Ultrasonic-assisted Extraction And Physico-chemical Properties Of Pectin Based On Different Molecular Weights From Apple Pomace

Pectin is a kind of natural high molecular compound widely-existed in green plants, together with fibers to play a role in combining with plant structures, including protopectin, pectin and pectinic acid. Pectin served as a natural food function factor added to food can not only play an effective role in stable agent, emulsifier, and thickener but also decrease blood lipoid, blood suger, cholestrol, and control the pervasion of cancer cell and the damage of antineoplastic drugs to gastrointestinal mucosa, etc. Pectin with high molecular weight can be used to prepare supersonic centrifuge membrane and electric osmotic membrane because of its better gelatification. Pectins we need maily depend on importation, which increases production cost and resource dependance. China is the first country to produce apples and apple juice in the world. Over one million tons of apple pomace is produced in the process of apple juice concentration production. The apple pomace resources contain the available rich pectins(10-16% calculated in terms of dried qualities). Rational use of apple pomace to turn the wastes into the valuables is not only benefit to environment protection, but also favorable for improving the added values of apples. Ultrafiltration has been used to purify concentrated pectin solution, and various kinds of polyoses have been separated by stages with a better result. Little has been reported on the separation conditions of apple pectin with different relative molecular weight stages and correlated physico-chemical properties. Accordingly, it is necessary to study the classification and separation conditions of apple pectin, correlated physicochemical properties and rheological properties, whereby providing a basis for the future in-depth exploration of apple pectin.In this paper, the following contents were particularly investigated:The optimal technical parameters of pectin extraction assisted by ultrasonic from apple pomace were studied. The best operational parameters of isolation of apple pectin by ultrafiltration and the method of cleaning ultrafiltration membrane were discussed. Apple pectins with different molecular weights had been obtained after ultrafiltration and the relationship between apple pectins with different molecular weights and their physico-chemical properties were investigated. Rheological properties of apple pectins with different molecular weights were evaluated.The results showed:1 The optimal technical parameters of pectin extraction assisted by ultrasonic from apple pomace were:ultrasonic power 180W, ultrasonic time 40min, proportion of materials and water 1:25, extraction temperature 45℃and pH 1.5.The extraction yield was 13.79%.2 When transmembrane pressue difference was 0.08 MPa at 50℃and material solution concentration was 1g·L, apple pectin could be better isolated. The flux recovery was very excellent in such a way that ultrafiltration membrane was washed in clean water for 20min, followed by alkaline cleaning for 2h, and then again was washed in clean water for 20min.3 Apple pectin solutions were classified and isolated via ultrafiltration to obtain 6 kinds of apple pectins with different molecular weights. Apple pectins with molecular weight over 300kDa were the majority, accounting for 68.04%, and that with molecular weight below 5kDa was minority, only accounting for 3.31%.It has been found through the studies of properties of pectin with different molecular weights isolated by ultrafiltration membrane that galacturonic acid contents, esterification degree, and gelatification degree in each classification dropped with a decrease in pectin molecular weights. In addition, owing to the absorptive function of ultrafiltration for pigments and impurities, pectin isolation by ultrafiltration had a better effect upon decoloration of pectin soultion.4 Apple pectin solutions exhibited a shear-thinning behaviour. When the concentration of apple pectins increased, the viscosity increased too. The viscosity of apple pectins solution was in direct ratio with molecular weights and in inverse ratio with solution temperature. The viscosity of the pectin solutions increased in the presence of sucrose, but decreased in the presence of salts.