Production Of L-lactic Acid From Waste Cellulosic Materials Using Microbial Mixed Culture

Lactic acid is one of the three organic acids that have the biggest market, and has been used in many fields. The molecular structure of lactic acid has the asymmetry carbon atom, which makes it to have three kinds of optical isomer: D, L and DL-lactic acid. In the foodstuff and pharmaceutical industry, application of D and DL-lactic acid is restricted because the human body can only metabolize L-lactic acid. Moreover, the potential use of L-lactic acid to produce poly-lactic acid for synthesis of biodegradeing plastic makes it a even greater potential market for L-lactic acid.Wheat straw, millet straw, sorghum straw, corn straw and paper sludge are wastes of agricultural production and papermaking industry. According to statistics, the total output of plants cellulose is more than 100 billion tons every year in the world, most of which are not being used. For example, most of the agricultural wastes of the straws of wheat, millet, sorghum, and corn, as well as the paper industry waste are not utilized, and have caused environmental pollution. Saccharification of the waste cellulosic materials for production of L-lactic acid is a useful way for resource regeneration in nowdays.The aim of this paper is to produce L-lactic acid from the waste cellulosic materials using microbial mixed culture of Penicillium decumbens Ju-A₁0 and Lactobacillus Rhamnosus ATCC 10863 .Firstly, the culture condition for production of cellulose measured by CMCase was made in respect of carbon source concentration, liquid volume, and revolving velocity, respectively. Secondly, a further optimization was made using response surface analysis method (RSA). For carbon source of millet straw, CMCase production was as hightest as 29.26IU/mL when carbon source concentration was 9.77 %, and the liquid volume was 64.7 mL, respectively. For carbon source of wheat straw, CMCase production was as hightest as 29.14 IU/mL when carbon source concentration was 8.69 %, and the liquid volume was 54.2 mL, respectively. For carbon source of paper mill sludge, CMCase production was as hightest as 29.8 IU/mL when carbon source concentration was 9.97 %, and the liquid volume was 54.2 mL, respectively. For carbon source of sorghum straw, CMCase production was as hightest as 37.57 IU/mL when carbon source concentration was 10.05 %, and the liquid volume was 49.65 mL, respectively. For carbon source of corn straw, CMCase production was as hightest as 29.43 IU/mL when carbon source concentration was 8.00 %, and the liquid volume was 55.25 mL, respectively. As a result, sorghum straw was chosen as the cabon source for further experimentations.Mixed culture of Aspergillus sp An76 and P. decumbens Ju-Aio was made inorder to have a balanced enzyme system for efficient hydrolysis of cellulosic materials.Mixed culture of P. decumbens Ju-Aio and L. Rhamnosus to produce L-lactic from sorghum straw was made. The fermentation process had two stages with the first aeration stage for cellulase production, and the second non-aeration stage for simultaneous cellulose hydrolysis and L-lactic acid fermentation. This research provided a new way for production of L-lactic acid from agricultural and industrial wastes and/or reproducible materials.