The Effect Of Heating Temperature On The Structure And Physicochemical Properties Of Pyrodextrin

Pyrodextrin is the intermediate product during the preparation of resistant dextrin.In the preparation process,some new glycoside bonds were generated,e.g.?-1,2,?-1,2,?-1,6 and 1,6-anhydro-?-_D-glucopyranosyl end groups,which is the reason of the anti-digestion property of pyrodextrin and resistant dextrin.Therefore,pyrodextrin can be used as dietary fiber.In this paper,corn starch was used as raw material to prepare pyrodextrin by dry heating treatment and acid heating treatment(140-200?),respectively.The effect of heating temperature on the structure and physicochemical properties of pyrodextrin was emphatically studied.And the thermodynamic patterns with baking temperature were analyzed.In addition,the formed sites and mechanisms of new glycoside bonds in the heating process were speculated of the pyrodextrin prepared from waxy corn starch.The aim of this study is providing theoretical basis for better guiding the production of pyrodextrin and resistant dextrin and improving the functional quality.Pyrodextrin was prepared by dry heating treatment.It was found that after heating treatment,the molecular weight of starch was decreased dramatically under because of the high temperature,and both content of X?1000-5000 and X?5000-20000 were decreased markedly.The crystal structure of pyrodextrin was destroyed by the high temperature,but it still retained the A type crystal.The surface of starch granules was not significantly changed and some particles were agglomerated.In addition,the molecular size is the main reason for the changes of physicochemical properties:with the decrease of the molecular size,the solubility of the pyrodextrin was increased slightly,the enthalpy of gelatinization and the peak viscosity were decreased,and the gels showed the hydrodynamic behavior of shear thinning.Pyrodextrin was prepared by the acid heating treatment.It was discovered that,the starch was reduced significantly within the catalysis of hydrochloric acid.And the content of X?12-24,X?1000-5000,X?5000-20000 were reduced,however,the content of X?36-100was increased,which showed that polymerization reaction occurred among short chains.Though the crystallinity was decreased,the crystal structure was not completely destroyed,and the particle structure remained intact,indicating that the repolymerization was more likely occurred in the amorphous region.Under the influence of molecular structure,the physicochemical properties of pyrodextrin were changed significantly:the solubility of pyrodextrin increased until 96.6%.The viscosity was reduced observably,and the characteristics of gelatinization solution were similar to Newton fluid.In order to manifest the formation mechanism of the pyrodextrin structure,a carious enzymatric hydrolysis reactions(glucoamylase,?-amylase,isoamylase and the synergistic action of isoamylase and?-amylase)were used to speculate the formation of new glycoside bonds in the acid heating process.The results showed that the molecular size and the enzymatic hydrolysis degree were decreased with the rise of baking temperature,demonstrating that the generation position of new glycosidic bonds were influenced hy the heating temperature:when heating temperature is low(140-160?),most of the new glycosidic bonds generated near the non-reducing end of a starch chain;when the heating temperature is high(170-200?),the new glycosidic bonds would generate near the non-reducing end of a starch chain and the branching points of amylopectin.And the content of new glycosidic bond was rose with the increase of temperature.