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Journal of Biological Sciences
Year: 2014  |  Volume: 14  |  Issue: 4  |  Page No.: 284 - 291

L-lactic Acid Production from Cassava Starch by Thermotolerant Rhizopus microsporus LTH23

Thalisa Yuwa-amornpitak and Kannika Chookietwattana    

Abstract: Lactic acid producing fungi were screened from soil samples at various temperatures. Several fungal strains were selected from 30 and 35°C and found that no fungal growth at 40 and 45°C. The results from starch hydrolysis and acid testing revealed that the highest lactic acid was produced by Rhizopus sp. LTH23. Effect of various parameters on lactic acid production were investigated. It was found that the enhancing temperature for higher lactic acid production was at 40°C from 5% starch medium and the medium should be adjusted to pH 9. Effect of N-sources on lactic acid production from NH4(SO4)2 and Urea at various concentrations were also studied. The results showed that more lactic acid production from the medium containing Urea than NH4(SO4)2. The optimum concentration of urea was at 7.5 g L-1. The effect of agitation speed on lactic acid production in batch fermentation showed that lactic acid of 20 g L-1 was produced during 60 h of cultivation at an agitation speed of 200 rpm, air flow rate of 0.5 vvm and maintained at a temperature of 40°C. Fed-batch fermentation system, a method for enhancing higher production yield was used. The result was indicated that lactic acid was produced 3 times higher than in the batch processing by adding 25% fresh medium at 10 h of cultivation. Fungal identification by ITS region sequence was used. It was proved that this fungus was 99.85% similar to Rhizopus microspores (Accession No. JX661044.1) from GenBank data base. Then named it as Rhizopus microsporus strain LTH23.

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