Optimisation of the extraction process of pectin polymer from red dragon skin (Hylocereus polyrhizus)

Background: The variation of pectin extracted from red dragon skin (Hylocereus polyrhizus) depends on the type of acid, temperature, and length of extraction time. Objective: This research was conducted to determine the characteristics of pectin produced from red dragon skin based on using citric, oxalic, and acetic acids at pH 4, extraction temperature of 60°C and 75°C, and duration of 120 minutes. Method: A total of six conditions for pectin extraction were performed and the obtained product was dried using the freeze-dryer. Furthermore, the optimisation included yield, moisture content (MC), equivalent weight (EW), methoxyl content (MeO), galacturonic acid content (GA), degree of esterification (DE), sugar and organic acid levels (SO), and Fourier Transform Infrared Spectroscopy (FT-IR) was performed. Result: The EW value of red dragon skin and commercial apple pectin were comparable but the MeO value was slightly different from those extracted with 75°C oxalic acid. Compared to commercial apple and orange skin, the GA value of red dragon pectin extracted with 75°C oxalic acid was not different. Conclusion: FT-IR spectra contained groups -OH, -CH, and C=O and were confirmed to have a GA structure. The best product was obtained by conducting extraction under the condition of 75°C for 120 minutes using oxalic acid.