European Food Research and Technology

, Volume 236, Issue 1, pp 119–128

Effect of oxidation and esterification on functional properties of mung bean (Vigna radiata (L.) Wilczek) starch

  • Maisa Bushra
  • Xu Xiao Yun
  • Si Yi Pan
  • Arine Hydamaka
  • Miao Wen hua
  • Wang Lu Feng
Original Paper

DOI: 10.1007/s00217-012-1857-x

Cite this article as:
Bushra, M., Yun, X.X., Pan, S.Y. et al. Eur Food Res Technol (2013) 236: 119. doi:10.1007/s00217-012-1857-x

Abstract

The chemical and physicochemical properties of mung bean starch oxidized by sodium hypochlorite and esterified with succinic anhydride were studied. Mung bean starch was modified by oxidation with sodium hypochlorite and esterified with succinic anhydride. The native mung bean starch (NMBS) granules were shown to have an irregular shape, which varied from oval to round to bean shape with a smooth surface. Succinylation led to partial rupture of the granule integrity while oxidation converted the smooth surface of the native granules to a surface with fissures. Swelling capacity improved through succinylation but was reduced after oxidation. Oxidation enhanced solubility; however, succinylation showed no uniform effect throughout the temperature range studied. Both modifications increased hydrophilic tendency and demonstrated decreased gelatinization temperature compared to the NMBS. Oil absorption capacity and syneresis of native starch was enhanced after oxidation but was reduced after succinylation. Both starch types, native and modified, exhibited non-Newtonian behavior, but to a different extent. The gel formation of oxidized starch revealed the highest storage modulus followed by native starch and then succinated starch.

Keywords

Mung bean starch Oxidation Succinylation 

Introduction

Native starches are excellent raw materials; however, they possess some undesirable properties limiting their use in industrial food applications. Often the desired functional characteristic (texture stability, solubility in cold water, thickening power after cooking) cannot be achieved by using a native starch. These limitations can be overcome by physically, chemically, or enzymatically producing modified starches with improved functional properties.

Chemical modifications of starches can be performed by oxidation, esterification, etherification, acid hydrolysis, and cross-linking. Oxidized starches are commonly used in food applications, where neutral tasting, clarity, binding properties, and low viscosity are required. Among oxidizing reagents, sodium hypochlorite is the most popular for commercial use. It is suggested that oxidized starch, especially having a low degree of substitution (DS), is an important component in basic food grade modified starch [1].

Succinated starch which can be produced by the esterification of native starch with succinic anhydride provides a number of desirable properties such as high viscosity, low gelatinization temperature, high thickening power, ability to swell in cold water, freeze–thaw stability, and ability to form good films.

Comprehensive research has been conducted on cassava, cereal, potato, and sweet potato starches because they are readily available and widely used in food and non-food applications [2, 3, 4, 5]. The growing demand for starches in the food industry has created interest in finding new sources for these polysaccharides, such as legume seeds and fruits [6]. Legumes are widely grown and consumed throughout the world owing to their high protein and carbohydrate contents [7, 8].

Among legumes, variations in native starch properties have been reported for cultivars of lentil [9], beans [10], field pea [11], dietary mung bean [12, 13], and different cultivars of black bean, chick pea, lentil, navy bean, smooth pea, and pinto bean [14]. The effects of different chemical modifications on the physicochemical and thermal properties of a starches isolated from jack bean, (Canavalia ensiformis) [15, 16], yam bean (Sphenostylis sternocarpa) [17], and sword bean, (Canavalia gladiata) [18] have been studied. Huang [19] studied the effect of acetylation on function–structure relationship of cowpea, chickpea, and yellow pea starches.

Mung bean (Vigna radiata (L.) Wilczek) or green gram is native to the northeastern India–Burma (Myanmar) region of Asia. Owing to its high protein content, edible seeds of mung bean are now also widely cultivated in Africa, South and North America, Australia, and the United States. Mung bean has a similar chemical composition to the other members of the legume family, with 24 % protein, 1 % fat, 63 % carbohydrate, and 16 % dietary fiber [20]. It is commonly eaten as bean sprouts, and extruded mung bean starch is used in the production of vermicelli or glass noodles, and traditionally, it has been used in the preparation of soup, pancake, and pyeon (Korean jelly-type dessert).

