Abstract
In order to evaluate effects of extraction techniques on the physicochemical characteristics and antioxidant activities of kiwifruit polysaccharides (KPS), and further explore KPS as functional food ingredients, both microwave-assisted extraction (MAE) and ultrasonic-assisted extraction (UAE) were optimized for the extraction of KPS. Furthermore, the physicochemical structures and antioxidant activities of KPS extracted by different techniques were investigated. The optimal extraction conditions of UAE and MAE for the extraction of KPS were obtained by response surface methodology. Different extraction techniques significantly affected the contents of uronic acids, molecular weights, molar ratios of constituent monosaccharides, and the degree of esterification of KPS. Results showed that KPS exhibited remarkable DPPH and ABTS radical scavenging activities, and reducing power. The high antioxidant activities observed in KPS extracted by the MAE method (KPS-M) might be partially attributed to its low molecular weight and high content of unmethylated galacturonic acid. Results suggested that the MAE method could be a good potential technique for the extraction of KPS with high antioxidant activity, and KPS could be further explored as functional food ingredients.
Highlights
When biologically reactive species such as reactive oxygen species (ROS) prevail over natural antioxidative defenses of the organism, oxidative stress emerges
The yield of kiwifruit polysaccharides (KPS) increased as the microwave power increased from 240 to 480 W and decreased when the microwave power was above 480 W (Figure 1A)
The results suggested that different extraction methods had significant effects on the contents of uronic acid in polysaccharides [13,14]
Summary
When biologically reactive species such as reactive oxygen species (ROS) prevail over natural antioxidative defenses of the organism, oxidative stress emerges. Synthetic antioxidants are used in the food industry to inhibit the overproduction of ROS, but they are restricted use due to their potential hazards to health [2]. The polysaccharides in natural sources have been noticed as novel potential antioxidants due to their low toxicity and high level of antioxidant capacity, such as their radical scavenging abilities [3]. Kiwifruit (Actinidia chinensis Planch.), which belongs to the Actinidia family, is one of the most valuable fruit crops for its flavor and nutritional qualities. Kiwifruit originates in China and it is Molecules 2019, 24, 461; doi:10.3390/molecules24030461 www.mdpi.com/journal/molecules
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