Influence of Temperature and Salt on Viscosity Property of Guar Gum

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1 Naresuan University Jurnal 2007; 15(2): Influence f Temperature and Salt n Viscsity Prperty f Guar Gum Anchalee Srichamren Department f Agr-Industry, Faculty f Agriculture, Natural Resurces and Envirnment, Naresuan University, Phitsanulk 65000, Thailand. Crrespnding authr. address: anchalee1@gmail.cm (A. Srichamren) Received 30 April 2007; accepted 4 July 2007 Abstract The viscsity f guar gum is ne f the factrs that may reduce nutrient (i.e. glucse, lipid) absrptin in the intestinal lumen. Sme studies have shwn that viscus guar gum did nt decrease nutrient absrptin. Thse studies, hwever, did nt reprt the effect f temperature r Krebs slutin n viscsity f guar gum used. Therefre, the present study determined the viscsity behavir f guar gum at different temperatures (4 C, 25 C, 37 C) and different slvents (water vs Krebs bicarbnate). When the 0.5% (w/w) guar gum was heated frm either 4 C r 25 C t physilgical temperature (37 C) and held fr 2 h, the viscsity measured at 37 C f bth slutins was similar. This result was similarly bserved with 1% (w/w) guar gum. Krebs bicarbnate decreased the viscsity f 0.25% (w/w) guar gum at 37 C, but it increased the viscsity f 0.5% (w/w) guar gum at 37 C. The results f this study may help t better understand the viscsity behavir f guar gum under prcessing and physilgical cnditins. Keywrds: Guar; Gum; Viscsity; Salt; Temperature Intrductin Guar gum is a hydrcllid btained frm the endsperm f the Cyanmpsis tetragnlbus belnging t the family Leguminsae. The structure f guar gum cnsists f a linear backbne f β(1,4)-linked D-mannse units with varius amunts f α(1,6)-linked D-galactse side chains. The rati f mannse t galactse is 2:1. Guar gum is an ecnmical thickener and stabilizer. It easily hydrates in cld water t give highly viscus slutin. The very high viscsity attained at lw cncentratins makes guar gum an excellent thickener in the fd industry, such as in sups, desserts, pie fillings (Dierckx & Dewettinck, 2002). It has been reprted that guar gum can reduce nutrient (i.e. glucse, lipids) absrptin in humans, whether taken as a large dse in slutin r in a slid fd (Jenkins et al., 1980; Jenkins et al., 2000). The prpsed mechanism f a reductin in the rate f glucse absrptin is due t the presence f viscus gum dispersin in the gastrintestinal tract t frm viscus slutin, which reduces the rate f transprt f slute acrss the intestinal epithelium. Hwever, the studies f the effect f guar gum n absrptin are cntradictry. Sme studies have shwn that viscus gum did nt delay nutrient absrptin acrss intestinal epithelium (Elsenhans et al., 1980; Frster & Hs, 1977; Schwartz & Levine, 1980). Leclere et al. (1994) indicated that the viscsity f guar gum did nt reduce the accessibility f luminal cntents tward the absrptive mucsal surface. One f the reasns fr these cntrversies may lie in the study design, fr example, the cncentratins f guar gum used r cnditins f the test slutin, which may give different viscsities in the intestinal lumen. Guar is a nn-inic gum which is nt affected by inic strength r ph. Hwever, strng acid and alkali at high cncentratin tend t reduce the viscsity. Studies shwed the changes in the rhelgical and thermal prperties f gum when salts were added in the slutin (Dyle et al., 2006; Richardsn & Nrtn, 1998). Whistler & BeMiller (1997) reprted that the viscsity f guar gum was markedly reduced by the presence f NaCl.

