Elsevier

Food Hydrocolloids

Volume 35, March 2014, Pages 546-556
Food Hydrocolloids

Guar and xanthan gum differentially affect shear induced breakdown of native waxy maize starch

https://doi.org/10.1016/j.foodhyd.2013.07.011Get rights and content

Highlights

  • Starches are pasted at mild temperatures and by using different shear rates.

  • Particle size and rheological properties of the resulting systems are characterized.

  • Xanthan and guar differently affect the pasting process and the starch granule properties.

  • Xanthan restricts shear induced breakdown.

  • Confocal microscopy illustrates the location of the gums in the mixed pastes.

Abstract

Starches and non-starch hydrocolloids or gums are used very often as texturizers in the food industry. The aim of this work was to investigate the effects of guar gum and xanthan gum on the mild temperature pasting behavior of waxy maize starch. Waxy maize starch dispersions containing either guar, xanthan or no gum were pasted at temperatures (70 and 72.5 °C) close to the gelatinization temperature by means of the starch pasting cell mounted on the rheometer. Different shear conditions were imposed (no shear, 50 s−1 and 150 s−1). Along with the pasting behavior, the particle size distribution of the swollen granules was derived by means of laser light scattering and the rheological behavior of the cooled pastes was determined to characterize the samples. Finally, confocal laser scanning microscopy was used to locate the fluorescently labeled gums in the swollen starch dispersions. Under the given conditions, both gums differently affected the starch during the heating steps. While xanthan gum lowered the shear induced breakdown of the granules, guar gum did not show this specific property. Consequently, guar gum primarily modified the rheological properties of the pastes by its presence in the continuous phase, whereas xanthan gum also induced indirect effects by better preserving the granular structure.

Introduction

Starch is frequently used in the food industry as a thickener or gelling agent. Very often, non-starch hydrocolloids or gums are added to improve the final properties and stability of starch-containing foodstuffs (Arocas et al., 2009, Dolz et al., 2006, Heyman et al., 2010, Sikora et al., 2008). Guar and xanthan are two of the most commonly used gums in combination with starches. Xanthan gum is an extracellular polysaccharide, produced by fermentation of Xanthomonas campestris and consists of 1,4-linked β-D-glucose residues having a trisaccharide side chain attached to O-3 of alternate D-glucosyl residues. The side chains are (3→1)-α-linked D-mannopyranose, (4→1)-β-D-mannopyranose and (2→1)-β-D-glucuronic acid (Born, Langendorff, & Boulenguer, 2005). Guar gum is derived from the ground endosperm of guar seeds (Cyamopsis tetragonoloba). This non-ionic polysaccharide has a main chain of (1→4)-linked β-D-mannopyranosyl units with single α-D-galactopyranosyl units attached to the O-6 position (Casas et al., 2000, Mudgil et al., 2012).

The specific effects of gums on the pasting and rheological properties of starches have been extensively studied. They appear to strongly depend on both gum and starch type as well as the applied concentrations and preparation conditions (BeMiller, 2011). The origin of their rheological synergies in particular has received much attention. Associations between starch and hydrocolloid molecules (Christianson et al., 1981, Freitas et al., 2003, Funami et al., 2005b, Shi and BeMiller, 2002) as well as their mutual exclusion (Achayuthakan and Suphantharika, 2008, Alloncle and Doublier, 1991, Alloncle et al., 1989, Biliaderis et al., 1997, Conde-Petit et al., 1997, Mandala et al., 2004) has been proposed to explain the observed rheological phenomena.

In addition to their direct effects in the bulk phase, gums could also indirectly govern the rheological behavior of starch pastes by modifying the properties of the granules. In this regard, the suggestion is made that they can compensate the shortcomings of native starches hence reducing the need for chemically modified starches (BeMiller, 2011, Brennan et al., 2004). When heated together, gums can influence the swelling and degradation behavior of the starch. In general, inhibition of the granule swelling due to the hydrocolloid is observed (Achayuthakan and Suphantharika, 2008, Biliaderis et al., 1997, Funami et al., 2005a, Kruger et al., 2003, Song et al., 2006, Temsiripong et al., 2005, Tester and Sommerville, 2003), with some rare observations of increased granule swelling (Achayuthakan et al., 2006, Mandala and Bayas, 2004). Kaur, Singh, Singh, and McCarthy (2008) found that the expansion of starches with a high swelling capacity was reduced whereas the effect on low swelling starches was limited. Both kinetic and chemical effects could be held responsible for the differing effects. Kruger et al. (2003) suggested that in the presence of gums, granule swelling was inhibited because of the lower heating rates and the reduced mobility of the water molecules. It was also demonstrated that gums can inhibit the leaching of starch polymers (primarily amylose) during pasting (Biliaderis et al., 1997, Chaisawang and Suphantharika, 2006, Hongsprabhas et al., 2007, Shi and BeMiller, 2002). In this manner swelling is restricted, resulting in more rigid granules which break up less easily. Some gums are expected to induce a smooth flow of starch dispersions, hereby preventing the abrasion of starch granules (Funami et al., 2008, Viturawong et al., 2008). On the contrary, the increased breakdown as derived from rapid visco-analyzer or Brabender pasting curves convinced other authors that instead of preserving their structure, gums stimulate rupture of the granules (Chaisawang and Suphantharika, 2006, Christianson et al., 1981, Mandala and Bayas, 2004). It was proposed that due to the higher medium viscosity, the shear forces exerted on the granules are increased, which results in more breakdown.

