Improvement of Riboflavin Production Using Mineral Support in the Culture of Ashbya gossypii

Riboflavin production in a culture of Ashbya gossypii was enhanced by adding mineral support with adsorbed soybean oil. When the support in an amount of 1 % to the amount of medium was added into the culture at agitation intensity corresponding to impeller rotation rate of 600 rpm, the attained riboflavin concentration was 2.5 g/L at the culture time of 4 days, i.e. 1.6 times higher than that in the culture without adding mineral support. Riboflavin yield coefficient based on consumed substrate was also 1.6-fold higher than that in the culture without mineral support. In order to investigate the effect of mineral support on the riboflavin production and mycelial morphology variation, intracellular oil droplets were investigated by staining mycelia with Nile red. The A. gossypii cells, growing in submerged culture using soybean oil as a carbon source, were found to form intracellular micro-lipid bodies. The oil droplets became bigger as the culture time increased, and then the riboflavin leakage began, whereas lipid bodies gradually disappeared. When the soybean oil adsorbed on mineral support was added to the culture, the diameter of A. gossypii mycelia was much thicker and more riboflavin crystals were accumulated than in the pool of culture without mineral support; and what is more, mycelial autolysis was delayed for 2 days due to the presence of mineral support.