Mung bean, on the other hand, has been primarily looked upon as a protein source rather than as a carbohydrate source, although carbohydrate is the major component of the dry seeds.

Compared to other starch types, there is no reported literature about oxidized and succinated mung bean starch and their functional properties. Limited research has been conducted on native mung bean starch (NMBS), relating mostly to its physicochemical properties and the improvement of noodle quality. The molecular structure and physical properties of mung bean starch isolated by two different techniques, namely sour liquid processing and centrifugation, have been investigated [21]. Yield and recovery, chemical composition, microscopic analysis, and physicochemical properties of starch isolated from whole and dehulled mung bean were determined [13]. Cowpea and mung bean starches were reported to have high intrinsic viscosity and high degree of polymerization of amylose and amylopectins [22]. The effects of a heat-moisture treatment on the formation and physicochemical properties of resistant starch from mung bean (Phaseolus radiatus) have been studied [23]. Physicochemical properties of sonicated mung bean starch were investigated by Chung [24].

The effects of oxidation and succinylation on the physicochemical rheological and thermal properties of mung bean starch have not been studied [25].

The aim of this study was to chemically modify mung bean starch in order to broaden its application in the food industry.

The specific objectives of this research were to obtain basic information on the physicochemical, morphological, thermal, and rheological properties of oxidized and succinated mung bean starch.

Materials and methods

Materials

Mung beans were purchased from local market in Wuhan-Hubei province, China. The seeds were screened manually to remove the damaged ones and other impurities. All chemicals used in this research were of reagent grade and were purchased from Sinopharm Chemical Reagent Co., Ltd., Shanghai, China.

Methods

Mung bean starch isolation

Mung beans (5 kg) were soaked in water (1:3, v/v) at 30 °C for 18 h and then manually peeled. The peeled seeds were blended using 0.05 N NaOH (1:15 w/v) in a Warring blender. The resulting slurry was screened using a 200-μm sieve and left overnight at 4 °C for starch sedimentation. The starch was mixed with water and centrifuged at 3,500 rpm for 15 min. This washing step was repeated for five times; then, the starch was dried overnight in an air drier at 40 °C, then ground to a powder, passed through 75-μm sieve and stored in a tightly closed polythene bag for further analysis.

Starch oxidation

The procedure of Forssel et al. [26] was followed with a slight modification to prepare the oxidized mung bean starch (OMBS). Starch solution (50 % w/v) was heated in a beaker at 35 °C using a heating mantle and mechanical stirrer. The pH was adjusted to 9.5 with 2 M NaOH. Oxidation was achieved by slowly adding 25 ml of an aqueous solution of sodium hypochlorite (NaOCl) (5 % active chlorine) into the starch slurry within 30 min while maintaining the pH at 9.5 with 1 M H2SO4 and temperature at 35 °C. The starch slurry was held at the same pH and temperature for an additional 3 h with stirring. The slurry was then neutralized to a pH of 7.0 with 1 M H2SO4, filtered, washed four times with deionized water, oven-dried at 40 °C for 48 h, ground, passed through 75-μm sieve, and then stored under dry condition for further analysis.

Starch succinylation

Succinated mung bean starch (SMBS) was prepared according to the method of Trubiano [27]. Mung bean starch (50 g, dry weight) was added to 3.3 % w/v sodium carbonate solution with shaking; then, 3.3 % w/v of succinic anhydride was added, and shaking was continued for 14 h at 25 °C. HCl 0.2 N was used to adjust the pH to 7.0; then, sample was centrifuged for 3 min at 3,500 rpm, washed four times with distilled water, oven-dried for 48 h at 40 °C, ground, passed through 75-μm sieve, and then stored under dry condition for further analysis.

