Comparison Of Lactic Acid Fermentation From Two Alkaline Pretreated Corncob By Bacillus Coagulans

Lactic acid（LA） is an important raw material that is widely applied in various fields. Especially, poly lactic acid（PLA）, based on the polymerization of lactic acid, has huge potential for market. Production of lactic acid from lignocellulosic biomass will greatly promote industrial development for LA and PLA, since it will avoid competence with food, and on the other hand, reduce the production, resulting in a win-win situation. However, a major barrier is that inhibitors after pretreatment process have a greatly negative effect on lignocellulosic biofuels and chemicals production. In order to eliminate inhibitors during the pretreatment process, we compared the lactic acid efficiency from two alkaline, Na OH and NH₃-H₂O₂ pretreated corncob by Bacillus coagulans, and the significant achievements were included below:1. The composition of corncob before and after pretreatments was determined. After NaOH pretreatment and washing, the lignin content decreased from 19.60% to 6.28%, and the hemicellulosic fraction was also decreased from 29.05% to 19.99%, compared to raw material without pretreatment; After NH₃-H₂O₂ pretreatment and washing, the lignin content decreased from 19.60% to 17.10%, but the hemicellulosic fraction had a slight change from 29.05% to 26.21%. The results showed NaOH pretreatment can efficiently dissolve lignin, but hemicellulose also suffered losses. However, NH₃-H₂O₂ pretreatment hadn’t obvious effect to remove lignin, but it can efficiently retain hemicellulose.2. The effect of NaOH and CaCO₃ as neutralizer on lactic acid fermentation using NaOH-pretreated and washed corncob was studied. Using CaCO₃ as the neutralizer, the titer and yield of lactic acid were 72.62 g/L and 0.91 g/g corncob, and using Na OH as the neutralizer, the titer and yield of lactic acid were 62.91 g/L and 0.79 g/g corncob. The result indicated CaCO₃ neutralizer is a better for lactic acid yield.3. Fed-batch fermentations were carried out using NaOH-pretreated corncob and NH₃-H₂O₂-pretreated and washed corncob under CaCO₃ as the neutralizer, respectively. At the beginning of fermentations, 8% alkaline-pretreated and washed corncob were used. Then alkaline-pretreated and washed corncob was fed to 16%（w/w）. In the fermentation using NaOH-pretreated and washed corncob, the overall LA titer, yield and productivity, which were 122.99 g/L, 0.76 g/g corncob and 1.37 g/L/h, respectively. In the fermentation using NH₃-H₂O₂- pretreated and washed corncob, the overall LA titer, yield and productivity, which were 118.60 g/L, 0.74 g/g corncob and 1.32 g/L/h, respectively. These results indicated NaOH-pretreatment and NH₃-H₂O₂- pretreatment had similar effect on LA fermentation. Although weak base can’t efficiently remove lignin, oxidizing agent had an effect on damaging structure of lignocellulose and alkaline-oxidizing method can improve the lactic acid fermentation.4. The fed-batch fermentations was carried out using NH₃-H₂O₂-pretreated and unwashed corncob. 8% NH₃-H₂O₂-pretreated and unwashed corncob were used to initiate fermentation. Then NH₃-H₂O₂-pretreated and unwashed corncob were fed to 18.4%（w/w）. The overall LA titer, yield and productivity, which were 79.47 g/L, 0.43 g/g corncob and 1.10 g/L/h, respectively. The result indicated that inhibitors had a serious effect on lactic acid fermentation. However, our result represents the higher LA yield in the field of lignocellulosic LA production.There is a key problem that inhibitors after pretreatment process have a greatly negative effect on LA fermentation from lignocellulosic biomass. Washing can efficiently eliminate the inhibitors, but it leads to water waste and environment pollution. In this study, the LA fermentation of NaOH-pretreated and NH₃-H₂O₂ pretreated corncob were carried out and their performances were investigated since H₂O₂ can eliminate inhibitors. These results suggested NH₃-H₂O₂ pretreatment lays a good foundation for LA fermentation from lignocellulosic materials without washing.