Influence of suspended solids in yeast viability during alcoholic fermentation

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Yeasts, predominantly from the species Saccharomyces cerevisiae, are responsible for the production of several commodities from different culture media. The extraordinary adaptability of yeasts is an important advantage for the development of new compositions of culture media for ethanol production, such as those obtained from corn hydrolysate or sugarcane syrup. Moreover, both culture media have reducing sugars, salts, and suspended solids in different ratios. The main goal of this study is to assess the effects of suspended solids in the fermentation process concerning cell viability. The alcoholic fermentation proposed was carried out with a culture medium obtained from corn hydrolysate, in which the water needed for the starch hydrolysis process was replaced by sugarcane syrup to supplement nutrients and different sugars contained in the feedstock to the corn mash, which is commonly low in nutrients. The culture medium was sterilized by saturated steam in an autoclave and then the initial concentration of total reducing sugars were adjusted to 150 g L-1. Two different treatments (T1 and T2) were applied to the culture medium to evaluate the influence of suspended solids in the alcoholic fermentation process. The culture medium was centrifugated at 13000 × g for 10 minutes at 4 °C in the T1 treatment, while T2 kept its initial composition. The fermentations were carried out in a 125 mL Erlenmeyer flask, containing 50 mL of culture media, in triplicate. The inoculum used in this work was the industrial yeast Thermosacc® with an initial concentration of 1 g L-1 (dry weight). Six batch fermentations were carried out in an incubator (Minitron, Infors HT®), under agitation of 130 rpm and temperature of 30 ± 1°C for 24 hours. Samples were periodically taken to measure cell viability. The results showed that cell viability went from 91.4% to 93.3% in the T1 treatment, and from 84.0% to 91.5% in T2. Similar behavior was observed between treatments throughout the fermentation process. After Tukey's test, at a significance level of 5%, it was observed that there were no significant differences between treatments. Therefore, it is implied that the presence of suspended solids in the fermentation medium does not influence cell viability.

  • 1 Departamento de Engenharia Química / Escola Politécnica / Universidade de São Paulo
  • 2 Departamento de Agroindústria, Alimentos e Nutrição / Escola Superior de Agricultura "Luiz de Queiroz" / Universidade de São Paulo
  • Innovation and Biotechnology
suspended solids
yeast viability