Carboxyl content

The carboxyl content was determined as described by Parovuori et al. [28]. OMBS was suspended in 0.01 M HCl to prepare 20 % w/v suspension, stirred for 30 min, filtered through porous glass filter, and then, the remaining starch paste was washed with distilled water until it was free of chloride ions which was checked by silver nitrate test. The washed sample was transferred to Erlenmeyer flask and dispersed by distilled water (300 ml), then gelatinized in a boiling water bath with continuous stirring for 20 min. The hot starch paste was titrated with 0.1 M NaOH to a pH of 8.3 using a pH meter. NMBS was used for the determination of the blank value following the same procedure.
$$ {\text{Carboxyl}}\,{\text{content}} = \frac{{({\text{sample}}\,{\text{titrate}} - {\text{blank}}\,{\text{titrate}})\,{\text{ml}} \times {\text{alkali}}\,{\text{molarity}} \times 0.045 \times 100}}{{{\text{weight}}\,{\text{of}}\,{\text{sample}}\, ( {\text{g)}}}} $$
(1)

Degree of succinylation

The method of Genung and Mallat [29] was employed to determine the succinyl group content and the DS of the SMBS. Starch sample (1 g) was added to 50 ml ethanol (75 % v/v) in a 250-ml conical flask, and the flask was loosely stoppered. The mixture was refluxed for 30 min at 50 °C. After cooling to room temperature, 40 ml of KOH 0.5 M was added and the mixture was held for 72 h with occasional shaking. The mixture was titrated with 0.5 M HCl to disappearance of the pink color using phenolphthalein as an indicator and re-titrated after 2 h to account for alkali that could leach from the starch sample. NMBS was used for the determination of the blank value following the same procedure.
$$ {\text{Succinylation}}\,( {\text{\%)}} = \frac{{({\text{blank}}\,{\text{titrate}} - {\text{sample}}\,{\text{titrate}})\,{\text{ml}} \times 0.1 \times {\text{acid}}\,{\text{normality}} \times 100}}{{{\text{weight}}\,{\text{of}}\,{\text{sample}}\, ( {\text{g)}}}} $$
(2)
$$ {\text{DS}} = \frac{{162 \times {\text{succinylation}},\,(\% )}}{{10.000 - (99 \times {\text{succinylation,}}\,(\% ))}} $$
(3)
where sample titrate is the ml of 0.5 M HCl used to titrate sample; blank titrate is the ml of 0.5 M HCl used to titrate blank

Amylose content

Amylose content of native and modified mung bean starch was measured according to the method of McGrance et al. [30] as modified by Hoover and Ratnayake [14]. Lipid-free starch (20 mg) and a series of mixtures of pure potato amylose and amylopectin (0–100 % amylose) were used in this experiment. The absorbance at 600 nm of the samples was determined, and then, the standard curve of the absorbance versus percentage amylose (w/w) for the mixtures of the amylose and amylopectin with iodine was plotted. The total amylose content of the native and modified mung bean starch was calculated from the regression equation of the standard curve as follows:
$$ ay = bx + c $$
where x = % amylose of the native or modified mung bean starch and y = absorbance of the native or modified mung bean starch at 600 nm

Granule morphology

Scanning electron micrographs of starch samples were obtained using a scanning electron microscope (SEM; JEOL, JSM-6390/LV; Japan). The samples were sprinkled on double-sided tape, fixed to an aluminum stub, and then coated with gold. The images were taken at an accelerating voltage of 10 kV [15].

Functional properties of native and modified starches

Swelling power and solubility

The method according to Waliszewki et al. [31] was used with a slight modification. Starch sample (0.2 g) was added to a centrifuge tube and weighed (W1); then, distilled water (18 ml) was added. The resultant suspension was heated for 30 min at 60 °C with continuous stirring, cooled to room temperature in ice water and centrifuged at 1,252×g for 20 min. An aliquot of 5 ml of the supernatant was dried in an evaporating dish at 103 °C until constant weight was obtained. The remaining paste in the tube was weighed (W2). This procedure was repeated at 70, 80, and 90 °C using the above-described protocol. Swelling power and solubility were determined according to the following equations:
$$ {\text{Swelling}}\,{\text{ power}} = \frac{{W_{2} - W_{1} }}{{{\text{Weight}}\,{\text{of}}\,{\text{sample}}\, ( {\text{g)}}}} $$
(4)
$$ {\text{Solubility}}\,\% = \frac{{{\text{dried}}\,{\text{supernatent}}}}{{{\text{Weight}}\,{\text{of}}\,{\text{sample}}\, ( {\text{g)}}}} \times 100 $$
(5)

Water and oil absorption

The oil and water absorption capacities of the NMBS and its derivatives were determined following the method of Beuchat [32]. A starch sample (1 g) was mixed with 10 ml of distilled water and/or oil (soybean oil, density 0.9 g/ml) using Variwhirl mixer for 1 min and left for 2 h at room temperature. The volume of the supernatant was recorded. The mass of oil or water absorbed was expressed as g/g starch on a dry weight basis.

