Comparison Of Lactic Acid Fermentation From Corncob With Different Particle Sizes By Bacillus Coagulans

Lactic acid is an important raw material widely used in various fields,in particular,polylactic acid plasitic synthesized from lactic acid has good biodegradability and has the potential to replace traditional plastic.Therefore,lactic acid production has attracted great potential using lignocellulosic materials,the most abundant biosource,as the substrate.The effects of different particle sizes and different pretreatments on the structure of corncobs were very different.The loosing of strcture affected the efficiency of enzymatic hydrolysis,which affected the lactic acid yield and titer.In this study,lactic acid fermentation efficiency from alkaline pretreated corncob with different particle sizes by Bacillus coagulans were studied.And the following results were obtained:1.Content analysis of un-pretreated and alkaline?NaOH and NH₃-H₂O₂?pretreated corncob.The cellulose,hemicellulose and lignin contents of non-pretreated corncobs with 5 mm and 0.3 mm particle sizes were 32.5%,35.43%,26.4%,28.3%,16.8% and 14.5%,respectively.After NaOH-pretreatment and washing,the cellulose of 5 mm and 0.3 mm corncob was increased by 27.0% and 5.7%,respectively;the lignin was reduced by 70.2% and 74.5%.After NH₃-H₂O₂ pretreatment and washing,cellulose of 5 mm and 0.3 mm sized corncob increased by 20.0% and 6.67%,and lignin decreased by 13.0% and 10.6%.The results showed that NaOH and NH₃-H₂O₂ has destroyed the corncob tissues especilly for the 5 mm grain corncob.And the physical barrier to the simultaneous saccharification of the lignocellulosic material is lifted.2.Electronic microscopy analysis of un-pretreated and two different alkalitreated corncobs showed that un-pretreatment corncob was closely packed by lignin.The Alkali-pretreated 5 mm corncob surface lignin was destroyed and the hemicellulose structure was observed faintly.The 0.3 mm corncob structure was not only loose but also perforated on the surface.The results show that the alkali pretreatments degraded the lignin of the corncob resulting loose structure,and this structure is favorable for the saccharification process.3.The pretreatment of NH₃-H₂O₂/ NaOH with 0.3 mm and 5 mm grain size were carried out respectively.The different particle sizes corncob treated with different alkali was used as substrate for enzymatic hydrolysis experiment with 8%substrate and 30 PFU/g of cellulase for 12 h.The final reducing sugar yields were almost identical to 0.25 g/g corncob.The results showed that the final enzymolysis rate of 5 mm corncob pretreated with NH₃-H₂O₂ but unwashed was 0.35 g/g,and the final enzymolysis rate of 0.3 mm corncob pretreated with NH₃-H₂O₂ but unwashed was 0.43 g/g.The results showed that the size of the corncobs pretreated with two kinds of alkali and washing was same,but the enzymatic hydrolysis rate was inhibited when the reducing sugar accumulated to a certain concentration during the enzymatic hydrolysis.4.Simultaneous saccharification and fermentations?SSF?by Bacillus coagulans LA204 were carried out using 8% pretreated with two alkali.The lactic acid titers from NaOH-pretreated and washed 5 mm and 0.3 mm corncob were 37.1 g/L and 53.3 g/L,respectively;and the yields were 0.46 g/g and 0.67 g/g corncob,respectively.Meanwhile,the lactic acid titers from NH₃-H₂O₂-pretreated and washed two corncobs were 34.8 g/L and 44.5 g/L,respectively,and the conversion rates were 0.43 g/g and 0.56 g/g corncob,respectively.The final lactic acid concentrations from NH₃-H₂O₂-pretreated and unwashed two corncobs were 21.1 g/L and 28.7 g/L,respectively,and the conversion rates were 0.26 g/g and 0.36 g/g corncob respectively.This results indicated that the lactic acid fermentation efficiency from corncob with 0.3 mm particle size was better than that with 5 mm particle size.5.The fed-batch SSF was carried out using pretreated corncob with different particle sizes at the initial concentration of 8% and the final concentration of 14% fed at 24 h.The final lactic acid titers and yield from NaOH-pretreated and washed 5 mm and 0.3 mm corncob were 50.93 g/L,0.35 g/g,and 56.59 g/L,0.40 g/g,respectively.And the titers and yields from NH₃-H₂O₂-pretreated and washed 5 mm and 0.3 mm corncob were 60.57 g/L,0.44 g/g and 71.79 g/L and 0.52 g/g respectively.The final titers and yields of lactic acid from NH₃-H₂O₂-pretreated and unwashed 5 mm and 0.3 mm corncob were 46.25 g/L,0.33 g/g and 54.74 g/L,0.39 g/g,respectively.The results showed that the difference of lactic acid production between corncob and 0.3 mm grain diameter was reduced by fed-batch SSF.This study showed that NaOH-pretreated or NH₃-H₂O₂-pretreated 5 mm and 0.3 mm corncobs obtained high yield by fed-batch SSF,suggesting that the acid production capacity of 0.3 mm corncob was better than 5 mm corncob.Thus,this study determined the size range of the corncob pellets required for lactic acid fermentation,laying the foundation for the energy saving and efficiency of corncob lactic acid fermentation.