## 3 Results and Discussion
### Pectin Compositions (Monosaccharide, Galacturonic Acid Content and Protein Content)  
The MAE and MAUPE pectins had a GalA content of 73.5% and 69.5-72.5%, respectively. The pretreatment influenced the GalA content of pectin. The total GalA content indicates the pectin purity [28]. From Table 1, it is understood that the decrease in GalA content of pectin corresponded to the rise in extraction pretreatment power and time. Therefore, this result is probably related to the existence of higher impurity, according to the protein content and monosaccharides composition. Figure 1: Yield values of extracted pectin using microwave-assisted extraction (MAE) and microwave-assisted extraction with ultrasonic pretreatment (MAUPE), which were shown using ultrasonication pretreatment power and time. Pretreatment increased the total neutral sugar content of the samples. The total amount of rhamnose, arabinose and galactose, which form the side chain of the pectin polymer, was significantly lower than GalA. Results showed that the HG index (GalA-Rha) [29] of pectin from MAE and MAUPE was 73.40%, and varied between 69.19% and 72.08%, respectively. Galactose and arabinose from the rhamn adjacent are involved in creating the branching parts of the pectin polymer [30]. [PERSON] et al. (2017) reported that pectin isolated from watermelon find contained HG and RG-I fractions [31]. From Table 1, it can be seen that the samples from MAUPE were richer in RG-I (5.32% to 7.68% of RG-I). However, in both methods, the proportion of HG was dominant. Based on the literature, pectin is physically trapped in the cellulose matrix, or strongly interacts with cellulose. The linkage between pectin and cellulose was found in RG-I rather than HG [32]. [PERSON] et al. proposed that in the RG-I side chains, galactose or arabinose units are covalently linked to cellulose [33]. According to these results, ultrasonic pretreatment can \begin{table}
\begin{tabular}{c c c c c c} \hline  & **MAE** & \multicolumn{4}{c}{**MAUPE**} \\  & & **150 W–10 min** & **150 W–20 min** & **300 W–10 min** & **300 W–20 min** \\ \hline Rhamnose (\%) & 0.29 & 0.47 & 0.41 & 0.39 & 0.31 \\ Arabinose (\%) & 0.55 & 0.70 & 0.65 & 0.86 & 0.77 \\ Galactose (\%) & 3.28 & 6.04 & 3.85 & 6.01 & 5.51 \\ Glucose (\%) & 2.50 & 3.23 & 2.95 & 3.28 & 4.82 \\ Xylose (\%) & 0.13 & 0.15 & 0.18 & 0.12 & 0.15 \\ Galacturonic acid (\%) & 73.5 & 72.5 & 71.6 & 70.0 & 69.5 \\ HM (\%) & 73.40 & 72.08 & 71.19 & 69.51 & 69.19 \\ RG-I (\%) & 4.37 & 7.68 & 5.32 & 7.64 & 6.92 \\ R1 (\%) & 31.10 & 24.66 & 25.85 & 23.53 & 15.79 \\ Protein (\%) & 5.84 & 8.22 & 8.57 & 8.37 & 8.81 \\ \hline \end{tabular}
\end{table} 
Table 1: Monosaccharide composition (%) of WRP extracted by MAE and MAUPE. Figure 2: Interaction effect of ultrasonication and extraction time (**a**) and time and power of ultrasonication (**b**) on the DE of extracted pectin. The vertical axis represents the DE value of the extracted pectin. us: ultrasonication, ext-time: extraction time. have the ability to increase the extraction yield and affect pectin monosaccharides which introduce the pectin with a higher RG-I content. Therefore, the higher amount of RG-I side chains obtained by MAUPE can probably be explained by the ultrasonic effect on covalent bonds (celloles-RG-I) in raw materials. Xylose was detected at a small percentage, which is due to the low presence of rhamn-II [7,19] in the structure of the samples. Thus, WRP is predominantly composed of HG and a small fraction of RG-I. The presence of glucose can be explained as a result of non-pectin polysaccharide degradation during extraction [30]. A lower glucose content of the sample from MAE than MAUPE indicates the lower amounts of co-extracted hemicelluloses, cellulosic oligomers or starch (impurity) in this sample compared to other samples. Morever, the (Rha + Ara + Gal + GalA)-Glc ratio reveals the pectin purity [29]; it compares the amount of pectin components to any co-extractants.