Effect of freeze–thaw cycles on gel syneresis

The method of Huang [19] was used to assess freeze–thaw stability. Starch mixtures (5 % w/v) prepared using distilled water were equilibrated at 25 °C for 30 min; then, 2 ml starch slurry was poured into a 4 ml tube, vigorously stirred and heated in a boiling water bath for 30 min with stirring. The slurry was cooled in ice water to improve starch retrogradation, kept at −20 °C for 20 h and thawed at 30 °C for 3 h. Free water was removed from the gel by placing it on several layers of tissue paper for 10 min. Five freeze–thaw cycles were performed. Syneresis was calculated as the ratio of free water to original paste weight.

Thermal properties

A Differential Scanning Calorimeter (DSC; NETZSCH 204F1; Germany) equipped with a thermal analysis data station was used to study the gelation properties [onset temperature (To), peak temperature (Tp), conclusion temperature (Tc], and enthalpy of gelatinization (ΔHg, J/g)) of the native and modified starches.

Starch sample was weighed into aluminum DSC pans (ratio of 1:3, starch to distilled water). The aluminum pans were hermetically sealed, reweighed and left for 24 h at room temperature to ensure equilibration, and then tested at a rate of 5 °C/min from 30 to 110 °C. An empty aluminum pan was used as a reference.

Rheological properties

Preparation of starch pastes

Starch–water dispersion (5 % w/v) was placed in a tightly closed beaker to minimize evaporation and then heated in a boiling water bath for 30 min with continuous stirring.

Flow behavior

A TA-RHEOMETER (AR2000EX; New Castle; DE, USA and Crawley, UK) was used to study the flow behavior of NMBS and its modified forms. The hot starch pastes were held at 50 °C for 15 min; flow curves were determined using a shear rate range of 1–300 s−1. To describe the steady shear rheological properties of the samples, the power law (Eq. 1) and Casson models (Eq. 2) were used.
$$ \sigma = Kr\prime^{n} $$
(6)
$$ \sigma^{0.5} = k_{\text{oc}} + (k_{\text{c}} \gamma \cdot )^{0.5} $$
(7)
where σ is the shear stress (Pa); \( r\prime \), the shear rate (s−1); K, the consistency index (Pa sn); n, the flow behavior index (dimensionless); (kc), the Casson plastic viscosity (Pa s); and (koc), Casson yield stress (Pa).

Determination of mechanical spectra of starch gels

The mechanical spectra of the native and modified mung bean starch gels were determined by placing hot pastes of the samples in the plate and allowing to stand for 15 min at 30 °C with the edges covered with paraffin oil to minimize water evaporation. Measurements were taken within the linear viscoelastic range at a constant strain of 0.03 % and a frequency range from 0.1 to 12 Hz.

Statistical analyses

Excel software package (MS-Office XP) was used for data analysis. Analysis of variance was performed to calculate the significant differences among means, and LSD (p < 0.05) was used to separate means (SPSS 17) [33]. Analyses were done in triplicate.

Results and discussion

Amylose content

The amylose content of NMBS (34.7 %) is in agreement with the range of values reported in other studies on NMBS [12, 21, 34]. Succinylation reduced amylose content to 30.5 % probably due to structural disintegration and losses during modification processes. Similar observation has previously been reported for succinylation of hybrid maize starch [35].

Amylose content increased after oxidation to 36 % due to the depolymerization of high-molecular-weight amylose molecules during hypochlorite oxidation which result in short amylose chain that could still be identified in the measurement [36, 37].

Degree of modification

Carboxyl content and DS as calculated from Eqs. 1 and 3 provided by oxidation and succinylation were found to have average values of 0.05 and 0.1, respectively. The low carboxyl content of OMBS might be due to the relatively high amylose content of NMBS. Kuakpetoon and Wang [38] claimed that the oxidizing agent was consumed first to depolymerize the amylose present in the amorphous lamella of the outer layers of the starch granules before the formation of carboxyl group. Similar observation was reported by Gonzalez-Soto et al. [39] in banana starch with 37 % amylose content.

