Antimicrobial delivery systems based on electrostatic complexes of cationic ɛ-polylysine and anionic gum arabic

ɛ-Polylysine (ɛ-PL) is a potent food-grade cationic antimicrobial but its application within foods and beverages is currently limited because of its tendency to associate with anionic substances, thereby increasing product turbidity or forming sediments. In this study, we examined a potential means of overcoming these problems by forming electrostatic complexes between cationic ɛ-PL and anionic gum arabic (GA). The nature of the complexes formed depended on the mass ratio of gum arabic-to-ɛ-PL (RGA–PL), since this determined their electrical charge, aggregation stability, and antimicrobial efficacy. The electrical charge on the complexes went from positive to negative with increasing RGA–PL, with the point of zero charge being around RGA–PL ∼15. Soluble complexes were formed at low and high RGA–PL levels, but insoluble complexes were formed at intermediate levels (i.e. 5 < RGA–PL < 25). The antimicrobial activities of the ɛ-PL–GA complexes were investigated in a model beverage system against two acid resistant spoilage yeasts: Zygosaccharomyces bailii (ZB) and Saccharomyces cerevisiae (SC). In general, the antimicrobial efficacy of ɛ-PL decreased with increasing amount of GA, and this effect also depended on microorganism type, with SC being less sensitive to increased levels of gum arabic than ZB. Finally, we showed that certain ɛ-PL–GA complexes (15 μg/mL ɛ-PL; RGA–PL ≥ 20) could be incorporated into model beverages without adversely affecting their appearance or physical stability. This work has shown that the function of a cationic antimicrobial (ɛ-polylysine) can be improved by incorporating it within electrostatic complexes using a food-grade anionic biopolymer (gum arabic).