Valorization of agri-food proteins by enzymatic processes to produce bioactive peptides and their application:
Structure-function relationships of the NKT peptide isolated from slaughterhouse coproducts
Pr. NEDJAR Naïma

UMR Transfrontalière BioEcoAgro N°1158, Univ. Lille, INRAE, Univ. Liège, UPJV, YNCREA, Univ. Artois, Univ. Littoral Côte d’Opale, ICV - Institut Charles Viollette, Université Lille, Poly’tech Lille, Avenue Paul Langevin, 59655 Villeneuve d’Ascq, France

The agri-food industry is gradually turning its attention towards the utilization of its wastes, which are sources of useful bioactive compounds that could become high-value products. Blood, a slaughterhouse coproduct generated in large volumes worldwide, mainly comprises hemoglobin, a protein containing active peptides released by hydrolysis with porcine pepsin. This hydrolysis was monitored over time to identify and characterize all intermediate and final peptides. This allowed us to understand the hydrolysis mechanisms and peptide mapping of each hemoglobin molecular chain. We then searched for antimicrobial peptides resulting from these hydrolyses using peptide maps. The minimal peptide motif linked to antimicrobial activity was also determined. Peptide structure-function relationships and mechanisms of action were then studied to have improved control over the active peptides production. Since enzymatic hydrolysis is complex, we modeled the enzymatic reactions and developed a mathematical model to predict the ideal conditions for obtaining active peptides. Among these, the α137-141 peptide was found to possess inhibitory activity against a broad spectrum of microbial food contaminants. However, isolation of this peptide from hydrolysates containing more that 100 other peptides appears to be a challenge for its use in the food industry. This can be overcome using electrodialysis with ultrafiltration (EDUF), a selective and eco-friendly approach to separate compounds according to molecular charge and mass. However, in conventional hydrolysis, chemical agents are required to adjust the pH of the solution, and the hydrolysates produced have high salt and mineral contents. To reduce this technical inconvenience, a green technology, the electrodialysis with a bipolar membrane (EDBM), has been proposed, as an alternative method, to produce purified bioactive peptides. The peptide α137-141 thus obtained was found to preserve ground beef, slowing rancidification and the growth of bacteria, molds, and yeast as effectively as the chemical preservative butylated hydroxytoluene (BHT). A study of structure-function relationship of antibacterial peptides to understand their mechanisms of action when they are in contact with a bacterial target also showed the possibility of incorporating them into active packaging.