Applying Sulfite Liquors as a Nutrient Medium for Cultivation of Lactic Acid Producer Rhizopus oryzae F-1030

The filamentous fungi Rhizopus oryzae are well known for their ability to hydrolyze plant polysaccharides. Representatives of this species are widely used for the production of various products, such as organic acids (lactic acid, fumaric acid), ethanol, and hydrolytic enzymes (glucoamylases, polygalacturonases). Various carbon sources such as pentose and hexose sugars are used for the synthesis of R. oryzae exoproducts. Expensive plant sugarcontaining raw materials are used in the lactic acid production by the microbiological method, which significantly increases the final cost of the product. The article demonstrates the possibility of using cheaper by-products of pulp and paper production such as sulphite liquors as an alternative source of carbon for microbiological synthesis of lactic acid. Sulphite liquors contain a large amount of carbohydrates – products of incomplete hydrolysis of cellulose such as hemicelluloses, mono- and oligomeric sugars. The composition of sulfite liquors allows us to consider them as a potential substrate for the synthesis of lactic acid by using different microorganisms. The paper considers the dependence of the lactic acid yield on the composition of the nutrient medium based on sulfite liquor and the cultivation method of the fungus R. oryzae F-1030. As additional sources of nitrogen and phosphorus, (NH4)2SO4 and KH2PO4 were introduced to the nutrient medium. The fungus R. oryzae F-1030 was cultivated by two methods: the semicontinuous culture method, when the nutrient medium was completely replaced after depletion of the reducing sugars in it; the batch culture method, when the lack of reducing sugars in the medium was compensated by the addition of concentrated sulfite liquor. Since the nutrient medium based on sulfite liquor contains the products of incomplete cellulose hydrolysis and xylans, the xylanase and cellulase activities of the fungus R. oryzae F-1030 were measured in order to determine its absorption degree of carbohydrates, contained in the nutrient medium. It was found that it is more expedient to use the semicontinuous method for the fungus R. oryzae F-1030 cultivation on a nutrient medium based on sulfite liquor in order to obtain more synthesized lactic acid. The addition of mineral sources of nitrogen and phosphorus has practically no effect on the final yield of lactic acid. For citation: Mingazova L.A., Kryakunova E.V., Kanarskaya Z.A., Kanarsky A.V. Applying Sulfite Liquors as a Nutrient Medium for Cultivation of Lactic Acid Producer Rhizopus oryzae F-1030. Lesnoy Zhurnal [Russian Forestry Journal], 2021, no. 5, pp. 163–173. DOI: 10.37482/0536-1036-2021-5-163-173