Otimização da produção de bacteriocinas de bactérias láticas em água residuária de indústria de fécula de mandioca

Abstract

Bacteriocins are antimicrobial peptides produced from lactic acid bacteria, which act against pathogenic bacteria and can be used as biopreservatives in food. Residues from cassava processing are usually associated with the presence of lactic acid bacteria, and can be used as a substrate for the isolation of lactic acid bacteria and as a culture medium for the production of bacteriocins. In this sense, the objective of this work was to optimize the production of bacteriocins in wastewater from the cassava starch industry, by lactic acid bacteria isolated from the residue of the cassava processing. Initially, a lactic acid bacteria was isolated from the liquid residue of the cassava flour industry, and then its potential for the production of bacteriocins was evaluated. Along with the strain of lactic bacteria isolated in the present work, a strain of Leuconostoc mesenteroides was also used, already isolated from the same residue and with proven bacteriocin production capacity. The isolated strain was identified by morphological and biochemical tests and by 16S genetic sequencing (V3-V4), being identified as Lactobacillus fermentum, with 99.48% homology. To select the factors that influenced the production of bacteriocins by L. mesenteroides and L. fermentum,experimental designs of the Plackett-Burman (PB) were carried out, with 5 factors (sucrose, yeast extract, potassium phosphate, magnesium sulfate, and Tween 80), with an incubation time of 36 hours, at 30 °C, and agitation of 100 rpm. The factors defined in the PB in 90%, for both strains, were: sucrose, yeast extract, and Tween 80. Then, kinetic tests were performed for both strains, in the total time of 35 h, with samples taken every 5 h, to identify the best fermentation time for the production of bacteriocins. Both strains showed the highest production in 20 hours of cultivation. Having defined the significant factors of PB for the production of bacteriocins and the best fermentation time, the Central Rotational Composite Design (CRCD) was performed for the strains of L. fermentum and L. mesenteroides, in order to optimize the production of bacteriocins. The factors for DCCR were: sucrose, yeast extract, and Tween 80, fermentation time of 20 hours, temperature of 30 °C, and agitation of 100 rpm. In the DCCR tests, the response surfaces and the significant effects of the independent variables on the dependent variable (production of bacteriocins) were evaluated to establish a statistical model to optimize the process. The results indicated that the best bacteriocin production for L. fermentum and L. mesenteroides was 11,751.03 and 3693.34 AU/mL, respectively. Finally, the co-culture of the two strains was evaluated; however, the production of bacteriocins decreased, demonstrating that the L. fermentum and L. mesenteroides strains showed incompatibility.