Efeito da aplicação de ultrassom em fermentação alcoólica de hidrolisado de farelo de arroz desengordurado

Abstract

The use of agroindustrial waste in bioprocesses has great relevance in the economic and socio-environmental aspects. Degreased rice bran (FAD), a byproduct from rice processing, has a large amount of carbohydrates that can be used in alcoholic fermentation, as well as several other nutrients that complement the substrate. For the purpose of improving fermentation efficiency, cell growth stimulation technologies may be employed to increase process yield. In this perspective, the application of ultrasonic energy during fermentation is expressive, since several studies have demonstrated its positive effects on the cellular physiology of microorganisms in various media. Thus, the objective of this study was to investigate the effects generated by ultrasonic waves on yeast in the alcoholic fermentation process of FAD hydrolyzate, besides analyzing the increase in bioethanol productivity. Initially, enzymatic hydrolysis of the milled FAD with proteases and amylases was performed using methodologies defined in a previous study (SIEPMANN, 2014). Alcoholic fermentation was performed in 500 mL Erlenmeyers incubated at 30 ºC and 100 rpm, with ultrasound application (frequency of 37 kHz, 15 seconds of intermittence and 15 minutes of total application), with variation in application time (2nd or Fermentation time), nominal power of the equipment (40, 70 or 100%) and exposure time (5, 10 or 15 seconds), based on two Complete Factor Planning (PFC) 22 defined in a preliminary study, with a total of 7 trials each. To monitor the process, samples were taken every 2 hours to evaluate cell viability, biomass concentration, reducing sugars and ethanol concentration, evaluating the process yield and productivity parameters in cells and ethanol over 10 hours. fermentation. In addition, tests were performed to measure the ultrasound power absorbed by the fermentation medium, measuring the temperature variation with the sonication time. The results showed positive effects on cell growth in both designs with ultrasonic stimulation, with more than 160% increase in the number of cells compared to the control medium, where there was no irradiation. When ultrasound was applied at the 4th hour of fermentation, better values ​​for bioethanol yield were obtained soon after stimulation (1.5 g · (L · h) -1), representing more than half of the average total productivity of all tests (2,3 g · (L · h) -1). These results highlight that the use of low frequency ultrasound energy can improve the performance of yeast cells during FAD hydrolyzate fermentation, being feasible to use them at low power and for short stimulation periods.