4th RMUTIC 2013 organized by Rajamangala University of Technology Phra Nakhon, Bangkok-Thailand Copyright © 2013, American-Eurasian Network for Scientific Information publisher JOURNAL OF APPLIED SCIENCES RESEARCH JOURNAL home page: http://www.aensiweb.com/jasr.html 2013 Special, 9 (12) pages: 6015-6020 Published Online :15 January 2014 Research Article Corresponding Author: Duangrutai Thumrongchote, Rajamangala University of Technology Krungthep, Faculty of Home- Economics Technology, Department of Food Technology and Nutrition 149 Chareankrung Rd., Yannawa, Sathorn, Bangkok 10120 , Thailand E-mail: duangrutai.t@rmutk.ac.th Tel. +662-211-2052 Effect of Microwave on Pasting Properties of Heat-Moisture Treated Tapioca Flour And Corn Flour Duangrutai Thumrongchote Rajamangala University of Technology Krungthep, Faculty of Home-Economics Technology, Department of Food Technology and Nutrition 149 Chareankrung Rd., Yannawa, Sathorn, Bangkok 10120, Thailand Received: 12 November 2013; Revised: 14 December, 2013; Accepted: 20 December 2013. © 2013 AENSI PUBLISHER All rights reserved ABSTRACT Tapioca and corn flour adjusted to 20% and 25% moisture (wet basis, w.b.) were heat-moisture treated in microwave oven at power 900 watts to determine the effect of microwave heating time at 15 sec, 30 sec, 45 sec, and 60 sec on pasting properties of the heated flours. It was found that pasting properties of tapioca and corn flour significantly changed after microwave heat treatment. At 20% moisture, tapioca flour heated in microwave oven showed increase heating time increased setback viscosity from 610 cP (non-treated flour) to 723 cP and pasting temperature from 72.0 0 C (non-treated flour) to 73.8 0 C after heating for 60 sec, while breakdown viscosity decreased from 1031 cP (non-treated flour) to 940 cP after heating for 60 sec. For 20% (w.b.) corn flour found that the pasting properties don’t significantly change after heated in microwave at duration 0 -60 sec. At 25% tapioca flour heated in microwave oven showed increase heating time increased setback viscosity from 610 cP (non-treated flour) to 719 cP, pasting time from 4.4 min (non-treated flour) to 4.7 min and pasting temperature from 72.0 0 C (non-treated flour) to 73.7 0 C after heating for 60 sec, while breakdown viscosity decreased from 1031 cP (non-treated flour) to 910 cP after heating for 60 sec. For 25% (w.b.) corn flour heated in microwave oven showed increase heating time increased breakdown viscosity from 150 cP (non-treated flour) to 172 cP and setback viscosity from 138 cP (non-treated flour) to 176 cP after heating for 60 sec. The data obtained in this study indicate that moisture content and heating time in microwave had affect on pasting properties of tapioca flour and corn flour. Key words: Microwave; Heat-moisture; Tapioca flour; Corn flour; Pasting properties INTRODUCTION Heat-moisture treatment (HMT), a physical modification technique for modified starch, was natural and safe when compared with chemical modification. This method involved treatment of flour or starch at temperature (80 – 120 0 C) below the gelatinization temperature, at very restricted moisture content (20-30% moisture w/w), and during time (15 min – 16 hr) [4,7,18]. Under the above condition, HMT induced changes in structure and properties of flour and starch. The size of protrusion on the surface of HMT starch decreased when compared with native starch [9]. The pasting properties of starch treated with heat-moisture method changed when compared with native starch such as lower paste viscosity in HMT canna starch [18], and changes pasting profiles of rice starch and rice flour especially rice flour [15]. Flour is fine powder which obtained by grinding the raw materials such as seed, grain, root or tuber. The composition of flour consists of starch, non-starch polysaccharide, protein, lipid, and inorganic materials. Khamthong and Lumdubwong [10] found that HMT induced β-turn conformation of rice proteins which causes the properties of HMT rice flour differ from HMT rice starch. Traditionally, the heating in HMT method for study the effect of heat-moisture treatment on the properties of starch used conventional air oven such as hot-air oven [1,12,9], or boiling [4]. Microwave oven is popular in the kitchens. In microwave processing, energy was supplied by electromagnetic field directly to food material and affect on various food materials differently from conventional cooking [17,3]. Under the condition of heat-moisture treatment, the microwave heating induced changes in structure and properties of HMT starches such as crystalline structure of potato starch changes from Type B to type A [14], increasing gelatinization temperature of wheat corn and waxy starch [13]. Fan et al. [5] studied the starch-water interaction during microwave heating. They found that vibration mechanisms of polar molecule accelerated the destruction of hydrogen bonds between starch and