2 56 Naresuan University Jurnal 2007; 15(2) Althugh it has been reprted that salts reduced the viscsity f guar slutin, it has never been demnstrated whether the Krebs bicarbnate, a physilgical buffer, affects the viscsity f guar slutin. Generally, the alkali cnditin in the lumen is a cmbinatin f many salts e.g. NaCl, KCl, NaHCO 3, KH 2 PO 4, MgSO 4. It is interesting t investigate the effect f physilgical buffer slutin (Krebs bicarbnate) n viscsity cmpared t that f the water. This may expand ur knwledge n the cntrversy whether guar gum reduces glucse absrptin in the gastrintestinal tract. Many viscus fd prducts are kept in either refrigeratr (4 C) r rm temperature (25 C) befre cnsumptin. Generally, increased temperature reduces the viscsity f gum (Burkus & Temelli, 2005). Since fd is digested in gastrintestinal tract apprximately 2-4 hurs, the physilgical temperature (37 C) fr such perid may affect viscsity f guar gum in the intestinal lumen. N previus studies reprted such the effect. It is interesting t study the viscsity prperty f guar gum when the slutin is heated frm the strage temperature f fd prducts t the physilgical temperature fr ver 2 h e.g. frm 4 C t 37 C r frm 25 C t 37 C When using guar gum fr reducing sugars and lipids absrptin in the intestinal lumen, there are at least tw factrs t be cncerned with: the physilgical temperature and buffer slutin. The bjectives f the present study were (a) t investigate the effect f temperatures, based n strage temperature (4 C and 25 C) and physilgical cnditin (37 C), n the viscsity f guar gum, and (b) t investigate the effect f Krebs bicarbnate slutin n the viscsity f guar gum. Materials and Methds Guar gum (100 mesh) was btained frm Danisc (Vernn, Texas). All chemicals (e.g. NaCl, MgSO 4, KH 2 PO 4, KCl, NaHCO 3 ) used in this study were f analytical grade and prcured frm Sigma Chemical (St. Luise, MO). Preparatin f Krebs slutin Krebs bicarbnate slutin was prepared by mixing f 0.3 g MgSO 4, 0.15g KH 2 PO 4, 0.35g KCl, 2.1 g NaHCO 3, 6.5 g NaCl in 2 litres f water, and then the slutin was adjusted t ph 7.4. The buffer slutins were prepared at tw fld f the final cncentratins in rder t be cmbined with guar slutins at the rati f 1:1. Preparatin f guar slutins fr the rdering temperature test Aqueus guar slutins were prepared n a weight-t-weight basis using reverse smsis water in a biling water bath fr 30 min, with gentle stirring t ensure hmgeneity. The slutins were cled and held at 4 C r 25 C fr 2 h, with gentle stirring t ensure hmgeneity. A crrectin was later made fr any lss f water due t evapratin prir t determining the viscsity. Thse slutins were then heated t 37 C and were held at 37 C fr 2 h in water bath, with gentle stirring t ensure hmgeneity. A crrectin was made fr any lss f water due t evapratin prir t measuring the viscsity. Preparatin f guar slutins fr the effect f Krebs bicarbnate test Since the Krebs bicarbnate slutin shuld nt be heated fr 30 min, guar slutins were prepared at tw fld f the final cncentratin in rder t be cmbined with Krebs slutin at the rati f 1:1. The preliminary study shwed that the maximum cncentratin f guar gum that cmpletely disslved in biling water withut clusters

3 Naresuan University Jurnal 2007; 15(2) 57 f gel-like was at 1% (w/w). Therefre, tw dses f guar gum, 0.5% and 1% (w/w), were prepared as tw fld f the final cncentratin in the present study. Guar gum at 0.5%, and 1% (w/w) were disslved in a biling water bath fr 30 min. After cling, the slutins were crrected fr any lss f water due t evapratin. These slutins were diluted with either water r Krebs bicarbnate slutin t a rati f 1:1, with gentle stirring t ensure hmgeneity fr 2 h at 37 C. The final cncentratins f guar gum in the test slutins were 0.25%, and 0.5% (w/w), respectively. Prir t measuring the viscsity, these slutins were crrected fr any lss f water due t evapratin. Determinatin f viscsity Viscsity measurements were recrded at cnsecutive fixed shear rates f s -1 using a Parr Physica UDS 200 rhemeter (Glenn, VA). The viscmeter was equipped with a Peltier heating system that cntrlled the sample temperature. Viscsity measurements were recrded at 4 C, 25 C, and 37 C using DG 27 cup and bb gemetry with a sample size f g. All analyses were perfrmed in duplicate. Samples were put in the cup f viscmeter until the desired temperatures were stable fr 3 min befre analyses. The same sample was used in the test f rdering-temperature measurements. The shear rate was reprted in s -1 after multiplying the rpm value by a cnversin factr f 1.29 s -1 prvided by the manufacturer. Statistical analyses Data f the viscsity f slutins were reprted as the mean + SEM. The viscsity f guar slutins in either water r Krebs slutin was statistically analyzed by ne way ANOVA, fllwed by Student-Newman-Keuls (SNK) as a pst-hc test. Statistical analyses f viscsity f slutins in rdering temperature test were calculated by repeated measurement analysis ANOVA, fllwed by SNK. The p level f < 0.05 was cnsidered t be statistically significant. Results Effect f rdering temperatures n viscsity f guar gum The viscsities f 0.5% and 1% (w/w) guar slutins at 4 C, 25 C, and 37 C were bviusly reduced when the shear rates were increased at all shear rates (Table 1 t 4). The viscsity f 0.5% (w/w) guar slutin at 4 C was significantly higher than that f slutin at 37 C (p<0.05, Table 1). The viscsity f 0.5% (w/w) guar slutin at 25 C was significantly higher than that f 37 C (p<0.05, Table 2). When cmpared the viscsity at 37 C between Table 1 and 2, the viscsities were nt different by greater than 10 milli pascal secnd (mpa.s) at the shear rates f 12.9, 25.8, 64.6, and 129 s -1. The viscsity f 1% (w/w) guar slutin at 4 C was significantly higher than that f slutin at 37 C (p<0.05, Table 3). The viscsity f 1% (w/w) guar slutin at 25 C was nt significantly different cmpared t that f slutin at 37 C at all shear rates (p>0.05, Table 4). When the viscsity at 37 C between Table 3 and 4 was cmpared, the viscsities were nt significantly different at the shear rate f 6.46 t 129 s -1 (p>0.05). Hwever, at very lw shear rate f 1.29 s -1, the viscsity f guar slutin with the beginning temperature at 4 C was significantly lwer than that f guar slutin with the beginning temperature at 25 C (p<0.05).

