## 3 Results and Discussion
### Antioxidant Capacity of Biscuits with Rapeseed Press Cake  
The different fats such as rapeseed oil, margarine, and coconut oil with the declared amounts of SAFA at 2.3, 7.8, and 24.9 g, respectively, and increasing RPC powder levels from 0 to 40 g, were used for the preparation of functional biscuits. It can be noted that as the concentration of RPC in the baked products increased, the biscuits became darker in color (Figure 1).  
The biscuits fortified with RPC were found to be darker than the control sample without RPC flour. This suggests that RPC flour is a rich source of chlorophyll. Moreover, the darkening of biscuits enriched with RPC can be due to the browning of RPC carbohydrates during baking.  
For comparison, with increasing concentrations of by-products, such as olive stone powder (5-15%), white grape pomace (10-30%), goji berry by-product (10-40%), defatted chia flour (5-20%), okara powder (20-40%), prickly pear peel (10-30%), defatted sunflower seed flour (18-36%) in doughs, the color of the enriched biscuits and cookies changed gradually from light brown to brown and finally to dark brown [1; 12; 13; 14; 15; 8].  
Furthermore, the DPPH values of the baked biscuits increased rapidly with the increasing content of the added RPC (Table 2).  
Therefore, the highest DPPH results (8375-10,088 \(\upmu\)mol TE/100 g and 4761-7395 \(\upmu\)mol TE/100 g) were revealed for methanolic extracts of biscuits with the highest RPC level (40 g) obtained after classical extraction and UAE, respectively. However, the DPPH (535-843 \(\upmu\)mol TE/100 g and 598-890 \(\upmu\)mol TE/100 g) were the lowest for the studied samples without RPC.  
The increase in DPPH values from 20.12 to 30.44%, 3.39-7.55 mmol TE/g, 198-236 mmol TE/g, and 1.5-2.9 mg TE/g was also observed when the biscuit doughs were fortified with increasing amounts of olive stone powder (5-15%), white grape pomace (10-30%), prickly pear peel (10-30%), and defatted sunflower seed flour (18-36%), respectively [1; 15; 8].  
Figure 1: Photograph of biscuits prepared from dough: (**a–c**) without, (**d–f**) with 20 g and (**g–i**) with 40 g of rapeseed press cake using rapeseed oil, margarine, and coconut oil, respectively.  
Interestingly, biscuits prepared by replacing coconut oil (lower DPPH = 87-118 umol TE/100 g) with margarine (higher DPPH = 171-217 umol TE/100 g) and the same content of RPC had a lower level of antioxidants capable of scavenging the free DPPH radical (Tables 1 and 2). Thus, replacement of fat with a richer in SAFA insignificantly increased the DPPH activity of the baked biscuits (Table 2, Duncan test). This can be explained by the fact that SAFA are strongly resistant to deterioration reactions during thermal oxidation, while antioxidants present in the dough are not consumed for the termination of oxidative processes by trapping free radicals.  
Unexpectedly, the DPPH results of fortified biscuits' extracts decreased significantly after ultrasonic treatment (Table 2, Duncan test). A decrease in DPPH values for extracts obtained by UAE indicates that natural antioxidants present in RPC were degraded by free radicals generated upon the ultrasound irradiation [27]. On the other hand, the thickness of the boundary layer (the fortified biscuits-solvent interface) did not sufficiently decrease during mixing by means of ultrasound due to the ultrasonic power dissipation (180 W) used for too short treatment time (5 min \(\times\) 3 times), and the transfer of antioxidants was limited.