## 3 Results and Discussion
### Grapefruit Polyphenol-Rich Extract Composition  
#### 3.2.1 TFC and TPC  
Phenolic compounds, found abundantly in plants and fruits like those of the Citrus genus, are recognized for their antioxidant and antimicrobial activities. Recent research has also associated them with additional health benefits, including lower blood sugar and cholesterol levels, as well as reduced inflammation [56]. The TPCs of the GF-EO and hydroethanolic extracts (GF-PE and GF-CE) are presented in Table 2. For the EO, the value was 13 mg GAE/g DE, while for the polyphenol-rich extracts GF-PE and GF-CE, the TPCs were 51 and 208 mg GAE/g DE, respectively. The crude polyphenol-rich extract (GF-CE) showed 4-fold higher values than those of the polyphenol-rich extract obtained after oil extraction (GF-PE) (\(p\) < 0.05). The reduction in the TPC value for the GF-PE may be due to the previously high temperature applied during the hydrodistillation process since high temperatures are the most common explanation for the degradation of polyphenols [57]. However, for the TFC, the opposite results are observed. The GF-PE had 29 \(\pm\) 0.01 mg QE/g DE, while the GF-CE had only 13 \(\pm\) 0.06 mg QE/g DE (\(p\) < 0.05). Flavonoids are sensitive to heat [58]. However, certain extraction methods and parameter combinations may enhance the release or extraction of flavonoids from the plant material because of the breakdown from the cell wall [59].  
The TPC and TFC in extracts from GF peels can vary depending on several factors, including the GF variety, ripeness, growing conditions, and the extraction method used. To the best of our knowledge, these TPC and TFC values for the extracts obtained from the fresh GF peels cultivated in Egypt have not been reported in the literature to date. However, for other geographical locations, the value of the TPC of the grapefruit peel  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**No.**} & \multirow{2}{*}{**Retention Time**} & **Molecular Weight** & **Base Peak** & **Molecular** & \multirow{2}{*}{**Compound**} & \multirow{2}{*}{**Area (\%)**} \\  & & **(M+)** & & & **Formula** & & \\ \hline
33 & 29.32 & 206 & 135 & C\({}_{15}\)H\({}_{26}\) & Nootkatol & 0.29 \\
34 & 30.41 & 218 & 135 & C\({}_{15}\)H\({}_{22}\)O & Cucuphenol & 0.35 \\
35 & 30.38 & 218 & 146 & C\({}_{15}\)H\({}_{22}\)O & Nootkatone & 24.33 \\  & & Total Area of the Identified Compounds & & & 97.11 \\ \hline \hline \end{tabular}
\end{table}
Table 1: _Cont._  
\begin{table}
\begin{tabular}{c c c} \hline \hline  & **TPC** & **TFC** \\  & **(mg GAE/g DE)** & **(mg QE/g DE)** \\ \hline GF-CE & 20.18 \(\pm\) 0.02 a  & 13.09 \(\pm\) 0.06 b  \\ GF-EO & 13.21 \(\pm\) 0.00 c  & – \\ GF-PE & 51.27 \(\pm\) 0.01 b  & 29.31 \(\pm\) 0.01 a  \\ \hline \hline \end{tabular}
\end{table}
Table 2: Total phenolic content (TPC) and total flavonoid content (TFC) of the grapefruit essential oil (GF-EO) and polyphenol-rich extracts (GF-CE and GF-PE). Values represent the mean \(\pm\) standard deviation. Different letters mean significant differences between the bioactive extracts (\(p\) < 0.05).  
extracts can range from approximately 50 to 200 mg GAE/extract [60; 61; 62; 63]. For instance, with 80% ethanolic extraction, the TPC was about of 20 mg GAE/g DE using GF peels cultivated in Pakistan [10]. On the other hand, studies from [PERSON] et al. [64] using ultrasound extraction with ethanol 70% (\(v/v\)) demonstrated a TPC of 667 mg GAE/g DE. Another study from [PERSON] et al. [62] with GF solid waste from Valencia, Spain reported an optimal TPC extraction of approximately 80 mg/g DE.  
Overall, the TPC constituted approximately 20%, 5%, and 1% of the entire extracts of GF-CE, GF-PE, and GF-EO, respectively. Consequently, other compounds, such as sugars, minerals, organic acids, soluble fibers, and proteins, were also extracted, while terpen were predominant in the GF-EO.