Antimicrobial and antioxidant activity of encapsulated tea polyphenols in chitosan/alginate-coated zein nanoparticles: A possible supplement against fish pathogens in aquaculture

Abstract

Abstract Due to the increase inaquaculture facilities, where a large number of animals live in a relatively small area, infectious diseases expanded, resulting in large losses in the sector. These infections not only affectfarmed fish but also spread the pathogens to the ecosystem. Regulation of antibiotic usecalls for the emergence of more sustainable alternative treatments. Epigallocatechin gallate (EGCG) is a secondary metabolite found mainly in the leaves of Camellia sinensiswith various biological activities. However, EGCG is very susceptible to degradation, which reduces its absorption in the digestive process. In this work, EGCG and green tea extract were encapsulated in zein nanoparticles stabilisedwith alginate and chitosan to reduce the degradation effect. For all formulations, nanoparticles with a hydrodynamic size of less than 300 nm and an absolute ζ -potential value >30 mV were obtained. The encapsulation efficiency gave values greater than 75% forpolysaccharide-stabilised particles. The antioxidant capacity (DPPH and ABTS assays) of the encapsulated substances, although lower than those of the free ones, maintained high levels, SC50 of 33.6 and 63.3 μg/mL forEGCG and GTE encapsulated, respectively. On the other hand, the evaluation ofantimicrobial activity, tested against five fish pathogenic bacteria, showed greater efficiency in terms of growth inhibition for nanoparticles with chitosan, with average overall values of around 60 %, although in the specific case of Photobacterium damselae, the most sensitive species, inhibition levels of more than 90 % were recorded. These results support encapsulation as a good strategy forpolyphenolic compounds, since it allows maintaining significant levels of antioxidant activity and increasing the potential for antimicrobial activity, in addition to conferring protection against hostile conditions they may face in their application in the aquaculture sector.