Granules morphology

SEM was used to observe the outer structure of the samples (Fig. 1). The native starch granules appeared to have irregular shapes, which varied from oval to round to bean shape with smooth surfaces free of fissures. Succinylation led to complete rupture of some granules, while the granular integrity of OMBS was not affected, but fissures could be observed on the surface of some granules at the studied level of active chlorine. This may due to low carboxyl content of oxidized starch. Similar results were obtained by Rutenberg and Solarek [40] who reported that the surfaces of corn and potato starch granules were unaffected by hypochlorite oxidation up to 6 % active chlorine. Vanier et al. [41] reported that the surface of bean starch granules was unaffected by hypochlorite oxidation at the level of 0.5 and 1.0 % active chlorine while the 1.5 % active chlorine level showed granules with rough surface.
Fig. 1

Scanning electron micrographs of a native mung bean starch (NMBS), b succinated mung bean starch (SMBS), c oxidized mung bean starch (OMBS)

Functional properties

Effect of temperature on swelling power and solubility of NMBS and its derivatives

The effect of temperature on the swelling power of NMBS and its derivatives is illustrated in Fig. 2a. Succinylation increased the swelling power throughout the studied temperature range. Increment in swelling power due to succinylation (49.1 g/g) at 60 °C was more pronounced than that of oxidation at the same temperature. Succinylation imparts a hydrophilic character to the NMBS. This would account for the difference in the bonding forces within the granules according to the modification which influence the swelling and solubility of the starch granules. OMBS displayed lower swelling power (1.55 g/g at 60 °C) compared to NMBS (3.5 g/g at 60 °C). A similar reduction in swelling power after oxidation has been reported for various starches [42, 43].
Fig. 2

Effect of temperature on a swelling power and b solubility of native mung bean starch (NMBS), oxidized mung bean starch (OMBS), succinated mung bean starch (SMBS)

Oxidation increased the solubility of NMBS from 5 to 10 % at 90 °C (Fig. 2b). Starch solubility was enhanced by structural disintegration which probably weakens the starch granules, thus increasing solubility after modifications.

SMBS solubility was reduced, following the increase in temperature (1 % at 90 °C). A similar trend for succinated starch heated to 80 °C was shown by Olayinka et al. [44].

Water and oil absorption capacity

Water and oil absorption capacities of NMBS and its derivatives are presented in Fig. 3. Water absorption capacity of the NMBS (1 g/g) increased, following oxidation (2.2 g/g) and succinylation (2.4 g/g); meanwhile, oil absorption capacity (1.7 g/g) increased, following oxidation (1.8 g/g) but decreased after succinylation (0.9 g/g). Increment in water absorption capacity was attributed to the introduction of functional groups on the starch structure which improve its binding and absorption ability, thus increasing hydrophilicity of the starch. Water binding ability can provide body and texture to foodstuffs enhancing starch use as a fat replacer. Long-chain hydrophilic succinyl substituents may impair oil absorption by succinated derivatives, leading to reduction in oil absorption capacity by SMBS. Oxidized mucuna bean (Mucuna pruriens) starch was observed to have reduced water absorption capacity (1.6 g/g) [42], when compared to the oxidized mung bean starch. However, oxidation did not affect the water and oil absorption capacity of great northern bean starch [45], while a decreased effect was observed for Mucuna Sloanei starch [46]. Succinylation was also found to have a higher effect on water and oil absorption capacity in mung bean starch than hybrid maize starch [35]. Results in this study are in accordance with observations reported by other researchers for different starches [15, 47].
Fig. 3

Water and oil absorption capacity of native mung bean starch (NMBS), oxidized mung bean starch (OMBS), succinated mung bean starch (SMBS)

Freeze–thaw stability

The NMBS gel syneresis was reduced from 31 % w/w (after 5 freeze–thaw cycles) to 13 % w/w after succinylation but increased after oxidation to 50.1 % w/w (Fig. 4).
Fig. 4

Effect of freeze–thaw cycles on native mung bean starch (NMBS), oxidized mung bean starch (OMBS), succinated mung bean starch (SMBS)

The water-holding capacity of the starch gel could be enhanced through the reduction of starch retrogradation by the introduction of the succinyl group during the esterification reaction. This in turn prevents alignment and movement of the starch chain via reducing the interchain bonding potential. In this study, mainly because of the high amylose content of the starch and low DS associated with the modified starches, the relatively high syneresis compared to others research, ranging from nil to 37.41 % w/w, was observed [48, 49, 50, 51]. The retrogradation of the starch molecules can either be increased or decreased by oxidation through two different mechanisms [36]. The degradation of the long-chain amylopectin or even amylose molecules in the amorphous lamellae could produce dextrin with an appropriate length for re-association which could boost starch retrogradation. In contrast, the formation of carboxyl or carbonyl groups on oxidized starch molecules would hinder the chain association that results in less affinity to retrogradation. Because of a low carboxyl content and high amylose content, the OMBS showed the highest gel syneresis among all native and modified starches.

