Characteristics Of Resistant Starches From Four Banana Cultivars And Their Changes During Post Ripening

Banana is a characteristic fruit in tropics and subtropics. It is high in yielding, with richnutrition as well as important medicinal and health care functions. It is a typical climactericfruit, which is difficult to store and apt to deteriorate, therefore, the post-harvest losses arevery serious. Bananas are frequently unsalable during harvest, but relative processing is lagbehind. The research on banana functional factors and changes during ripening are beneficialfor the development and application of banana and promoting the development of bananaindustry.In this thesis, resistant starches (RS) were extracted from four banana cultivars(including Xiangyajiao, Dajiao, Fenjiao and Huangdijiao) at the first grade of ripening stage.Their purities were measured, and then their granule morphologies, molecular conformations,optical properties and crystalline structures were observed. And in the meantime the changesof their structures and physicochemical properties were studied during post-ripening. Finally,the influences of different heating treatments on the physicochemical properties of plantain(Dajiao) resistant starch were investigated.The results show that the purity of resistant starch of Fenjiao was the highest, which ofHuangdijiao showed the lowest, and the purities of the other two cultivars had no significantdifference, which were between the formers. The RS granules of Xiangyajiao were large,Dajiao were elongated, Fenjiao were round, Huangdijiao were predominant small. The starchgranules of four banana cultivars all had smooth surfaces, intact structures, apparent inclinedcross polarizations, and their intersections closed to one end. It was revealed that Xiangyajiaoand Dajiao had B-type crystallite, while Fenjiao and Huangdijiao had C-type crystallite, andthe degrees of absolute crystallinity ranked: Fenjiao>Huangdijiao>Xiangyajiao>Dajiao, theratios of microcrystalline areas ranked: Fenjiao>Xiangyajiao, Dajiao>Huangdijiao, therefore,the resistance capabilities to enzymolysis ranked: Fenjiao>Xiangyajiao, Dajiao>Huangdijiao.It also showed that the four banana cultivars had the same functional groups by the infraredspectra analysis.With the increase stages of ripening, it was founded that the content of resistant starcheswere decreased, the granule structure became loose, and the relative crystallinity degrees and resistance capabilities were reduced. Similar functional groups existed in the extractedresistant starches at all stages of ripening. And the extracted resistant starches showed thetendency to have larger water binding capacity and solubility, less transparency and peak areaon the iodine absorbency curves during post ripening. With regards to the resistant starches ofXiangyajiao, Dajiao and Huangdijiao, the peak viscosity and final viscosity were decreased;retrogradation was more difficult with the increase stages of ripening. As for Fenjiao, the peakviscosity was decreased, the final viscosity was increased and retrogradation was much easierwith the increase stages of ripening.To the plantain resistant starch, higher dry heating temperature would decrease thesolubility and dilatation, increase water binding capacity, and weaken Polarization cross.When the dry heating temperature reach to90℃, the content of RS would be reducedsignificantly. The content of RS, solubility and dilatation were reduced as the time of dryheating was extended. Higher wet heating temperature would reduce solubility and brightnessof RS. When the wet heating temperature reach to90℃, the content of RS would besignificantly reduced. The solubility and brightness of RS were reduced and the polarizationcross of the RS was weakened as the wet heating time was extended. RS content was reducedand the color and polarization cross were weakened, while the solubility and dilatation wereincreased as the microwave heating time was extended.