## 4 Discussion
No joint trend in changes in total polyphenols and anthocyanin contents during frozen storage was observed, which agree with our findings. As [PERSON] et al. (2002) [43] report, antioxidant activity increases by 3.45%, when raspberries are stored at \(-30\)\({}^{\circ}\)C due to easier extraction of antioxidant compounds after cell disruption occurring during the freezing process [44]. The assessment of the direction of changes occurring in antioxidants during frozen storage is a difficult issue. It is influenced by many variables, starting with the freezingtechnique and thus the extent of ice crystal formation, as well as the method of thawing. Environmental conditions and cultivation method, the plant variety, and its degree of maturity are also affecting factors [19]. The lower polyphenol content may result from the increased interaction of these compounds with oxidative enzymes, which are formed when cells are destroyed during the freezing and ice crystal formation process [19]. Degradative enzymes, not decomposed before the freezing process, start changes in the structure and colour of the fruit and in the content of antioxidant compounds [19]. The above changes are also affected by the freezing method used. According to [PERSON] et al. [45], quick freezing of strawberry fruit caused less adverse changes in the colour, structure, and antioxidant activity of the fruit than static freezing. During freezing with the films, raspberry fruits were in contact with only one side of the experimental material, which may explain differences in the content of bioactive compounds. Therefore, it is worth considering whether to carry out studies involving spray or dip application of films [46]. Research proves that the use of gel-based coatings and alginate with additives increases the amount of antioxidants in fresh fruit pieces [47; 48]. Examination of fresh biocomposites films and after storage together with raspberries after 12 months shows what changes occurred in them after that period. As observed in a Figure, absorbance spectrum of base (1a) differ significantly from the remaining spectra. It depends on the overlapping spectra of mixed polysaccharides. In the same Figure 1a, one can observe a strong peak at ~270-280 nm. Since these samples did not contain extracts, these peaks are likely due to anthocyanins contained in raspberries. A typical UV-Vis spectrum of an anthocyanin shows two basic maximum peaks of absorbance (as well as all flavonoids) [49]. The first peak is being recorded at UV region (260-280 nm) and the other one at 490-550 nm which corresponds to visible region [49]. This is related to their long chromophore of eight conjugated double bonds and presence of a positive charge on the heterocyclic oxygen ring, observed in acidic conditions [50; 51]. In our spectra analysis, only the peak characteristic for the UV range was observed. It is worthy to know that spectra and intensity of peaks depends on pH [52] and type of anthocyanins predominant in a sample [53]. The other spectra displayed a significant peak at around 285 nm. These data confirm the successful interaction between extracts and base film. Slight shifts were recorded in the absorption peak of samples. The shifts in band positions indicate the involvement of the polyphenol and anthocyanins aromatic resonance electrons in the interaction with the host molecules (base) [54]. The main anthocyanins found in raspberries composed of aglycone cyanidin. This structure has several hydroxyl substitutions and is highly unstable [53]. The interaction with host polysaccharides and guest (polyphenols from the extracts) causes a shift in UV-Vis spectrum. In the ATR-FTIR spectrophotometry study, there was a very limited number of changes between the obtained absorption spectra for base film and films with addition of extracts before storage. A comparative evaluation of the FTIR bands indicated that most of the bands were similar in their band characteristics such as peak position and broad nature.