Rice bran extract as an alternative nutritional supplement for Kluyveromyces marxianus

The Kluyveromyces marxianus yeast has been arousing great interest as a biocatalyst for biorefineries due to its ability to assimilate different sugars, in addition to its rapid growth, thermotolerance, and GRAS status. In this research, different sources of nutrients, such as rice bran and extracts of malt, yeast, and peptone, were evaluated for the cultivation of K. marxianus ATCC 36,907 aiming at ethanol production in submerged fermentations conducted in a batch system. Mineral supplementation of the medium was also evaluated. The best results of process performance for production, yield, and productivity in ethanol were obtained in the medium supplemented with rice bran extract, calcium chloride, and ammonium sulfate (25.50 g/L; Y (P/S) 0.49 g/g; Q P 2.13 g/Lh), and the medium supplemented only with yeast-malt extract peptone (YMP) (24.88 g/L; Y (P/S) 0.50 g/g; Q P 2.06 g/Lh), after 12 h of cultivation. Supplementation of the medium with malt extract without adding mineral salts also contributed to similar values of production and yield in ethanol after 24 h of cultivation (25.59 g/L; Y (P/S) 0.50 g/g; Q P 1.16 g/Lh −1 ). The results revealed no need for mineral supplementation of the media added with YMP or malt extract for ethanol production by the yeast. On the other hand, rice bran extract, mainly associated with calcium chloride and ammonium sulfate, represents an excellent and inexpensive source of nutrients for this yeast and has the potential to replace traditional commercial supplements.