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Interaction of wheat and rice starches with yellow mustard mucilage
Food Hydrocolloids 17 (2003) 863–869 www.elsevier.com/locate/foodhyd
Interaction of wheat and rice starches with yellow mustard mucilage Huijuin Liua, N.A. Michael Eskina,*, Steve W. Cuib b
a Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Man., Canada R3T 2N2 Food Research Program, Agri-Food and Agriculture Canada, 93 Stone Road West, Guelph, Ont., Canada N1G 5C9
Received 16 October 2002; accepted 21 May 2003
Abstract The effect of yellow mustard mucilage (YMM) on gelatinization and retrogradation of wheat and rice starches were studied. Considerable interactions were observed between YMM and wheat and rice starches which were accompanied by a marked increase in viscosity. DSC studies showed that the presence of YMM did not affect peak gelatinization temperature ðTp Þ of wheat and rice starches, but slightly increased melting enthalpy ðDHÞ and the phase transition temperature range ðTc 2 T0 Þ: Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM– locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. The swelling power as well as solubilized starch and amylose were decreased for both starches in the presence of YMM. Syneresis in wheat and rice starches was also decreased by the presence of YMM. q 2003 Elsevier Ltd. All rights reserved. Keywords: Yellow mustard mucilage; Starches interactions; Rheological properties; Gelatinization; Retrogradation; Syneresis
1. Introduction The physical properties of native starches and their colloidal sols limit their usefulness in many commercial applications. Aggregation and recrystallization of starch molecules can lead to increased rigidity and syneresis of the starch paste. This phenomenon of retrogradation is further exacerbated during freezing with detrimental effects to the texture, acceptability and digestibility of starch-containing foods (Berry, I’Anson, Miles, Morris, & Russell, 1988). Chemical modification of starch can improve cooking characteristics, decrease retrogradation as well as increase freeze – thaw stability of starch pastes. However, obtaining regulatory approval for new chemical reagents combined with consumer concerns regarding the chemical treatment of foods has led to alternative ways to modify starch such as blending with other hydrocolloids. Hydrocolloids have been shown to alter the gelatinization and retrogradation characteristics of starches (Alloncle, Lefebvre, Llamas, & Doublier, 1989; Biliaderis, Arvanitoyannis, Izydorczyk, & Prokopowich, 1997; Christianson, Hodge, Osborne, & Detroy, 1981; Ferrero, Martino, & Zaritzky, 1994; Yoshimura, Takaya, & Nishinari, 1996, * Corresponding author. Tel.: þ 1-204-474-8078; fax: þ1-204-474-7593. E-mail address: [email protected] (N.A.M. Eskin). 0268-005X/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-005X(03)00107-3
1999). Christianson et al. (1981) found guar gum, xanthan and carboxymethyl cellulose hastened the onset of initial paste viscosity and substantially increased final peak viscosity of wheat starch due to the greater leaching out of amylose. Biliaderis and co-workers (1997) showed that polysaccharides varying in molecular size (xanthan, bglucan, arabinoxylan and guar gum) did not affect the gelatinization temperature of waxy maize and wheat starches. However, these hydrocolloids increased the phase transition temperature range ðTc 2 T0 Þ and the melting enthalpies ðDHÞ of the starch crystallites. Yoshimura et al. (1998) found that the addition of a small amount of konjac-glucomannan prevented the development of syneresis during the storage of corn starch. Gudmundson, Eliasson, Bengtsson, and Aman (1991) reported rye arabinoxylan had no effect on DH of waxy maize starch but slightly reduced the DH of maize and potato starches while slightly increasing DH of wheat starch. A number of studies have demonstrated synergistic interactions between native starches and gums resulting in significant increases in viscosity of the starch pastes (Alloncle et al., 1989; Christianson et al., 1981; Crossland & Favor, 1948; Sajjan & Rao, 1987; Sandstedt & Abbott, 1964; Sudhakar, Singhal & Kulkarni, 1996). Modifications of starch gelatinization and retrogradation characteristics by hydrocolloids make
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these combinations useful as food ingredients (Fanta & Christianson, 1996). Previous research in our laboratory showed yellow mustard mucilage (YMM) exhibited unique rheological properties with considerable potential as a food thickener and stabilizer. YMM was shown to be composed of both neutral sugars and uronic acids (Cui, Eskin, & Billaderis, 1993). The monosaccharides identified were primarily glucose, arabinose, xylose, rhamnose, galactose and mannose (Cui, Eskin, & Billaderis, 1993; Siddiqui, Yiu, Jones, & Kalab, 1986; Theander, Aman, Miksche, & Yasuda, 1977; Vose, 1974). Small strain oscillatory rheological tests showed significant synergistic interactions between YMM and locust bean gum (LBG) resulting in a marked increase in viscosity (Cui et al., 1995). The optimum ratio for synergism was 9:1 for YMM:LBG systems. Further work confirmed a marked interaction between YMM and native and acetylated pea starch which increased starch paste viscosity and altered the degree of pseudoplasticity of the corresponding starch pastes (Liu & Eskin, 1998). This study examined the effects of YMM on the gelatinization and retrogradation characteristics of wheat and rice starches including pasting and thermal properties, swelling and solubility, gel structure and syneresis.
2. Materials and methods Commercial wheat and rice starches and LBG were obtained from Sigma (St Louis, MO). YMM was extracted following the patented procedure of Cui, Eskin, Han, Duan, and Zhang (2001), freeze-dried and stored in a desiccator. Pasting properties of starch suspensions (8%, w/w) with or without added YMM gum (0.2, 0.5 and 0.8%, w/w) or YMM mixed with LBG (9:1; 0.5%), were monitored using a rapid Visco-analyzer model 3D (RVA) (Newport Scientific Pty, Ltd, Narrabeen, Australia). Samples were placed in an aluminum RVA sample cannister. A programmed heating and cooling cycle was used, in which the sample was held at 50 8C for 1 min.; heated to 95 8C for 3 min 42 s; held at 95 8C for 2 min 30 s; cooled to 50 8C for 3 min 48 s; then held at 50 8C for a further 2 min. Thermal analyses were conducted on granular starch dispersions and aging/hydrocolloid gels using a DuPont thermal analyzer (9900; Wilmington, DE) equipped with a DSC cell (Dupont 910). Starch (40%, w/w) was suspended in previously prepared gum solutions (0.2, 0.5 and 0.8% w/w), with an aliquot of the starch dispersions (10 mg) pipetted into DSC pans and hermetically sealed. The starch suspensions were heated from 20 to 120 8C at 10 8C/min to gelatinize the granules. The onset temperature, peak temperature, conclusion temperature as well as transition enthalpy ðDHÞ were recorded. After DSC testing, the samples were stored at 5 8C for 3, 6, and 15 days. The aged starch/hydrocolloids gels were re-scanned from 20 –120 8C at 10 8C/min to estimate the extent of
retrogradation from the magnitude (transition enthalpy, DH) of the amylopectin endotherm. After RVA testing, the starch pasted in the sample cannister was covered and held at 5 8C in a refrigerator for 24 h. Gel texture was determined using a TA-TX2 Texture Analyzer (Stable Micro Systems, Godalming, Surrey, England). The gel was compressed at a speed of 1.0 mm/s to a distance of 10 mm with a cylindrical flat-ended probe of 6 mm diameter. The peak height at 10 mm compression was termed hardness. The negative area from the curve during the retraction of the probe was termed adhesiveness. Swelling power was determined following the method of Sasaki et al. with slight modification (Sasaki, Yasui, & Matsuki, 2000). Starch gum dispersions (1.25% starch and 0.031, 0.078, 0.125% gum) were put into tubes with coated screw caps and heated in a boiling water bath for 10 min. A starch –water mixture similarly treated served as the control. After cooling in ice for 5 min, samples were centrifuged at 11,200g at 5 8C for 15 min and the supernatant removed for measurement of solubilized starch. Swelling power was determined as the ratio in weight of the wet sediment compared to the initial weight of the dry starch. The method of Gibson et al. was used to determine total carbohydrates in the recovered supernatant (Gibson, Solah, & McCleary, 1997), while amylose content was measured following the colorimetric method of Chrastil (1987). The extent of syneresis was measured on starch suspensions (4% w/w) in water or gum solutions (0.2, 0.5, and 0.8%) heated in a boiling water bath for 10 min. Following cooling, samples were stored at 5 8C for 15 days. Syneresis was estimated by the weight of water separated and expressed as the ratio of separated water to starch gel. Data reported were average values of replications.
