Nisin is an antimicrobial peptide with a molecular weight of 3.5 kDa derived from Lactococcus lactis, and it is a potential natural substitute for traditional antimicrobial additives. Its broad-spectrum activity against Gram-positive bacteria makes this peptide a promising candidate for applications in food preservation, pharmaceuticals, and healthcare [1]. However, due to its protein nature, nisin is sensitive to proteolytic degradation, which creates a barrier to its effective use in various applications. Encapsulation methods can be used to mitigate this problem. Among the eco-friendly materials, biopolymers (mainly polysaccharides) are an excellent choice due to their natural availability from plants and animals or microbes. Negatively charged polysaccharides can interact with positively charged peptides to form nanospheres.
The aim of this study is to prepare nisin-loaded particles and compare their proteolytic stability with free nisin when exposed to protease from Rhizopus chinensis. Members of the genus Rhizopus produce subtilisin-type serine proteases with very high proteolytic activity. These enzymes frequently attack and spoil functional peptides, resulting in a loss of functional stability in food and pharmaceutical systems [2]. On the other hand, bioencapsulation in biopolymer matrices is a way out of this problem, since the primary effect is shielding both physical and electrostatic.
Nisin Z was encapsulated using four different biopolymers: fucoidan, low and high esterified pectins, and pectic acid. The preparation of nisin-loaded particles was based on electrostatic interactions. The final concentration of nisin and the carriers in all particle samples was 0.4 mg/ml, and the pH was 4. The proteolysis was performed at pH 4 for 2 hours at 37 ⁰C, and the final enzyme concentration was 0.3 mg/ml. Capillary electrophoresis and determination of free amino groups by the TBNS (2,4,6-trinitrobenzenesulfonic acid) assays were used to study proteolysis.
The study showed that nisin in particles is more protected from proteolytic action compared to free nisin. It was also found that fucoidan used for nisin encapsulation provided better protection against protease from Rhizopus chinensis than pectins, regardless of their degree of esterification.