Study On L-Lactic Acid Production With Uncooked Raw Sweet Potato Flour Fermentationand Screening And Breeding A High-Productive Strain

The　optimal　production　medium　and　fermentation　conditions　of　a　mutant　strain　of　Rhizopus　oryzae　3.1179　with　a　high　and　stable　yield　of　L-lactic　acid　were　studied　by　means　of　an　orthogonal　design.　From　the　shake-flask　experiments,the　optimal　fermentation　medium　consisted　of　the　following　composition(%):uncooked　raw　sweet　potato　12,(NH4)2SO4　0.3,KH2PO4　0.03,MgSO4·7H2O　0.025,ZnSO4·7H2O　0.005,CaCO3　6.　The　optimal　fermentation　conditions　were:fermentation　temperature　30℃,liquid　level　50mL　in　250mL　total　volume,fermentation　time　48　hours.　In　shaking　flask　culture,the　yield　of　Rhizopus　oryzae　3.1179　can　be　up　to　89.5　g/L　in　the　optimal　fermentation,and　the　conversion　rate　of　glucose　was　as　high　as　62.3%　under　the　optimum　condition.　Based　on　the　strain　breeding　theory　and　metabolic　engineering　theory,the　mutant　W69　was　obtained　after　mutagenized　with　ultraviolet　rays　and　being　selected　from　differents　selection　agar　surface　plate.　After　fermentation　for　48　hours　in　the　optimum　condition,the　production　of　W69　were　reached　of　116.38　g/L,　30.03%　higher　than　that　of　the　parent　strain　and　the　conversion　rate　of　glucose　was　as　high　as　73.8%,18.46%　higher　than　that　of　the　parent　one.