Study On The Aging Mechanism Of Hot-packed Steamed Bread Starch

Chinese steamed bread(CSB)as a traditional staple food in China,plays an important role in both diet and culture of Chinese.Staling and microbial spoilage are the main factors affecting the industrial production of CSB.Thermal-vacuum package,a novel technology developed for the storage of CSB,can prevent the microbial spoilage and starch retrogradation of CSB,extending the shelf-life of CSB up to 90 days at room temperature.Understanding the starch retrogradation mechanism of wheat CSB and oat-wheat CSB,could promote the development of traditional staple food industrialization and miscellaneous grains.Therefore,the insights of present study were to evaluate the effect of packaging conditions(sealed package,vacuum package,thermal-vacuum package),packaging temperature(90℃,70℃,50 ℃),oatmeal addition(0%,10%,30%)on the vacuum,moisture migration and starch retrogradation of CSB during storage at room temperature.(1)During storage at room temperature,the moisture content of the thermal-vacuum package CSB firstly increased,then decreased,and remained stable at the end of the storage.Moisture migration of CSB was from the crust to the core during storage at room temperature,with bounded water molecules gradually dissociating from gluten network to free water.During the long-term starch retrogradation,the space of amylopectin in the layer structure became narrowing;And the B-type staucture was observed,forming a typical diffraction peak at 17°.Long-range ordering,crystallinity,thermal enthalpy,and tightness were increased.The hardness measured by TPA was gradually increased and the semi-crystalline growth ring structure was destroyed.(2)Thermal-vacuum package could delay the speed of water desorption,blocked the interaction among water molecules,gluten and starch as compared to sealed package and vacuum package.The moisture content of the thermal-vacuum package CSB was about 39%during storage;It kept a higher T23 value in CSB,therefore slowed the adhesion between starch granule;And T-VP inhabited the growth of CSB starch crystallinity,which further delayed starch retrogradation,and extended the shelf-life to 84 days at room temperature.(3)As the packaging temperature increased,the degree of vacuum in the thermal package bag also increased,thereby delaying the crystallization of the amylopectin of starch,reducing the intensity and relative crystallinity of the diffraction peak of starch,and hindering the formation of the orderly structure and tightness of the starch.The change of vacuum degree of steamed bread did not affect the change of moisture composition of steamed bread,and had no significant effect on the water mobility of steamed bread during storage(p<0.05).(4)Oatmeal increased the water holding capacity of CSB and restricted water migration,thus reducing the content of immobilized water and increasing the content of free water.With the increase of oatmeal,the enthalpy,and the relative crystallinity of CSB reduced.The addition of oatmeal retarded a stable and ordered state of starch structure formed in CSB during storage at room temperature.Oatmeal decreased the starch retrogradation rate constant k,indicating its inhibitory effect on the formation of starch crystal.Thermal-vacuum package technology as an anti-retrogradation packaging system for CSB preservation by delaying the water loss in the storage process and affecting water mobility of CSB,could extend the shelf-life of CSB.Our findings revealed that oatmeal could retard starch retrogradation in CSB.