The aim of this experimental setup was to gain a better insight in the effects of two commercially important gums, guar and xanthan, on the behavior of waxy maize starch during pasting. By using waxy starches, which consist almost entirely of amylopectin, effects of gums on amylose leaching and amylose gelation can be excluded. However, in its native form this type of starch is vulnerable to both thermal and shear-induced breakdown (Schirmer, Höchstötter, Jekle, Arendt, & Becker, 2013), which restricts its use in industrial applications. Therefore it is interesting to search for ways to better preserve their structure, for example by the addition of gums or by the use of adjusted processing conditions. In most experimental setups, the intense heating of the starches results in microstructurally complex systems of granule remnants and granule ghosts within a macromolecular solution of amylopectin and gums, because the majority of the granules is broken down (Hermansson and Svegmark, 1996, Tsai et al., 1997). Therefore, it is difficult to draw conclusions regarding the effect of gums on the granule swelling and degradation. As demonstrated in our recently published research (Heyman, Depypere, Van der Meeren, & Dewettinck, 2013), the processing of waxy starches at temperatures close to the gelatinization range, helps to limit their breakdown. Furthermore it was shown that at these mild temperatures, the presence of xanthan gum induced larger granule diameters in the final paste. However, the underlying mechanisms were unclear. The comparison of guar and xanthan gum should clarify if these phenomena are caused by a specific feature of xanthan gum or if another effective food thickener can induce similar effects. Furthermore, in order to elucidate the underlying mechanisms, the pastes were prepared under varying conditions: heating (70 or 72.5 °C) was performed under static as well as under shearing conditions.

Due to its anionic nature, xanthan gum is sensitive to variations in salt content, which in turn affects its functionality when combined with starches (Samutsri and Suphantharika, 2012, Viturawong et al., 2008). Throughout the manuscript, a salt concentration of 0.01 M will be maintained, however, the effect of varying salt concentrations will be briefly touched as well.

Section snippets

Materials

Xanthan gum (Satiaxane CX911, pyruvic acid content >1.5%) and guar gum (Viscogum MP41230) were acquired from Cargill Texturizing Solutions (Ghent, Belgium). Native waxy maize starch (Merizet 300) was provided by Tate & Lyle Benelux.

Preparation of gum solutions

Xanthan gum powder was dispersed in deionized water, whilst continuously stirring with a magnetic stirrer. The NaCl concentration was adjusted to 0.01 M for all the experiments, except for one part of the setup, where no salt was added to the xanthan solutions (this

Flow behavior of the gum solutions

The hydrocolloid solutions that were later on used to perform the pasting experiments, were first rheologically characterized. Two concentrations were selected for both hydrocolloids: 0.2% and 0.4% (w/w). The flow curves of the obtained gum solutions were recorded at two temperatures: 20 °C and 72.5 °C (example curves are depicted in Fig. 1). The curves confirm a strong shear thinning behavior of xanthan gum as the viscosity drops over several logarithmic scales with increasing shear rate. This

Conclusions

The effects of guar and xanthan gum on the mild temperature pasting behavior of waxy maize starch were studied in this setup. The use of the starch pasting cell geometry of the rheometer allowed to accurately control the preparation conditions of the pastes. In particular the effects of different shearing conditions (no shear, 50 s−1 and 150 s−1) were compared to elucidate the influence of the gums on granule swelling and breakdown.

At the concentrations studied here, the gums did not induce

Acknowledgments

The financial support of the Hercules Foundation (AUGE/013), the Belgian Research Fund (B/11599/17) is gratefully acknowledged. Tate & Lyle and Cargill, are thanked for providing samples of the products. This research is conducted with the financial support of the Special Research Fund of Ghent University, Grant 01D03909. The authors would also like to thank Mrs. Beatrijs Vermeule for practical assistance with the labeling of the gums.

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