Effects of light wavelength and intensity on the production of ethanol by Saccharomyces cerevisiae in batch cultures

Background: Photoreceptors have been identified in Saccharomyces cerevisae, however, the influence of light on the performance of ethanol fermentation of S. cerevisiae is not yet clear. The aims of this study are to elucidate the influence of light wavelength and intensity on the growth and ethanol production of S. cerevisiae and to describe a novel two-stage LED light process to optimize ethanol fermentation. Results: Experimental results indicated that maximum biomass concentration X_max of the batch under red LED light increased monotonically with light intensity, and the optimal specific product yield Y_p/x was 13.2 g g^-1 at 600 lux. Maximum ethanol concentration P_max of the batch under blue LED light increased monotonically with light intensity, and the optimal Y_p/x was 18.4 gg^-1 at 900 lux. A novel two-stage LED light process achieved maximum P_max, of 98.7 g dm^-3 resulting in 36% improvement compared with that of the batch in the dark. Conclusion: The light wavelength and its intensity significantly affected cell growth and ethanol formation of S. cerevisiae. Red LED light (630 nm) stimulated cell growth but slightly inhibited ethanol formation. In contrast, blue LED light (470 nm) significantly inhibited cell growth but stimulated ethanol formation. A novel two-stage LED light process has been successfully demonstrated to optimize ethanol fermentation of S. cerevisiae.