XYLITOL PRODUCTION FROM OIL PALM EMPTY FRUIT BUNCHES VIA ENZYMATIC HYDROLYSIS AND FERMENTATION

• Main Author: Mardawati, Efri
• Format: Dissertations
• Language: Indonesia
• Subjects: Teknik kimia
• Online Access: https://digilib.itb.ac.id/gdl/view/33411
• Institution: Institut Teknologi Bandung

Increasing demand for crude palm oil (CPO) leads to the increase in production of palm oil and consequently the accumulation of oil palm empty fruit bunch (EFB). EFB is the biomass waste from the palm oil industry, generated after the digestion process. It may comprise about 20-22% of the fresh fruit bunches. Currently, EFBs are burned for energy or dumped back in the farm for fertilizer and mousla, which give low additional values to the industry. The abundant availability of EFB provides a great potential to be used further as the raw material for various processes. EFB mainly composes of cellulose, hemicelluloses, lignin and extractive materials. Further characterization of EFB reveals that EFB is composed of ±19.6% xylose. Xylose can be converted into xylitol, a natural sugar that is highly valued by the food, chemical and pharmaceutical industries. Xylitol has the sweetness level similar to sucrose,but has lower calorie. It is an important sugar substitute for diabetics patients. It has a substantially low viscosity and negative heat of solution causing the cold sensation and it is safe for teeth. The reduction of xylose to xylitol can be performed chemically via the hydrogenation of xylose at high pressures and temperatures by reacting pure xylose with hydrogen gas using a metal catalyst. This process requires pure xylose as the raw material. Alternatively, the reduction process can be carried out via fermentation. This process does not require high purity of xylose as the raw material and thus EFB hydrolyzate can be used. EFB hydrolyzate can be obtained via either chemical or enzymatic hydrolysis of EFB. Currently, xylose is mostly produced from xylan via chemical hydrolysis processes. However, the process is normally conducted at high temperature and pressure, which is costly. The severity of the chemical hydrolysis processes are normally related to the inhibitory potentials of the hydrolyzates, such as sugar degradation products: furfural or hydroxymethylfurfural, acetic acid, and fragments of soluble lignin; to the microbial metabolism for xylitol production. As an alternative method, enzymatic hydrolysis of xylan to xylose offers vi environmentally friendly biotechnological process, which is performed at ambient temperature and pressure with high specificity albeit its slower reaction rate. Overall, this study proposed the production of xylitol from EFB via a combination of enzymatic hydrolysis and fermentation process. The availability of xylanolytic enzymes or the so called xylanase is still limited and its price in the commercial marketis very expensive. This research started from the evaluation of xylanase production via solid state fermentation using EFB as substrate. The study covered microbial strain selection and the evaluation of optimal cultivation condition operation such as the ratio of solid substrate, EFB to the liquid medium (S/L), temperature, and cultivation time. All the fungal evaluated, A.niger ITBCC L51, T.viride ITBCC L67dan Penicillium sp. ITBCC L96, were found to be potential xylanase producers. The highest xylanse activity was produced by T.viride ITBCC L61 at 32.8oC and substrate S/L ratio of 0.63 and 36 h incubation time giving xylanase activity of 740.6 U/mL or 5095.3 U/g substrate. The crude enzyme was also found to have cellulase and laccase activities. The optimization of enzymatic hydrolysis process using crude enzyme extract were conducted on pH and temperature to obtain the highest concentration of xylose and highest xylose-glucose ratio. Glucose will always be produced in the hydrolysis of EFB, because the enzyme used is crude enzyme extract which also contains cellulase activity. The optimum conditions of enzymatic hydrolysis was achieved at pH 4.6 and temperature 41.6oC. The enzymatic hydrolysis could be well expressed by the Michaelis Menten kinetic model, with Km = 6.896 g/L and Vm = 0.045 g/L/min. EFB hydrolyzate was used as the substrate for xylitol fermentation. The study of xylitol fermentation from EFB hydrolysate was performed to obtain themaximum yield of xylitol. In the preliminary study using synthetic hydrolyzate, two yeast strains, aeration conditions, addition of glucose as co-substrate, initial cell concentration and pH of the fermentation were evaluated. The fermentation using yeast D. hanseniion semiaerobic condition with initial xylose of 10 g/L and the addition of glucose as co-substrate of 2.5 g/L provided the best xylitol production. The initial cell concentration and pH significantly affected xylitol production. The optimum fermentation condition then was applied to the xylitol fermentation using EFB hydrolysate giving xylitol concentration of 3.088 g/L, with the xylitol yield of 0.24 g xylitol/g xylose and the xylitol volumetric productivity of 0.03 g/L/h. However, in this condition only 66% of xylose was utilised. Xylitol was produced during the growth and stationary phases. Compared to fermentation using synthetic hydrolyzate, more glucose found in the hydrolyzate could reduce the yield of xylitol. The fermentation process then was modeled using the Monod kinetic for growth and Luedeking Piret model for xylitol formation. Overall, the integration of enzymatic hydrolysis and fermentation could be applied for xylitol production from EFB. The low substrate utilization leads to the low vii concentration of xylitol. Further the resulting xylitol solution from fermentation requires the separation and purification of the product. These problems need further attention before this process can be implemented at larger scale. The successful implementation of an integrated process to convert EFB into xylitol will open the way for Indonesian bio based economy. Keyword : enzymatic hydrolysis, kinetic modelling, palm oil empty fruit bunches(EFB), xylanase, xylitol, and xylose,