Modified Bentonite By Thermal Activation And Chitosan-Loaded Bentonite For Mango’s Preservation

Modification for Ca-bentonite and Na-bentonite carried out by thermal activation. The effects of activation temperature on water absorption capabilities of bentonites were researched. The bentonite preservation suspensions based on200℃activated Ca-bentonite and chitosan loaded it were used in mango’s preservation by casting. Main physiological and biochemical index were measured, they were weight loss, respiratory rate, turning yellow and decay index, souble sugar, souble solid, souble titratable acid, soluble pectin, vitamin C and so on. Sensory evaluation and flavor of mango’s slices were also served as evaluating indicators. Structures of activated bentonite and chitosan loaded bentonite were tested through infrared spectroscopy, scanning electron microscope and X-ray diffractomer, respectively. The contents of heavy metal elements in pulp were analyzed before and after treating by preservation. Preservative mechanisms of the materials were explored. In addition, effects of bentonite and chitosan on mango’s anthracnosises were studied, repectively. The results follow as:1. With calcination temperature increasing, water absorption rates of Ca-bentonite and Na-bentonite exhibited an upward trend and then downward trend. Moreover, value of water absorption rate reached the highest when the temperature was around at200℃. The water absorption rate of Ca-bentonite was higher than that of Na-bentonite, but its saturated water absorption content was lower than that of Na-bentonite.2. Bentonite displayed an excellent absorption for anthracnosises, and its absorption ability increased with increase of bentonite concentration. However, bentonite could not inhibit growth of anthracnosises. Chitosan could effectively inhibit mango’s anthracnosises.3. The suspension made of200℃activated Ca-bentonite with the mass ratio10:1of liquid and solid was used to casting mangos for preservatipon. The results showed a good effect. The weight loss of mangos by treating could be effectively reduced, decay index and peel turning into yellow color were decreased, and respiration peaks of mangos were postponed. Hence, mangos’s ripening was effectively slowed down, and life-shelf would be extended. Using the suspenstion with mass ratio10:2of activated Ca-bentonite and chitosan to cast mangos for preservation, the results were better than that of activated Ca-bentonite alone.4. The results of infrared spectroscopy, scanning electron microscope and X-ray diffractomer indicated that basic structure of bentonite had not been changed after thermal activated and chitosan loaded. But bentonite’s curling structure on its edge disappeared after thermal activated at400℃. As far as chitosan loaded bentonite, it was suggested there was an association reaction between chitosan and water molecules in layers of bentonite, part of chitosan molecules entered into bentonite’s layers, and cation exchange would be happened.5. Composite material of bentonite with chitosan loaded has a preservative action via coupling, the reseans depend on bentonite’s water absorption, adsorption, and cation exchange; chitosan’s antibacterial property as well as film-forming of bentonite and chitosan. Water loss was effectively reduced, anthracnosis one of mango’s pathogenic bacteria was inhibited, attack of outside bacteria was prevented, at the same time, it could also inhibit production of ethylene and a series of physiological actions due to guiding from ethylene. Moreover, the film covering mango’s surface constructed an environment for adjusting gas’s exchange, it was lower O2and higher CO2, in such environment, the physiological metabolism of fruits retarded.