Properties Of Dry-heated Wheat Flour And Its Mechanism

Chinese pastry products are one kind of traditional foods with specific characteristics and popularity,and some of them are prepared with addition of dry-heated wheat flour.However,so far,it is still unclear that the effect of this dry heat processing on the properties of wheat flour and its related mechanism.Here,wheat flour,wheat starch,and wheat gluten were dry heated at the temperature of 110,130,and 150? for 1,2,3,and 4 h,respectively.Meanwhile,the properties of dough with addition of dry-heated wheat flour were also investigated.The main conclusions were summarized as follows:Compared with the control,dry-heated wheat flour had a lower gelatinization temperature,with a decrease in gelatinization enthalpy at 130 and 150 ?.XRD revealed that the relative crystallinity of treated wheat flour gradually decreased with increasing time,along with the change of the crystal type of wheat flour dry heated at 150 ?.The gelatinization viscosity of wheat flour increased after dry heat treatment and reached the maximum value when heated at 130 ? for 1 h.In addition,wheat flour with dry heat treatment had lower setback value in comparison with the control,apart from the samples dry heated at 150 ? for 3 or 4 h.It suggests that the starch structure of the samples dry heated at 150 ? for 3 or 4 h was damaged.Furthermore,addition of dry-heated wheat flour increased the formation time,stability,and the tensile resistance of dough,but reduced the elongation of dough.Finally,the results of SDS-PAGE indicated remarkable protein aggregations in dry-heated wheat flour and dough,with increasing aggregations via crossing of disulfide bonds as treated temperature and time increased.The solubility,amylose content and relative crystallinity of dry-heated wheat starch increased,and rearrangement of starch chains resulted in changes of thermal properties and gelatinization properties.Meanwhile,dry heat treatment caused an increase in digestion rate of starch,with weaker gel strength due to a decrease in G? and an increase in tan? of gel.A remarkable aggregation of dry-heated wheat gluten was observed,which might be the interactions of non-covalent and covalent bonds between protein molecules.In details,ionic bonds,hydrogen bonds and hydrophobic interactions increased at 110 ? for 4 h,while ionic bonds and hydrogen bonds were destroyed to varying extent at 150 ? for 2 h.Furthermore,the content of free sulfhydryl group decreased significantly at 110 and 130 ?,but increased slightly at 150 ? for 2 h.Finally,surface hydrophobicity,G? and G?? of dry-heated wheat gluten increased,and the intermolecular ?-sheet and anti-parallel ?-sheet of the protein were converted into ?-helix,?-turn and ?-sheet.