MALAYSIAN JOURNAL OF ANALYTICAL SCIENCES FRACTIONATION OF HEMICELLULOSE FROM RICE STRAW BY ALKALINE EXTRACTION AND ETHANOL PRECIPITATION

Abstract Hemicelluloses were extracted from rice straw using alkaline extraction and ethanol precipitation. The effects of different extraction conditions; temperature (45 -65 °C), pH (4.5 -6.5), and concentrations of NaOH (0.25 -1 M) on the hemicellulose yield were investigated. Two hemicelllulosic fractions namely Ha 1 and Ha 2 were obtained by precipitation of alkaline soluble hemicellulose in 0.2 volumes and 4 volumes ethanol, respectively. The Ha 1 and Ha 2 were further characterized to obtain total sugar, monosaccharides and Klason Lignin content. The highest hemicellulose yield for Ha 1 was 4.00 % obtained at 55 °C and pH 5.5 with 0.25 M of NaOH, whereas the highest hemicellulose yield for Ha 2 was 19.88 % obtained at 55 °C and pH 5.5 with 0.5 M of NaOH. This study revealed that hemicellulose yield is dependent on the pH, temperature and concentration of NaOH in the alkaline extraction. Keywords: hemicelluloses, rice straw, alkaline extraction, ethanol precipitation Abstrak Hemiselulosa daripada hampas batang padi telah diekstrak melalui pengekstrakan beralkali dan pemendakan etanol. Kesan perbezaan kondisi pengekstrakan; suhu (45 -65 °C), pH (4.5 -6.5), dan kepekatan NaOH (0.25 -1 M) ke atas hasil hemiselulosa dikaji. Dua pecahan hemiselulosa, Ha 1 and Ha 2 telah diperolehi melalui pemendakan hemisellulosa larut alkali dalam isipadu etanol 0.2 dan 4 masing-masing. Ha 1 and Ha 2 dicirikan oleh jumlah gula, kandungan monosakarida dan Klason Lignin. Hasil hemiselulosa tertinggi untuk Ha 1 adalah 4.00 % yang diperolehi pada suhu 55 °C, pH 5.5 and 0.25 M NaOH, manakala untuk Ha 2 adalah 19.88 % diperolehi pada suhu 55 °C, pH 5.5 and kepekatan 0.5 M NaOH. Kajian ini membuktikan hasil hemisellulosa bergantung kepada pH, suhu dan kepekatan NaOH dalam pengekstrakan beralkali. Kata kunci: hemiselulosa, hampas batang padi, pengekstrakan beralkali, pemendakan etanol Introduction The main cereal crop in the whole wide world is rice, which is being produced in more than 148 million hectares with huge range of ecosystem. The scientific name of paddy is Oryza sativa. It is an important cereal crop that produce a lot of residues which is rice stra