706e2713. Desplanques, S., Renou, F., Grisel, M., & Malhiac, C. (2012). Impact of chemical composition of xanthan and acacia gums on the emulsification and stability of oil-in-water emulsions. Food Hydrocolloids, 27(2), 401e410. Dickinson, E. (2003). Hydrocolloids at interfaces and the influence on the properties of dispersed systems. Food Hydrocolloids, 17(1), 25e39. Doki
c, P., Doki
c, L., Dap cevi
c, T., & Krstonosi
c, V. (2008). Colloid characteristics and emulsifying properties of OSA starches. In Colloids for nano-and biotechnology (pp. 48e56). Springer. Dulong, V., Mocanu, G., & Le Cerf, D. (2007). A novel amphiphilic pH-sensitive hydrogel based on pullulan. Colloid and Polymer Science, 285(10), 1085e1091. Eenschooten, C., Guillaumie, F., Kontogeorgis, G. M., Stenby, E. H., & SchwachAbdellaoui, K. (2010). Preparation and structural characterisation of novel and versatile amphiphilic octenyl succinic anhydrideemodified hyaluronic acid derivatives. Carbohydrate Polymers, 79(3), 597e605. Elmanan, M., Al-Assaf, S., Phillips, G. O., & Williams, P. A. (2008). Studies on Acacia exudate gums: Part VI. Interfacial rheology of Acacia senegal and Acacia seyal. Food Hydrocolloids, 22(4), 682e689. Fauconnier, M.-L., Blecker, C., Groyne, J., Razafindralambo, H., Vanzeveren, E., Marlier, M., et al. (2000). Characterization of two Acacia gums and their fractions using a Langmuir film balance. Journal of Agricultural and Food Chemistry, 48(7), 2709e2712. Flindt, C., Al-Assaf, S., Phillips, G., & Williams, P. (2005). Studies on acacia exudate gums. Part V. Structural features of Acacia seyal. Food Hydrocolloids, 19(4), 687e701. Huang, X., Kakuda, Y., & Cui, W. (2001). Hydrocolloids in emulsions: Particle size distribution and interfacial activity. Food Hydrocolloids, 15(4), 533e542. Jayme, M., Dunstan, D., & Gee, M. (1999). Zeta potentials of gum arabic stabilised oil in water emulsions. Food Hydrocolloids, 13(6), 459e465. Leroux, J., Langendorff, V., Schick, G., Vaishnav, V., & Mazoyer, J. (2003). Emulsion stabilizing properties of pectin. Food Hydrocolloids, 17(4), 455e462. Liang, R.-h., Wang, L.-h., Chen, J., Liu, W., & Liu, C.-m. (2015). Alkylated pectin:

7

Synthesis, characterization, viscosity and emulsifying properties. Food Hydrocolloids, 50, 65e73. Li, X., Fang, Y., Al-Assaf, S., Phillips, G. O., Nishinari, K., & Zhang, H. (2009). Rheological study of gum arabic solutions: Interpretation based on molecular selfassociation. Food Hydrocolloids, 23(8), 2394e2402. Li, C., Fu, X., Luo, F., & Huang, Q. (2013). Effects of maltose on stability and rheological properties of orange oil-in-water emulsion formed by OSA modified starch. Food Hydrocolloids, 32(1), 79e86. Liu, C. M., Zhong, J. Z., Liu, W., Tu, Z. C., Wan, J., Cai, X. F., et al. (2011). Relationship between functional properties and aggregation changes of whey protein induced by high pressure microfluidization. Journal of food science, 76(4), E341eE347. Mahendran, T., Williams, P., Phillips, G., Al-Assaf, S., & Baldwin, T. (2008). New insights into the structural characteristics of the Arabinogalactan protein (AGP) fraction of gum arabic. Journal of Agricultural and Food Chemistry, 56(19), 9269e9276. Marcazzan, M., Vianello, F., Scarpa, M., & Rigo, A. (1999). An ESR assay for a-amylase activity toward succinylated starch, amylose and amylopectin. Journal of Biochemical and Biophysical Methods, 38(3), 191e202. Meng, F., Zheng, L., Wang, Y., Liang, Y., & Zhong, G. (2014). Preparation and properties of konjac glucomannan octenyl succinate modified by microwave method. Food Hydrocolloids, 38, 205e210. Miao, M., Li, R., Jiang, B., Cui, S. W., Zhang, T., & Jin, Z. (2014). Structure and physicochemical properties of octenyl succinic esters of sugary maize soluble starch and waxy maize starch. Food Chemistry, 151, 154e160. Nie, S.-P., Wang, C., Cui, S. W., Wang, Q., Xie, M.-Y., & Phillips, G. O. (2013). The core carbohydrate structure of Acacia seyal var. seyal (Gum arabic). Food Hydrocolloids, 32(2), 221e227. Pan, J., Yang, L., & Qiu, D. (2015). Optimization of a synthesis process for octenylsuccinic anhydride modified gum arabic. Food Science and Biotechnology, 24(1), 7e13. Patel, S., & Goyal, A. (2015). Applications of natural polymer gum arabic: A review. International Journal of Food Properties, 18(5), 986e998. Qiu, D., Bai, Y., & Shi, Y.-C. (2012). Identification of isomers and determination of octenylsuccinate in modified starch by HPLC and mass spectrometry. Food Chemistry, 135(2), 665e671. Randall, R., Phillips, G., & Williams, P. (1988). The role of the proteinaceous component on the emulsifying properties of gum arabic. Food Hydrocolloids, 2(2), 131e140. Randall, R., Phillips, G., & Williams, P. (1989). Fractionation and characterization of gum from Acacia senegal. Food Hydrocolloids, 3(1), 65e75. Ray, A. K., Bird, P. B., Iacobucci, G. A., & Clark, B. C. (1995). Functionality of gum arabic. Fractionation, characterization and evaluation of gum fractions in citrus oil emulsions and model beverages. Food Hydrocolloids, 9(2), 123e131. Renard, D., Garnier, C., Lapp, A., Schmitt, C., & Sanchez, C. (2012). Structure of arabinogalactan-protein from Acacia gum: From porous ellipsoids to supramolecular architectures. Carbohydrate Polymers, 90(1), 322e332. Sarkar, S., Gupta, S., Variyar, P. S., Sharma, A., & Singhal, R. S. (2013). Hydrophobic derivatives of guar gum hydrolyzate and gum arabic as matrices for microencapsulation of mint oil. Carbohydrate Polymers, 95(1), 177e182. Sarkar, S., & Singhal, R. S. (2011). Esterification of guar gum hydrolysate and gum arabic with n-octenyl succinic anhydride and oleic acid and its evaluation as wall material in microencapsulation. Carbohydrate Polymers, 86(4), 1723e1731. Siddig, N., Osman, M., Al-Assaf, S., Phillips, G., & Williams, P. (2005). Studies on acacia exudate gums, part IV. Distribution of molecular components in Acacia seyal in relation to Acacia senegal. Food Hydrocolloids, 19(4), 679e686. Viswanathan, A. (1999). Effect of degree of substitution of octenyl succinate starch on the emulsification activity on different oil phases. Journal of Environmental Polymer Degradation, 7(4), 191e196. Wang, Q., Burchard, W., Cui, S. W., Huang, X., & Phillips, G. O. (2008). Solution properties of conventional gum arabic and a matured gum arabic (Acacia (sen) SUPER GUM). Biomacromolecules, 9(4), 1163e1169. Wang, Q., Huang, X., Nakamura, A., Burchard, W., & Hallett, F. R. (2005). Molecular characterisation of soybean polysaccharides: An approach by size exclusion chromatography, dynamic and static light scattering methods. Carbohydrate Research, 340(17), 2637e2644. Wang, Y. J., & Wang, L. (2002). Characterization of acetylated waxy maize starches prepared under catalysis by different alkali and alkaline-earth hydroxides. €rke, 54(1), 25e30. Starch-Sta Wang, H., Williams, P. A., & Senan, C. (2014). Synthesis, characterization and emulsification properties of dodecenyl succinic anhydride derivatives of gum Arabic. Food Hydrocolloids, 37, 143e148. Xu, Y., Huang, Q., Fu, X., & Jane, J.-L. (2015). Modification of starch octenylsuccinate by b-amylase hydrolysis in order to increase its emulsification properties. Food Hydrocolloids, 48, 55e61. Xu, J., Zhou, C.-W., Wang, R.-Z., Yang, L., Du, S.-S., Wang, F.-P., et al. (2012). Lipasecoupling esterification of starch with octenyl succinic anhydride. Carbohydrate Polymers, 87(3), 2137e2144.

Please cite this article in press as: Shi, Y., et al., Characterization and emulsifying properties of octenyl succinate anhydride modified Acacia seyal gum (gum arabic), Food Hydrocolloids (2016), http://dx.doi.org/10.1016/j.foodhyd.2016.10.043