Enhancing the biomass and riboflavin production of Ashbya gossypii by using low-intensity ultrasound stimulation

The riboflavin (vitamin B-2) produced by the fermentation of Ashbya gossypii is an essential nutrient for humans and animals. In this study, favorable low-intensity ultrasound (US) with a power of 210 W was applied to stimulate A. gossypii for 45 min at 33 kHz during the logarithmic phase of 48 h. Compared with those of the untreated A. gossypii, the extracellular riboflavin, total riboflavin, and biomass of the US-stimulated A. gossypii increased by 23.5%, 26.95%, and 71.99%, at the 168th h, respectively. The optimal US stimulation increased the mycelial membrane permeability, decreased the mycelial diameter, and changed mycelial morphology to promote mass transfer, causing the enhancement of biomass and riboflavin production. Furthermore, US stimulation also increased the reactive oxygen species generation of A. gossypii, which may be attributed to this fungus' US-induced stress defense that enhanced riboflavin production. Therefore, combining US and fermentation is a feasible and efficient method for enhancing the production of riboflavin and other compounds.