Produção de etanol a partir de melaço de soja hidrolisado enzimaticamente

Abstract

The soybean molasses is a by-product of soybean meal concentrate. It is rich in sugars, mainly composed of sucrose, raffinose and stachyose. Stachyose and raffinose are not directly fermentable to ethanol, but hydrolyzed by enzymes can be metabolized by the yeast Saccharomyces cerevisiae. In this work we studied the production of ethanol from molasses by fermentation of soybean molasses in three situations: 1) production of ethanol from soybean molasses "in natura" by fermentation with S. cerevisiae, 2) the enzymatic hydrolysis of soybean molasses by α-galactosidase and subsequent fermentation with yeast S. cerevisiae, 3) ethanol production by simultaneous enzymatic hydrolysis and fermentation of soybean molasses. Preliminary studies were used for monitoring substrate concentration in fermentations to obtain kinetic profiles, monitoring of the hydrolysis compounds and central composite design (CCD) for each situation. Studies of the experiments and kinetic profiles of CCD occurred in a bioreactor operated in batch with a working volume of 1.5 L. The results showed that for the fermentation of molasses "in natura" the concentration of soybean molasses and inoculum that maximize the efficiency of fermentation is between 330 and 400 g / L and between 30 and 45 g / L, respectively a process of 9 hours. The range that minimizes the total residual sugar concentration is between 180 and 250 g / L molasses and between 25 and 45 g / L inoculum. We observed in the enzymatic hydrolysis of soybean molasses that the best condition is between 50 and 55 ° C and pH 4.5. The hydrolysis conditions that maximized the efficiency of fermentation and the concentration of residual sugars were evaluated at pH 4.5 and 5.5 in the hydrolysis process. For pH 4.5, the approximate range of enzyme corresponding to the maximum yield is between 0.045 and 0.080% on the weight of the substrate. For temperature, the track that maximizes the yield is between 54.0 and 56.5 ° C. The bands that minimize the concentration of total residual sugars were between 0.045 and 0.07% for the enzyme and 54 to 57oC temperature. For pH 5.5, it was noted that the region increases the yield of fermentation is between 0.035 and 0.055% for percentage of enzyme and temperature above 58oC and the region that minimizes the amount of residual sugar fermentation is between 0.045 and 0, SM 07% of enzyme and temperature above 59oC. The hydrolysis time was 10 hours at 55 ° C and hydrolyzed molasses fermentation stabilized in 4 hours. For the process of simultaneous hydrolysis and fermentation, the maximum yield is in the range from 0.02 to 0.08% enzyme, 30 and 55 g / L inoculum and between 30 and 38oC temperature. The minimum concentration of residual sugar is in the process range from 0.02 to 0.05% enzyme, 35 and 50 g / L inoculum and between 32 and 36oC temperature. Soybean molasses proved to be a potential substrate for ethanol production with Saccharomyces cerevisiae in batch bioreactor in the three cases studied: fresh molasses fermentation, enzymatic hydrolysis and subsequent fermentation and simultaneous hydrolysis and fermentation.