## 3 Results and Discussion
### Physicochemical Properties of Baked Meat, Hybrid, and Plant Burgers  
Thermal processing aims to ensure the safety and desired sensory characteristics of food. It causes structural changes, generating mass losses (usually water), which determine the yield of the final product. Therefore, heat treatment is one of the key stages of food processing from a technological and economic point of view [54; 55]. The cooking yield of the burgers ranged from 81.7 to 90.8%. There were no statistically significant differences in the mean value of this parameter, regardless of the proportion of meat and plant parts and the recipe variant (Table 4). This could be due to the similarity in the basic chemical composition of the meat and plant parts, as well as the comparable ability of the ingredients contained to retain water and fat in the structure. Contrary to this, [PERSON] et al. [28] observed significantly smaller mass losses when baking plant-based burgers (cooking yield of about 88%) compared to meat burgers (cooking yield of about 77%), which they explained by the occurrence of considerable shrinkage of muscle tissue and the release of fluids during heat treatment. Moreover, [PERSON] et al. [21] observed a significant increase in the cooking yield of burgers as a result of replacing the meat with white bean flour. In this case, ingredients with a high water-holding capacity, such as starch and fiber, were introduced and contributed to the structural stabilization of the stuffing [53]. Important food quality indicators that allow for predicting its stability and safety are water activity and pH [56]. The produced burgers did not differ (\(p>0.05\)) in terms of water activity, which ranged from 0.949 to 0.962 (Table 4). Similar results were obtained by [PERSON] et al. [57] for full-meat burgers, as well as [PERSON] et al. [58] in the case of meat burgers with the addition of mushroom flours. Other sources in the literature [59; 60] show that plant-based meat analogs may have slightly higher water activity (up to approx. 0.990). \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Recipe**} & \multicolumn{5}{c}{**Sample Type**} \\ \cline{2-6}  & **M100\_P0** & **M75\_P25** & **M50\_P50** & **M25\_P75** & **M0\_P100** \\ \hline \hline \multicolumn{6}{c}{**Cooking Yield [\%]**} \\ \hline I & 81.68 \(\pm\) 2.00 aA & 85.86 \(\pm\) 1.78 aA & 86.88 \(\pm\) 1.86 aA & 88.91 \(\pm\) 1.30 aA & 89.41 \(\pm\) 1.06 aA \\ II & 81.68 \(\pm\) 2.00 aA & 89.10 \(\pm\) 1.57 aA & 90.68 \(\pm\) 1.43 aA & 90.81 \(\pm\) 1.28 aA & 89.74 \(\pm\) 1.76 aA \\ \hline \multicolumn{6}{c}{**Water Activity [–]**} \\ \hline I & 0.960 \(\pm\) 0.006 aA & 0.957 \(\pm\) 0.002 aA & 0.954 \(\pm\) 0.006 aA & 0.950 \(\pm\) 0.003 aA & 0.949 \(\pm\) 0.004 aA \\ II & 0.960 \(\pm\) 0.006 aA & 0.962 \(\pm\) 0.013 aA & 0.956 \(\pm\) 0.011 aA & 0.954 \(\pm\) 0.003 aA & 0.951 \(\pm\) 0.010 aA \\ \hline \multicolumn{6}{c}{**pH Level [–]**} \\ \hline I & 5.66 \(\pm\) 0.31 aA & 5.61 \(\pm\) 0.26 aA & 5.60 \(\pm\) 0.53 aA & 5.58 \(\pm\) 0.55 aA & 5.60 \(\pm\) 0.28 aA \\ II & 5.66 \(\pm\) 0.31 aA & 5.79 \(\pm\) 0.41 aB & 5.84 \(\pm\) 0.31 aB & 5.81 \(\pm\) 0.64 aB & 5.83 \(\pm\) 0.43 aB \\ \hline \hline \end{tabular} For the demomination of meat, hybrid and plant burger samples, see Table 1. Different lowercase letters between means values \(\pm\) standard deviations in the same row for indicate significant differences (grouping variable: sample type), \(p\leq 0.05\). Different uppercase letters between means values \(\pm\) standard deviations in the same column indicate significant differences (grouping variable: recipe variant), \(p\leq 0.05\).  
\end{table} 
Table 4: Cooking yield, water activity, and pH level of baked meat, hybrid, and plant burgers. Regarding pH values, meat, hybrid, and plant burgers did not differ significantly within the same recipe variant. The pH levels of hybrid or plant burgers based on recipe variant II were significantly (\(p\leq 0.05\)) higher compared to those from recipe variant I (Table 4).