3. Results and discussion The effects of YMM on the amylograms of wheat and rice starches are shown in Figs. 1 and 2 and Table 1. Both YMM (0.8%, w/w) or YMM– LBG mixture (9:1, 0.5% w/w) showed negligible viscosity using the amylograph. However, addition of the hydrocolloid to wheat or rice starches resulted in the onset of viscosity at a lower temperature compared to the starch control. The magnitude of the onset temperature of the amylograms decreased depending on the concentration of the hydrocolloid. For example, the higher the concentration of YMM was, the more the onset temperature decreased. Normally, starch does not exhibit viscosity during the early stages of granule swelling (55 – 70 8C). However, a number of researchers showed that when starch was heated in a viscous media containing CMC, xanthan gum, guar gum or LBG, an increase in viscosity occurred earlier during the heating period due to interaction with the gum (Alloncle et al., 1989; Christianson et al., 1981; Crossland & Favor, 1948). Christianson et al. (1981) attributed the earlier development of viscosity to the changing starch granule structure by
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Fig. 1. Effect of YMM on the amylogram of wheat starch. Starch concentration: 8%(w/w); YMM concentration: 0.2, 0.5, 0.8%, (w/w); 2gummixture: YMM:LBM ¼ 9:1, 0.5%, (w/w).
the gum medium. Bean and Yamazaki (1978) found a rapid increase in granule swelling between 58 and 70 8C which corresponded to the onset of viscosity produced in the wheat starch – CMC amylograph curve. In this study, however, addition of YMM inhibited the swelling of wheat and rice starches (Table 4). The decrease in the onset temperature of amylograms by YMM (Figs. 1 and 2) may be due to interaction of YMM with the small amount of amylose released by the limited swelling of the starch granules. Compared to YMM (0.5% w/w), addition of the gum mixture (0.5%, YMM:LBG ¼ 9:1) into starch further hastened the onset of initial paste viscosity. Addition of YMM resulted in a marked increase in peak and cool paste viscosities for both wheat and rice starches (Figs. 1 and 2). For example, the viscosity of wheat starch increased 1.4, 1.9 and 2.3-fold in the presence of 0.2. 0.5 and
0.8% YMM. In the case of rice starch the increase in viscosity was slightly higher corresponding to 1.5, 2.2 and 2.8-folds in the presence of 0.2, 0.5 and 0.8% YMM. For both wheat and rice starches, the gum mixture (YMM:LBG ¼ 9:1, 0.5%) produced a higher viscosity compared to YMM (0.5%). An increase in starch peak viscosity in the presence of a hydrocolloid has been reported previously (Alloncle et al., 1989; Liu & Eskin, 1998; Sasaki et al., 2000). Christianson et al. (1981) attributed the increase in viscosity to interaction between exudate from the starch granule (solubilized amylose and low-molecularweight amylopectin) and gums. A second explanation given was that addition of thickening gums enhanced the forces being exerted on the starch granules in the shear field compared to starch – water suspension with equal starch concentrations. Alloncle et al. (1989) proposed a model to
Fig. 2. Effect of YMM on the amylogram of rice starch. Starch concentration: 8% (w/w); YMM concentration: 0.2%, 0.5%, 0.8% (w/w); 2 gum mixture: YMM:LBM ¼ 9:1, 0.5% (w/w).
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Table 1 Effect of YMM on the pasting properties of wheat and rice starches Starcha
Peak viscosity (RVU)
Trough (RVU)
Breakdown (RVU)
Final viscosity (RVU)
Setback (RVU)
Peak time (min)
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixtureb
58.67 83.42 109.92 136.58 143.25
49.25 72.92 99.42 125.50 137.50
9.42 10.50 10.50 11.08 5.75
64.08 90.50 120.58 151.75 152.00
14.83 17.58 21.17 26.25 14.50
6.53 7.33 7.73 7.80 8.13
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixtureb
46.00 70.08 99.25 126.83 131.67
43.58 69.08 96.33 120.33 128.42
2.42 1.00 2.92 6.50 3.25
66.17 102.92 135.92 157.75 153.42
22.58 33.83 39.58 37.43 25.00
6.53 6.87 7.13 7.60 8.53
a b
Starch concentration: 8%, w/w. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
interpret these effects in which the gums were located within the continuous phase of the starch pastes. In this model, the volume of the continuous phase accessible to the gum was reduced, yielding an increase in gum concentration within the continuous phase, which was accompanied by a dramatic increase in viscosity. Yoshimura et al. reported that addition of hydrocolloids increased the effective starch concentration by immobilizing water molecules (Yoshimura, Takaya, & Nishinari 1996). The marked increase in viscosity following addition of YMM could be similarly explained. YMM could also form a strong entanglement with amylose released from the starch granule and with swollen (amylopectin) particles. Both of these effects could result in the increased viscosity of the starch paste. The DSC results for starches with and without added hydrocolloids are summarized in Table 2. The gelatinization temperature and enthalpy ðDHÞ of rice starch was higher than that for wheat starch. Addition of YMM did not affect the peak temperature ðTp Þ of wheat or rice starch. A slight increase in melting enthalpy ðDHÞ and phase transition
temperature range ðTc 2 T0 Þ was observed, however, when YMM was added compared to the control. The effect of hydrocolloids on gelatinization properties of starches has been observed previously. Biliaderis et al. (1997) reported that the addition of polysaccharides (xanthan, b-glucan, arabinoxylan and guar gum) at levels ranging from 1 to 2% on a starch basis did not affect the gelatinization temperature of waxy maize and wheat starches. However, they did observe an increase in the phase transition temperature ðTc 2 T0 Þ and melting enthalpy ðDHÞ of the starch crystallites. Gudmundsson et al. showed that the addition of rye arabinoxylan at levels of 1 – 2%, on a dry basis, increased DH of wheat starch, slightly decreased DH of maize and potato starches, but had no effect on DH of waxy maize starch (Gudmundsson, Eliasson, Bengtsson, & Aman, 1991). Liu and Eskin (1998) found that YMM (0.35%) did not change the gelatinization temperature of pea starch. Sugars and polyhydroxy compounds have been shown to increase the gelatinization temperature of starch (Kim & Walker, 1992; Spies & Hoseney, 1982). The stabilizing effect of polyhydroxy