Thermal properties

Gelatinization properties of NMBS and its derivatives are shown in Table 1. An important feature of succinated mung bean starch is that, by selective succinylation, the transitions temperatures (To, Tp, and Tc) can be reduced for advantages in energy consumption and food functionality; this can be confirmed by the reduction in the enthalpy of gelatinization (ΔHg) which represents the amount of energy required for the gelatinization process.
Table 1

Gelatinization characteristics of native (NMBS), oxidized (OMBS), and succinylated mung bean starches (SMBS)

Type of starch

Transition temperaturesa

TC − To (°C)b

ΔHg (J/g)c

To (°C)

Tp (°C)

TC (°C)

NMBS

58.5 ± 0.1a

66.1 ± 0.1a

71.7 ± 0.1a

13.2 ± 0.1a

17.5 ± 0.005a

OMBS

57.1 ± 0.1b

66 ± 0.05a

68.0 ± 0.1b

10.9 ± 0.1b

16.9 ± 0.005b

SMBS

53.7 ± 0.1c

57.3 ± 0.1b

60.9 ± 0.1c

7.2 ± 0.1c

12.3 ± 0.1c

All values are means of triplicate determinations ± SD. Means within columns with different letters are significantly different (p < 0.05)

a To, Tp, and Tc are the temperatures at the onset, midpoint, and end of gelatinization, respectively

b Tc − To indicates the gelatinization temperature range

c ΔHg indicates the enthalpy of gelatinization

Meanwhile, oxidation showed no significant reduction (p > 0.05). The decline in the gelatinization temperature following succinylation could be attributed to the weakness of the biopolymer structure that develops with the introduction of the bulky groups, with the simultaneous structural rearrangement that results in a weakening of intragranular and intergranular binding forces within the starch molecules; thus, less energy would be required for gelatinization.

Rheological properties

Flow behavior

Rheological properties of mung bean starch and its derivatives were investigated using a TA-rheometer.

All starches (native and modified) exhibited non-Newtonian, shear-thinning flow behavior, where the viscosity decreased when shear rate increased, with the tendency to yield stress.

Power law and Casson model equations were used to explain the flow properties of NMBS and its derivatives (Table 2). A power law index of 1 refers to Newtonian behavior; a decreasing n value denotes a stronger shear-thinning behavior indicating non-Newtonian (pseudoplastic) nature. The NMBS paste shows the lowest n value that increased following succinylation and oxidation, respectively, indicating a reduction in their resistance to flow a decrease in viscosity. Native starch showed the highest consistency coefficient and yield stress after cooling to 50 °C, which is attributed to the retrogradation of amylose long chains that increases the tendency of the aqueous starch dispersion to form a paste with high strength [52]. Succinated starch as compared to the native starch has been subjected to re-arrangement because of introducing of functional groups that limits the formation of such binding forces; hence, it is less prone to such retrogradation resulting in a paste with lower viscosity (0.48 Pa s) than NMBS (0.54 Pa s) did.
Table 2

Parameters of the power law and Casson models describing the flow curves of native mung bean starch (NMBS), oxidized mung bean starch (OMBS), and succinated mung bean starch (SMBS). Pastes (5 % concentration) at 50 °C

Samples

Power law

Casson model

R2

Consistency coefficient (k) (Pa sn)

Flow behavior index (n) (−)

R2

Casson yield stress (koc, pa)

Casson plastic viscosity(Pa s) (ηc)

NMBS

0.99

20.73 ± 0.01a

0.37 ± 5.005a

0.96

4.9 ± 0.1a

0.54 ± 0.01a

OMBS

0.99

2.49 ± 0.01b

0.47 ± 0.01b

0.99

1.62 ± 0.01b

0.30 ± 0.05b

SMBS

0.99

9.11 ± 0.01c

0.44 ± 0.005c

0.97

3.24 ± 0.01c

0.48 ± 0.01c

All values are means of triplicate determinations ± SD. Means within columns with different letters are significantly different (p < 0.05)

Low viscosity associated with OMBS (0.30 Pa s) compared to the native starch can be attributed to the starch–starch interactions that are already reduced by thermal and shear forces, not allowing the short amylose chain, depolymerized by oxidation, to re-associate.

