Modelling and Optimization of Rice (Oryza sativa L.) Paddy Pre-Treatments for Optimum Chemical Property using Response Surface Methodology

Abstract

Rice (Oryza sativa L. variety OS-6) paddy pre-treatments condition was optimized with respect to proximate, amylose and free fatty acids (FFA) composition. Soaking duration (1, 3 and 5 days), initial soaking temperature (30, 65 and 100 0 C), parboiling temperature (80, 100 and 120 0 C) and drying temperature (30, 50 and 70 0 C) were used as independent factors in D-optimal response surface design methodology. AOAC methods were used for determination of proximate and free fatty acid composition. Amylose content was determined using standard method. Moisture, ash, fat, protein, crude fibre, carbohydrate, amylose contents and FFA of the rice were 4.22-10.24%, 0.24-0.71%, 0.62-1.73%, 7.41-9.57%, 0.60-1.71%, 78.31-84.65%, 17.41-22.34% 25 and 0.70-3.80%, respectively. The R 2 for the model fitted ranged from 0.457 to 0.922. The range of R 2 and p-value obtained for moisture, carbohydrate, energy, FFA and amylose affirms the degree of fitness of models obtained. The optimum rice paddy pre-treatment condition obtained was 1 day: 4.8 minutes, initial soaking temperature of 35 o C, Parboiling temperature of 98.03 o C and drying temperature of 70 o C. Contribution/Originality: This study provided detailed changes that occur in the chemical properties of rice (Oryza sativa L. variety OS-6) as affected by paddy pre-treatments. Effect of variation in pre-treatment conditions was reported, while processing conditions for optimum chemical composition of rice was also established. 1. INTRODUCTION Rice being one of the most important cereals of the world is widely consumed and cultivated in most countries. Oryza glaberrima Steud and O. sativa L. are the cultivated species in Nigeria (Abulude, 2004; Adeyemi, Fagade, & Ayotade, 1986). Rice variety OS-6 being one of the earliest released Ofada rice can be described as a short grain robust rice (National Cereal Research Institute (NCRI) & Africa Rice Centre (WARDA), 2007). Ofada is a generic name used to describe all rice produced and processed in the rice producing clusters of the SouthWest Nigeria (Adekoyeni., Akinoso, & Malomo, 2012; Longtau, 2003). Different ecological zones in Nigeria adopt different paddy pre-treatments method (Sanni, Okeleye, Soyode, & Taiwo, 2005). This among other factors is responsible for numerous variation in milled rice quality produced in Nigeria. Rice is mostly consumed as milled or white rice produced by dehulling and milling processes which involves the removal of the hull and bran layers of the rough rice kernel (paddy) respectively. However, Anuonye, Daramola, Chinma, and Banso (2016) reported significant variation in proximate composition due to different processing