Table 2 Effect of YMM on the thermal properties of wheat and rice starches Starcha
Retrogradation DH (J/g)
Gelatinization Tp (C)
DH (J/g)
Tc 2 T0
Day 3
Day 6
Day 15
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixturec
61.27 ^ 0.04b 61.04 ^ 0.12 61.49 ^ 0.31 61.51 ^ 0.20 61.43 ^ 0.35
9.99 ^ 0.24 10.80 ^ 0.08 10.72 ^ 0.32 10.72 ^ 0.21 10.58 ^ 0.14
31.21 ^ 0.41 35.34 ^ 0.85 36.16 ^ 1.25 36.02 ^ 0.10 35.80 ^ 0.71
3.67 ^ 0.13 3.55 ^ 0.20 3.63 ^ 0.06 3.89 ^ 0.31 4.03 ^ 0.41
5.06 ^ 0.18 4.94 ^ 0.41 5.01 ^ 0.32 4.73 ^ 0.11 4.63 ^ 0.13
6.32 ^ 0.09 5.72 ^ 0.24 5.38 ^ 0.43 5.17 ^ 0.35 5.24 ^ 0.20
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
74.31 ^ 0.24 74.49 ^ 0.06 74.51 ^ 0.11 74.57 ^ 0.30 74.43 ^ 0.21
11.59 ^ 0.09 12.36 ^ 0.28 12.55 ^ 0.13 12.62 ^ 0.34 12.48 ^ 0.39
28.52 ^ 0.79 32.30 ^ 1.13 33.73 ^ 0.16 33.45 ^ 0.67 34.06 ^ 0.35
4.95 ^ 0.17 4.67 ^ 0.14 4.52 ^ 0.26 4.54 ^ 0.41 4.87 ^ 0.30
6.67 ^ 0.43 6.50 ^ 0.15 6.55 ^ 0.22 6.21 ^ 0.09 6.00 ^ 0.39
7.95 ^ 0.17 7.13 ^ 0.22 7.04 ^ 0.37 6.90 ^ 0.21 6.45 ^ 0.40
a b c
n ¼ 2: Starch concentration: 40%, w/w. Standard deviation of duplicate. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
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Table 3 Effect of YMM on the gel texture of wheat and rice starches Starcha
Hardness
Adhesiviveness
Chewiness
Resilience
Springiness
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixtureb
24.08 32.09 29.04 30.66 2.16
2 57.74 2 82.16 2 106.00 2 103.09 2 26.05
11.11 12.50 12.36 13.04 1.01
0.098 0.065 0.059 0.047 0.030
0.899 0.922 0.915 0.938 0.901
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
8.10 21.29 18.57 21.04 2.45
2 29.61 2 31.64 2 43.95 2 57.47 2 23.39
3.37 8.62 8.91 10.29 1.24
0.069 0.044 0.046 0.047 0.041
0.892 0.932 0.935 0.934 0.854
a b
Starch concentration: 8%. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
compounds on starch molecular structure has been attributed to either competition for water between starch and sugar (D’Appolonia, 1972) or to an interaction between sugar and starch forming a cross-linking structure involving hydrogen bonds (Spies & Hoseney, 1982). The slight increase in the phase transition temperature range and melting enthalpy of starches by YMM (Table 2) may be due to either interaction between YMM and starch or competition with starch for water. This could result in a greater requirement for energy to gelatinize the starch granule. Gel texture measurements for wheat and rice starches are summarized in Table 3. Addition of YMM resulted in an increase in hardness, adhesiveness, chewiness and springiness and a decrease in resilience for both wheat and rice starch gels. In the presence of YMM –LBG (0.5%; 9:1), however, the gel texture was totally different from the gel made with 0.5% YMM. This was characterized by significant decreases in gel hardness, adhesiveness, chewiness and resilience. It is possible that when different polymers are mixed they tend to become incompatible for thermodynamic reasons, resulting in phase separation (Morris, 1990a). Such phase separation could affect gel firmness. Yoshimura et al. (1996) suggested that hydrocolloids increase the effective starch concentration
by immobilizing water molecules. Sasaki et al. (2000) reported that the hydrocolloid concentration within the continuous phase around the swollen starch granules also increases when starch swells during gelatinization. Either of these effects could contribute to increasing gel hardness. Another explanation is that when starches are heated to their gelatinization temperatures in the presence of YMM, the hydrocolloid forms hydrogen bonds with the soluble starch in the swollen granule. This reinforces the entanglement structure made by YMM resulting in a bicontinuous high viscosity starch paste (Figs. 1 and 2). Meanwhile, the crosslinking of YMM with amylose and amylopectin also makes the starch gel more elastic, increasing hardness, adhesiveness, chewiness and springiness. However, when starches were gelatinized in the presence of YMM –LBG (9:1, 0.5%) mixture the gel structure was totally different. The effects of YMM on the swelling power and solubilized wheat and rice starches are shown in Table 4. Addition of YMM resulted in a slight decrease in swelling power, as well as in the amount of solubilized starch and amylose in both wheat and rice starches. The swelling power did not change much when starch was dissolved in different concentrations of YMM. An increase in YMM concentration, however, did result in a decrease in solubilized starch
Table 4 Effect of YMM on the swelling power, solubilized starch and amylose of wheat and rice starches Starcha
Swelling power (g/g)
Solubilized starch(%)
Solublized amylose (%)
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixturec
12.51 ^ 0.16b 11.29 ^ 0.28 11.10 ^ 0.08 11.09 ^ 0.33 10.98 ^ 0.23
16.96 ^ 0.31 16.37 ^ 0.41 16.05 ^ 0.37 15.58 ^ 0.22 15.78 ^ 0.41
14.28 ^ 0.23 13.65 ^ 0.35 13.48 ^ 0.10 13.08 ^ 0.31 13.49 ^ 0.47
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
13.70 ^ 0.06 12.30 ^ 0.20 12.29 ^ 0.35 12.27 ^ 0.30 12.07 ^ 0.11
19.45 ^ 0.18 18.42 ^ 0.45 18.30 ^ 0.35 17.21 ^ 0.27 18.08 ^ 0.54
12.13 ^ 0.16 11.65 ^ 0.25 11.29 ^ 0.44 10.69 ^ 0.34 11.40 ^ 0.27
a b c
Starch concentration: 1.25%, w/w. Standard deviation of duplicate. 2gum mixture: YMM:LBG ¼ 9:1, 0.5%, w/w.
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and amylose content. The swelling power, solubilized starch and amylose for wheat and rice starches dissolved in the YMM – LBG (9:1; 0.5%) mixture did not show much difference compared to starch dissolved in YMM (0.5%). Christianson (1982) studied the morphological changes occurring during the heating of starch granules. Cold water can diffuse and penetrate freely into the amorphous regions of the starch granule without disturbing the crystalline regions. High-molecular weight solutes are unable to penetrate the granule, and consequently, water is sorbed selectively. In comparison, small soluble molecules, specifically maltotriose and maltoheptose, can be sorbed into the amorphous regions of the starch granule through submicropores (Brown & French, 1977). Christianson (1982) proposed that during heating, the submicropores may be enlarged resulting in other hydrophilic hydroxylated chains, even a portion, could sorb into the amorphous regions. The remaining portion of the longer chain would cover the surface of the granule and extend from the granule into the media. This could affect both swelling and starch solubilization. These researchers also found that when starch was heated in the presence of different hydrocolloid (e.g. xanthan, guar, CMC), the shape of the starch granules and the amount of soluble amylose were different. The present study showed a decrease in the swelling power and solubility of starches mixed with YMM suggesting interaction may occur within the starch granule via hydrogen bonds, inhibiting starch swelling and solubility. The DSC scan for wheat and rice starch gels stored at 5 8C for 3, 6 and 15 days with and without added YMM is shown in Table 2. Transition enthalpy ðDHÞ increased with storage time as a result of amylopectin retrogradation. Rice starch exhibited higher retrogradation enthalpy than wheat starch. Addition of the hydrocolloid did not decrease retrogradation of wheat starch until after 15 days, while a slight decrease in enthalpy was observed for both wheat and rice starches. The change in syneresis for starch – water and starch – hydrocolloid systems with storage time at 5 8C is shown in Fig. 3. Rice starch developed syneresis faster than wheat starch. Addition of the hydrocolloid markedly reduced syneresis in both wheat and rice starches. The degree of syneresis decreased with increase in hydrocolloid concentration. The syneresis of rice starch in YMM –LBG (9:1, 0.5%) was higher than in YMM (0.5%) with the opposite observed for wheat starch. Starch retrogradation is considered as crystallization of amylose and amylopectin (Miles, Morris, Orford, & Ring, 1985; Morris, 1990b). Transition enthalpies measured by DSC correspond to the heat involved in melting down the retrogradated amylose and/or amylopectin (Ferrero et al., 1994). Amylopectin retrogradation is a reversible process under 100 8C while amylose retrogradation requires more energy to revert crystal formation (Biliaderis, 1992; Russell et al., 1989). Only amylopectin retrogradation can be quantified by DSC within the assayed range of temperatures. Ferrero et al. (1994) reported that amylopectin
Fig. 3. Effect of YMM on the syneresis of wheat and rice starches. Concentration of wheat and rice starches: 4%, w/w; storage temperature: 5 8C; syneresis was expressed as H2O% separated from starch paste. B, starch only; V, starch and 0.2% YMM; O, starch and 0.5% YMM; X, starch and 0.8% YMM; W, starch and 0.5% gum mixture (LBG:YMM ¼ 9:1).
crystallization detected by DSC is not the only phenomenon occurring during starch retrogradation. Coupled with the increase of the thermogram peak of amylopectin crystallization, amylose retrogradation also developed when the starch gel was stored at 2 1 and 2 5 8C. These researchers speculated that during gelatinization, amylopectin remains mostly inside the starch granules while amylose is released outside. After cooling, amylose forms a gel matrix surrounding the granules. Thus, amylose now with greater exposure has the potential to undergo molecular interaction with other components of the paste. The entanglements of hydrocolloid with amylose will probably compete successfully with amylose – amylose interaction that is essential for retrogradation to occur. Sudhakar et al. (1996) also stated that improvements in freeze –thaw stability could be due to interaction between the hydrocolloid and amylose, thereby slowing down retrogradation. A decrease in syneresis by YMM (Fig. 3) could be attributed to its interaction with amylose. YMM, however, also appears to retard amylopectin retrogradation over long storage periods (Table 2).
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4. Conclusion This study revealed that the addition of yellow mustard mucilage did not affect the gelatinization temperature and retrogradation of wheat and rice starches significantly. However, considerable interactions were observed between yellow mustard gum and wheat and rice starches resulting in a marked increase in viscosity. Yellow mustard gum was also found to influence the thermal property and gel structure of these starches as well as decrease in syneresis of the gels. Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM – locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. Further research is required to fully understand the mechanisms of the interactions and explore the applications of these interactions in food processing.
Acknowledgements This work was supported by a grant from the Natural Science and Engineering Research Council (NSERC) of Canada.
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Cui, W., Eskin, N. A. M., Billaderis, C. G., & Mazza, G. (1995). Synergistic interaction between yellow mustard polysaccharides and galactomannans. Carbhydrate Polymer, 27, 123– 127. Cui, W., Eskin, N.A.M., Han, N.F., Duan, Z.Z., Zhang, X.Y., (2001). Extraction process and use of yellow mustard gum. US Patent No. 6, 194, 016B1. D’Appolonia, B. L. (1972). Effect of bread ingredients on starch gelatinization properties as measured in the amylograph. Cereal Chemistry, 49, 532–543. Fanta, G. F., & Christianson, D. D. (1996). Starch–hydrocolloid composites prepared by steam jet cooking. Food Hydrocolloids, 10, 173 –178. Ferrero, C., Martino, M. N., & Zaritzky, N. E. (1994). Corn starch–xanthan gum interaction and its effect on the stability during storage of frozen gelatinized suspensions. Starch/Starke, 46, 300 –308. Gibson, T. S., Solah, V. A., & McCleary, B. V. (1997). A procedure to measure amylose in cereal starches and flours with concanavalin A. Journal of Cereal Science, 25, 111–119. Gudmundsson, M., Eliasson, A.-C., Bengtsson, S., & Aman, P. (1991). The effects of water soluble arabinoxylan on gelatinization and retrogradation of starch. Starch/Starke, 43, 5–10. Kim, C. S., & Walker, C. E. (1992). Effects of sugars and emulsifiers on starch gelatinization evaluated by differential scanning calorimetry. Cereal Chemistry, 69, 212 –217. Liu, H., & Eskin, N. A. M. (1998). Interactions of native and acetylated pea starch with yellow mustard mucilage, locust bean gum and gelatin. Food Hydrocolloids, 12, 37 –41. Miles, M. J., Morris, V. J., Orford, P. D., & Ring, S. G. (1985). The roles of amylose and amylopectin in the gelation and retrogradation of starch. Carbohydrate Research, 135, 271–281. Morris, E. R. (1990a). In P. Harris (Ed.), Food gels (p. 291) London: Elsevier. Morris, V. J. (1990b). Starch gelation and retrogradation. Trends in Food Science and Technology, 1, 2–6. Russell, P. L., Berry, C. S., & Greewell, P. (1989). Characterisation of resistant starch from wheat and maize. Journal of Cereal Science, 9, 1–15. Sajjan, S. U., & Rao, M. R. R. (1987). Effect of hydrocolloids on the rheological properties of wheat starch. Carbohydrate Polymer, 7, 395–402. Sandstedt, R. M., & Abbott, R. C. (1964). Cereal Science Today, 9, 13– 18. Sasaki, T., Yasui, T., & Matsuki, J. (2000). Influence of non-starch polysaccharides isolated from wheat four on the gelatinization and gelation of wheat starches. Food Hydrocolloids, 14, 295–303. Siddiqui, I. R., Yiu, S. H., Yiu, J. D., Jones, J. D., & Kalab, M. (1986). Mucilage in yellow mustard (Brassica hirta) seeds. Food Microstructure, 5, 157–162. Spies, R. D., & Hoseney, R. C. (1982). Effect of sugars on starch gelatinization. Cereal Chemistry, 59, 128–131. Sudhakar, V., Singhal, R. S., & Kulkarni, P. R. (1996). Starch – galactomannan interaction: functionality and rheological aspects. Food Chemistry, 55, 259– 264. Theander, O., Aman, P., Miksche, G. E., & Yasuda, S. (1977). Carbohydrates, polyphenols and lignin in seed hulls of different colors from turnip rapeseed. Journal of Agricultural Food Chemistry, 25, 270–273. Vose, J. R. (1974). Chemical and physical studies of mustard and rapeseed coats. Cereal Chemistry, 51, 658–665. Yoshimura, M., Takaya, T., & Nishinari, K. (1996). Effects of konjacglucomannan on the gelatinization and retrogradation of corn starch as determined by rheology and differential scanning calorimetry. Journal of Agricultural Food Chemistry, 44, 2970– 2976. Yoshimura, M., Takaya, T., & Nishinari, K. (1998). Rheological studies on mixtures of corn starch and konjac-glucomannan. Carbohydrate Polymer, 35, 71–79. Yoshimura, M., Takaya, T., & Nishinari, K. (1999). Effects of xyloglucan on the gelatinization and retrogradation of corn starch as studied by rheology and differential scanning calorimetry. Food Hydrocolloids, 13, 101–111.
