Production Of High-titer L-lactic Acid From Tobacco Waste By Immobilized Rhizopus Oryzae

As a high-value industrial crop,tobacco is grown widely in many developing countries.However,tobacco-related processes generate large quantities of solid wastes.The main feature of these tobacco wastes is a high content of water-soluble nicotine,which is potentially genotoxic and can end up in water-bearing strata.Since nicotine is especially hazardous for human beings and the environment,tobacco wastes are identified as toxic wastes by European Union Regulations.How to deal with these wastes environmental friendly,economically and efficiently has became one of the most urgent problem that need to be solved in the world,particularly for developing countries.Rhizopus oryzae,a saprobe ubiquitous in soil,has a great potential for lactic acid production for its high optical purity and high value byproduct.However,Rhizopus oryzae is difficult to use in large-scale industrial production process due to its complex cells morphology causing many difficulties in mixing,aeration and separation.Cell immobilization can control fungal cell morphology and achieve higher cell density and product yield.Moreover,immobilized Rhizopus oryzae cells can easily be taken out from fermentor and couple fermentation and separation step,enhance the productivity,shorten the fermentation time,and lower the power input.By studying the characteristics of immobilized Rhizopus oryzae and tobacco waste,this article developed a kind of efficient use of tobacco waste in the production of high value L-lactic acid.Due to the increasingly serious food crisis,the studies of using industrial and agricultural waste instead of food as fermentation substrate for L-lactic acid fermentation has constantly increased.Tobacco waste containing a higher proportion of cellulose and hemicellulose,can be considered an ideal source of fermentable sugars.First of all,results show that the lactic acid production of glucose is four times of the xylose.Pectin and its hydrolysis products completely can not used in lactic acid production.However,when the pectin is sole carbon source,biomass was the highest,which makes it has a possibility to be used in pre-culture medium for cell growth.The results showed that the pectin with 1 g/L glucose can make immobilized Rhizopus oryzae reached the lactic acid production level that using traditional glucose pre-culture medium.The results for the following experiments indicate the two questions: 1)in order to improve the conversation of tobacco waste into lactic acid,xylose metabolism should be enhaced;2)useing pectin and other carbon source instead of glucose as the pre-culture medium carbon source is feasible,which will provides a theoretical basis for the comprehensive utilization of tobacco waste.Before then,according to the experimental results,a waste tobacco extract is used for immobilized Rhizopus oryzae growth.It can replace the traditional glucose preculture medium and can effectively increase the xylose metabolism in Rhizopus oryzae.The results showed that the extract of tobacco waste with 5 g/L glucose and 0.1 g/L of vitamin C improves the highest xylose consumption rate 2.12-fold and L-lactic acid yield 1.73-fold.In fed-batch fermentation,the highest L-lactic acid concentration was obtained,which is 173.5 g/L,corresponding production rate 1.45 g/L/h,yield 0.86 g/g.Finally,for the industrialization of production of lactic acid from tobacco waste,steam explosion was selected to pre-treat tobacco waste,because it can improve the hydrolysis rate 2-fold,and is a green and clean technology.Use liquidation technology reduced 93% of the liquid viscosity and shortens 40.0% of the subsequent fermentation time and increased 66.2% final L-lactic acid.After the optimization of simultaneous saccharification fermentation conditions,L-lactic acid concentration is 125.2 g/L,which can meet the requirements of the production of industrial organic acid.Finally,a total of 50.1% of the tobacco waste substrate was converted to L-lactic acid.