## 3 Results and Discussion
### Comparison of MW-HPCO\({}_{2}\) and CE Methods  
Pectin yield varied depending on the extraction method. While the GPP yield obtained by MW-HPCO\({}_{2}\) hydrolysis under optimum conditions was 27.69 \(\pm\) 0.07%, the pectin yield obtained by CE method was 24.74 \(\pm\) 0.07% (Table 3). MW-HPCO\({}_{2}\) hydrolysis resulted in shorter processing time and higher pectin yield compared to CE method; this can be explained by combined effect of local heating and nonthermal effect (cell deformation) of  
Figure 1: Effect of MW-HPCO\({}_{2}\) extraction variables on pectin yield (\(\%\)). (**A**) extraction temperature–time, (**B**) extraction temperature–liquid/solid ratio, (**C**) extraction time–liquid/solid ratio. microwave power, acidity caused by dissolving CO\({}_{2}\), and high pressure during the process. [PERSON] et al. [3] stated that grapefruit peels contain between 21.60% and 28.00% pectin. This suggests that MW-HPCO\({}_{2}\) extraction is an effective method for extracting nearly all of the pectin from GP. Pectin yield achieved in this research was superior to the previously reported study by [PERSON] and [PERSON] [32], who performed microwave pectin extraction from GP, as well as the reports provided by [PERSON] et al. [6], who studied both acid and alkali extraction of pectin from GP. Unlike several MAE-based studies on pectin extraction from GP, in this study high-yield pectin was obtained without using any chemicals (acid or base). Furthermore, the extraction time was very short. Moisture contents of MW-HPCO\({}_{2}\)-GPP and CE-GPP were determined as 4.52 \(\pm\) 0.08% and 4.29 \(\pm\) 0.03%, ash contents were determined as 2.88 \(\pm\) 0.11% and 3.86 \(\pm\) 0.15%, and protein contents were determined as 3.77 \(\pm\) 0.10% and 3.67 \(\pm\) 0.24%, respectively. The ash content of pectin is an important criterion for its purity and quality. Pectin with low ash content has higher purity and shows better gelling properties [5; 33]. MW-HPCO\({}_{2}\)-GPP had a very low ash content compared to CE-GP because there is no use of any mineral acid in the MW-HPCO\({}_{2}\) method. In a study performed by [PERSON] et al. [34], it was revealed that the acetyl groups and protein in the structure of pectin affect the emulsion-forming ability of pectin and increase emulsion stabilization. The protein content of pectin extracted from GP using MW-HPCO\({}_{2}\) was higher than that of pectin extracted using acid and alkali, as reported by [PERSON] et al. [6]. This suggests a superior emulsion property of the GPP obtained in this study. Compared to MW-HPCO\({}_{2}\)-GPP, the pectin derived from citrus limetta in a study performed by [PERSON] et al. [35] exhibited a high ash value and low protein value. Additionally, the protein content of pectin obtained from orange peel and lemon peel using the CE method was also low, as reported by [PERSON] et al. [24]. Therefore, it can be inferred that MW-HPCO\({}_{2}\)-GPP has superior emulsification properties. GalA and DE values are used to determine pectin purity. The main constituent of the pectin backbone is GaIA. The GaIA contents of GPP obtained from MW-HPCO\({}_{2}\) and CE were 83.90 \(\pm\) 0.06% and 73.79 \(\pm\) 0.23%, respectively (Table 3). The GaIA content of MW-HPCO\({}_{2}\) pectin was higher than that of CE pectin. Differences in GaIA content may be related to the different pH applied in the methods. Higher acidity in CE may lead to lower GaIA content [22]. The DE contents of MW-HPCO\({}_{2}\)-GPP and CE-GPP were 71.76 \(\pm\) 0.81% and 69.30 \(\pm\) 0.92%, respectively; the difference between them was insignificant (\(p\) < 0.05). Harsh conditions in CE (low-pH extraction and long process time) enhance the esterification of polygalacturonic chains, which may be the reason for the difference in GaIA between them [22]. Similarly, in a study performed by [PERSON] and [PERSON] [26], microwave extraction of lime