- 3:15 PM

From Raw Cassava Pulp to L-Lactic Acid Via Fermentation by Rhizopus Oryzae

Nuttha Thongchul1, Surapong Navankasattusas1, and Shang-Tian Yang2. (1) Institute of Biotechnology and Genetic Engineering, Chulalongkorn University, Institute Building 3, Chulalongkorn Soi 62, Phayathai Road, Pathumwan, Bangkok, Thailand, (2) Chemical and Biomolecular Engineering, Ohio State University, 140 W. 19th Ave., Columbus, OH 43210

Currently the natural crude oil depletion has been brought into awareness. Due to the political crisis in Middle East and the booming economics in Asia, the oil price is inevitably increasing, affecting many industries including petrochemical manufacturing. As a result, there are many attempts to develop novel processes to produce substitutes to such petrochemical products including plastics. Polylactic acid, made from polymerization of optically pure isomer of lactic acid, is one of such examples. In addition to the application in food and pharmaceutical industries, lactic acid can be used as a chemical building block for plastics and solvent. Nowadays lactic acid is produced via fermentation by lactic acid bacteria, which require complex media and produce a racemic mixture of lactic acid. In contrast, Rhizopus oryzae is capable of producing an optically pure L-lactic acid from simple and inexpensive media consisting of starchy materials and pentose sugars. Raw cassava pulp is one of the starchy materials which are abundant in Thailand. It was found that raw pulp disposal from cassava mill contained approximately 56% starch (dry basis), which could be used in L-lactic acid fermentation by R. oryzae. Therefore, in this study we investigated L-lactic acid production from raw cassava pulp. Raw cassava pulp was pretreated by acid or enzymatic hydrolysis prior to fermentation. The effects of hydrolysis conditions, including acid type and concentration, unit of enzyme activity, temperature, and time, on starch recovery and glucose production were observed. It was found that when hydrolyzing cassava pulp at 121oC for 15 min with 1.0 M HCl (1 g dry pulp to 9 mL HCl solution), the maximum starch recovery (88%) and the highest glucose production (98 g/L) were obtained. In enzymatic hydrolysis, amylases easily attacked starch granules after digesting raw pulp with cellulases. This also resulted in high glucose production (~80-100 g/L). The kinetics of L-lactic acid fermentation using pulp hydrolysates from different pretreatment conditions as the carbon source was also studied. Free ions present in pulp hydrolysates affected L-lactic acid production. R. oryzae was capable of utilizing hydrolysate containing Cl- ions for growth and product formation. However, instead of L-lactic acid, ethanol was produced as a major product in the fermentation. While no growth and product formation were observed in the presence of a high concentration of PO43-.