Physico-chemical characterization of alkaline extracted crude hemicelluloses from oil palm frond (Elaeis guineensis)

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Date
2009
Authors
Ismail, Zaleha
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Abstract
In this study, crude hemicelluloses were extracted from oil palm frond (OPF) using alkaline extraction method. Extracted hemicelluloses were then fractionated into hemicelluloses A (HA) and hemicelluloses B (HB) and physic-chemical properties such as pH, moisture content, ash content, lignin content, uronic acid content, monosaccharide composition, molecular weight distribution, percentage of relative crystalline, water binding capacity, intrinsic viscosity, solubility, mineral binding capacity, flow and thermal properties were determined. Yield of HA was 62.17 ± 2.84 % and HB was 37.83 ± 3.67 %. HA showed higher pH value (5.69 ± 0.20), lignin content (20.93 ± 1.79 %), molecular weight distribution (457 921 g/mol), percentage of relative crystalline (47.68 ± 1.24 %), water binding capacity (5.78 ± 0.19 %) and intrinsic viscosity (56.53 ± 1.26 ml/g) compared to HB. Meanwhile, HB showed higher moisture content (8.06 ± 0.26 %), ash content (16.63 ± 0.86 %) and uronic acid content (1.33x10-5 ± 0.06x10-5 μg/g) as compared to HA. Monosaccharide composition of HA and HB was determined by high performance liquid chromatography method (HPLC). The results revealed that xylose was the major monosaccharide present in both hemicelluloses (HA; 100.90 ± 1.25 mg/g and HB; 105.80 ± 1.05 mg/g) followed by arabinose (HA; 32.57 ± 0.61 mg/g and HB; 92.10 ± 1.25 mg/g) and glucose (HA; 15.90 ± 0.79 mg/g and HB; 55.93 ± 1.19 mg/g). Decrease in ratio of xylose to arabinose was found increased to the percentage of solubility of hemicelluloses. Solubility properties of HA and HB was analyzed using four parameters: types of solvent (acetic acid 0.1 M, distilled water, potassium hydroxide 0.1 M); pH (3, 7 10); time (30 minutes, 120 minutes and 180 minutes); temperature (37 oC, 60 oC, 100 oC). Both HA and HB showed the highest solubilization at pH 10. Mineral binding capacity of HA and HB were studied using mineral (NaCl, CaCl2, MgCl2); pH (3, 5, 7, 8, 10); concentration (20 ppm, 40 ppm, 60 ppm, 80 ppm, 100 ppm); ratio of hemicelluloses to mineral solution (HA; 0.8, 2.0, 3.2, 4.0, 4.8 mg/ml and HB; 1.0, 3.0, 5.0, 7.0 dan 9.0 mg/ml). Mineral binding capacity of HB was significantly influenced by the increased in pH (P < 0.05). Flow and thermal analysis were conducted by rheometer and differential scanning calorimetry (DSC) respectively. HA and HB exhibited pronounced thixotropic behavior and HA showed the highest consistency (328.02 ± 0.47 Pa.sn) in pH 3 solution while, HB presented the highest consistency (2.07 ± 0.01 Pa.sn) in pH 7. The presence of mineral ions at different pH caused the changes of the flow parameters (yield stress (σ), flow index (n) and consistency (K)). In general, thermal properties of HA and HB were influenced by mineral ions presence at different pH. The results showed the transition temperatures were onset temperature (To), peak temperature (Tp) and ending temperature (Te) of HA shifted to higher temperature range when the pH is increased in presence of mineral ions. HA and HB showed the highest enthalpy value at pH 3.
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Master
Keywords
Industrial technology , Alkaline extracted , Oil palm frond
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