Interaction of wheat and rice starches with yellow mustard mucilage Huijuin Liua, N.A. Michael Eskina,*, Steve W. Cuib b
a Department of Human Nutritional Sciences, University of Manitoba, Winnipeg, Man., Canada R3T 2N2 Food Research Program, Agri-Food and Agriculture Canada, 93 Stone Road West, Guelph, Ont., Canada N1G 5C9
Received 16 October 2002; accepted 21 May 2003
Abstract The effect of yellow mustard mucilage (YMM) on gelatinization and retrogradation of wheat and rice starches were studied. Considerable interactions were observed between YMM and wheat and rice starches which were accompanied by a marked increase in viscosity. DSC studies showed that the presence of YMM did not affect peak gelatinization temperature ðTp Þ of wheat and rice starches, but slightly increased melting enthalpy ðDHÞ and the phase transition temperature range ðTc 2 T0 Þ: Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM– locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. The swelling power as well as solubilized starch and amylose were decreased for both starches in the presence of YMM. Syneresis in wheat and rice starches was also decreased by the presence of YMM. q 2003 Elsevier Ltd. All rights reserved. Keywords: Yellow mustard mucilage; Starches interactions; Rheological properties; Gelatinization; Retrogradation; Syneresis
1. Introduction The physical properties of native starches and their colloidal sols limit their usefulness in many commercial applications. Aggregation and recrystallization of starch molecules can lead to increased rigidity and syneresis of the starch paste. This phenomenon of retrogradation is further exacerbated during freezing with detrimental effects to the texture, acceptability and digestibility of starch-containing foods (Berry, I’Anson, Miles, Morris, & Russell, 1988). Chemical modification of starch can improve cooking characteristics, decrease retrogradation as well as increase freeze – thaw stability of starch pastes. However, obtaining regulatory approval for new chemical reagents combined with consumer concerns regarding the chemical treatment of foods has led to alternative ways to modify starch such as blending with other hydrocolloids. Hydrocolloids have been shown to alter the gelatinization and retrogradation characteristics of starches (Alloncle, Lefebvre, Llamas, & Doublier, 1989; Biliaderis, Arvanitoyannis, Izydorczyk, & Prokopowich, 1997; Christianson, Hodge, Osborne, & Detroy, 1981; Ferrero, Martino, & Zaritzky, 1994; Yoshimura, Takaya, & Nishinari, 1996, * Corresponding author. Tel.: þ 1-204-474-8078; fax: þ1-204-474-7593. E-mail address: [email protected] (N.A.M. Eskin). 0268-005X/03/$ - see front matter q 2003 Elsevier Ltd. All rights reserved. doi:10.1016/S0268-005X(03)00107-3
1999). Christianson et al. (1981) found guar gum, xanthan and carboxymethyl cellulose hastened the onset of initial paste viscosity and substantially increased final peak viscosity of wheat starch due to the greater leaching out of amylose. Biliaderis and co-workers (1997) showed that polysaccharides varying in molecular size (xanthan, bglucan, arabinoxylan and guar gum) did not affect the gelatinization temperature of waxy maize and wheat starches. However, these hydrocolloids increased the phase transition temperature range ðTc 2 T0 Þ and the melting enthalpies ðDHÞ of the starch crystallites. Yoshimura et al. (1998) found that the addition of a small amount of konjac-glucomannan prevented the development of syneresis during the storage of corn starch. Gudmundson, Eliasson, Bengtsson, and Aman (1991) reported rye arabinoxylan had no effect on DH of waxy maize starch but slightly reduced the DH of maize and potato starches while slightly increasing DH of wheat starch. A number of studies have demonstrated synergistic interactions between native starches and gums resulting in significant increases in viscosity of the starch pastes (Alloncle et al., 1989; Christianson et al., 1981; Crossland & Favor, 1948; Sajjan & Rao, 1987; Sandstedt & Abbott, 1964; Sudhakar, Singhal & Kulkarni, 1996). Modifications of starch gelatinization and retrogradation characteristics by hydrocolloids make
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these combinations useful as food ingredients (Fanta & Christianson, 1996). Previous research in our laboratory showed yellow mustard mucilage (YMM) exhibited unique rheological properties with considerable potential as a food thickener and stabilizer. YMM was shown to be composed of both neutral sugars and uronic acids (Cui, Eskin, & Billaderis, 1993). The monosaccharides identified were primarily glucose, arabinose, xylose, rhamnose, galactose and mannose (Cui, Eskin, & Billaderis, 1993; Siddiqui, Yiu, Jones, & Kalab, 1986; Theander, Aman, Miksche, & Yasuda, 1977; Vose, 1974). Small strain oscillatory rheological tests showed significant synergistic interactions between YMM and locust bean gum (LBG) resulting in a marked increase in viscosity (Cui et al., 1995). The optimum ratio for synergism was 9:1 for YMM:LBG systems. Further work confirmed a marked interaction between YMM and native and acetylated pea starch which increased starch paste viscosity and altered the degree of pseudoplasticity of the corresponding starch pastes (Liu & Eskin, 1998). This study examined the effects of YMM on the gelatinization and retrogradation characteristics of wheat and rice starches including pasting and thermal properties, swelling and solubility, gel structure and syneresis.
