Resumo

The use of residues as biotechnological substrates may decrease the cost of fermentative processes and their environmental impact. One of the possible alternative carbon sources is the glycerin effluent from biodiesel production, which is heavily contaminated, cheap and can be metabolized by many fungi. In this work, it was investigated the fermentation of residual glycerin to total acid by the Penicillium sp. T14.1 isolate, which was previously selected by its potential to convert glycerol to organic acids. Citric acid fermentation conditions were employed and varied according to a factorial planning 2^n-1 with 6 variables and 2 levels: glycerol (9.6%-28.8%); K2HPO4 (0.0-5.0 g/L); sucrose (0.0-1.0g/L); CaCl2 (0.0-0.2 g/L); pH (2.0-7.0) and time (3-9 days). 35 fermentations were performed at 30 ºC and 150 rpm. Total acidity was determined in culture filtrates and expressed as citric acid. The highest total acidity (5 g/L) was obtained by combining the higher level of variables glycerol, K2HPO4, sucrose and time with the lower levels of pH and CaCl2. Data were analyzed with the software Statistica 7.0 (95% significance). Sucrose and K2HPO4 presented positive and significant effects on the total acid production. According to the analysis, the higher levels of these variables should stimulate acid accumulation by strain T14.1. The effect of pH was negative for acid production, and the lower level (pH 2,0) favored the total acidity response. However, the effect of pH/ sucrose interaction was negative and more intense. Since sucrose were more significant than pH, analysis showed that to increase acid production it is necessary to combine sucrose and pH higher levels. Mass balance between sucrose concentration (1 g/L) and total acidity expressed as citric acid (5 g/L) suggests that addition of this carbohydrate stimulated conversion of glycerol to acid. Although the total acidity produced was inferior to the ones obtained with traditional strains and processes, results of planned fermentations indicated the possibility of converting residual glycerol to organic acids. Finally, data analysis allowed to conclude which values of the significant variables should be combined in a further central composite design for process improvement.