Co-optimization of polysaccharides and polyphenols extraction from mangosteen peels using ultrasound-microwave assisted extraction (UMAE) and enzyme-ultrasound assisted extraction (EUAE) and their characterization

Natural functional and bioactive compounds extracted from agricultural wastes using green techniques have attracted great attention due to their health benefits, numerous potential applications and less environmental impacts. Therefore, this study aimed to co-optimize the processes of ultrasound-microwave assisted extraction (UMAE) and enzyme-ultrasound assisted extraction (EUAE) to simultaneously maximize the yields of polysaccharides (PSY) and phenolics (TPC) from mangosteen (Garcinia mangostana L.) peels with the aid of Box-Behnken design. The chemical structure of the polysaccharides and the bioactive activities of the phenolics extracted by two methods were also determined and compared. At the optimal conditions, the results revealed that UMAE produced a less amount of polysaccharides (18.4%) but required a shorter total treatment time (66 min) than EUAE. In contrast, EUAE generated much higher PSY (32.86%) and had an additional advantage of using the medium with less acidity (pH 4.7 as compared with pH 2). Both approaches resulted to a quite equivalent amount of phenolics (104–111 mg gallic acid equivalent per g dry weight). The FTIR spectra explored that the UMAE polysaccharides had a similar chemical structure with commercial pectin while the EUAE ones had distinguished peaks, appropriately related to the complex network structure of rhamnogalacturonan, homogalacturonan and polygalacturonic acid. On the other hand, both UMAE and EMAE phenolic extracts had similarly high inhibitory effect against α-glucosidase with their IC₅₀ of 1.16–1.18 mg/mL. However, the EMAE phenolic extract had nearly doubled 2, 2-diphenyl-1-1-picrylhydrazyl (DPPH) scavenging activity (4080 μg TE/mL extract) as compared to the UMAE one. These findings conclude that polysaccharides and polyphenols from both extraction methods could be used as ingredients for nutraceutical products and food processing with desirable characteristics.