2. Materials and methods Commercial wheat and rice starches and LBG were obtained from Sigma (St Louis, MO). YMM was extracted following the patented procedure of Cui, Eskin, Han, Duan, and Zhang (2001), freeze-dried and stored in a desiccator. Pasting properties of starch suspensions (8%, w/w) with or without added YMM gum (0.2, 0.5 and 0.8%, w/w) or YMM mixed with LBG (9:1; 0.5%), were monitored using a rapid Visco-analyzer model 3D (RVA) (Newport Scientific Pty, Ltd, Narrabeen, Australia). Samples were placed in an aluminum RVA sample cannister. A programmed heating and cooling cycle was used, in which the sample was held at 50 8C for 1 min.; heated to 95 8C for 3 min 42 s; held at 95 8C for 2 min 30 s; cooled to 50 8C for 3 min 48 s; then held at 50 8C for a further 2 min. Thermal analyses were conducted on granular starch dispersions and aging/hydrocolloid gels using a DuPont thermal analyzer (9900; Wilmington, DE) equipped with a DSC cell (Dupont 910). Starch (40%, w/w) was suspended in previously prepared gum solutions (0.2, 0.5 and 0.8% w/w), with an aliquot of the starch dispersions (10 mg) pipetted into DSC pans and hermetically sealed. The starch suspensions were heated from 20 to 120 8C at 10 8C/min to gelatinize the granules. The onset temperature, peak temperature, conclusion temperature as well as transition enthalpy ðDHÞ were recorded. After DSC testing, the samples were stored at 5 8C for 3, 6, and 15 days. The aged starch/hydrocolloids gels were re-scanned from 20 –120 8C at 10 8C/min to estimate the extent of
retrogradation from the magnitude (transition enthalpy, DH) of the amylopectin endotherm. After RVA testing, the starch pasted in the sample cannister was covered and held at 5 8C in a refrigerator for 24 h. Gel texture was determined using a TA-TX2 Texture Analyzer (Stable Micro Systems, Godalming, Surrey, England). The gel was compressed at a speed of 1.0 mm/s to a distance of 10 mm with a cylindrical flat-ended probe of 6 mm diameter. The peak height at 10 mm compression was termed hardness. The negative area from the curve during the retraction of the probe was termed adhesiveness. Swelling power was determined following the method of Sasaki et al. with slight modification (Sasaki, Yasui, & Matsuki, 2000). Starch gum dispersions (1.25% starch and 0.031, 0.078, 0.125% gum) were put into tubes with coated screw caps and heated in a boiling water bath for 10 min. A starch –water mixture similarly treated served as the control. After cooling in ice for 5 min, samples were centrifuged at 11,200g at 5 8C for 15 min and the supernatant removed for measurement of solubilized starch. Swelling power was determined as the ratio in weight of the wet sediment compared to the initial weight of the dry starch. The method of Gibson et al. was used to determine total carbohydrates in the recovered supernatant (Gibson, Solah, & McCleary, 1997), while amylose content was measured following the colorimetric method of Chrastil (1987). The extent of syneresis was measured on starch suspensions (4% w/w) in water or gum solutions (0.2, 0.5, and 0.8%) heated in a boiling water bath for 10 min. Following cooling, samples were stored at 5 8C for 15 days. Syneresis was estimated by the weight of water separated and expressed as the ratio of separated water to starch gel. Data reported were average values of replications.
3. Results and discussion The effects of YMM on the amylograms of wheat and rice starches are shown in Figs. 1 and 2 and Table 1. Both YMM (0.8%, w/w) or YMM– LBG mixture (9:1, 0.5% w/w) showed negligible viscosity using the amylograph. However, addition of the hydrocolloid to wheat or rice starches resulted in the onset of viscosity at a lower temperature compared to the starch control. The magnitude of the onset temperature of the amylograms decreased depending on the concentration of the hydrocolloid. For example, the higher the concentration of YMM was, the more the onset temperature decreased. Normally, starch does not exhibit viscosity during the early stages of granule swelling (55 – 70 8C). However, a number of researchers showed that when starch was heated in a viscous media containing CMC, xanthan gum, guar gum or LBG, an increase in viscosity occurred earlier during the heating period due to interaction with the gum (Alloncle et al., 1989; Christianson et al., 1981; Crossland & Favor, 1948). Christianson et al. (1981) attributed the earlier development of viscosity to the changing starch granule structure by
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Fig. 1. Effect of YMM on the amylogram of wheat starch. Starch concentration: 8%(w/w); YMM concentration: 0.2, 0.5, 0.8%, (w/w); 2gummixture: YMM:LBM ¼ 9:1, 0.5%, (w/w).
the gum medium. Bean and Yamazaki (1978) found a rapid increase in granule swelling between 58 and 70 8C which corresponded to the onset of viscosity produced in the wheat starch – CMC amylograph curve. In this study, however, addition of YMM inhibited the swelling of wheat and rice starches (Table 4). The decrease in the onset temperature of amylograms by YMM (Figs. 1 and 2) may be due to interaction of YMM with the small amount of amylose released by the limited swelling of the starch granules. Compared to YMM (0.5% w/w), addition of the gum mixture (0.5%, YMM:LBG ¼ 9:1) into starch further hastened the onset of initial paste viscosity. Addition of YMM resulted in a marked increase in peak and cool paste viscosities for both wheat and rice starches (Figs. 1 and 2). For example, the viscosity of wheat starch increased 1.4, 1.9 and 2.3-fold in the presence of 0.2. 0.5 and
0.8% YMM. In the case of rice starch the increase in viscosity was slightly higher corresponding to 1.5, 2.2 and 2.8-folds in the presence of 0.2, 0.5 and 0.8% YMM. For both wheat and rice starches, the gum mixture (YMM:LBG ¼ 9:1, 0.5%) produced a higher viscosity compared to YMM (0.5%). An increase in starch peak viscosity in the presence of a hydrocolloid has been reported previously (Alloncle et al., 1989; Liu & Eskin, 1998; Sasaki et al., 2000). Christianson et al. (1981) attributed the increase in viscosity to interaction between exudate from the starch granule (solubilized amylose and low-molecularweight amylopectin) and gums. A second explanation given was that addition of thickening gums enhanced the forces being exerted on the starch granules in the shear field compared to starch – water suspension with equal starch concentrations. Alloncle et al. (1989) proposed a model to
Fig. 2. Effect of YMM on the amylogram of rice starch. Starch concentration: 8% (w/w); YMM concentration: 0.2%, 0.5%, 0.8% (w/w); 2 gum mixture: YMM:LBM ¼ 9:1, 0.5% (w/w).
