## 4 Discussion
We also observed a decrease in activity (assessed using the FRAP method) below 14 mmol FeSO\({}_{4}\)/L when we shortened the processing time to under 9 min and extended it to above 14 min. The highest polyphenol content (>1.6 g GA/L) was observed during 8-10 min of UAE. Therefore, the optimal extraction time of _S. officinalis_ herb in terms of the antioxidant activity and total polyphenol content was 10 min. As noted, extending the extraction time above certain values may have an adverse effect on plant extracts' antioxidant potential or polyphenol content. This could be due, among other things, to the reaction of phenols with other plant components, which makes their extraction difficult. In such a situation, extending the process duration will result in greater losses of polyphenols [29]. [PERSON] et al. (2012) noted a linear decrease in the FRAP activity during the extraction of edible wild mushrooms (_Pleurotus porigens_) from 240 to 420 min [29], while [PERSON] et al. (2010) noted a decrease in polyphenol content as a result of prolonging the extraction time of _Morinda citrifolia_. In their study, an extraction time of 20-120 min significantly affected the antioxidant activity (using the DPPH and ABTS methods) and the TPC but not the total flavonoid content (TFC). The authors explain the difference in the optimal extraction times for the TPC and TFC by the different degrees of phenol polymerisation, their solubility, and their interactions with other components, which leads to the difference in time needed to reach an equilibrium between the solution in the solid matrix and in the bulk solution [42]. Therefore, optimising the extraction time of a specific plant raw material in terms of appropriate activity or the content of a specific group of biologically active compounds is a key element in planning the extraction process. Many studies have focused on optimising the extraction time using the response surface methodology [43; 44; 45; 46; 47; 48]. It should be remembered that an additional parameter accelerating the process of the extraction of compounds with antioxidant potential was the grinding of the raw material and the use of the powdered fraction. [PERSON] and [PERSON] (2015) optimised the time (in the range of 6-18 min) of the UAE of antioxidants from two rapeseed varieties. Before the extraction process, the tested plant material was ground, and a 0.5 mm fraction was used for the process. The optimal extraction time for the tested plant material varieties was 13.8 min [49]. [PERSON] et al. (2016) optimised the time (range 0-30 min) of UAE on the antioxidant activity of _Jatropha integerrima_ flowers using the RSM. For extraction, they used a ground fraction of the raw material smaller than 0.3 mm. The optimal process time was 7 min [50]. [PERSON] et al. (2023) optimised UAE for the TPC, TFC, and antioxidant activity of _Thuja orientalis_ leaf powder. The optimal UAE time was 2 min. In comparison, the optimal microwave-assisted extraction (MAE) time was even shorter, at just 90 s [51]. [PERSON] et al. (2013) optimised the extraction of _Sanguisorbe radix_ for flavonoid content. Test samples were prepared by heating, refluxing, and extraction. The optimal time for the extraction technique they used was 90 min [46]. [PERSON] et al. (2021) found that the optimal UAE time (range 10-80 min) for ground freeze-dried _Citrus sinensis_ peels for antioxidant activity, TPC, and TFC was 44 min [52]. The cited results confirm the importance of optimising the plant material's extraction time in terms of the expected activity or content of a specific group of biologically active compounds as well as the importance of preparing the plant material for the extraction process. Therefore, the use of mathematical modelling, including the response surface methodology, allows for the optimisation of process parameters with a significantly smaller number of tests, which directly translates into a lower energy and solvent consumption. We tested the optimised _S.