Consolidated Bioprocessing Study Of Lactic Acid Production From Kitchen Waste By Recombinant Pichia Pastoris

With the continuous development of economy,our living standards constantly improving,causing an increase in kitchen waste.If we don't handle this well,not only can kitchen waste pollute environment,but also cause a lot of resources being wasted.To solve this problem,simple and effective method should be developed immediately for kitchen waste resource disposal.In this work,the genes of lactate dehydrogenase from Bacillus coagulans,amylase from Aspergillus oryzae and glucoamylase from Aspergillus niger were cloned and respectively transformed into Pichia pastoris for heterologous expression.The highest amylase activity of 1.15 U/mL was achieved in 96 h cultivation of the recombinant strain expressing amylase gene while the highest glucoamylase activity of 1.06 U/mL was achieved in 72 h.27.65 g/L of lactic acid was produced by the recombinant strain expressing lactate dehydrogenase from 40 g/L glucose,which was 66% of the theoretical value,and 5.892 g/L of ethanol was also produced as by-product at the same time.To construct a consolidated bioprocess to produce lactic acid from kitchen waste,the above mentioned three genes,amylase,glucoamylase and lactate dehydrogenase were co-expressed in Pichia pastoris.The highest total strarch hydrolysis activity of 3.08 U/m L was achieved in 96 h of cultivation.Using strarch as the sole carbon source,25.182 g/L of lactic acid was produced by the recombinant strain that expessed the three genes from 40 g/L of strarch,while 6.35 g/L of byproduct ethanol was also produced.The productivity of lactic acid was 0.63 g/g strarch.Without adding any commercial amylase,the highest yield of lactic acid of 16.8 g/L(48% of theoretical yield)was obtained by directly fermenting kitchen waste using the recombinant strain.