ORIGINAL PAPER Thermal and rheological properties of the supersaturated sucrose solution in the presence of different molecular weight fractions and concentrations of dextran Mohanad Bashari • Mehdi Nikoo • Zhengyu Jin • Yuxiang Bai • Xueming Xu • Na Yang Received: 12 November 2011 / Revised: 11 January 2012 / Accepted: 16 January 2012 / Published online: 1 February 2012 Ó Springer-Verlag 2012 Abstract In our current research work, we investigated the effects of molecular weight (M w ) and the concentration of dextran presence during cane sugar manufacturing on the rheological and glass transition properties of supersat- urated sucrose solution. Three dextrans of various M w , namely 100,000 g/mol (T 100 ), 500,000 g/mol (T 500 ) and 2,000,000 g/mol (T 2000 ), were admixed in concentrations between 1,000 and 10,000 ppm with 65 and 75% w/w sucrose solution. The results indicated that both the apparent viscosity and dynamic modulus increased with an increase in dextran concentrations and they demonstrated strong dependence on its M w . Glass transition temperature (T g ) of the samples was measured by differential scanning calorimetry, and their dependence on dextran M w and concentration was analyzed by the Fox and expanded Gordon–Taylor mathematical models. It was found that the higher the M w and concentration of the dextran, the greater the increase in T g . The expanded Gordon–Taylor equation has proved useful in predicting the T g of the sucrose solution in the presence of polymer. Keywords Dextran  Supersaturated sucrose solution  Rheological properties  Glass transition  Molecular weight  Concentration Introduction Dextran is a water-soluble polysaccharide that consists mainly of a-(1-6) linked D-glucopyranose residues with a low percentage of a-(1-2), a-(1-3) and a-(1-4) linked side chains [1]. Its structure and structural properties vary widely, and its M w ranges from 1,500 to several million Da [2]. In sugar production, dextrans are undesirable com- pounds synthesized by contaminant microorganisms from sucrose [3]. They lead to a false high polarization, increased viscosity, slowing of filtration, lower evaporation rates, elongated crystals, longer wash and separation cycles in centrifuges and an increase of sugar loss to molasses [4–6]. The most damaging effects of elevated dextran concentrations in a technical sucrose solution are foreseen in the crystallization process. It is estimated that for every 300 ppm dextran in syrup there is a 1% increase in molasses purity (the percentage ratio of sucrose) in total solids in a sugar solution [7–9]. However, most of the major processing problems associated with dextran in the raw sugar factories are due to its large M w . Dextran fractions occurring in sugarcane are almost entirely produced by Leuconostoc mesenteroides, a ubiq- uitous bacterium especially prevalent in any sugar field [10]. They enter the cane at places of exposed tissue caused by machine harvesting, cutting, burning, freezing, disease and pests [6]. Many investigations suggested a minimiza- tion of dextran levels in the cane sugar factories by con- trolling microorganisms from cane harvesting to juice extraction [11]. It was found that sugar recovery could be improved by preventing bacterial polysaccharides produc- tion in cane juice [12]. Furthermore, due to the high sol- ubility of most dextrans in water (above 30 mg/ml), it is very difficult to remove dextrans from juice by filtration processes [13, 14]. M. Bashari  M. Nikoo  Z. Jin (&)  Y. Bai  X. Xu  N. Yang The State Key Laboratory of Food Science and Technology, School of Food Science and Technology, Jiangnan University, 1800 Lihu Road, Wuxi 214122, China e-mail: jinlab2008@yahoo.com M. Bashari e-mail: mohanad.81@hotmail.com 123 Eur Food Res Technol (2012) 234:639–648 DOI 10.1007/s00217-012-1673-3