Compostos antimicrobianos de resíduo agroindustrial: Produção em reator AnSBR e nanoencapsulação

Abstract

Using agricultural waste to generate biotechnological compounds is an innovative and sustainable approach. In this study, wastewater from the cassava flour industry (ARFM), a byproduct of cassava processing, was employed to isolate lactic acid bacteria (LAB) that produce antimicrobial metabolites. These compounds, found in the cell-free supernatant (CFS), are stable, productive, and have a low sensory impact on food. In this context, the main objective of this work was to evaluate the production of antimicrobial compounds from LAB in an anaerobic sequencing batch reactor (AnSBR) using cassava processing wastewater (ARF) as a substrate and to examine the microencapsulation of these compounds. The study focused on the CFS of two LAB strains isolated from cassava residues: Leuconostoc mesenteroides and Lactobacillus fermentum. Antimicrobial activity was tested against various strains, including Lactobacillus sakei (ATCC 15521), Listeria monocytogenes ATCC 1911, Escherichia coli ATCC 25922, Staphylococcus aureus ATCC 25923, Pseudomonas aeruginosa ATCC 27853, Salmonella enterica Enteritidis ATCC 13076, and Salmonella enterica Typhimurium ATCC 14028. Tandem mass spectrometry (LC-MS/MS) was used to identify the proteins influencing antimicrobial activity. Bench-scale production in the AnSBR was evaluated under different operational conditions, such as type of feeding (batch and fed-batch), use of support medium, sterilized and raw substrate, and cycle times of 12, 16, and 20 hours. The microencapsulation of antimicrobial compounds was performed using the electrospinning technique with the biopolymer pullulan (PUL). The produced fibers and films were characterized for their morphology, optical, thermal, and mechanical properties, as well as their antimicrobial and antioxidant activity. The results showed antimicrobial activity against various pathogenic strains, with inhibition zones of 27.56 mm against Salmonella enterica Enteritidis and 23.68 mm against Listeria monocytogenes, using metabolites from L. mesenteroides and L. fermentum, respectively. LC-MS/MS analysis identified the genes cas5b, dnaK, and atpD, which contribute to antimicrobial activity. The best production performance in the AnSBR was observed with sterilized ARF, without immobilized biomass, a 20-hour cycle time, and batch feeding, producing 3015.03 ± 514.94 AU/mL of antimicrobial compounds. The fibers and films made with the CFS of L. fermentum and L. mesenteroides were uniform and showed antimicrobial activity against L. sakei, E. coli, and S. aureus. Application of these fibers to cheeses resulted in a reduction of approximately 2.5 logs in E. coli counts for soft cheese and 2 logs for aged cheese. The observed results indicate that the CFS produced by L. fermentum and L. mesenteroides have antimicrobial potential and are promising for the food industry.