Application of the Williams–Landel–Ferry model to the viscosity–temperature relationship of Australian honeys P.A. Sopade a,b, * , P. Halley b , B. Bhandari a , B. D’Arcy a , C. Doebler b ,N.Caffin a a Food Science and Technology Group, School of Land and Food Sciences, University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia b Department of Chemical Engineering, Material Characterisation and Processing Centre, University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia Received 14 December 2000; accepted 27 March 2002 Abstract TherheologicalbehaviourofnineunprocessedAustralianhoneyswasinvestigatedfortheapplicabilityoftheWilliams–Landel– Ferry(WLF)model.Theviscosityofthehoneyswasobtainedoverarangeofshearrates(0.01–40s 1 )from2 ° to40 °C,andallthe honeys exhibited Newtonian behaviour with viscosity reducing as the temperature was increased. The honeys with high moisture wereoflowerviscosity.Theglasstransitiontemperaturesofthehoneys,asmeasuredwithadifferentialscanningcalorimeter(DSC), ranged from 40° to 46 °C, and four models (WLF, Arrhenius, Vogel–Tammann–Fulcher (VTF), and power-law) were inves- tigated to describe the temperature dependence of the viscosity. The WLF was the most suitable and the correlation coefficient averaged 0:999  0:0013asagainst0:996  0:0042 for the Arrhenius model while the mean relative deviation modulus was 0–12% for the WLF model and 10–40% for the Arrhenius one. With the ‘‘universal’’ values for the WLF constants, the temperature de- pendenceoftheviscositywasbadlypredicted.Fromnon-linearregressionanalysis,theconstantsoftheWLFmodelsforthehoneys wereobtained(C 1 ¼ 13:7–21:1; C 2 ¼ 55:9–118:7)andaredifferentfromtheuniversalvalues.TheseWLFconstantswillbevaluable for adequate modeling of the rheology of the honeys, and they can be used to assess the temperature sensitivity of the honeys. Ó 2002 Elsevier Science Ltd. All rights reserved. Keywords: Arrhenius model; Vogel–Tammann–Fulcher model; Glass transition; Newtonian; Rheology; Honey 1. Introduction Rheological properties of food materials are very valuable and useful in their processing, handling and storage (Rielly, 1997; Steffe, 1996). With special refer- ence to honey, various studies have reported the rela- tionship between the viscosity of different honeys and shear rate or temperature or both (Assil, Sterling, & Sporns, 1991; Junzheng & Changying, 1998; White, 1975,1978).Morerecently,Bhandari,D’Arcy,andChow (1999a) and Mossel, Bhandari, D’Arcy, and Caffin (2000) reported on Australian honeys, and used the Arrhenius model to describe the influence of tempera- ture (1°–40 °C) on the viscosity of the honeys. Apart from moisture content (or composition), honeys are generally very highly sensitive to temperature (White, 1975), the more reason why this must be critically esti- mated and modeled. The Arrhenius model is widely used for temperature dependence of a property but models such as the Wil- liams–Landel–Ferry (WLF), Vogel–Tamman–Fulcher (VTF), and power-law have proved equally useful for the viscosity–temperature relationship of food systems (Ollett & Parker, 1990; Soesanto & Williams, 1981; Williams, Landel, & Ferry, 1955). Although the last three models can be used with the glass transition tem- perature (T g ) as a parameter, temperatures within the experimental range can serve as a reference (Peleg, 1992). However, none of these models, which can be termed viscosity-glass-transition (VGT) models, has been applied to honeys. Perhaps, the handicap was the absence of the glass transition temperatures of the honeys studied and/or their glass viscosity. Glass tran- sition occurs when a food material changes from the rubberystatetotheglassystateduringcooling,andthe (rangeof)temperature(s)atwhichthisoccursisreferred Journal of Food Engineering 56 (2002) 67–75 www.elsevier.com/locate/jfoodeng * Corresponding author. Address: Department of Chemical Engi- neering, Material Characterisation and Processing Centre, University of Queensland, St. Lucia, Brisbane, Qld 4072, Australia. Tel.: +61-7- 336-53931; fax: +61-7-336-54199. E-mail address: p.sopade@cheque.uq.edu.au (P.A. Sopade). 0260-8774/02/$ - see front matter Ó 2002 Elsevier Science Ltd. All rights reserved. PII:S0260-8774(02)00149-8