## 4 Conclusions  
The extraction yields of the total phenolic content, total saponin content and antioxidant activity from _Curculigo orchioides_ Gaernt rhizomes were significantly influenced by the extraction time, the temperature and especially the solvent-to-material ratio. The optimal conditions for the extraction of TSC were predicted and validated as 60 min, 57 \({}^{\circ}\)C and a 80 mL/g solvent-to-material ratio, while those for the recovery of TPC were 178 min, 45 \({}^{\circ}\)C and a 68 mL/g solvent-to-material ratio. Extraction with the optimal conditions resulted in the maximum yields of TSC and TPC of 11.33 mg AE/g DW and 23.58 mg GAE/g DW, respectively. The highest DPPH antioxidant activity of the extracts was 133.45 \(\upmu\)M TE/g DW, which was obtained when the _Curculigo orchioides_ Gaernt rhizome was extracted for 180 min, at 40 \({}^{\circ}\)C, with a solvent-to-material ratio of 80 mL/g. Verification experiments using the optimal conditions confirmed that the actual values were not significantly different from the values predicted by the optimization models. In addition, ultrasound-assisted extraction helped to reduce the extraction time by up to 18 times (10 min), while achieving equivalent extraction yields to the maceration extraction process, using the same type and amount of solvent for the TPC, TSC and antioxidant activity. The results of this study can be used as a scientific basis for the development of efficient extraction processes for _Curculigo orchioides_ Gaernt rhizomes at larger production scales.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Output Responses** & **Parameters** & **Maceration** & **UAE** \\ \hline TPC & Extraction time & 178 min & 10 min \\ (mg GAE/g DW) & Recovery yield & 23.73 \(\pm\) 0.77 a & 23.58 \(\pm\) 2.24 a \\ \hline TSC & Extraction time & 60 min & 15 min \\ (mg AE/g DW) & Recovery yield & 11.27 \(\pm\) 0.82 b & 11.33 \(\pm\) 1.20 b \\ \hline Antioxidant activity & Extraction time & 178 min & 10 min \\ (\(\upmu\)M TE/g DW) & Recovery yield & 141.85 \(\pm\) 10.12 c & 133.45 \(\pm\) 19.95 c \\ \hline \hline \end{tabular} Different characters indicate statistically significant differences between values in a row (\(p<0.05\)).  
\end{table}
Table 5: Comparison of extraction efficiency obtained by ultrasound-assisted extraction and maceration extraction processes.  
**Author Contributions:** Conceptualization, T.D.B. and V.C.H.; methodology, T.D.B. and V.C.H.; software, V.C.H.; validation, T.D.B. and V.C.H.; formal analysis, V.C.H.; investigation, T.D.B. and V.C.H.; resources, T.N.D.D. and L.T.K.D.; data curation, V.D.P. and V.C.H.; writing--original draft preparation, T.D.B.; writing--review and editing, V.C.H. and L.T.K.D.; visualization, T.N.D.D. and V.D.P.; supervision, V.C.H.; project administration, T.N.D.D. and L.T.K.D.; funding acquisition, V.C.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by project number T2023-16 of Ho Chi Minh City University of Technology and Education (HCMUTE), Vietnam.  
Not applicable.  
**Data Availability Statement:** The original contributions presented in the study are included in the article, further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.