Reducing cracking and breakage of soybean grains under combined near-infrared radiation and fluidized-bed drying Sakchai Dondee a , Naret Meeso a,⇑ , Somchart Soponronnarit b , Sirithon Siriamornpun a,c a Research Unit of Drying Technology for Agricultural Products, Mahasarakham University, Thailand b School of Energy Environment and Materials, King Mongkut’s University of Technology Thonburi, Tungkru, Bangkok 10140, Thailand c Department of Food Technology and Nutrition, Mahasarakham University, Thailand article info Article history: Received 5 October 2010 Received in revised form 13 November 2010 Accepted 18 November 2010 Available online 25 November 2010 Keywords: Near-infrared radiation Fluidized-bed Soybean grains Cracking Breakage abstract Near-infrared radiation was combined with fluidized-bed drying to reduce the cracking and breakage of soybean grains because of its advantages such as a decrease in the moisture gradient and the stresses development within the grain kernel, leading to high quality of product. Physical qualities, i.e. cracking, breakage and colour, were investigated together with microstructure of soybean grains. Protein solubility and urease activity were also determined. The parameters studied were near-infrared radiation powers of 4, 6 and 8 kW, air velocity of 4.5 m/s, air temperature of 40 °C and grain bed depth of 6 cm. Results showed that the drying rate was increased with the increase of near-infrared radiation power. The mois- ture content was reduced from an initial moisture content of 20% d.b. to the final moisture contents of 13.5% d.b. (4 kW), 12.8% d.b. (6 kW) and 12.5% d.b. (8 kW). The cracking and breakage of soybean grains occurred negligible, which was lower than 4.4% and 5.3% for cracking and breakage, respectively. At near- infrared radiation powers of 4 and 6 kW was accepted for both soybean grains trade and animal feed industries in Thailand. The total colour difference changes (DE) were varied in the range of to 2.9–4.2. The protein solubility of final product was in an acceptable range (77–82%) for feed meal. The reduction of residual urease was varied in the range of to 39–70%. This study has demonstrated that the soybean grains under combined near-infrared radiation and fluidized-bed drying was properly treated. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Over the past decennia, the use of soybeans in the animal feed and human food industry has increased steadily. Of the total world production of soybeans, more than 90% is used in animal feed in the form of soybean meals or soy product, and other is directly used for human consumption (USDA, 2003). The dominant posi- tions of soybeans are the high qualities in respect to protein, oil and amino acid (Prachayawarakorn et al., 2006). Nevertheless, raw soybeans after harvest cannot be used suc- cessfully in animal feed or human food because they normally con- tain high moisture content, leading to the quality deterioration of soybean grains during storage and subsequent handle and anti- nutritional factors, affecting the nutrition and health in the animals and the human. The proper treatments of raw soybeans to reduce the moisture content and the anti-nutritional factors are thus necessary with the basic trade standards for the animal feed and human food industry which the main factors to consider for the raw soybean qualities are urease activity, and physical qualities such as moisture content, cracking, breakage and colour (Soponronnarit et al., 2001; Wiriyaumpaiwong et al., 2004). In the treatment of raw soybeans after harvest, several methods are available. Most of the methods that used on-farms is hot-air drying which is account of the lower investment cost in relation to the price of the machines and the simplicity of the cooperation as compared to other methods such as cooking, roasting and microwave. Hot-air drying processes are all based on the interac- tion of temperature, time and moisture content, resulting in the coupled reductions of moisture and anti-nutritional factors (Overhults et al., 1973; Tia et al., 1990; Hirunlabh et al., 1992; Osella et al., 1997; Barrozo et al., 1998). Fluidized-bed drying is one of the hot-air drying processes to be used for raw soybean drying in Thailand during the last few years due to high heat and mass transfer rates between the hot-air and the soybean grains. This, consequently, induces simultaneously the drying and the inactivation of anti-nutri- tional factors in soybean grains faster than the conventional hot-air drying; moreover, it can reduce the anti-nutritional fac- tors in the acceptable level for the animal feed and the human food industry in Thailand (Overhults et al., 1973; Soponronnarit et al., 2001). 0260-8774/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2010.11.018 ⇑ Corresponding author. Tel.: +66 43 754363; fax: +66 43 754316. E-mail addresses: n_meeso@yahoo.com, n_meeso@hotmail.com (N. Meeso). Journal of Food Engineering 104 (2011) 6–13 Contents lists available at ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng