## 3 Results  
### DSC Isothermal Oxidative Stability Test of Lipids Extracted from Wafers  
Thermo-oxidative stability of lipids extracted from two types of wafers, namely standard wafers (LWS) and wafers with extract (LWE), was measured by means of the DSC technique using the isothermal mode. Oxidation induction time, measured isothermally at 100 \({}^{\circ}\)C (OIT100) and 120 \({}^{\circ}\)C (OIT120), expresses the starting point of the oxidation process, calculated from the oxidation curves as the intersection of the baseline with the tangent to the descending curve. Figure 1 shows the isothermal oxidation curves of the samples (LWS, LWE) measured at a temperature of 120 \({}^{\circ}\)C at the beginning of storage (0 month). Oxidation of lipids manifested during DSC analysis as a sharp exothermic descending curve. The decline of the curve is caused by the initiation of the oxidation process due to heat evolving during the reaction [26; 27]. As can be seen in Figure 1, differences are visible between the DSC oxidation curve for the control sample (LWS) and the sample with extract (LWE). In the case of the LWE sample, the oxidation induction time is much longer (shifted to higher values) compared to the sample LWS, which indicates effective protection of the fruit extract against oxidation of the lipid fraction during thermal treatment. Figure 2 shows the results of OIT100 (a) and OIT120 (b), determined from the curves obtained during the whole storage period of 13 months. It can be seen that the higher the oxidation temperature, the faster the oxidation occurred. At the beginning of the storage period (0 month) the OIT values for the LWS sample were 28.3 min at 100 \({}^{\circ}\)C and 9.2 min at 120 \({}^{\circ}\)C, whereas for LWE they were 96.6 min (OIT100) and 56.4 min (OIT120). As a reference, the HORO oil as a raw material used for the production of wafers was also investigated and oxidation curve was presented in the supplementary material (Figure S1). The analysis was carried out in isothermal conditions at 120 \({}^{\circ}\)C. It can be seen that the fresh HORO oil was characterized by high thermal stability expressed by OIT120 value at 50.1 min (Figure S1), which was lower than for LWE sample (56.4 min). Figure 1: Differential scanning calorimetry (DSC) oxidation induction time (OIT) curves measured for fresh LWS and LWE samples at 120 \({}^{\circ}\)C temperature. In the case of both measurements (OIT100, OIT120), higher values of the OIT index were stated for sample LWE from the \"0\" time of storage until the 10 th month for OIT 100 (Figure 2a) and until the 8 th month for OIT120 (Figure 2b). ANOVA analysis revealed the significant effects of the time of storage and addition of the extract on the OIT values (\(p\leq 0.05\)). OIT values decreased during storage, which indicates that the oxidation process was progressing over time. However, the addition of the fruit extract increased the oxidative stability of the lipids in the wafers. The OIT100 decreased from 96.6 min (0 month) through 20.27 min (10 th month) to 8.5 min (13 th month) for LWE, while for the LWS samples it changed from 28.3 min (0 month) through 11.5 min (10 th month) to 7.5 min (13 th month). A similar tendency was observed at 120 \({}^{\circ}\)C, as the OIT120 values of LWE were higher than the OIT values of LWS, but statistically significant differences between samples were observed during 8 months of storage (Figure 2b). The OIT120 decreased from 56.4 min (0 month) through 2.3 min (8 th month) to 0 min (13 th month) for LWE and from 9.2 min (0 month) to 0 min (after the 8 th month of storage) for LWS samples. It can be stated from Figure 2a,b that the fruit extract effectively enhanced the oxidative stability during 10 months of storage, and after this time there was no significant difference in the OIT values between the LWS and LWE samples (\(p>0.05\)). [PERSON] et al. [5] and [PERSON] et al. [28] applied also the DSC technique to monitor the oxidative stability of cookies with green tea extracts.