## 3 Results and Discussion
### The Results of Chemical Analyses  
The change in pH in fish burgers during the shelf-life period is shown in Figure 2. The pH of the control burger ranged from 7.05 \(\pm\) 0.04 to 7.16 \(\pm\) 0.00. Burgers with extracts maintained lower pH values compared to the control. The pH values recorded for JB and PCJ burgers increased from 6.87 \(\pm\) 0.01 to 6.89 \(\pm\) 0.01 and from 6.91 \(\pm\) 0.02 to 6.93 \(\pm\) 0.02 during the storage period, respectively. The lowest pH was recorded for the BCV burgerand ranged from 6.51 \(\pm\) 0.01 to 6.62 \(\pm\) 0.00, suggesting that the extract may have acidifying properties. These results are in agreement with the pH values reported for sea bass fillets treated with plant extracts and packed under a modified atmosphere. The authors reported a pH between 6.45 and 7.11 during the storage period of 20 days [16; 39]. Spoilage through lipid oxidation is one of the most common forms of fish product deterioration. The burgers were made from fresh, lean fish with lipid content of <3%, and they were vacuum-packed and stored at a low temperature. Both hake and sea bass have low initial TBARS values, usually in the range of 0.3-0.9 \(\upmu\)mol MDA per 100 g of fish [40]. The TBARS results for fish burgers are shown in Figure 3. In comparison to the control, all additions inhibited the lipid oxidation of the burgers and their TBARS values stayed below the acceptable limit for MDA content of 1.4-2.8 \(\upmu\)mol MDA/100 g of fish throughout the storage period [40]. A significant increase in TBARS was observed only in the control samples, from 0.58 \(\pm\) 0.00 \(\upmu\)mol MDA/100 g at the beginning of the storage period to 2.62 \(\pm\) 0.02 \(\upmu\)mol MDA/100 g at the end of the shelf-life period (Figure 3). The final recorded TBARS values were 0.80 \(\pm\) 0.02 \(\upmu\)mol MA/100 g for JB burgers, 0.62 \(\pm\) 0.01 \(\upmu\)mol MA/100 g for PCJ burgers, and 0.71 \(\pm\) 0.01 \(\upmu\)mol MA/100 g for BCV burgers. Lipid oxidation in fish is a complex process, but it can be concluded that the presence of natural antioxidants (plant, algae extracts, and pure phenolics) showed a protective effect in terms of lipid oxidation [9; 41; 42]. Brown algae like Padina are rich in polyphenols (e.g., phlorotannins) and have shown excellent antioxidant activity [28] as have other studied extracts [22; 27; 28; 43; 44]. The content of total phenolic compounds and activity of the dominant phenolics have previously been correlated with the antioxidant power of plants and algae [25; 27; 28; 45]. The original scientific studies of their direct application in fish burgers or similar products are very limited. [PERSON] et al. [16] found that Padina (and other extracts) in MAP sea bass prevented lipid oxidation over 18 days of storage and had the ability to exhibit ~64% radical scavenging activity when incorporated into coatings/films [28]. Juniper species also contain antioxidants (e.g., flavonoids, essential oils) that, in the form of essential oil, demonstrated an antioxidant effect in trout fillets. In the control samples,  
Figure 2: The pH results for burgers over 13 days of storage at 0 \(\pm\) 2 \(\lx@math@degree\)C. CON—burger without extracts; JB—burger with 2% of 1:2 common juniper by-product/blackberry leaves extract; PCJ—burger with 2% of 1:1 _Padina paronica_/prickly juniper needles extract; BCV—burger with 2% of 2:1:1 blackberry leaves extract/catechin/vanillic acid. initial TBARS value rose from \(\sim\)1.34 mg MDA/kg to 5.67 mg/kg in air-packaged products, but only to 3.74 mg/kg in vacuum + juniper (0.6%) samples [46]. Catechin-rich extracts were previously shown to be effective antioxidants in fish. Tea catechins prevent lipid oxidation in fish mince, lowering TBARS during chilled and frozen storage [47]. [PERSON] [48] observed that adding 0.5-1% of pomerangate seed extract (rich in catechin-like tannins) to fish burgers significantly lowered TBARS during 8-day chilled storage in comparison to control burgers. TVB-N and TMA results are shown in Figures 4 and 5.