Evaluation of antimicrobial effectiveness of pimaricin-loaded thermosensitive nanohydrogel coating on Arzúa-Ulloa DOP cheeses

Abstract

Pimaricin is a fungicide commonly used on the cheese surface. In this work poly(N-isopropylacrylamide) nanohydrogels copolymerized with acrylic acid (PNIPA-20AA(5)) were proposed to encapsulate pimaricin and release it in a controlled manner to prevent a real food product, Arzúa-Ulloa DOP cheese, from food spoilage. The results reflect that the nanohydrogel coating neither impart any adverse effects (compared to the control) nor influence the natural ripening process of Arzúa-Ulloa DOP cheese. In the bioassay with artificial contamination, the total fungal counts in cheeses with the pimaricin-loaded nanohydrogel coating (NP) were lower than those of all the other treatments, during all the assay (30 days). Despite significant (p < 0.05) differences were not maintained for a long time, probably due to the very high initial microbial load, the antimicrobial effect of the NP-coating evidenced its protective effect in cheeses. A new qPCR method that allows the total fungal counts to be quantified directly from the cheese samples was also developed to avoid the inconveniences associated with the traditional methods based on Standard Plate Count (SPC). The efficiency of the reaction in the cheese matrix was good, and the qPCR assay was highly linear. A good correlation between both analysis (SPC and qPCR) was observed (around 100% of accuracy). The results obtained in this work reveal the usefulness of thermosensitive nanohydrogels for encapsulating and releasing pimaricin to reduce the amount of free pimaricin in the foods bulk but getting sufficient inhibition of fungal growth.