# Chitosan Films with Caffeine and Propolis as Promising and Ecofriendly Packaging Materials
## 1 Introduction
While chitosan solutions have demonstrated antimicrobial capabilities against specific pathogenic bacteria, chitosan films produced from these solutions do not seem to retain these properties. This discrepancy is probably attributable to the way chitosan binds within the films, limiting immediate interaction between its molecular chains and microbial cells [12]. Therefore, researchers are exploring the addition of natural components, for example, essential oils or botanical extracts, to enhance the microbial activity of chitosan films [13; 14]. Propolis is a natural material gathered by honeybees from resinous and balsamic plant materials, including flowers, pollen, branches and tree exudates [15]. Throughout history, bee glue has been employed in traditional medicinal practices because of the various advantageous qualities found in its extracts. These include antibacterial, antifungal, anticancer, anti-inflammatory, and antioxidant properties, inter alia [16; 17]. The diverse biological effects of propolis extract are linked to their intricate chemical composition. According to the literature data, propolis samples from diverse geographic sources encompass phenolic compounds (flavonoids, aromatic acids, and their esters), alcohols, terpenes, enzymes, vitamins, amino acids, sugars, and minerals [16; 18]. Propolis extracts exhibit activity against a wide spectrum of bacterial strains, including microorganisms that cause foodborne illnesses, such as _Staphylococcus aureus_, _Listeria monocytogenes_, _Bacillus cereus_, _Salmonella Enteritidis_, _Escherichia coli_ and _Pseudomonas fluorescens_ [19; 20; 21]. As a result, propolis extracts have been incorporated as additives in films composed of biopolymers, among others, chitosan [9; 22; 23; 24; 25; 26]. Caffeine is an organic chemical compound (1,3,7-trimethylxanthine) found in coffee, tea, energy drinks and some carbonated beverages [27]. It stands as one of the most widely recognized and frequently consumed stimulants on a global scale [28; 29]. Caffeine is a chemical compound that exhibits antimicrobial and antioxidant properties, making it a potentially important ingredient in many pharmaceutical and cosmetic products [29; 30; 31]. Caffeine displays potent antioxidant characteristics, shielding the body from harmful free radicals and potentially lowering the likelihood of diseases linked to oxidative stress [32]. Coffee extracts exhibit antimicrobial activity against Gram-positive bacteria (_S. aureus_, _L. monocytogenes_, _Streptococcus mutans_), Gram-negative bacteria (_E. coli_) and yeast (_Candidia albicans_) [33; 34; 35]. The literature data show that caffeine as an additive can be used in the production of natural biopolymer films and affect their mechanical or antioxidant properties [36]. In this investigation, films made from chitosan obtained from crabs were produced, incorporating both propolis extract (EP) and caffeine (CAF). Two solvents, acetic acid and citric acid, were employed to formulate solutions for film production. The primary objective of this research was to assess the functional attributes of these materials, which encompass mechanical properties, oxygen and water vapor barrier properties, structural features, and antibacterial activity, with the aim of evaluating appropriateness for application in the food packaging sector.