Study On The Change Of Quality Of Frozen Steamed Bread During Storage And Re-steaming Process

Frozen steamed bread is a common method for preservation of steamed bread.The study of the quality change during freezing storage and re-steaming has practical guiding significance for the industrial production of steamed bread.This paper uses diffraction of x-rays,differential scanning calorimeter and texture analyzer to study the quality changes of steamed bread produced by one time fermentation during freezing storage?at-18??and re-steaming process.The effect of temperature fluctuation?20?,25?,and 30??and freezing method?-18?and-30??on quality of steamed bread were researched,and this study discussed the influence of re-steaming conditions?re-steaming power,re-steaming time,braised time and steaming pad type?on appearance evaluation?bubble,crack,color,and bottom?of steamed bread.The main research results were as follows:1.During the freezing process,the moisture content,pH,specific volume,whiteness,gelatinization degree and sensory score of steamed bread showed a downward trend.The gelatinization temperature,enthalpy,crystallinity and total number of bacterial colony gradually increased.Starch content and ratio,protein content and molecular weight did not change significantly.During freezing storage,The moisture content decreased gradually and starch aged.The starch showed a single diffraction peak at 19.5°,belonging to the V type of Crystal.After 90d of freezing storage,the degree of gelatinization decreased from 88.69%to86.45%;The onset gelatinization temperature,peak gelatinization temperature,termination gelatinization temperature and gelatinization enthalpy increased from 48.89?,54.75?,62.21?and 0.370J/g to 52.58?,55.82?,65.58?and 0.514J/g respectively;The crystallinity of starch increased from 16.78%to 18.47%,increased by 10.07%;The hardness and chewiness of the steamed bread increased to 3164.106g and 2305.221 respectively;The sensory score decreased from 97.5 to 66.0,decreased by 32.31%;The pH of steamed bread decreased from 5.41 to 5.10;The total number of bacterial colony increased from 0.35?CFU/g?to 1.44?CFU/g?.The storage at-18?can not completely inhibit aging of starch and growth of microorganisms.2.During the temperature fluctuation,the specific volume,whiteness,springiness,resilence and sensory score of steamed bread gradually decreased,the hardness and chewiness showed an increasing trend,and the higher fluctuation temperature,the greater change of each index.That is,the specific volume,whiteness,springiness,resilence,sensory score,and total number of bacterial colony of the steamed bread:-18?>20?>25?>30?;the hardness,chewiness of steamed bread:30?>25?>20?>-18?.Temperature fluctuations can significantly increase the total number of bacterial colony during the storage,and it have a serious effect on the blistering,gap,whitening and mouthfeel of the steamed bread.There are differences in the quality of the frozen bread in the two freezing temperature of-18?and-30?.The specific volume,whiteness,springiness,resilence and sensory score of two kinds of steamed bread showed a downward trend,and the hardness and chewiness of the steamed bread increased.The steamed bread?at-30??has a larger specific volume,whiteness,springiness,resilence and sensory score,and it has a smaller hardness and chewiness.The variational range of-30?is lesser than-18?.So the quality of the steamed bread?at-30??is better.3.At the beginning of re-steaming,the steamed bread quickly absorbs heat,the internal ice crystals melt,the moisture content and water activity increase,the mass,volume,specific volume and whiteness of the frozen steamed bread increase,and the transverse relaxation time T₂ shifts to the right,the fluidity increased.The elasticity and recovery of the steamed bread increased,and the hardness and chewiness decreased gradually;In the middle of re-steaming,the starch of is gelatinized,the boundary between the starch crystals becomes more and more blurred,the gelatinization degree of the starch increases,the gelatinization temperature and gelatinization rate were decreased,The gelatinization temperature and gelatinization enthalpy increased,the content and ratio of starch were not changed greatly,the epidermis,color,softness,mouthfeel,flavor score and sensory score of bread increased;At the end of steaming,A large amount of flavor compounds generate,such as hydrocarbons,esters,aldehydes,alcohols,phenols,ketones,aromatic and so on,which impart specific flavor of steamed bread.4.The re-steaming power,re-steaming time,braised time and steaming pad type have an influence on the appearance score of steamed bread.Low-power re-steaming was easy to cause blister;Middle-power re-steaming generated blistering and gap,and skin color of the steamed bread improved.High-power steaming resulted in larger degree of blistering and gap.The longer re-steaming time is,the greater level of blister,gap and boiler bottom becomes,and the lower total appearance score is.The braised time hugely changed the blistering,color and the boiler bottom score of steamed bread.While it had no change to the gap of the steamed bread.The steamed bread using silicone pad had the highest score of blistering,gap and boiler bottom,the score of steamed steamed using gauze was medium,and the score of bare steamed steamed was lowest.