Examination of Medium Supplementation for Lactic Acid Fermentation

Abstract

Batch fermentation experiments were performed to evaluate the potentials of different fractions of wheat as alternative carbon and nitrogen source during the economical production of lactic acid by a homofermentative mesophilic bacterium. Hydrolysing the starch content of wheat results in well consumable glucose solution, and simultaneously hydrolysing the insoluble protein content (gluten) of wheat the nitrogen source can be assured as well. The necessary yeast extract concentration was 30 g l-1 on hydrolysed wheat starch solution without gluten fraction, and it resulted in 2.01 g l-1 h-1 volumetric lactic acid productivity. Other possible (and usually applied) supplementations (corn steep liquor, yeast autolysate) are neither available in Hungary nor they are economically considerable alternatives. Using the gluten fraction can substitute the major part of the added yeast extract as nitrogen source, but since there is a need for other microcomponents (vitamins, amino acids etc.) of yeast extract, thus a minimal amount of yeast extract is necessary for lactic acid fermentation. The optimized gluten containing medium resulted 2.31 g l-1 h-1 productivity which is an industrially acceptable result, showing to be an effective and alternative nitrogen source.