The stoichiometric relationship between carbon dioxide (CO2) generated and glucose consumed during fermentation can be utilized to predict glucose consumption as well as yeast growth by measuring the CO2 concentration. Dissolved CO2 was chosen as opposed to off-gas CO2 due to the high solubility of CO2 in the fermentation broth as well as its ability to reflect on yeast growth more accurately than off-gas CO2. Typical very-high-gravity (VHG) ethanol fermentation is plagued by incomplete glucose utilization and longer durations. Aiming to improve substrate utilization and enhance VHG fermentation performance, characteristics of dissolved CO2 concentration in fermentation broths using Saccharomyces cerevisiae were studied under batch conditions. Based on this study a novel control methodology based on dissolved CO2 was developed and its effectiveness on enhancing VHG fermentation was evaluated by measuring the fermentation duration, glucose conversion efficiency and ethanol productivity. Four different initial concentrations 150, 200.05±0.21, 250.32±0.12, and 300.24±0.28 g glucose/L were used for batch ethanol fermentation without control. Zero substrate was indicated for 150 and 200.05±0.21 g glucose/L by a characteristic abrupt drop in dissolved CO2 concentration. On the other hand sluggish fermentation and incomplete substrate utilization were witnessed for 250.32±0.12, and 300.24±0.28 g glucose/L. A material balance equation was developed to compensate for the inability of the dissolved CO2 profiles to accurately predict the different growth phases of yeast. Dissolved CO2 was controlled at three distinct levels of 500, 750 and 1000 mg/L using aeration rates of 820 and 1300 mL/min for initial concentrations of 259.72±7.96 and 303.92±10.66 g glucose/L. Enhancement of VHG fermentation was achieved in the form of complete glucose utilization and higher ethanol productivities and shorter fermentation duration in comparison to batches without control. Complete glucose utilization was facilitated under ~250 and ~300 g glucose/L in 27.02±0.91 and 36.8±3.56 h respectively. Irrespective of the control set points and aeration rates, ethanol productivities of 3.98±0.28 g/L-h and 3.44±0.32 g/L-h were obtained for 259.72±7.96 and 303.92±10.66 g glucose/L respectively. The glucose conversion efficiencies for both 259.85±9.02 and 299.36±6.66 g glucose/L when dissolved CO2 was controlled were on par with that of batches without control.

Fatty acid components on yeast plasma membrane were critical in maintaining proper cell activity during bioethanol fermentation. The alteration of fatty acid composition on yeast plasma membrane was recognized as an adaptive response to several environmental stress including osmotic pressure, ethanol inhibition and nutrients limit. These stresses were exacerbated under very-high-gravity condition in which excessive fermentable sugar was provided in feedstock. Controlling redox potential was proved beneficial in improving yeast performance under very-high-gravity condition. Fatty acid synthesis and desaturation pathways involved dissolved oxygen as well as balance between NAD+/NADH and NADP+/NADPH which could be influenced by the regulation of redox potential in media. In this study, fatty acid composition profiles under different glucose concentrations and different redox potential control level were examined. Its connection with yeast cell growth, ethanol productivity and other metabolites’ concentrations were studied as well to reveal any causal correlation between redox potential control, membrane fatty acid composition and yeast activity. Two glucose concentrations used in this study were 200 g/L and 300 g/L which represented normal and very high gravity respectively in bioethanol fermentation. In 300 g/L fermentation, three redox conditions were adopted while two different redox conditions were used in 200 g/L fermentation. Biomass concentration, ethanol productivity and fatty acid composition were observed to be affected by both gravity and ORP control strategy. Final biomass concentrations were 4.302 g/L in 200 g/L glucose with no ORP control condition and 7.658 in 200 g/L glucose with ORP controlled at -100 mV condition. In 300 g/L glucose fermentation, final biomass concentrations were 3.400 g/L for no ORP control, 4.953 g/L for -150 mV ORP control and 5.260 for -100 mV ORP control. Ethanol productivities were 2.574 g/Lh for 200 g/L glucose without ORP control and 3.780 g/Lh for 200 g/L glucose with -100 mV ORP control. In 300 g/L glucose fermentation, ethanol productivity decreased to 1.584 g/Lh when no ORP control was imposed. ORP control at -150 mV could improve the ethanol productivity to 1.693 g/Lh while -100 mV ORP control was able to further enhance the ethanol productivity to 1.829 g/Lh. Fatty acid composition was observed to shift to more saturated components when no ORP control was applied. Such trend of saturation was increased by higher gravity condition. ORP control was shown to change this tendency to saturation and help restore fatty acid components on plasma membrane to a more balanced distribution.

