Process Biochemistry 46 (2011) 599–603 Contents lists available at ScienceDirect Process Biochemistry journal homepage: www.elsevier.com/locate/procbio Short communication Microwave irradiation-assisted isomerization of glucose to fructose by immobilized glucose isomerase Dahai Yu ∗ , Hao Wu, Aijun Zhang, Li Tian, Ludong Liu, Chuanming Wang, Xuexun Fang ∗∗ Key Laboratory for Molecular Enzymology and Engineering of Ministry of Education, Jilin University, 2519 Jiefang Road, Changchun 130021, China article info Article history: Received 5 August 2010 Received in revised form 28 September 2010 Accepted 28 September 2010 Keywords: Microwave irradiation Conventional heating Glucose Fructose Isomerization abstract The isomerization of glucose to fructose by immobilized glucose isomerase (IGI, produced from Strep- tomyces murinus and immobilized on silica) was conducted under two different conditions—microwave irradiation and conventional heating to compare their overall effects. It was found that compared with conventional heating, microwave irradiation significantly enhanced the activity of IGI and the effects of acceleration might be non-thermal microwave effect. Under the optimum conditions of microwave irradiation-assisted isomerization (magnesium ion concentration of 50 mM, 0.1 M pH 7.5 phosphate buffered saline (PBS) buffer, 70 ◦ C, microwave power of 480 W, agitation speed of 150 rpm, glucose con- centration of 0.8 M and 2% IGI based on the solution weight percentage), 45% yield of fructose could be achieved in 16 h, while only 43% yield of fructose was obtained until 24 h by using conventional heating. These results indicated that microwave irradiation might be a fast and efficient method for enzyme-catalyzed isomerization of glucose to fructose. © 2010 Elsevier Ltd. All rights reserved. 1. Introduction Fructose is widely used in the food industry as a sweetener, a diuretic or a special food for diabetics [1]. It is a simple monosac- charide, and as an isomer of glucose, it shares the same empirical formula (C 6 H 12 O 6 ) with glucose, but has different structure, which considerably determines its physicochemical properties [2]. The primary reason for fructose to be used commercially in foods and beverages production is its low cost to produce high relative sweet- ness. It is considered to be the sweetest sugar found in nature. The sweetening capacity in glucose is 70–75% of that in sucrose, whereas fructose is twice as sweet as sucrose. This benefits prod- ucts containing fructose by making them less caloric with a similar degree of sweetness [3–5]. Fructose is also found in the synthet- ically manufactured sweetener, high-fructose corn syrup (HFCS) [6,7]. Moreover, fructose is usually used as a diabetic sweetener because it is only slowly reabsorbed by the stomach and does not influence the glucose level in blood [8–10]. The chemical conversion from glucose to fructose, which has been known for the past 100 years, constitutes one of a group of reactions collectively known as the Lobry de Bruyn-Alberda van Ekenstein transformation [11]. These reactions are usually carried out at high pH and temperature and the reaction is nonspecific in terms of the formation of nonmetabolizable sugars such as psi- ∗ Corresponding author. Tel.: +86 431 88498113; fax: +86 431 88980440. ∗∗ Co-corresponding author. Tel: +86 431 85155219; fax: +86 431 85155219. E-mail addresses: dahaiyu.lipase@yahoo.com.cn (D. Yu), fangxx@jlu.edu.cn (X. Fang). cose and other undesirable colored products. Moreover, chemically produced fructose has off flavors and reduced sweetness, which cannot be easily remedied. Therefore, it cannot be used commer- cially [12]. The enzymatic isomerization of glucose to fructose has attracted considerable interest recently, since it is more efficient and highly selective, involves less energy consumption, and pro- duces less side products [13]. Enzymatic glucose isomerization was first accomplished on an industrial scale in the United States by using glucose isomerase (GI) (xylose isomerase, EC 5.3.1.5). It could catalyze the reversible isomerization of d-glucose to d-fructose in an efficient way [14]. However, from an economic point of view, enzymes activity is still low and large quantities of enzyme are needed in enzyme-catalyzed isomerization of glucose to fructose [15]. Therefore it is necessary to find a proper method to increase the reaction rate to promote the application of enzyme-catalyzed isomerization. Microwave irradiation, which is proved to be clean, fast, and convenient energy source [16], has been widely used in organic chemistry [17]. Traditionally, organic synthesis is carried out by conductive heating with an external heat source. It is compar- atively slow and inefficient to transfer energy into the reaction system as it depends on the thermal conductivity of the media, which might results in the higher temperature of the reaction ves- sel than that of the reaction mixture if the thermal conductivity of the media is low. In contrast, microwave irradiation produces effi- cient internal heating by directly coupling microwave energy with the solvent, reagent, and catalyst molecules in the reaction mixture, and it usually shortens the reaction time with a higher yield [18]. Considering the above mentioned advantages, microwave-assisted 1359-5113/$ – see front matter © 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.procbio.2010.09.026