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Table 1 Effect of YMM on the pasting properties of wheat and rice starches Starcha
Peak viscosity (RVU)
Trough (RVU)
Breakdown (RVU)
Final viscosity (RVU)
Setback (RVU)
Peak time (min)
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixtureb
58.67 83.42 109.92 136.58 143.25
49.25 72.92 99.42 125.50 137.50
9.42 10.50 10.50 11.08 5.75
64.08 90.50 120.58 151.75 152.00
14.83 17.58 21.17 26.25 14.50
6.53 7.33 7.73 7.80 8.13
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixtureb
46.00 70.08 99.25 126.83 131.67
43.58 69.08 96.33 120.33 128.42
2.42 1.00 2.92 6.50 3.25
66.17 102.92 135.92 157.75 153.42
22.58 33.83 39.58 37.43 25.00
6.53 6.87 7.13 7.60 8.53
a b
Starch concentration: 8%, w/w. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
interpret these effects in which the gums were located within the continuous phase of the starch pastes. In this model, the volume of the continuous phase accessible to the gum was reduced, yielding an increase in gum concentration within the continuous phase, which was accompanied by a dramatic increase in viscosity. Yoshimura et al. reported that addition of hydrocolloids increased the effective starch concentration by immobilizing water molecules (Yoshimura, Takaya, & Nishinari 1996). The marked increase in viscosity following addition of YMM could be similarly explained. YMM could also form a strong entanglement with amylose released from the starch granule and with swollen (amylopectin) particles. Both of these effects could result in the increased viscosity of the starch paste. The DSC results for starches with and without added hydrocolloids are summarized in Table 2. The gelatinization temperature and enthalpy ðDHÞ of rice starch was higher than that for wheat starch. Addition of YMM did not affect the peak temperature ðTp Þ of wheat or rice starch. A slight increase in melting enthalpy ðDHÞ and phase transition
temperature range ðTc 2 T0 Þ was observed, however, when YMM was added compared to the control. The effect of hydrocolloids on gelatinization properties of starches has been observed previously. Biliaderis et al. (1997) reported that the addition of polysaccharides (xanthan, b-glucan, arabinoxylan and guar gum) at levels ranging from 1 to 2% on a starch basis did not affect the gelatinization temperature of waxy maize and wheat starches. However, they did observe an increase in the phase transition temperature ðTc 2 T0 Þ and melting enthalpy ðDHÞ of the starch crystallites. Gudmundsson et al. showed that the addition of rye arabinoxylan at levels of 1 – 2%, on a dry basis, increased DH of wheat starch, slightly decreased DH of maize and potato starches, but had no effect on DH of waxy maize starch (Gudmundsson, Eliasson, Bengtsson, & Aman, 1991). Liu and Eskin (1998) found that YMM (0.35%) did not change the gelatinization temperature of pea starch. Sugars and polyhydroxy compounds have been shown to increase the gelatinization temperature of starch (Kim & Walker, 1992; Spies & Hoseney, 1982). The stabilizing effect of polyhydroxy
Table 2 Effect of YMM on the thermal properties of wheat and rice starches Starcha
Retrogradation DH (J/g)
Gelatinization Tp (C)
DH (J/g)
Tc 2 T0
Day 3
Day 6
Day 15
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixturec
61.27 ^ 0.04b 61.04 ^ 0.12 61.49 ^ 0.31 61.51 ^ 0.20 61.43 ^ 0.35
9.99 ^ 0.24 10.80 ^ 0.08 10.72 ^ 0.32 10.72 ^ 0.21 10.58 ^ 0.14
31.21 ^ 0.41 35.34 ^ 0.85 36.16 ^ 1.25 36.02 ^ 0.10 35.80 ^ 0.71
3.67 ^ 0.13 3.55 ^ 0.20 3.63 ^ 0.06 3.89 ^ 0.31 4.03 ^ 0.41
5.06 ^ 0.18 4.94 ^ 0.41 5.01 ^ 0.32 4.73 ^ 0.11 4.63 ^ 0.13
6.32 ^ 0.09 5.72 ^ 0.24 5.38 ^ 0.43 5.17 ^ 0.35 5.24 ^ 0.20
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
74.31 ^ 0.24 74.49 ^ 0.06 74.51 ^ 0.11 74.57 ^ 0.30 74.43 ^ 0.21
11.59 ^ 0.09 12.36 ^ 0.28 12.55 ^ 0.13 12.62 ^ 0.34 12.48 ^ 0.39
28.52 ^ 0.79 32.30 ^ 1.13 33.73 ^ 0.16 33.45 ^ 0.67 34.06 ^ 0.35
4.95 ^ 0.17 4.67 ^ 0.14 4.52 ^ 0.26 4.54 ^ 0.41 4.87 ^ 0.30
6.67 ^ 0.43 6.50 ^ 0.15 6.55 ^ 0.22 6.21 ^ 0.09 6.00 ^ 0.39
7.95 ^ 0.17 7.13 ^ 0.22 7.04 ^ 0.37 6.90 ^ 0.21 6.45 ^ 0.40
a b c
n ¼ 2: Starch concentration: 40%, w/w. Standard deviation of duplicate. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
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Table 3 Effect of YMM on the gel texture of wheat and rice starches Starcha
Hardness
Adhesiviveness
Chewiness
Resilience
Springiness
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixtureb
24.08 32.09 29.04 30.66 2.16
2 57.74 2 82.16 2 106.00 2 103.09 2 26.05
11.11 12.50 12.36 13.04 1.01
0.098 0.065 0.059 0.047 0.030
0.899 0.922 0.915 0.938 0.901
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
8.10 21.29 18.57 21.04 2.45
2 29.61 2 31.64 2 43.95 2 57.47 2 23.39
3.37 8.62 8.91 10.29 1.24
0.069 0.044 0.046 0.047 0.041
0.892 0.932 0.935 0.934 0.854
a b
Starch concentration: 8%. 2gum mixture: (YMM:LBG ¼ 9:1, 0.5%, w/w).
