Abstract
In order to explore snow chrysanthemum polysaccharides (SCPs) as functional food ingredients and natural antioxidants for industrial applications, both microwave-assisted extraction (MAE) and ultrasonic-assisted extraction (UAE) were firstly optimized for the extraction of SCPs. Furthermore, the effects of conventional hot water extraction, UAE, and MAE on the chemical structures and antioxidant activities of SCPs were investigated. The maximum extraction yields of SCPs extracted by UAE (4.13 ± 0.24%) and MAE (4.26 ± 0.21%) were achieved at the optimized extraction parameters as follows: ultrasound amplitude (68%) and microwave power (500 W), ultrasound extraction time (21 min) and microwave extraction time (6.5 min), and ratio of liquid to raw material (42.0 mL/g for UAE and 59.0 mL/g for MAE). In addition, different extraction methods significantly affected the contents of uronic acids, the molecular weights, the molar ratio of constituent monosaccharides, and the degree of esterification of SCPs. SCPs exhibited remarkable DPPH (IC50 ≤ 1.702 mg/mL), ABTS (IC50 ≤ 1.121 mg/mL), and nitric oxide (IC50 ≤ 0.277 mg/mL) radical scavenging activities, as well as reducing power (≥ 80.17 ± 4.8 μg Trolox/mg), which suggested that SCPs might be one of the major contributors toward the antioxidant activities of snow chrysanthemum tea. The high antioxidant activities (DPPH, IC50 = 0.693 mg/mL; ABTS, IC50 = 0.299 mg/mL; nitric oxide, IC50 = 0.105 mg/mL; and reducing power, 127.79 ± 2.57 μg Trolox/mg) observed in SCP-M extracted by the MAE method might be partially attributed to its low molecular weight and high content of unmethylated galacturonic acids. Results suggested that the MAE method could be an efficient technique for the extraction of SCPs with high antioxidant activity, and SCPs could be further explored as natural antioxidants for industrial application.
Highlights
Oxidative stress is usually caused by reactive oxygen species (ROS) [1]
In order to reduce the interference of different monosaccharides on the response of the phenol-sulfuric acid method, a mixture standard was prepared by 40% galacturonic acid (GalA), 30% Ara, and 30% Gal according to the constituent monosaccharides in snow chrysanthemum polysaccharides (SCPs) determined by a high-performance liquid chromatography (HPLC, ThermoFisher scientific, Waltham, MA, USA)
The results showed that the molecular weights of SCP-U extracted by ultrasonic-assisted extraction (UAE) were similar with those of SCP-M extracted by microwave-assisted extraction (MAE)
Summary
Oxidative stress is usually caused by reactive oxygen species (ROS) [1]. Elevated level of ROS results in the generation of free radicals which can cause deleterious effects on protein, lipids, and deoxyribonucleic acid (DNA) [2]. Chemical structures and antioxidant activities of polysaccharides, which abundant exist in snow chrysanthemum tea [15], have seldom been investigated. Several studies have demonstrated that natural polysaccharides extracted by MAE and UAE exhibit much higher antioxidant activity than that of HWE [25,28,29,30]. To the best of our knowledge, the optimization of microwave-assisted extraction and ultrasonic-assisted extraction of SCPs and the effects of different extraction methods on their chemical characteristics and antioxidant activities have seldom been investigated. SCPs as functional food ingredients and natural antioxidants for industrial applications, both MAE and UAE were firstly optimized for the extraction of SCPs, and the chemical structures and antioxidant activities of SCPs extracted by different methods (MAE, UAE, and HWE) were systemically investigated and compared
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