Pemanfaatan Hidrolisat Pati Sagu sebagai Sumber Karbon pada Produksi Bioplastik Polihidroksialkanoat secara Fed-Batch oleh Ralstonia eutropha

Abstract

The problems concerning the global environment and solid waste management caused by petrochemical based plastic disposal wastes have created much interest in the development of biodegradable plastics (bioplastics). Polyhydroxyalkanoates (PHAs) have been considered as one of the most promising bioplastics because of its similar physical properties to petrochemical plastics, biocompatibility and complete biodegradability. PHAs are the polymer of hydroxyalkanoates accumulated as a carbon and energy storage material in various microorganisms, usually under unfavorable growth conditions, such as limitation of N, P, S, Mg, or O2 in the presence of excess carbon source. However, one of the problems hindering commercialization of PHA is its high price. The utilization of hydrolyzed sago starch, an indigenous Indonesian crop, as main cultivation substrate is one effort to reduce the production cost of PHA. This research was conducted to investigate the ability of Ralstonia eutropha to grow and produce PHA on cultivation media containing hydrolyzed sago starch. The accumulation of intracellular PHA was increased by implementing fed-batch cultivations. The fed-batch treatment was the kind of substrate feedings, including complete media (F1), hydrolyzed sago starch (F2), hydrolyzed sago starch + MgSO4 (F3), and hydrolyzed sago starch + MgSO4 + (NH4)2HPO4 (F4). Limitation of aeration at stationary growth phase was then treated to the best fedbatch cultivation. The characteristics of PHA obtained were analyzed. As the results, R. eutropha grown on hydrolyzed sago starch with initial sugar concentration of 30 g/L showed the best value of maximum spe cific growth rate (μmax) of 0,108 h-1. Kinetic parameters in 96 hour-batch cultivation including the final cell concentration, Yx/s, Yp/x, Yp/s and ?S/So were 4,41 g/L, 0,15 g cell/g sugar, 0,38 g PHA/g cell, 0,06 g PHA/g sugar and 99%, respectively. The kind of feeding substrate on fed-batch cultivations affected the final PHA concentration and PHA content (P/X) but did not affect the final cell concentration (a = 0,05). Limitation of aeration and its interaction with the best fed-batch treatment did not affect the final cell concentration, PHA concentration and PHA content. Feeding with stock solution containing only hydrolyzed sago starch in fed-batch cultivation was the best treatment which resulted in 4,86 g/L of final cell concentration and 3,72 g/L of final PHA concentration (76,54% of cell dry mass). The fed-batch cultivation increased the final PHA concentration more than two folds compared to the batch one. It indicated that N, P, Mg, and S were limiting factors which could increase intracellularly PHA accumulation of R. eutropha but O2 was not. PHA obtained from the experiment was poly-(3-hydroxybutyrate) (PHB) which had melting temperature of 163,96 oC and relative purity compared to the PHB standard of 76,6%. The PHB functional groups identified from FTIR (Fourier Transform Infrared) analysis were C=O, -C-O-, -CH2-, -CH3, -C-C- and (C-O-C).