compounds on starch molecular structure has been attributed to either competition for water between starch and sugar (D’Appolonia, 1972) or to an interaction between sugar and starch forming a cross-linking structure involving hydrogen bonds (Spies & Hoseney, 1982). The slight increase in the phase transition temperature range and melting enthalpy of starches by YMM (Table 2) may be due to either interaction between YMM and starch or competition with starch for water. This could result in a greater requirement for energy to gelatinize the starch granule. Gel texture measurements for wheat and rice starches are summarized in Table 3. Addition of YMM resulted in an increase in hardness, adhesiveness, chewiness and springiness and a decrease in resilience for both wheat and rice starch gels. In the presence of YMM –LBG (0.5%; 9:1), however, the gel texture was totally different from the gel made with 0.5% YMM. This was characterized by significant decreases in gel hardness, adhesiveness, chewiness and resilience. It is possible that when different polymers are mixed they tend to become incompatible for thermodynamic reasons, resulting in phase separation (Morris, 1990a). Such phase separation could affect gel firmness. Yoshimura et al. (1996) suggested that hydrocolloids increase the effective starch concentration
by immobilizing water molecules. Sasaki et al. (2000) reported that the hydrocolloid concentration within the continuous phase around the swollen starch granules also increases when starch swells during gelatinization. Either of these effects could contribute to increasing gel hardness. Another explanation is that when starches are heated to their gelatinization temperatures in the presence of YMM, the hydrocolloid forms hydrogen bonds with the soluble starch in the swollen granule. This reinforces the entanglement structure made by YMM resulting in a bicontinuous high viscosity starch paste (Figs. 1 and 2). Meanwhile, the crosslinking of YMM with amylose and amylopectin also makes the starch gel more elastic, increasing hardness, adhesiveness, chewiness and springiness. However, when starches were gelatinized in the presence of YMM –LBG (9:1, 0.5%) mixture the gel structure was totally different. The effects of YMM on the swelling power and solubilized wheat and rice starches are shown in Table 4. Addition of YMM resulted in a slight decrease in swelling power, as well as in the amount of solubilized starch and amylose in both wheat and rice starches. The swelling power did not change much when starch was dissolved in different concentrations of YMM. An increase in YMM concentration, however, did result in a decrease in solubilized starch
Table 4 Effect of YMM on the swelling power, solubilized starch and amylose of wheat and rice starches Starcha
Swelling power (g/g)
Solubilized starch(%)
Solublized amylose (%)
Wheat Wheat þ 0.2%YMM Wheat þ 0.5%YMM Wheat þ 0.8%YMM Wheat þ 2gum mixturec
12.51 ^ 0.16b 11.29 ^ 0.28 11.10 ^ 0.08 11.09 ^ 0.33 10.98 ^ 0.23
16.96 ^ 0.31 16.37 ^ 0.41 16.05 ^ 0.37 15.58 ^ 0.22 15.78 ^ 0.41
14.28 ^ 0.23 13.65 ^ 0.35 13.48 ^ 0.10 13.08 ^ 0.31 13.49 ^ 0.47
Rice Rice þ 0.2%YMM Rice þ 0.5%YMM Rice þ 0.8%YMM Rice þ 2gum mixture
13.70 ^ 0.06 12.30 ^ 0.20 12.29 ^ 0.35 12.27 ^ 0.30 12.07 ^ 0.11
19.45 ^ 0.18 18.42 ^ 0.45 18.30 ^ 0.35 17.21 ^ 0.27 18.08 ^ 0.54
12.13 ^ 0.16 11.65 ^ 0.25 11.29 ^ 0.44 10.69 ^ 0.34 11.40 ^ 0.27
a b c
Starch concentration: 1.25%, w/w. Standard deviation of duplicate. 2gum mixture: YMM:LBG ¼ 9:1, 0.5%, w/w.
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and amylose content. The swelling power, solubilized starch and amylose for wheat and rice starches dissolved in the YMM – LBG (9:1; 0.5%) mixture did not show much difference compared to starch dissolved in YMM (0.5%). Christianson (1982) studied the morphological changes occurring during the heating of starch granules. Cold water can diffuse and penetrate freely into the amorphous regions of the starch granule without disturbing the crystalline regions. High-molecular weight solutes are unable to penetrate the granule, and consequently, water is sorbed selectively. In comparison, small soluble molecules, specifically maltotriose and maltoheptose, can be sorbed into the amorphous regions of the starch granule through submicropores (Brown & French, 1977). Christianson (1982) proposed that during heating, the submicropores may be enlarged resulting in other hydrophilic hydroxylated chains, even a portion, could sorb into the amorphous regions. The remaining portion of the longer chain would cover the surface of the granule and extend from the granule into the media. This could affect both swelling and starch solubilization. These researchers also found that when starch was heated in the presence of different hydrocolloid (e.g. xanthan, guar, CMC), the shape of the starch granules and the amount of soluble amylose were different. The present study showed a decrease in the swelling power and solubility of starches mixed with YMM suggesting interaction may occur within the starch granule via hydrogen bonds, inhibiting starch swelling and solubility. The DSC scan for wheat and rice starch gels stored at 5 8C for 3, 6 and 15 days with and without added YMM is shown in Table 2. Transition enthalpy ðDHÞ increased with storage time as a result of amylopectin retrogradation. Rice starch exhibited higher retrogradation enthalpy than wheat starch. Addition of the hydrocolloid did not decrease retrogradation of wheat starch until after 15 days, while a slight decrease in enthalpy was observed for both wheat and rice starches. The change in syneresis for starch – water and starch – hydrocolloid systems with storage time at 5 8C is shown in Fig. 3. Rice starch developed syneresis faster than wheat starch. Addition of the hydrocolloid markedly reduced syneresis in both wheat and rice starches. The degree of syneresis decreased with increase in hydrocolloid concentration. The syneresis of rice starch in YMM –LBG (9:1, 0.5%) was higher than in YMM (0.5%) with the opposite observed for wheat starch. Starch retrogradation is considered as crystallization of amylose and amylopectin (Miles, Morris, Orford, & Ring, 1985; Morris, 1990b). Transition enthalpies measured by DSC correspond to the heat involved in melting down the retrogradated amylose and/or amylopectin (Ferrero et al., 1994). Amylopectin retrogradation is a reversible process under 100 8C while amylose retrogradation requires more energy to revert crystal formation (Biliaderis, 1992; Russell et al., 1989). Only amylopectin retrogradation can be quantified by DSC within the assayed range of temperatures. Ferrero et al. (1994) reported that amylopectin
Fig. 3. Effect of YMM on the syneresis of wheat and rice starches. Concentration of wheat and rice starches: 4%, w/w; storage temperature: 5 8C; syneresis was expressed as H2O% separated from starch paste. B, starch only; V, starch and 0.2% YMM; O, starch and 0.5% YMM; X, starch and 0.8% YMM; W, starch and 0.5% gum mixture (LBG:YMM ¼ 9:1).
crystallization detected by DSC is not the only phenomenon occurring during starch retrogradation. Coupled with the increase of the thermogram peak of amylopectin crystallization, amylose retrogradation also developed when the starch gel was stored at 2 1 and 2 5 8C. These researchers speculated that during gelatinization, amylopectin remains mostly inside the starch granules while amylose is released outside. After cooling, amylose forms a gel matrix surrounding the granules. Thus, amylose now with greater exposure has the potential to undergo molecular interaction with other components of the paste. The entanglements of hydrocolloid with amylose will probably compete successfully with amylose – amylose interaction that is essential for retrogradation to occur. Sudhakar et al. (1996) also stated that improvements in freeze –thaw stability could be due to interaction between the hydrocolloid and amylose, thereby slowing down retrogradation. A decrease in syneresis by YMM (Fig. 3) could be attributed to its interaction with amylose. YMM, however, also appears to retard amylopectin retrogradation over long storage periods (Table 2).
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4. Conclusion This study revealed that the addition of yellow mustard mucilage did not affect the gelatinization temperature and retrogradation of wheat and rice starches significantly. However, considerable interactions were observed between yellow mustard gum and wheat and rice starches resulting in a marked increase in viscosity. Yellow mustard gum was also found to influence the thermal property and gel structure of these starches as well as decrease in syneresis of the gels. Addition of YMM markedly changed wheat and rice starch gel textures by increasing hardness, adhesiveness, chewiness and springiness. The addition of YMM – locust bean gum (LBG) mixture (9:1) similarly increased the viscosity of wheat and rice starches but decreased gel hardness. Further research is required to fully understand the mechanisms of the interactions and explore the applications of these interactions in food processing.
Acknowledgements This work was supported by a grant from the Natural Science and Engineering Research Council (NSERC) of Canada.
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