This study aimed to evaluate the influence of concentrations of sugars in the must, on the performance of ethanol fermentation conducted in fed batch with variable flow of power to define the best concentrations of ART in the must (juice, molasses and mixed) that lead to improved efficiencies and productivity in ethanol fermentation.In the preparation of mash mix were used the following proportions (20% molasses + 80% broth, 40% molasses + 60% broth, 50% molasses + 50% broth, 60% molasses + 40% broth, 80% molasses + 20% broth ). The profile power was declining, varying the flow rate from 0.75 to 0.25 Lh-1, with time filling the fermenter 3 hours for all tests, ranging from 30 to 30 minutes to feed flow wort in fermenter 4L workload (3 liters of wine and 1 liter of inoculum), evaluating diferente concentrations of ART in three types of wine studied. We evaluated performance parameters such as fermentation and process efficiencies and productivity in ethanol. Musts were quantified in pH, sulfuric acid, Brix and ART.In the middle fermented (wine), pH, acidity, residual sugar and ethanol content and quantity of cells. The kinetic profile was defined by quantifying the concentrations of cells, substrate and ethanol (in 1 hour). The figures in this study as a starting point for industrial use are 16 to 18 Brix (ART 114.25 to 125.86 g / L), 16 to 18 ° Brix (ART 127.70 to 141.24 g / L) and around 16 ° Brix (ART 113.68 g / L to 123.30), respectively, for juice of molasses, juice and mix (juice + molasses).The fermentation efficiencies were 77.17 to 90.30% for grape juice, from 74.4 to 86.51% for wine and mixed wine from 61.84 to 84.06 for molasses. Yields were obtained from 6.85 to 8.21 g / Lh for wine broth, 5.90 to 7.77 g / Lh for wine mixed and 4.04 to 6.72 g / Lh for grape molasses. These tracks serve to subsidize recommended as a starting point, the conduct of industrial ethanol fermentation conducted in fed batch with variable flow supply, since the conditions for conducting the tests, as well as the raw materials used in the preparation of musts were similar to those used industrially. / Fundação de Amparo a Pesquisa do Estado de Alagoas / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / Este estudo objetivou avaliar a influência das concentrações de açúcares nos mostos, sobre o desempenho da fermentação etanólica conduzida em batelada alimentada com vazão variável de alimentação, para a definição das melhores concentrações de ART nos mostos (de caldo, de melaço e misto) que conduzam a melhores eficiências de fermentação e produtividade em etanol. Na preparação do mosto misto foram utilizadas as seguintes proporções (20% melaço + 80% caldo, 40% melaço + 60% caldo, 50% melaço + 50% caldo, 60% melaço + 40% caldo, 80% melaço + 20% caldo). O perfil de alimentação foi decrescente, variando-se a vazão de 0,75 a 0,25 L.h-1, com tempo de enchimento do fermentador de 3 horas para todos os ensaios, variando-se de 30 em 30 minutos a vazão de alimentação de mosto, em fermentador de 4L de volume de trabalho (3 litros de mosto e 1 litro de inoculo), avaliando-se diferentes concentrações de ART nos 3 tipos de mosto estudados. Foram avaliados parâmetros de desempenho, como eficiências fermentativa e de processo e produtividade em etanol. Nos mostos foram quantificados pH, acidez sulfúrica, Brix e ART. No meio fermentado (vinho), pH, acidez, Açúcares Residuais e teor de etanol e quantidade de células. O perfil cinético foi definido, quantificando-se as concentrações de células, substrato e etanol (em intervalos de 1 hora). Os valores indicados neste estudo, como ponto de partida para utilização industrial, são Brix de 16 a 18 (ART 114,25 a 125,86 g/L), de 14 a 18 °Brix (ART de 112,90 a 141,24 g/L) e próximo de 16 °Brix (ART de 113,68 g/L a 123,30), respectivamente para mostos de melaço, caldo e misto (caldo + melaço). As eficiências de fermentação foram: 77,17 a 90,30%, para mosto de caldo, 74,4 a 86,51% para mosto misto e 61,84 a 84,06 para mosto de melaço. As produtividades obtidas foram 6,85 a 8,21g/L.h, para mosto de caldo, 5,90 a 7,77g/L.h para mosto misto e 4,04 a 6,72g/L.h para mosto d melaço. Estas faixas recomendadas servem para subsidiar, como ponto de partida, a condução da fermentação etanólica industrial conduzida em batelada alimentada com vazão variável de alimentação, visto que as condições de condução dos ensaios, assim como as matérias-primas utilizadas na preparação dos mostos, foram semelhantes às utilizadas industrialmente.