18-23: Improvement of ethanol yield by the chemical treatment of blackstrap molasses for the elimination of microbial contaminants

Sugarcane molasses, the main substrate for ethanol production in tropical Latin American countries, is commonly contaminated with microbial strains which either compete with yeast or inhibit yeast growth or metabolic activity during alcohol fermentation.

Three different antimicrobial compounds were tested for the elimination of competing microbial contaminants present in selected blackstrap molasses. Isothiazolinone, hydrogen peroxide and monensin were used to treat concentrated (55-65 °Bx) molasses.  Hydrogen peroxide at 100 to 1000 ppm and isothiazolinone at 0.1 to 1 ppm drastically reduced the microbial count after 1 h treatment of concentrated molasses. Yeast growth, fermentation efficiency and ethanol yield were strongly increased when selected, highly deteriorated molasses, were treated with combinations of isothiazolinone and hydrogen peroxide, before full dilution and inoculation.

Monensin, a polyether with ionophore activity, successfully controlled grampositive bacterial growth in musts after yeast inoculation. The best monensin concentration for bacterial suppression ranged from 5 to 10 ppm.

An extensive study on selective activity of the disinfectants tested, against different microbial groups, is now under way