ABSTRACT
Nisin, an antimicrobial peptide produced by Lactococcus lactis strains, is a promising natural preservative for the food industry and an alternative to antibiotics for the pharmaceutical industry against Gram-positive bacteria. Nisin purification is commonly performed using salting out and chromatographic techniques, which are characterized by their low yields, the use of solvents and the production of large volumes of effluents. In the present work, the purification of nisin from a cell-free supernatant (CFS), after the production of nisin by fermentation on a whey permeate medium, was studied using ammonium sulfate precipitation and electrodialysis (ED) as a promising eco-friendly process for nisin purification. Results showed an increase in nisin precipitation using a 40% ammonium sulfate saturation (ASS) level with a purification fold of 73.8 compared with 34.5 and no purification fold for a 60% and 20% ASS level, respectively. The results regarding nisin purification using ED showed an increase in nisin purification and concentration fold, respectively, of 21.8 and 156 when comparing the final product to the initial CFS. Nisin-specific activity increased from 75.9 ± 4.4 to 1652.7 ± 236.8 AU/mg of protein. These results demonstrated the effectiveness of ED coupled with salting out for nisin purification compared with common techniques. Furthermore, the process was noteworthy for its relevance in a circular economy scheme, as it does not require any solvents and avoids generating polluting effluents. It can be employed for the purification of nisin and the recovery of salts from salting out, facilitating their reuse in a circular economy.
ABSTRACT
Lignin is the second most abundant polymer after cellulose in lignocellulosic biomass. Its aromatic composition and recalcitrant nature make its valorization a major challenge for obtaining low molecular weight aromatics compounds with high value-added from the enzymatic depolymerization of industrial lignins. The oxidation reaction of lignin polymer using laccases alone remains inefficient. Therefore, researches are focused on the use of a laccase-mediator system (LMS) to facilitate enzymatic depolymerization. Until today, the LMS system was studied using water-soluble lignin only (commercial lignins, modified lignins, or lignin model compounds). This work reports a study of three LMS systems to depolymerize the three major industrial lignins (organosolv lignin, Kraft lignin, and sodium lignosulfonate). We show that an enzymatic depolymerization of these lignins can be achieved by LMS using laccase from Trametes versicolor, 2,2'-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt as mediator and a cosolvent (25% of 1,4-dioxane) to enhance the solubilization of lignins.
