The effect of Thai glutinous rice cultivars, grain length and cultivating locations on the quality of rice cracker (arare) Suwimon Keeratipibul a, * , Naphatrapi Luangsakul b , Thiti Lertsatchayarn c a Department of Food Technology, Faculty of Science, Chulalongkorn University, Phayathai Road, Pathumwan, Bangkok 10330, Thailand b Faculty of Agricultural Industry, King Mongkut’s Institute of Technology Ladkrabang, Bangkok 10520, Thailand c SMTC Co., Ltd., Samutprakarn, Thailand Received 24 July 2007; received in revised form 26 November 2007; accepted 21 December 2007 Abstract Physicochemical and thermal properties of two Thai glutinous rice cultivars (RD6 and Short Grain) differing in grain length (whole grain and broken rice) and cultivating locations (the upper northeastern and the middle northeastern regions) and the quality characteristics of glutinous rice cracker produced from them were studied. RD6 cultivar was different in amylose content, gel consistency, volume expansion and hardness of rice cracker with those of Short Grain cultivar. Broken rice significantly gave greater amylose content, harder cool gel texture, less swelling, lower volume expansion and harder texture of rice cracker than whole grain rice. Furthermore, structure of starch molecule of broken rice differed from that of whole rice. The physicochemical, thermal properties and the qualities of rice crackers of RD6 cultivated from the upper northeastern and the middle northeastern regions showed no significant difference. To obtain good qualities of rice cracker, the rice should have lower amylose content, softer cool paste texture, greater breakdown value and less setback of amylogram. Amylose content and alkali gel con- sistency (120 mg flour) were significantly correlated with several other rice properties. The analysis of both properties is useful for the industry in controlling the quality of glutinous rice being used as raw material. Ó 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. Keywords: Glutinous rice; Arare; Glutinous rice cracker; Broken rice 1. Introduction Glutinous rice (Oryza sativa), also called waxy or sweet rice, is the staple food of Asian people. In Thailand, large quantities are consumed as principal food for daily meals in the north and northeastern parts of the country. Both regions are also the main cultivating sources of the glutinous rice. Un- like non-glutinous rice, glutinous rice is cooked by steaming after overnight soaking instead of boiling. The long soaking time needed is due to less water uptake value determined in glutinous rice than in non-glutinous rice (Juliano & Perez, 1983; Sowbhagya, Ramesh, & Ali, 1994). Thai glutinous rice cultivars derived from Indica rice have long kernel length. These include upland rice, low land rice, and floating rice. The popular cultivars are Sanpatong, RD6 as well as RD10. RD4 cultivar, on the other hand, is not quite popular because its cooked rice has harder texture compared to the ones from RD6 and RD10. Among the physicochemical properties, amylose content is considered to be the principal property affecting the texture and gloss of cooked non-glutinous rice. The higher the amylose content, the harder, less sticky texture and less gloss cooked rice is obtained (Juliano, Onate, & del Mundo, 1965). Glutinous rice has almost no amylose content (0e2%). Therefore, the kernels of the cooked rice are sticky and adhere together. Despite the very low-amylose content, each cultivar gives different eating quality characteristics to the processed rice products. The different characteristics of glutinous rice render many useful utilizations such as stabiliz- ing sauces, gravies and puddings against water separation during freezeethaw cycles encountered in frozen foods (Bean, Esser, & Nishita, 1984; Juliano & Hicks, 1996). Such * Corresponding author. Tel.: þ66 2 218 5515; fax: þ66 2 254 4314. E-mail address: suwimon.K@chula.ac.th (S. Keeratipibul). 0023-6438/$34.00 Ó 2008 Swiss Society of Food Science and Technology. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.lwt.2007.12.008 Available online at www.sciencedirect.com LWT - Food Science and Technology 41 (2008) 1934e1943 www.elsevier.com/locate/lwt