Frequency sweep

The storage G′ and loss G″ modulus in the viscoelastic solids assess the stored energy, signifying the elastic portion, and the heat dissipated energy that characterizes the viscous portion, respectively. The frequency dependence of G′ and G″ provides valuable information about gel structure. The changes in G′, G″, and phase angle (δ) of starch gels are shown in Fig. 5. It is apparent that both moduli increased with the frequency. As shown in Fig. 5a, b, the G′ is higher than the G″ in the whole frequency range that suggests that the elastic behavior of all samples predominates its viscous behavior and the swollen granules of the samples exhibited mechanical stiffness at 30 °C. G′ of OMBS was higher than that of NMBS and SMBS, respectively, indicating OMBS produced a strong gel at 30 °C during the cooling period. Guerra-Della [52] reported that this can be attributed to the starch reorganization of amylose chains that solubilized during the heating period; in addition, the introduction of carboxyl and carbonyl groups can retard recrystallization resulting in a gel with higher response of storage modulus. The ratio of loss and storage modules (tan δ) or phase angle is a measure of the energy lost compared to energy stored in deformation. As shown in Fig. 5(c), the values of tan δ, at frequency range from 0.1 to 12 Hz, were found to be 0.08, 0.2, and 0.6, for OMBS, NMBS, and SMBS, respectively, which confirm the increase in gelling properties of slightly oxidized starch gel at 30 °C, a temperature that usually is used in dessert home cooking.
Fig. 5

Plots of a storage modulus (G′), b loss modulus (G″), and c: phase angle (δ) versus frequency (Hz) of native mung bean starch (NMBS), oxidized mung bean starch (OMBS), succinated mung bean starch (SMBS). Starch gels (5 % w/v) at 30 °C

Conclusions

Chemical modifications of mung bean starch resulted in different properties with respect to the native starch. Reduction of the gelatinization temperature was apparent in modification by succinylation; thus, modified mung bean starch can be used as thickening and stabilizing agents in food product including ice creams, fruit jellies, and baked products. Succinated mung bean starch can also have application as carbohydrate-based fat replacer because of its high binding capacity of water that can add volume, thicken, and stabilize foods. Oxidized starch showed an apparent increase in starch solubility which enhances its digestibility. All starches, native and modified, showed a non-Newtonian behavior, in which viscosity decreases with increased stress (breakdown of structural units in a food due to the hydrodynamic forces generated during shear). Thus, it can be used in several food products like salad dressing, ketchup, and some concentrated fruit juices. Owing to their different physicochemical and rheological properties, the modified starches may act to improve the textural characteristics of food products, thus improving the use of mung bean starch in food processing.

Acknowledgments

The first author is grateful to Professor Pan Si Yi, the head of the collage of Food Science and Technology, Huazhong Agricultural University, Wuhan, China, for offering the financial support and required facilities to conduct this research. Thanks were also due to Dr. Xu Xiao Yun for her support and suggestion. Acknowledgements with gratitude are due to all members of food analysis laboratory in Huazhong Agricultural University-Wuhan-Hubei, China, for their enthusiastic help during the period of the study.

Conflict of interest

The authors declare that they have no conflict of interest.

Copyright information

© Springer-Verlag Berlin Heidelberg 2012

Authors and Affiliations

  • Maisa Bushra
    • 1
  • Xu Xiao Yun
    • 1
  • Si Yi Pan
    • 1
  • Arine Hydamaka
    • 2
  • Miao Wen hua
    • 1
  • Wang Lu Feng
    • 1
  1. 1.College of Food Science and TechnologyHuazhong Agricultural UniversityWuhanChina
  2. 2.Department of Food Science, Faculty of Agricultural and Food ScienceUniversity of ManitobaWinnipegCanada

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