Journal of Food Physics Vol. 27. (2014.)

K. Laos, M. Harak The viscosity of supersaturated aqueous glucose, fructose solutions

The viscosity of supersaturated aqueous glucose, fructose and glucose-fructose solutions K. Laos1,2, M. Harak1

1 Tallinn University of Technology, Abstract. The viscosity of supersaturated aqueous Faculty of Chemical and glucose-fructose solutions has been measured, using flow Materials Technology. curves on an Anton Paar RheolabQC rotating viscometer. Department of Food Three different concentration (85%, 83%, 81%) and five Processing, different glucose:fructose ratios (60:40, 55:45, 50:50, 2 Competence Centre of 45:55, 40:60) has been selected in a similar composition to Food and Fermentation honey. Measurements were taken at temperatures ranging Technologies, Tallinn from +10 to +50 °C. All systems exhibited Newtonian behaviour, meaning [email protected] that the viscosity is independent of the shear rate. The viscosity of the supersaturated solutions was decreasing with increasing temperature and increasing with increasing Keywords: the concentration. Aqueous solutions of fructose are somewhat more viscous than glucose solutions. For supersaturation, aqueous glucose-fructose solutions, the increase of fructose glucose, concentration increases the solutions viscosity. fructose, viscosity

INTRODUCTION industrial processes like pumping, filtration, mixing and packaging. Viscosity is widely acknowledged as a There have been several studies key physical property in understanding the looking at viscosities of aqueous sugar flow of raw materials, processing solutions. The viscosity-temperature intermediates and final products (Ferry, relationship in aqueous sugar amorphous 1980). Aqueous solutions of glucose and phases in partially frozen systems has been fructose at different temperatures and evaluated by Maltini & Anese (1995) and concentrations are found in several food in liquid supercooled pure sugar systems processes and basis to formulation of a has been evaluated by Kerr & Reid (1994). number of food products or ingredients in Several studies have been performed with the bakery, ice cream, and confectionary solutions of sucrose, glucose and/or industries (Telis et al., 2007). The fructose in a range of temperatures and confectionary products as well as honey concentrations with objective of contain high amount of sugar and knowing comparing different models (Arrhenius, the flow properties of supersaturated sugar Williams-Landel-Ferry (WLF), Vogel- solutions are important in designing Taumman-Fulcher (VTF), and power law) to fit experimental data (Recondo, et al.,

K. Laos, M. Harak The viscosity of supersaturated aqueous glucose, fructose solutions

2006; Quintas et al., 2006; Telis et al., RESULTS AND DISCUSSION 2007). All the models can be employed All systems exhibited Newtonian time quite satisfactorily to describe the independent behaviour in the whole experimental behaviour. However, the domain of temperature, meaning that the Arrhenius model predicts the lower viscosity is independent of the shear rate. temperature dependence, while the WLF This is according to other published predicts the higher temperature works, sugar solutions as well as honey are dependence close to the Tg value (Telis et reported to be Newtonian fluids (Recondo al., 2007). et al., 2006; Telis et al., 2007; Lazaridou et There is a lack of data on al., 2004). supersaturated aqueous sugar systems The supersaturated 83% glucose similar to honey. The aim of the present solution showed the low viscosity 2.14 ± work was to determine experimental 0.30 Pa*s at 20 °C compared to other values of viscosities for supersaturated tested solutions. The supersaturated 83% aqueous glucose-fructose solutions as a fructose solution had viscosity 9.27 ± 0.23 function of temperature and concentration. Pa*s and 83% glucose-fructose solutions had slightly higher viscosity values than MATERIALS AND METHODS fructose solutions, ranging from 11.0 ± 0.3 Supersaturated solutions of glucose, Pa*s (G50:F50) to 13.15 ± 1.32 Pa*s fructose and glucose-fructose were (G40:F60) at 20 °C. The viscosity of prepared by appropriate amounts of supersaturated 83% glucose-fructose glucose (Cargill) and fructose (Cargill), up solutions increased with an increase in to complete dissolution in distilled water at fructose content (Figure 1). This is in 95 °C. Three different concentration (85%, agreement with Sopade et al. (2004) work. 83%, 81% w/w) and five different glucose Glucose and fructose are chemically (G):fructose (F) ratios (60:40, 55:45, different. Fructose is a ketose sugar, while 50:50, 45:55, 40:60) has been selected in a glucose is an aldose sugar, and the similar composition to honey. positions of the hydroxyl groups in these Flow properties of samples at sugars can influence hydrogen bonding temperatures in the range of 10 – 50 °C at with water. 10 °C intervals were measured with a The viscosity of the supersaturated RheolabQC rotating viscometer (Anton solutions was decreasing with increasing Paar, Germany) fitted with CC27 system, temperature (Figure 2a). As temperature with temperature controlled water bath. increases, viscosity falls, due to less The apparent viscosity η was measured as molecular friction and reduced a function of shear rate γ ̇ (1 – 100 s-1). hydrodynamic forces (Mossel et al., 2000). Moreover, the apparent viscosity was The value of viscosity had a dramatic measured as a function of shear time (2 decrease in the low range of temperature. minutes), while keeping the shear rate Similar results have been obtained in constant (50 s-1). Samples were allowed to different studies (Recondo et al., 2006; rest for about ten minutes before to Sopade et al., 2004; Telis et al., 2007). measuring their rheological properties. All Generally, at a low temperature, the determinations were performed in viscosity of materials is usually very high triplicate. as they tend towards the glassy state (Rahman, 1995).

