Abstract
Lactic acid recently became an important chemical where it is widely used in many industries such as food, cosmetic, chemical and pharmaceutical industry. The present study focuses on the screening for lactic acid production from rice starch waste using a thermophilic amylolytic bacterium, Geobacillus stearothermophilus . There is no information available on direct fermentation of lactic acid from rice starch waste using G. stearothermophilus . The effects of different parameters such as temperature, pH, incubation time, agitation speed, concentration of nitrogen and carbon sources on the lactic acid production were assessed. The highest concentration of lactic acid produced was 5.65 ± 0.07 g/L at operating conditions of 60°C, pH 5.5, 48 h, 200 rpm of agitation speed with 5% concentrations of both carbon and nitrogen source. The findings indicated that rice starch waste can be successfully converted to lactic acid by G. stearothermophilus .
Highlights
Lactic acid is considered to be one of the most important chemicals recently where it is widely used in many industries such as food, cosmetic, chemical and pharmaceutical.Besides that, the attraction for using it as a monomer in the manufacture of biodegradable and bio-compatible poly or PLA has been increasing recently
The findings indicated that rice starch waste can be successfully converted to lactic acid by G. stearothermophilus
Fermentation for lactic acid production was conducted using mineral salt medium with rice starch waste as a sole carbon source by varying the process parameters according to the Plackett-Burman designs
Summary
Lactic acid is considered to be one of the most important chemicals recently where it is widely used in many industries such as food, cosmetic, chemical and pharmaceutical. The attraction for using it as a monomer in the manufacture of biodegradable and bio-compatible poly (lactic acid) or PLA has been increasing recently. It is an environmentally friendly and alternative to non-biodegradable plastics which are derived from petrochemicals. G. stearothermophilus is a thermophilic amylolytic bacterium that can convert starch directly to lactic acid. Most of the lactic acid producing microorganisms require hydrolysis of starch containing carbon sources to glucose before the fermentation process represents an advantage of using this particular bacterium. The other characteristics of this bacterium are facultative anaerobic and gram-positive from the phylum Firmicutes, with an optimum growth temperature between 50°C and 60°C, while pH of 6.2 and 7.5 [2, 3]
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