4 58 Naresuan University Jurnal 2007; 15(2) Table 1. Viscsity f 0.5% (w/w) guar slutin at 4 C and 37 C * indicates a significant difference ( p<0.05) f the viscsity between 4 C vs. 37 C at the same shear rate. Table 2. Viscsity f 0.5% (w/w) guar slutin at 25 C and 37 C * indicates a significant difference ( p<0.05) f the viscsity between 25 C vs. 37 C at the same shear rate. Table 3. Viscsity f 1% (w/w) guar slutin at 4 C and 37 C * indicates a significant difference ( p<0.05) f the viscsity between 4 C vs. 37 C at the same shear rate. Table 4. Viscsity f 1% (w/w) guar slutin at 25 C and 37 C Effect f Krebs bicarbnate slutin n viscsity The viscsity f 0.25% (w/w) guar slutin disslved in Krebs slutin markedly decreased at all shear rates cmpared t that f guar disslved in water at 37 C (p<0.05, Table 5). On the cntrary, the viscsity f 0.5% (w/w) guar slutin disslved in Krebs slutin significantly increased at all shear rates when cmpared t that f guar disslved in water at 37 C (p<0.05, Table 6).

5 Naresuan University Jurnal 2007; 15(2) 59 Table 5. Viscsity f 0.25% (w/w) guar slutin mixed with either water r Krebs bicarbnate slutin at 37 C *indicates a significant difference (p<0.05) f the viscsity f guar slutin mixed with water vs. Krebs slutin at the same shear rate. Table 6. Viscsity f 0.5% (w/w) guar slutin mixed with either water r Krebs bicarbnate slutin at 37 C *indicates a significant difference (p<0.05) f the viscsity f guar slutin mixed with water vs. Krebs slutin at the same shear rate. Discussin Guar gum attained at lw cncentratin in water prvides high viscus slutin. When guar gum is dispersed in water, the galactse side chain f the mlecule interacts with water mlecule, leading t inter-mlecular chain entanglement f the guar gum in aqueus slutins, and causing the viscsity f the slutin. With the increase in cncentratin f guar gum, the degree f inter-mlecular chain interactin r entanglement wuld be enhanced, which results in increased viscsity (Zhang et al., 2005). The viscsity f 1% (w/w) guar slutin in the present study was significantly higher than that f 0.5% (w/w) guar slutin when cmpared at the same determining temperature (Table 1 vs. 3; Table 2 vs. 4). Guar slutin in the present study shwed the decreased viscsity with increasing shear rates (Table 1 t 4), thus this material has shear-thinning behavir and nn-newtnian flw, particularly in pseudplastic sub-class (Burne, 2002). Temperature causes the water mlecules t lse their rdering arund the guar mlecules, thus affecting the cnfrmatin and resulting in reduced-viscsity behavir (Finney & Sper, 1994). Results f this study shwed that the viscsity f 0.5% (w/w) guar slutins was decreased when the gaur slutins were heated and held in the physilgical-temperature fr 2 h e.g. frm 4 C t 37 C and 25 C t 37 C (Table 1 & 2). This may be due t elevated temperature increasing the energy dissipatin mvement f the mlecule, r decreasing the inter-mlecular interactins, which in turn decrease the interference f the hydrdynamic dmain (Chen & Chen, 2001). Interestingly, the result shwed that the viscsity f 1% (w/w) guar slutin at 37 C was similar t that f slutin at the beginning temperature f 25 C (Table 4). This indicates that the viscsity f 1% (w/w) guar slutin was nt influenced by the small-increased temperature. It is pssible that the inter-mlecular interactins

