Transparent Biocompatible Polyelectrolyte Multilayer Coatings on Apples: Formation and Properties

Polyelectrolyte multilayers (PEMs) are nanocoatings with possible applications in various areas, such as biomedicine and food technology. Recently, PEMs have been getting a lot of attention as potential food coatings for the prevention of fruit decay during transportation, storage, and shelf life. In this study, we fabricated thin films made of biocompatible polyelectrolytes, positively charged polysaccharide chitosan (CS), and negatively charged carboxymethyl cellulose (CMC) on apple surface and compared the results with the same multilayers formed on a model silica surface. The aim of our research is to correlate the fundamental aspects of the PEM build-up with their applications and to examine if contact angle measurements could be a useful tool for studying the formation of PEMs on apple surfaces. The influence of various experimental conditions on PEM formation was examined, and it was shown that the PEM build-up and properties such as thickness and hydrophobicity strongly depend on the applied experimental conditions (e.g., pH of the polyelectrolyte solutions). Moreover, for the first time we showed that the PEM build-up on apples could be verified using contact angle measurements. The most dominant zigzag pattern on both silica and apple surfaces at pH(CS) = 5.0 and pH(CMC) = 3.0 highlights the optimal conditions for multilayer formation and suggests that this process can be effectively monitored by using contact angle measurements. All of the results obtained in our study could serve as a basis for obtaining tuned biocompatible transparent polyelectrolyte multilayers on apples with optimized physicochemical properties, which could lead to the enhanced applications of the PEMs in the field of food technology.