Nisin is a cationic antimicrobial peptide, that has activity against gram-positive bacteria [1]. K2 toxin is an antimicrobial protein produced by Saccharomyces cerevisiae that is active against other yeasts [2]. Both of these compounds are of protein origin. This means that their activity could be reduced by environmental stresses, proteolysis, and undesirable interactions with food components [1]. Encapsulation is often used to overcome this problem. It also provides controlled release which is important to ensure food safety and to extend the shelf life [1]. In this study, fucoidan was used for the encapsulation of the components.
Fucoidan is an anionic, sulfated polysaccharide that is produced by brown seaweeds. It also has excellent anti-inflammatory, anticoagulant, antithrombotic, antitumor, and antioxidant activities, which could also provide additional beneficial properties for food products [3].
This study researched physicochemical properties of K2 toxin-fucoidan and K2 toxin-nisin-fucoidan particles. Particles were synthesized using two fucoidan concentrations (0.1 and 0.4 mg/mL), two pH values (pH 4.0 and 5.0). K2 toxin was purified by ion exchange chromatography and the concentration in the particles was 3.6 µg/mL and the nisin concentration was 0.1 mg/mL. Control fucoidan samples without K2 toxin and nisin were also prepared. The size and zeta potential of the particles were measured at the initial moment and after 4 weeks of storage at 4 ⁰C using Zetasizer NanoZS device.
When a lower concentration of fucoidan was used, the particles were much larger than those obtained using higher concentration of fucoidan. This difference is clear when comparing K2 toxin-nisin-fucoidan and nisin-fucoidan particles. The size of these particles is also pH dependent. When a lower concentration of fucoidan was used, smaller particles were formed, when the pH of the sample was 4.0. K2 toxin-fucoidan particles were the smallest and their size was close to 200 nm at pH 5.0 and from 100 to 300 nm at pH 4.0. When a higher concentration of fucoidan was used, the size of all the particles was always similar. The results show that control fucoidan and the particle samples differ in size. This confirms, that the components interact and particles are truly formed. When comparing particle size at the initial moment and after 4 weeks, it can be seen that there is not much of a difference. This means, that the particles are stable and do not change significantly after 4 weeks of storage.
The zeta potential of the samples was also measured. The results show that there is not much of a difference depending on fucoidan concentration and pH. The particles had a zeta potential between -18 and -35 mV. K2 toxin-nisin-fucoidan particles may be more stable compared to K2 toxin-fucoidan particles. The results show, that the zeta potential of the particles does not change significantly after 4 weeks. This could also mean that the particles remain stable during this time.