K. Laos, M. Harak The viscosity of supersaturated aqueous glucose, fructose solutions

15 14 13 R2=0,7242 12 11 10 9 8 Viscosity, Pa*s Viscosity, 7 6 5 0,6 0,8 1,0 1,2 1,4 1,6 Glucose/fructose

Figure 1 Viscosity of supersaturated 83% glucose-fructose solution as a function of glucose-fructose ratio at 20 oC A 70

60 83% Glucose 83% G50:F50 83% Fructose 83% G55:F45 50 83% G40:F60 83% G60:F40 83% G45:F55 40

20 Viscosity, Pa*s Viscosity, 10

10 20 30 40 50 Temperature, oC

B 250 81% G50:F50 200 83% G50:F50 85% G50:F50

150

100

50 Viscosity, Pa*s

10 20 30 40 50 Temperature, oC

Figure 2 Viscosity of sugar solutions as a function of temperature (a) and solid content (b) at shear rate 50 s-1.

K. Laos, M. Harak The viscosity of supersaturated aqueous glucose, fructose solutions

Increase in moisture content (decrease Lazaridou, A., Biliaderis, C.G., in solids) (Figure 2b) exponentially reduce Bacandritsos, N., & Sabatini, A.G. (2004). the viscosity of aqueous supersaturated Composition, thermal and rheological glucose/fructose solutions. This is in behaviour of selected Greek honeys. accordance with published studies on Journal of Food Engineering, 64:9-21. honeys and other foods (Munro, 1943; Maltini, E., & Anese, M. (1995). Sopade et al., 2004). The temperature have Evaluation of viscosities of amorphous more effect on more concentrated phases in partially frozen systems by WLF solutions. kinetics and glass transition temperatures. Food Research International, 28:367-372. CONCLUSIONS Mossel, B., Bhandari, B., D’Arcy, B., & Caffin, N. (2000). Use of an Arrhenius Supersaturated aqueous glucose, model to predict rheological behaviour in fructose and glucose-fructose solutions some Australian honeys. Food Science and showed Newtonian time independent Technology, 33:545-552. behaviour. The glucose solution showed Munro, J.A. (1943). The viscosity and the low viscosity compared to other tested thixotropy of honey. Journal of solutions. Increases in moisture, glucose Entomology, 36:769-777. and temperature reduced the viscosity Quintas, M., Barandao, T.R.S., Silva, while the increase in fructose content C.L.M., & Cunha, R.L. (2006). Rheology increased the viscosity of supersaturated of supersaturated sucrose solutions. glucose-fructose solutions. Journal of Food Engineering, 77:844-852. Rahman, S. (1995). Food Properties ACKNOWLEDGEMENTS Handbook. Boca Raton: CRC Press. Recondo, M.P., Elizalde, B.E., & This work was supported by the Buera, M.P. (2006). Modelling institutional research funding IUT (1927) temperature dependence of honey of the Estonian Ministry of Education and viscosity and of related supersaturated Research and by the EU Regional model carbohydrate systems. Journal of Development Fund (project EU29994). Food Engineering, 77:126-134 Sopade, P.A., Halley, P.J., D’Arcy, REFERENCES B.R., Bhandari, B., & Caffin, N. (2004). Dynamic and steady-state rheology of Ferry, J.D. (1980). Viscoelastic Australian honeys at subzero temperatures. Properties of Polymers. New York: John Journal of Food Process Engineering, Wiley & Sons. 27:284-309. Kerr, W.L., & Reid, D.S. (1994). Telis, V.R.N., Telis-Romero, J., Temperature dependence of the viscosity Mazzotti, H.B., & Gabas, A.L. (2007). of sugars and maltodextrins in coexistence Viscosity of aqueous carbohydrate with ice. Lebensmittel-Wissenchaft und – solutions at different temperatures and Technologie, 27:225-231. concentrations. International Journal of Food Properties, 10:185-195.