6 60 Naresuan University Jurnal 2007; 15(2) may nt be decrease when the temperature was nt much different at high cncentratin f guar gum. Hwever, 1% (w/w) guar slutin used in this study was prepared as qualitative analyses. Thus, it requires further investigatin in higher vlume f water. The preliminary study shwed that the viscsity was decreased when the slutin was heated. When such slutin was recled, the viscsity returned t the similar value at its beginning temperature (data nt shwn). This indicates that temperature caused reversible change in the viscsity f guar gum. Interestingly, results in the present study shwed that heating 1% (w/w) guar slutin frm either 4 C r 25 C t 37 C, the viscsity f bth slutins at 37 C was nt significantly different (p>0.05, Table 3 & 4). This result was cnsistent with 0.5% (w/w) guar slutin but nly at the shear rate f 12.9 t 129 s -1 (Table 1 & 2). Althugh n infrmatin is available n shear rates within the intestine, it is perhaps relevant t nte that the values f 50 t a few hundreds per secnd have been suggested fr the muth during masticatin (Sherman, 1976). Results f viscsity at 37 C in the present study are useful fr physilgical applicatin. Fr example, if it is desired t use guar-cntaining prducts which kept in different strage temperature e.g., ice cream, beverages, jelly, by expecting the similar value f viscsity at physilgical temperature, the amunt f guar gum used in fd prducts culd be at either 0.5% r 1% (w/w). The presence f Krebs bicarbnate slutin markedly decreased the viscsity f 0.25% (w/w) guar slutin cmpared t that f guar in water alne (Table 5). This reduced viscsity may be due t a decrease f the effective vlume fractin, r a less entangled state f guar slutin upn the additin f salts. The pssible mechanism is based n the hypthesis that salts are hydrphilic mlecules that strngly interact with water (Cybulska & De, 2002). Results in the present study suggest that high cncentratins f salts reduce the availability f water in the slutin preventing the expansin f the guar netwrks, thereby decreasing the viscsity. Cnsistent with this hypthesis, it was reprted that added salts restricted the hydratin f guar gum in the slutin (Dyle et al., 2006). Cntrarily, results in this study shwed that the viscsity f the 0.5% (w/w) guar slutin significantly increased when the salts were added (Table 6). This suggests that the inter-mlecular netwrks f guar and water were nt disturbed. The pssible mechanism t explain the result is that the presence f salts can facilitate the frmatin f intermlecular aggregates due t the alteratin f the charge density and cnfrmatin f gum (Gittings et al., 2001). Zhang reprted that the imprved viscsity f the slutin with increased salt cncentratin was due t the additin f salt disrupting the intra- and intermlecular assciatins, resulting in the expansin f the chain cnfrmatin. (Zhang et al., 2005). Hwever, it is t early t cnclude the mechanism at this pint. It requires further investigatin fr structure and functinal relatinship f guar gum in Krebs slutin. Guar gum had been used t reduce the glucse absrptin frm the intestinal lumen. Many researchers fund that the higher cncentratin f guar gum was mre effective than the lwer cncentratin (Jenkins et al., 2001). This may be attributed t the high viscsity prperty f the higher cncentratin f guar gum in the intestinal lumen. In the present study, the increased viscsity f 0.5% (w/w) guar slutin in Krebs bicarbnate, but decreased viscsity f 0.25% (w/w) guar slutin in Krebs bicarbnate, suggests that 0.5%(w/w) guar gum may be able t decrease the rate f glucse absrptin mre than 0.25% (w/w) guar gum.

