# Chitosan Films with Caffeine and Propolis as Promising and Ecofriendly Packaging Materials
## 3 Results and Discussion
### Antibacterial Activity of Films  
One of the primary factors leading to the hastened deterioration of food is its contamination with microorganisms during processing or transportation [53]. Hence, there is a quest for innovative and environmentally friendly solutions to facilitate food packaging while simultaneously shielding against the detrimental impact of microorganisms. In this context, the use of films featuring antimicrobial properties seems to be a good solution, with chitosan films being promising examples. The effectiveness of chitosan-based films in inhibiting the growth of pathogenic and probiotic bacterial strains was assessed, and the findings are outlined in Table 2.  
Figure 1: Antiradical activity of chitosan-based solutions. Different letters indicate samples that were significantly different (\(p<0.05\)). The obtained results showed that the films were characterized by varied activity against pathogenic bacteria. All films, also with natural additives, obtained using acetic acid to dissolve chitosan, showed no antimicrobial activity against any tested strains of bacteria. On the other hand, films with citric acid used as a chitosan solvent showed activity against all the tested strains of pathogenic bacteria--the inhibition zone ranged from 17 to >28 mm. The exception was the chitosan film without additives, which was not active against _S. aureus_. The findings indicated that utilizing citric acid as a solvent positively impacted the antimicrobial effectiveness of the resulting films. None of the films made from chitosan exhibited any activity against probiotic bacterial strains. This is a very favorable result and shows that the obtained films can be used in packaging functional food which contains such strains, and their elimination would be unfavorable. Chitosan-based films can also serve as a beneficial option for encapsulating probiotic strains. The results obtained align with existing literature, affirming the potential utility of chitosan materials for encapsulating viable probiotic bacteria, among other applications [54; 55]. Literature data show that caffeine exhibits antibacterial activity against _P. fluorescens_, _E. coli_ and _P. aeruginosa_[30; 31]. However, the antibacterial activity of the caffeine-chitosan films was comparable and, in the case of _P. aeruginosa_ and _P. fluorescens_, even lower than that of films prepared with chitosan alone. The films with the most substantial antibacterial effectiveness were those produced using chitosan dissolved in citric acid, along with the inclusion of CAF and EP. Numerous literature data indicate that propols extract has antibacterial activity against many strains of pathogenic bacteria, mainly Gram-positive, such as _S. aureus_, _B. subtilis_, _B. cereus_ and _E. faecalis_. However, it is less effective against Gram-negative bacteria, including _E. coli_ or _P. aeruginosa_[19; 20; 56]. The antagonistic activity of Polish propolis extracts against such bacterial strains as _S. aureus_, _Salmonella epidermidis_, _Klebsiella pneumoniae_, _E. coli_, _P. aeruginosa_ and _L. monocytogenes_ has already been demonstrated [57; 58]. Literature reports indicate that the antimicrobial activity of poplar-type propols may be associated with the high content of phenolic compounds [59; 60; 61]. The results described by [PERSON] and [PERSON] [9] indicated that chitosan films containing propolis extract showed activity against _S. aureus_, _S. Enteritidis_, _E. coli_ and _P. aeruginosa_ in contrast to films obtained from chitosan alone. In turn, propolis-chitosan nanoparticle films strongly inhibited the growth of _L. monocytogenes_, _E. coli_ and _S. Enteritidis_[62]. Furthermore, packaging materials based on cellulose and containing the active combination of chitosan and propolis complex exhibited antibacterial properties against _L. innocua_ and _S. aureus_[24]. The literature data indicated that films based on high molecular weight chitosan with