Characterization of Functional Ingredients Extracted with Ethanol Solvents from Ponkan (Citrus reticulata) By-Products Using the Microwave Vacuum Drying Method Combined with Ultrasound-Assisted Extraction

Abstract

For this study, microwave vacuum drying (MVD) was combined with ultrasound-assisted extraction to compare the effects of different ethanol volumes on ponkan extract and to evaluate the total phenolic content (TPC), total flavonoid content (TFC), and total ascorbic acid content (TAAC). High-performance liquid chromatography with photodiode array detection (HPLC-PDA) was used to analyze the flavanone contents and antioxidant activity of ponkan (Citrus reticulata) peels. The experimental results showed that the TPC and TFC increase with ethanol volume. Ethanol extraction (75%) showed significant advantages by increasing the TPC to 17.48 mg GAE/g (DW) and the TFC to 2.96 mg QE/g (DW) of ponkan extract and also exhibited the highest antioxidant activity. The TAAC improved along with increased water content. Water extraction showed the highest content (13.07 mg VitC/100 g, DW). The hesperidin content analyzed by HPLC-PDA was 102.95–622.57 mg/100 g (DW), which was the highest among the flavanones. Then, the ethanol insoluble residue extracts were taken from the pectin with four different solvents, evaluating TPC, TFC, and antioxidant activity. The TPC, TFC, and antioxidant capacity of pectin are significantly lower than those of the peels. Combining MVD and 75% ethanol with ultrasound-assisted extraction in the pre-treatment process can effectively eliminate polyphenols, flavonoids, and other compounds, thus enabling the extraction of high-methoxyl pectin. The total dietary fiber (TDF) content of MVD ponkan by-products was 25.83%. Ponkan by-products have the potential for the future development of functional foods and supplements.