Valorization of carrot and yeast discards for the obtention of ethanol

Every day, carrots and beer yeast are discarded in large quantities in the province of Santa Fe, Argentina. At present, these agro-industrial discards are employed for cattle feeding but, despite their high energy potential, they receive no treatment destined to their valorization. The present work proposes the utilization of both discards in a fermentative process leading to the obtention of ethanol. To this end, the ethanol yield of the fermentative process was evaluated by assaying the biocatalyst, its inoculum, substrate concentration, initial pH and ion concentration. It was observed that a 1011 cell L−1 inoculum of discarded yeast (Saccharomyces cerevisiae CCUB) and the adjusted initial pH (4.5) allowed increasing ethanol yield (Yps = 0.408 g g−1) and productivity (10.4 g L−1 h−1) without having to dilute the carrot must or add ions. Even though under these conditions fermentation could begin without sterilizing the carrot must, results indicated that a thermal treatment at 121 °C for 10 min would not modify the ethanol yield. To evaluate the useful lifetime of these discards, they were stored at 4 °C, resulting in 54 days for discarded carrots, and 6 days for yeast. The results obtained indicate that it is possible to valorize the two regional agroindustrial discards by employing them for ethanol obtention. The remaining vinasse could then be evaluated for animal feeding. In addition, the ethanol yield could also be enriched by adding 0.10 g g−1 of another agro-industrial discard (cane molasses) with no need to add a nitrogen source.

► In this study we offer an integrated, sustainable solution, using two regional waste materials.
► Must of discarded carrot juice was fermented by discarded Saccharomyces cerevisiae CCUB.
► Results indicated that adjusting initial pH, Yps reached 0.408 g g−1
►  The yield could be enriched by adding only refined sugar discard.
► The useful productive life of discarded carrots and yeast is good for the proposed process.