**1. Introduction**

Polysaccharides have gained increasing attention in biomedicine within the last decade. Due to their exquisite properties such as non-toxicity, biodegradability, and biocompatibility, they are listed as excellent candidates for use in various biomedical formulations.

Pectin is a linear polysaccharide mainly consisting of galacturonic acid units which are connected via α-(1-4) bonds. Gelling properties of pectin depend on the ratio of esterified and amidated acid groups, and particularly the type of pectin (low methoxyl pectin, high methoxyl pectin, or amidated pectin) [1]. Different gelation methods have been reported in the literature: ionotropic gelation with Ca2+ [2], ionotropic gelation with ethanolic solution of Ca2+ [3], emulsification in oil followed by coagulation in ethanol [4], and ethanol gelation [5]. Pectin aerogels are highly water soluble in the same way as pectin. They could be used for improving the dissolution and bioavailability of poorly water-soluble drugs [6].

Chitosan is a linear polysaccharide consisting of linked β-(1-4)-glucosamine units. It can be obtained by deacetylation of chitin from seafood industry waste, such as squid pens and crab shells. Gels can be formed either by irreversible covalent links with chemical cross-linkers, such as glutaraldehyde, or by various reversible links with ions and polyelectrolyte complexes. The latter are formed by dissolution of chitosan in an acidic medium, followed by precipitation in an alkaline solution, which is the simplest way of preparing chitosan gels [7]. Chitosan aerogels, in the literature usually referred to as scaffolds, are in most cases used for tissue engineering applications [8]. Unlike pectin, chitosan

is soluble in an acidic medium, in lower pH ranges. This property is very important and opens up possibilities for new applications.

The drug release properties from water-soluble polysaccharides, such as pectin, suffer some problems. The main disadvantage is the burst release of active substances due to quick breakdown of gels in vitro. To improve the performance of water-soluble polysaccharides, chitosan coatings can be added to protect the core and prolong the release of active substances trapped inside. There are efforts in the literature to achieve these formulations and mentioned effect [9–13].

Curcumin is a yellow pigment present in the spice turmeric (*Curcuma longa*). It is associated with antioxidant, anti-inflammatory, anticancer, antiviral, and antibacterial activities, confirmed by more than 6000 citations and hundreds of clinical studies [14]. Curcumin, however, has poor absorption, biodistribution, metabolism, and bioavailability. There are suggestions to overcome these problems, by incorporating curcumin into formulations such as nanoparticles, liposomes, micelles, and phospholipid complexes [15–18].

The aim of this study was to improve the bioavailability of curcumin by attaching it to highly water-soluble pectin aerogels in the first step. Secondly, the curcumin release was optimized by adding a chitosan layer over the pectin core.

To the best of our knowledge, this is one of the first studies on the topic of chitosan coatings over pectin aerogels.
