Polysaccharides From Different Kiwifruits:Extraction Optimization,Physicochemical Characteristics,and Biological Activities

In order to explore green extraction methods for preparation of polysaccharides from kiwifruit,to better understand the relationship between the chemical structures and biological activities of polysaccharides from kiwifruit,and to evaluate the effects of different varieties and origins on the chemical structures and bioactivities of kiwifruit polysaccharides,the ultrasonic-assisted and microwave-assisted extraction conditions of polysaccharides from kiwifruit were optimized,and the effects of different extraction methods on their physicochemical characteristics and antioxidant activity were compared.Furthermore,the physicochemical characteristics and biological activities of polysaccharides from kiwifruits of different varieties and different regions were evaluated and compared.The main results are as follows:(1)Extraction optimization,physicochemical characteristics,and antioxidant activities of polysaccharides from kiwifruitIn this study,the"Hongshi"kiwifruits was selected as the research material,both microwave-assisted extraction(MAE)and ultrasonic-assisted extraction(UAE)were optimized for the extraction of polysaccharides from kiwifruit(KP)by response surface method,and the physicochemical characteristics and antioxidant activities of KPs extracted by different methods were investigated.Results showed that the yields of KPs extracted by MAE(2.92%±0.08%)and UAE(2.82%±0.10%)under the optimal extraction conditions were not significantly different from that of traditional hot water extraction(2.86±0.13%),while the extraction time was greatly shortened.Besides,different extraction methods significantly affected the contents of uronic acids,molecular weights,molar ratios of constituent monosaccharides,and the degree of esterification of KP.Furthermore,KP exhibited remarkable DPPH and ABTS radical scavenging activities,and reducing power.The high antioxidant activities observed in KP-M extracted by the MAE method might be partially attributed to its low molecular weight and high content of unmethylated galacturonic acid.Results suggested that the microwave-assisted extraction method could be a good potential method for the extraction of KP with high antioxidant activity,and KP could be further explored as functional food ingredients.(2)Comparison of physicochemical characteristics and biological activities of polysaccharides from different varieties of kiwifruitsFourteen representative cultivars of five species(Actinidia chinensis,A.deliciosa,A.arguta,A.macrosperma and A.polygama)of kiwifruits growing in China were selected and their polysaccharides were extracted by microwave-assisted extraction method.The extraction yields,physicochemical characteristics,and biological activities of polysaccharides from kiwifruits of fourteen different varieties were compared.The extraction yields,uronic acid contents,and molecular weights of polysaccharides from kiwifruits of different varieties were ranged from 2.35%±0.06%to 5.58%±0.10%,30.87%±1.34%to 43.04%±1.49%,and 1.06×10~5 Da to 15.04×10~5 Da,respectively.The polysaccharides in A.arguta,A.macrosperma and"Honghua"kiwifruit have higher molecular weights and apparent viscosities,while the polysaccharides from Hayward,"Cuxiang",and"Xuxiang"kiwifruit,which belong to A.deliciosa,have lower molecular weights.Galacturonic acid,arabinose,and galactose are the main monosaccharide components of polysaccharides from kiwifruits of different varieties.Moreover,the varieties of kiwifruits have certain effects on the type and molar ratio of monosaccharides of polysaccharides.The polysaccharides from kiwifruits of different varieties have similar structures,while the degrees of esterification(DE)were significantly different.The values of DE were ranged from 33.98%±0.12%to 45.69%±0.23%.Furthermore,the polysaccharides from A.arguta,A.macrosperma,and"Hongyang"kiwifruit have higher antioxidant and antiglycation activities,which might be related to its higher unmethylated galacturonic acid content.Besides,the antioxidant activity and anti-glycation activity are related.Furthermore,the polysaccharides from A.polygama,A.arguta,A.macrosperma,and"Hongyang"kiwifruit have stronger prebiotic activity,which might be related to the molecular weight and monosaccharide composition of the polysaccharide.The polysaccharides from A.polygama,A.arguta,and"Hongshi"kiwifruit could promote the production of more types and contents of short-chain fatty acids by probiotics,and the contents of short-chain fatty acids have a positive correlation with the growth promotion effect of probiotics.(3)Comparison of physicochemical characteristics and biological activities of polysaccharides from kiwifruits collected from different origins "Hongyang"kiwifruit from fouteen origins in six regions of Sichuan Province(Pujiang County,Qionglai City,Dujiangyan City,Yibin City,Dazhou City and Guangyuan City)was selected and their polysaccharides were extracted by microwave-assisted extraction method.The extraction yields,uronic acid contents,degrees of esterification,and molecular weights of polysaccharides from kiwifruits of different origins were ranged from 2.69%±0.07%to 4.06%±0.14%,38.11%±1.74%to 45.90%±2.59%,40.14%±0.79%to 47.45%±0.43%,and 3.85×10~5 Da to 7.99×10~5 Da,respectively.The molecular weights of polysaccharides from kiwifruits growning in Guangyuan are relatively higher among six regions of kiwifruits,which corresponds to its higher apparent viscosity.Origins have less impact on the type of monosaccharides of polysaccharides from kiwifruits,while they have significant effect on the molar ratio of monosaccharide components.Origins have certain effects on the antioxidant and antiglycation activities of polysaccharides from kiwifruits.The antioxidant and antiglycation activities of polysaccharides from kiwifruits growning in Qionglai are the strongest,which might be related to its lower molecular weight and higher content of unmethylated galacturonic acid.The polysaccharides from kiwifruits growning in Qionglai and Pujiang possess the stronger prebiotic activity,which might be related to their relatively lower molecular weights and higher proportions of galactose and arabinose.The polysaccharides from kiwifruits growing in Qionglai and Pujiang could promote probiotics to produce more short-chain fatty acids,and the contents of short-chain fatty acids are related to the role of probiotics in promoting growth.