## 4 Conclusions  
Herbs and agricultural by-products are valuable sources of antioxidant compounds that can be recovered by green eco-solvents and employed to improve the quality of food and cosmetic products.  
The present study revealed that B:U (1:1), among six synthesized DESs, had the highest capacity for extraction antioxidants from LB, M, and ChoP able to reduce Cu(II) ions (CUPRAC = 339.5-429.9 umol TE/g) as well as to scavenge ABTS\({}^{\bullet+}\) cation radicals (136.8-146.5 umol TE/g) and DPPH\({}^{\bullet}\) radicals (145.2-170.3 umol TE/g). However, Gu:U (1:1) with various amounts of water achieved the best extraction efficiency for antioxidants from Cha, N, and BH (CUPRAC = 43.2-103.6 umol TE/g and ABTS = 40.5-136.5 umol TE/g for extracts prepared in Gu:U-30, while DPPH = 101.7-111.5 umol TE/g for extracts obtained in Gu:U-50). On the contrary, ChCl:CitA and B:CitA at a 1:1 ratio showed the lowest extractability of total bioactive compounds with antioxidant potential from these three plant materials (CUPRAC = 0.0-47.6 umol TE/g, ABTS = 0.0-23.5 umol TE/g, and DPPH = 13.5-31.2 umol TE/g).  
Moreover, the results of PCA and HCA indicated that components of six synthesized DESs significantly affected the antioxidant potential of herbs and agro-food residues.  
For this reason, a new ChCl:U mixture and RSM were utilized to evaluate the influence of UAE conditions, such as the molar ratio of ChCl and U, the amount of water (WC) added to this DES, and ultrasonication time (t), on antioxidant properties of LB because this herb was the richest source of antioxidants. WC had a greater effect than the ultrasonication time and ChCl:U molar ratio on CUPRAC, ABTS, and DPPH results of LB extracts. The PCM can be applied to optimize the DES-UAE conditions to obtain LB extracts with potent ACs. The calculated optimal conditions were ChCl:U = 1.01 mol/mol, WC = 40%, and t = 15 min. The experimental CUPRAC (133.9-493.7 umol TE/g), ABTS (53.9-273.5 umol TE/g), and DPPH (84.9-209.5 umol TE/g) values very closely matched the predicted results (CUPRAC = 133.9-493.7, 53.9-273.5, and 84.9-209.5 umol TE/g, respectively). Therefore, chemometric tools such as BBD, in conjunction with RSM, can be successfully used for the preparation of natural extracts with a high content of bioactive compounds by the DES-UAE technique.  
The proposed UAE technique using different DESs enhances the efficiency of antioxidant extraction and reduces the use of solvents and reagents, providing the cost-effective production of high-quality extracts with more respect for the environment and human health. A green UAE based on DESs sheds light on future perspectives of industrial applications of herbs and agro-food waste extracts with high antioxidant potential in developing innovative and sustainable food packaging materials and improving the preservation of food products and their physicochemical and sensory characteristics.  
Conceptualization, A.S.-C., P.L. and M.H.; methodology, A.S.-C. and M.H.; software, A.S.-C. and M.H.; validation, A.S.-C. and M.H.; formal analysis, M.H.; investigation, A.S.-C. and M.H.; resources, A.S.-C.; data curation, M.H. and A.S.-C.; writing--original draft preparation, M.H.; writing--review and editing, A.S.-C.; visualization, A.S.-C. and M.H.; supervision, A.S.-C. and P.L.; project administration, A.S.-C. and P.L.; funding acquisition, A.S.-C. All authors have read and agreed to the published version of the manuscript.  
This research received no external funding.  
Not applicable.  
The data presented in this study are available on request from the corresponding author.  
The authors declare no conflicts of interest.