Otimização da produção de ácido lático por Lactobacillus casei NRRL B-442 em suco de caju clarificado

Abstract

Lactic acid is a compound that has several industrial applications in the chemical, pharmaceutical, food, polymer, textile and tanning industries. In addition, lactic acid has being recognized as safe by the Food and Drug Administration (FDA). Lactic acid has become an important monomer in the plastic industry where it has been polymerized into biodegradable plastics. It can be obtained industrially by chemical synthesis or fermentation process. It is most commonly produced by fermentation process using raw materials and waste materials of agricultural source. Cashew apple has a high nutritional value in terms of vitamins, minerals and sugars and it is estimated that 88% of its production is lost due the high spoilage, thus it has great potential as substrate in fermentative processes. This work aimed to optimize lactic acid production by submerged fermentation in a medium containing clarified cashew apple juice as substrate using the Lactobacillus casei NRRL B-442. From available information in the literature regarding temperature, pH, initial concentrations of substrate and initial ammonium sulfate, a kinetic study was carried out changing the initial concentration of substrate from 20 to 60 g/L and maintaining the ideal ratio of 12% of ammonium sulfate in relation of the initial total reducing sugars. The experiments were carried out in a batch reactor of 1.0 L with 0.5 L of reaction medium. The temperature was set at 37 °C and the pH was adjusted to 6.5 and controlled during the process. From the experimental data, a phenomenological model was developed and a computer program was built in Fortran 90. The mathematical model was statistically validated according to the F value of the Fisher test. With the representative model of the reaction system, it was possible to accomplish optimizations in batch and fed-batch fermentation for lactic acid production. The results in batch and fed-batch were compared, in relation to the final efficiency of the system, lactic acid production and costs of raw materials and reagents, with the costs of the final price of the lactic acid in the market. For the optimization in batch reaction, it was found that the fermentation which had the best results was obtained from an inoculum of 0.3 g/L and a initial concentration of total reducing sugars of 50 g/L, resulting in the production of 39.31 g/L of lactic acid and an efficiency of 72.2%. Regarding the fed-batch process, the simulations showed that the best results was obtained from an inoculum of 0.3 g/L with 40 g/L of initial total reducing sugars, with a feed of clarified cashew apple juice at flow rate of 3 L/h and a concentration of 200 g/L, resulting in the production of 38.0 g/L of lactic acid concentration and an efficiency of 63.8%. Therefore, for lactic fermentation using Lactobacillus casei NRRL B-442 and the clarified cashew juice as substrate and the conditions studied in this work, the process in batch was the most advantageous