ABSTRACT In the last 40 years, several scientific and technological advances in microbiology of the fermentation have greatly contributed to evolution of the ethanol industry in Brazil. These contributions have increased our view and comprehension about fermentations in the first and, more recently, second-generation ethanol. Nowadays, new technologies are available to produce ethanol from sugarcane, corn and other feedstocks, reducing the off-season period. Better control of fermentation conditions can reduce the stress conditions for yeast cells and contamination by bacteria and wild yeasts. There are great research opportunities in production processes of the first-generation ethanol regarding high-value added products, cost reduction and selection of new industrial yeast strains that are more robust and customized for each distillery. New technologies have also focused on the reduction of vinasse volumes by increasing the ethanol concentrations in wine during fermentation. Moreover, conversion of sugarcane biomass into fermentable sugars for second-generation ethanol production is a promising alternative to meet future demands of biofuel production in the country. However, building a bridge between science and industry requires investments in research, development and transfer of new technologies to the industry as well as specialized personnel to deal with new technological challenges.

Ethanol is the most suitable substitute for oil-based fuels. The performance of the fermentation is affected by several factors, therefore the aim of this work was to evaluate the efficiency of the fermentation of a hydrolyzed must of sweet potato using three strains of the Saccharomyces cerevisiae. It was also evaluated the effect of three forms of the processes conduction in the fermentation yield, efficiency and viability of yeast at the end process. Among the parameters evaluated, only the cell viability showed significant difference. The strain PE-2 would be the most suitable for the fermentation of the hydrolysed sweet potato.

A fermentação dos carboidratos de reserva, glicogênio e trealose é um procedimento para aumentar o nível de proteína das células de leveduras com simultâneo aumento na produção de etanol. Este trabalho estudou a cinética de degradação do glicogênio e trealose em duas linhagens industriais de Saccharomyces cerevisiae (PE-2 e SA-1), bem como o efeito de diferentes temperaturas (38º, 40º, 42º e 44ºC) na velocidade de degradação. A fermentação endógena foi conduzida com suspensão de leveduras a 20% (m/v) em massa úmida, no vinho com 3 a 4,5% (v/v) de etanol. A degradação dos carboidratos de reserva, a 40ºC, seguiu uma cinética de primeira ordem, mostrando que sua taxa é dependente da concentração dos carboidratos na célula. A taxa especifica de degradação (k) variou de 0,0387 a 0,0746 h-1. Em relação a outros parâmetros analisados a 40ºC, foi observado que a viabilidade e biomassa seca e úmida foram reduzidas, enquanto a reserva de proteína celular e etanol, glicerol e nitrogênio no meio aumentaram. A degradação do glicogênio e trealose em diferentes temperaturas (38ºC, 40ºC, 42ºC e 44ºC) mostrou que a 38ºC a taxa de degradação foi a menor, ao passo que a partir de 42ºC ou superior, a degradação do glicogênio não mais progrediu após poucas horas de incubação. Portanto, do ponto de vista prático, a melhor temperatura de incubação é em torno de 40ºC. A aplicação da equação de Arrheniusmostrou que as energias de ativação de 40ºC a 42ºC foram 165,90 e 107,94 kcal.ºK-1.mol-1 para trealose e glicogênio respectivamente para a linhagem PE-2, e 190,64 e 149,87 kcal.ºK-1/mol-1, para a linhagem SA-1 respectivamente.

The fermentation of yeast reserve carbohydrates, glycogen and trehalose is a procedure to increase protein level of yeast cells and improve ethanol production. This work studied on the degradation kinetics of glycogen and trehalose carried out with two industrial strains of Saccharomyces cerevisiae (PE-2 and SA-1) and the effect of different temperatures (38º, 40º, 42º and 44ºC) on degradation rate. Endogenous fermentation was carried out in a yeast suspension at 20% (w/v) based on wet weight, suspended in fermented media with 3.0 to 4.5 % (v/v) of ethanol. The degradation of the carbohydrate reserves at 40ºC followed first-order kinetics, showing that its rate is mainly dependent on the carbohydrate concentration in the cell. The degradation rate (k) ranged from 0.0387 to 0.0746 h-1. Analyzing other parameters at 40ºC, it was observed that viability and dry and wet yeast biomass were reduced while cell protein, ethanol, glycerol and nitrogen in the medium increased. Glycogen and trehalose degradation at different temperatures (38º, 40º, 42º e 44ºC) showed that at 38ºC the degradation rate was slow and from 42ºC on the degradation of glycogen stopped after few hours of incubation. Thus, from a practical point of view, the best incubation temperature is around 40ºC. The application of the Arrhenius equation showed that activation energy from 40º to 42ºC was 165.90 and 107.94 kcal.ºK-1.mol-1 for trehalose and glycogen respectively for PE-2 strain, and 190.64 and 149.87 kcal.ºK-1.mol-1 respectively for SA-1 strain.