Avaliação da presença de ácido láctico no processo de produção de etanol e identificação das etapas críticas para o seu monitoramento

Abstract

Bacterial contamination is a serious problem faced by the sugar and alcohol industries. The bacteria present in the sugar cane juice consume sucrose and produce lactic acid, which is reflected in losses of yield and productivity in the manufacture of ethanol, in addition to harming the yeast in the fermentation process. In this context, specific studies of the lactic acid presence in the fermentation process may contribute important information in the process control. The present study was conducted with samples collected at a sugar and alcohol mill in the state of Minas Gerais during the 2016/2017 harvest. Analyzes of pH, total acidity and lactic acid quantification were performed. The low pH of the PCTS broth (unprocessed cane juice) may indicate deterioration in the raw material, where the presence of lactic acid serves as indicator of microbiological quality. The average pH found in cane and PCTS broth was 4.90 and 4.98 indicating early cane deterioration. The increasing lactic acid content in the process may indirectly evidence contamination in equipment and consequently fermentable sugar losses. In this study, increasing lactic acid values were obtained from the must prior to the heat exchanger, with a value of 556 mg/L, and at the beginning of the process (PCTS broth and secondary broth) the values were on average 106 mg/L And 149 mg/L. In the fermentation tanks, lactic acid values of 932 mg/L, 1199 mg/L and 1559 mg/L were found. In the evaluation of the correlation between total acidity determined by titration and analysis of lactic acid by instrumental method, it was found that about 93% of the increase in the value of total acidity can be explained by a linear relation with the production of lactic acid during the Alcoholic fermentation, thus the total acidity can be used as an indirect indicator of lactic acid contamination in the manufacturing process. The formation of lactic acid during the ethanol production process, characterized by the presence of contaminating bacteria in the process, induces significant losses of ethanol. The monitoring of the presence of lactic acid in the ethanol production process must be constant, intensifying from the treatment stage of the broth, composition of the wort and mainly in the fermentation.