Kinetic models for batch ethanol production from sweet sorghum juice under normal and high gravity fermentations: Logistic and modified Gompertz models

- Empirical models for ethanol production from sweet sorghum juice are proposed.
- Logistic and modified Gompertz models were used to describe biomass production.
- The use of the models is shown to depend on what to be acquired from the data set.
- Ethanol formation was predicted well by modified Gompertz model.

The aim of this study was to model batch ethanol production from sweet sorghum juice (SSJ), under normal gravity (NG, 160 g/L of total sugar) and high gravity (HG, 240 g/L of total sugar) conditions with and without nutrient supplementation (9 g/L of yeast extract), by Saccharomyces cerevisiae NP 01. Growth and ethanol production increased with increasing initial sugar concentration, and the addition of yeast extract enhanced both cell growth and ethanol production. From the results, either logistic or a modified Gompertz equation could be used to describe yeast growth, depending on information required. Furthermore, the modified Gompertz model was suitable for modeling ethanol production. Both the models fitted the data very well with coefficients of determination exceeding 0.98. The results clearly showed that these models can be employed in the development of ethanol production processes using SSJ under both NG and HG conditions. The models were also shown to be applicable to other ethanol fermentation systems employing pure and mixed sugars as carbon sources.