## 3 Results and Discussion
### Effect of Different Extraction Methods on Stevioside and Rebaudioside A Yield  
As mentioned in Section 2.8, the extraction was carried out at a variable temperature in an insulated vessel to retain the heat generated during the ultrasound. The increase in temperature with time is as shown in Figure 6. The temperature has reached values of 35.7 \({}^{\circ}\)C, 61.5 \({}^{\circ}\)C, 65.5 \({}^{\circ}\)C, 81.5 \({}^{\circ}\)C, and 88.00 \({}^{\circ}\)C during sonication after 1, 3, 5, 7, and 10 min of extraction, respectively. According to the literature, the samples used for extraction are usually placed in a cooling bath to absorb the heat generated by ultrasonication. UAE with a circulating water bath is higher energy consumption compared to UAE under uncontrolled temperature (variable temperature) at the same duration due to (i) the energy required to bring the temperature to a certain degree and (ii) the energy needed to keep the temperature at constant. It was surprising that the energy used during sonification (with a cooling bath) was excessively large, making such treatment highly impractical. As can be seen from Table 6, the stevioside and rebaudioside A content in the hot water extract was 5.34 \(\pm\) 0.006 and 2.07 \(\pm\) 0.015 g/100 g dry leaves, respectively. These values are within the range of steviol glycosides found in different varieties of the stevia plant (stevioside 4-13 g/100 g dry leaves, rebaudioside A 2-4 g/100 g dry leaves) [7; 36; 39; 41]. From the results shown in Table 6, the stevioside content in the extracts obtained by UAE at different times has remained relatively constant (5.02, 5.48, 5.37, 5.33, and 5.47 g/100 g dry leaves with extraction times 1, 3, 5, 7, and 10 min, respectively) compared with hot water extraction (90 \({}^{\circ}\)C, 1 h). Similarly, the yield of rebaudioside A was 2.00 \(\pm\) 0.004, 2.13 \(\pm\) 0.009, 2.09 \(\pm\) 0.039, 2.06 \(\pm\) 0.001, and 2.15 \(\pm\) 0.024 g/100 g dry leaves after 1, 3, 5, 7, and 10 min of sonication, respectively. It can be concluded that an exposure extraction time of a few minutes appears to be sufficient to recover most of the bioactives from _Stevia rebaudiana_ fine powder (200 \(\upmu\)m) via ultrasound as a novel technology as \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Method**} & \multirow{2}{*}{**Extraction Time (min)**} & **Stevioside Yield \%** & **Rebaudioside A Yield** \\  & & **(g/100 g Dry Leaves)** & **\% (g/100 g Dry Leaves)** \\ \hline Hot water, 90 \({}^{\circ}\)C & 60 & 5.34 \(\pm\) 0.006 & 2.07 \(\pm\) 0.015 \\ \hline \multirow{6}{*}{UAE} & 1 & 5.02 \(\pm\) 0.009 & 2.00 \(\pm\) 0.004 \\  & 3 & 5.48 \(\pm\) 0.017 & 2.13 \(\pm\) 0.009 \\ \cline{1-1}  & 5 & 5.37 \(\pm\) 0.066 & 2.09 \(\pm\) 0.039 \\ \cline{1-1}  & 7 & 5.33 \(\pm\) 0.009 & 2.06 \(\pm\) 0.001 \\ \cline{1-1}  & 10 & 5.47 \(\pm\) 0.030 & 2.15 \(\pm\) 0.024 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Stevioside and rebaudioside A yield using hot water and UAE methods. compared to the classical hot water extraction (90 \({}^{\circ}\)C, 1 h) in this study. By decreasing the raw material particle size, rapid extraction could happen. Figure 5: Total of selected bioactive terpenoids in Manuka samples with particle size of: **(a)** d \(\leq\) 200, **(b)** d = 100 \(\upmu\)m, **(c)** d = 68 \(\upmu\)m.  
This, again, supports our hypothesis that most of the bioactive compound is released during grinding since the increase of extraction time did not have any effect. The extraction of stevioside and rebaudioside A from _Stevia rebaudiana_ fine powder (250 \(\upmu\)m) was conducted and compared by[36]. The extraction was performed by microwave-assisted extraction (MAE) and compare it with cold maceration. The results showed that MAE (1 min, 50 \({}^{\circ}\)C) was more efficient than cold maceration (12 h, 25 \({}^{\circ}\)C). The higher extraction yield of microwave-assisted extraction can be explained by the elevated temperature used in MAE.