7 Naresuan University Jurnal 2007; 15(2) 61 Cnclusin The viscsity f 0.5% (w/w) guar gum at 4 C was significantly higher than that f slutin at 25 C (p<0.05). When these tw slutins were heated and held at 37 C fr 2 h, their viscsities at 37 C were similar. This result was cnsistent with 1% (w/w) guar gum. These results suggest that if it is desired t use guar-cntaining prducts which kept in different strage temperature e.g., ice cream, beverages, jelly, by expecting the similar value f viscsity at physilgical temperature, the amunt f guar gum used in fd prducts culd be at either 0.5% r 1% (w/w). The viscsity f 0.25% (w/w) guar gum mixed with Krebs bicarbnate buffer was markedly decreased when cmpared t that f guar gum in water. In cntrast, the viscsity f 0.5% (w/w) guar gum mixed with Krebs bicarbnate buffer was significantly increased when cmpared t that f guar gum in water. These cntrary results suggest that tw different mechanisms might be applied fr different cncentratins f guar gum mixed with Krebs slutin. If 0.25% (w/w) guar gum is used, Krebs bicarbnate may impede the entanglement frmatin f guar gum, thereby decreasing the viscsity. Hwever, if 0.5% (w/w) guar gum is used, Krebs bicarbnate may facilitate the frmatin f intermlecular aggregates r alter the charge density f the slutin thereby increasing the viscsity. Nevertheless, these prpsed mechanisms require further investigatin. References Burne, M. C. (2002). Fd texture and viscsity: Cncept and measurement (2 nd ed.). New Yrk: Academic Press. Burkus, Z., & Temelli, F. (2005). Rhelgical prperties f barley β-glucan. Carbhydrate Plymers, 59, Chen, R. H., & Chen, W. Y. (2001). Rhelgical prperties f the water-sluble mucilage f a green laver, Mnstrma nitidium. Jurnal f Applied Phyclgy, 13, Cybulska, B., & De, P. E. (2002). Water and fd quality. In Z. E. Sikrski (Ed.), Chemical and functinal prperties f fd cmpnents (pp ). Lndn: CRC Press. Dierckx, S., & Dewettinck, K. (2002). Seed gums. In E. Vandamme, S. De Baets, A. Steinbuchel (Eds.), Plysaccharides frm eukartes, biplymers: Vl. 6. Plysaccharides II (pp ). Berline: Wiley VCH. Dyle, J. P., Giannuli, P., Martin, E. J., Brks, M., & Mrris, E. R. (2006). Effect f sugars, galactse cntent and chainlength n freeze-thaw gelatin f galactmannans. Carbhydrate Plymers, 64, Elsenhans, B., Sufke, U., Blume, R., & Caspary, W. F. (1980). The influence f carbhydrate gelling agents n rat intestinal transprt f mnsaccharides and neutral amin acids in vitr. Clinical Science, 59, Finney, J. L., & Sper, A. K. (1994). Slvent structures and perturbatin in slutins f chemical and bilgical imprtance. Chemical Sciety Reviews, 23, Frster, H., & Hs, I. (1977). Influence f gums n intestinal absrptin. Nutritin & Metablism, 21(Suppl. 1), Gittings, M. R., Cipelletti, L., Trappe, V., Weitz, D. A., In, M., & Lal, J. (2001). The effect f slvent and ins n the structure and rhelgical prperties f guar slutins. Jurnal f Physical Chemistry A, 105,

8 62 Naresuan University Jurnal 2007; 15(2) Jenkins, D. J. A., Kendall, C. W. C., Axelsen, M., Augustin, L. S. A., & Vuksan, V. (2000). Viscus and nnviscus fibres, nnabsrbable and lw glycaemic index carbhydrates, bld lipids and crnary heart disease. Current Opinin in Lipidlgy, 11, Jenkins, D. J. A., Reynlds, D., Slavin, B., Leeds, A. R., Jenkins, A. L., & Jepsn, E. M. (1980). Dietary fiber and bld lipids: Treatment f hyperchlesterlemia with guar crispbread. American Jurnal f Clinical Nutritin, 33, Jenkins, A. L., Vladimir, V., & Jenkins, D. J. A. (2001). Fiber in the treatment f hyperlipidemia. In G. A. Spiller (Ed.), CRC Handbk f dietary fiber in human nutritin (pp ). New Yrk: CRC Press. Leclere, C. J., Champ, M., Billt, J., Guille, G., Lecannu, G., Mlis, C., et al. (1994). Rle f viscus guar gums in lwering the glycemic respnse after a slid meal. American Jurnal f Clinical Nutritin, 59, Richardsn, P. H., & Nrtn, I. T. (1998). Gelatin behavir f cncentrated lcust bean gum slutins. Macrmlecules, 31, Schwartz, S. E., & Levine, G. D. (1980). Effect f dietary fiber n intestinal glucse absrptin and glucse tlerance in rats. Gastrenterlgy, 79, Sherman, P. (1976). The shear rate. In Y. Chen (Ed.), Characterizatin f mechanical prperties f fd materials (pp ). New Jersey: Rutgers University Press. Whistler, R. L., & BeMiller, J. N. (1997). Carbhydrate chemistry fr fd scientists. St. Paul: Eagan Press. Zhang, L. M., Zhu, J. F., & Hui, P. S. (2005). A cmparative study n viscsity behavir f water-sluble chemically mdified guar gum derivatives with different functinal lateral grups. Jurnal f the Science f Fd and Agriculture, 85,

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