330 INSTANT RICE PROCESS DEVELOPMENT: EFFECT OF RICE COOKING METHODS ON THE QUALITY OF JASMINE INSTANT RICE DRIED BY INDUSTRIAL MICROWAVE OVEN Patsakul Phukasmas 1 , Sirichai Songsermpong* 1 Address(es): Dr. Sirichai Songsermpong, 1 Department of Food Science and Technology, Faculty of Agro-Industry, Kasetsart university, Bangkok 10900, Thailand. *Corresponding author: sirichai.so@ku.ac.th ABSTRACT Keywords: Cooking methods, Industrial microwave oven, Instant rice, Quality INTRODUCTION Rice is considered as a major agricultural product of Thailand, and it is the main Thai staple food. In 2017, Thailand exports the highest amount to the world rice market (USDA, 2017). In the present day, the lifestyle has changed, Thai people have a hustle life, more convince and less attention for food preparation (Srichamnong et al., 2016). Jasmine rice (KDML 105 variety) is the most popular aromatic rice variety grown in Thailand because of its famous reputation in appearance, cooking quality and high aroma level. Jasmine rice is well known rice cultivar, since unique aroma from 2-acetyl-1-pyrroline, which exhibit popcorn-like aroma (Ranalli et al., 2003). Furthermore, cooked jasmine rice has specific characteristic with the soft and sticky texture (Phanchaisri et al., 2007). Instant rice could be an answer for this lifestyle situation, including for travelers, and natural disaster victims (Prasert and Suwannaporn, 2009). There are many different ways to cook rice and have an effect with the quality of instant rice (Kassem et al., 2011; Sripinyowanich and Noomhorm, 2011; Wang et al., 2013). Drying of instant rice plays a pivotal role in the quality of the product. Most researches used hot air drying and faced the problem of long dehydration time and slow rehydration rate (Tein et al, 1998; Zhao et al., 2007; Sripinyowanich and Noomhorm, 2011). Therefore, the quality of instant rice doesn’t meet the needs of consumers. However, commercial instant rice is still faced with many problems such as long rehydration time, poor quality and physical appearance including rice agglomeration. There are many researches which solve the instant rice production but still cannot rehydrate within 3 minutes with good quality (Narkrugsa and Thunyawanith, 2002; Rewthong et al., 2011; Chen et al., 2014; Huang et al., 2014). A very interesting method is microwave drying (Seremet et al., 2016). Jaroenkit et al. (2013) produced instant rice by using home microwave oven that could produce instant rice with good quality and did not change the nutritional value. It was found that drying by microwave resulted in the better quality of instant rice products. Moreover, the water uptake ratio increased and the rehydration time decreased as the drying temperature increased (Sripinyowanich and Noomhorm, 2012) and high- temperature drying resulted in large porous structure within the rice grain, which helped to rehydrate grain (Prasert and Suwannaporn, 2009). The objective of this work was to investigate the effect of rice cooking methods on the quality of instant rice dried by industrial microwave oven. Drying curve, whiteness, volume expansion, microstructure, texture and rehydration time of instant rice were investigated. In order to produce fast rehydration instant rice, loosed grain and good physical appearance. The microwave drying method was used to dehydrate instant rice. Therefore, it is hoped that this research can help to solve the problem of surplus and low price and prolong the shelf life, and can increase the export value of rice to foreign countries as well. MATERIAL AND METHODS Preparation of instant rice Jasmine rice (Khao Dok Mali 105) was obtained from the Office of Agricultural Cooperatives, Roiet, with the moisture content of 12.73 ± 0.07% dry basis (d.b.). The rice sample was kept in storage room at 0°C until use. Cooking methods for instant rice Jasmine rice was brought to room temperature and cooked by a pressure cooker (Siam Medical Import Co., Ltd., Thailand) and cooked by stainless steel pot (Satien Stainless Steel Public Co., Ltd., Thailand) for conventional methods, using 500 grams of rice per condition. (McCabe, 1976; Narkrugsa and Thunyawanith, 2002; Prasert and Suwannaporn, 2009). Four cooking method were investigated; Boiling in a pressure cooker (BPC), Steaming in a pressure cooker (SPC), Boiling in a stainless steel pot (BL), and Steaming in a stainless steel pot (SM). For Boiling in a pressure cooker (BPC) and boiling in a stainless steel pot (BL). The rice to water ratio was 1:5 (w/w). The temperature was set at 105°C and held for 10 minutes in pressure and conventional rice cooker for BPC and BL condition respectively. BPC and SPC in pressure cooker had the temperature controller. BL and SM could be controlled cooking temperature of each method were determined using a programmable temperature data logger and commercial electric hot plate. Then cooked rice was submerged in cold water (0°C) for 1 minutes and drain prior to drying process. For steaming rice in a pressure cooker (SPC) and steaming in a stainless steel pot (SM), the rice was immersed in water at room temperature until rice has the moisture content of 30% dry basis with 1:3 (w/w) ratio of rice to water for 1 Rice is considered as a staple food, which approximately half of the world population consumes. However, it is apparent that rice surplus and low price problem still remain. Consequently, instant rice has been promoted in order to tackle with the present issue and open more choices to the consumers. The current problem of commercial instant rice is slow rehydration and poor quality. This research focused on the rice cooking methods to improve the quality of instant rice dried by industrial microwave oven. Four cooking methods were investigated: Boiling in a pressure cooker (BPC), Steaming in a pressure cooker (SPC), Boiling water method (BL) and Steaming method (SM). The industrial microwave oven (6,400 watt, 2,450 MHz) was used to dry the cooked rice in each treatment to the moisture content lower than 14% (w.b.). The results showed that the hardness, stickiness and whiteness of rehydrated rice cooking by different methods had no significant difference with freshly cooked rice. BPC method is the recommended method for instant rice processing since it could provide more porous structures after drying, which relate to fast rehydration for 3 minutes in boiling water and better quality. Furthermore, after rehydration process, the grain appearance was pretty good and did not stick together. Therefore, this knowledge can be applied for the instant rice production at the industrial level. ARTICLE INFO Received 14. 10. 2018 Revised 20. 6. 2019 Accepted 20. 6. 2019 Published 1. 10. 2019 Regular article doi: 10.15414/jmbfs.2019.9.2.330-334