| The rapid development of domestic and international frozen food can meet the demandfor fast life. Processing and preservation of frozen food is a key impact on the quality.Thesubject selected cooked and frozen buns as example and depthly studied productionprocesses and preservation techniques.Frozen buns inherited the features of traditional bunsand extended the shelf life. However, in the course of processing and storage,manyproblems still existed.This paper improved the quality of frozen buns by processingtechnology,cooling way,prediction of the shelf life,thawing methods.1.The add of Water-retaining agent in the bun doughFrozen food is easy to happen shrinking and cracking because of water erosion in theprocess of storage. Modified starch and guar gum is natural water retention agent that isextracted from plants.they play a significant role in water conservation.Selection of modified starch:choosing a more suitable three modified starch from cassavaprepaste starch,cassava cross linked hydroxypropyl starch,potato acetate starch,potatoprepaste starch,waxy maize hydroxypropyl starch,potato cross linked esterification starchaccording to heat resistance of bun dough in the process of steamed, freezing resistance inthe process of frozen and anti-aging during storage.The freeze-thaw stability of cassavacross linked hydroxypropyl starch was the best among the six modified starch, the thermalstability of waxy maize hydroxypropyl starch was the best and the retrogradation value ofcassava pregelatinized starch was the lowest.Single factor respectively included the added amount of waxy maize hydroxypropylstarch and guar gum.Because they have better comprehensive properties.and texture, colorand dehydration rate were selected as the indicators.The optimal adding of waxy maizehydroxypropyl starch was2%and guar gum was0.3%in single factor experiment.Orthogonal experiment included types of modified starch, the added amount of modifiedstarch and the added amount of guar gum.Texture result of orthogonal experiment showedthe optimized parameters were as follows: the added amount of waxy maize hydroxypropylstarch was4%; the added amount of guar gum was0.3%with principal componentanalysis.The measurement results of color and water loss rate had consistent with textureanalysis result.2.The optimization of fermentation processThe size of expansion of dough is related with taste and aroma. We did experiments toexplore the best fermentation conditions by the added amount of yeast,the add amount ofbaking powder and fermentation time.Single factor experiment showed that when the added amount of yeast was0.8%, Lvalue was highest. At the same time, the principal component scores of texure was highest. The add amount of baking powder was2%and fermentation time was45min with thesame indicators.Selecting colour as indicators, response surface methodology optimizedfermentation conditions. The results showed that: the added amount of yeast0.84%, theadd amount of baking powder1.65%, fermentation time44min.3.Effect of different cooling methods on quality of cooked bunsBuns needed to cool after cooking and then they could be packaged and stored, thepurpose of the study was to find the most suitable cooling method. The products used fourdifferent ways for cooling including natural cooling,blast cooling,vacuum cooling andhybrid cooling.These methods were compared for qualitative changes of the buns duringstorage time in the same temperature. The results showed that: different cooling methodshad different effects on the shelf life (P<0.05). It was feasible to use hybrid cooling toreplace the conventional cooling and vacuum cooling. The qualitative loss of hybridcooling was significantly lower than vacuum cooling and cooling rate was significantlyfaster than conventional cooling methods; Hybrid cooling could improve color to becomebrighter than vacuum cooling; Hybrid cooling and conventional cooling had significantdifferences in hardness and electronic nose analysis results (P<0.05), but it had improvedrelative to vacuum cooling, and hybrid cooling had no significant differences withconventional cooling methods in cohesiveness,viscosity and chewing aspects (P>0.05);Itsacceptability of sensorial score was significantly better than vacuum cooling. In terms ofchemical indexes: hybrid cooling and vacuum cooling had no obvious influence on pH (P>0.05)and could reduce the aging of bun′s skin; Hybrid cooling and vacuum cooling couldsignificantly retard microbial contamination and fatty oxidation, so they could achieve thepurpose of extending the shelf life of food.4. Determination of glass transition temperature and shelf-life prediction of stuffin bunsStoring under the glass transition temperature can improve the quality of food. Glasstransition temperature of stuffing buns (chicken) were measured by using differentialscanning calorimetry (DSC), measured result was-18.52℃. Detection of chicken meat offvolatile basic nitrogen、total bacterial count,color,pH,moisture content,sensory evaluationindicators at different storage temperatures (4℃,7℃,15℃). The results show that: volatilebasic nitrogen and total bacterial count gradually increased with storage time, L*values,a*values,b*values,moisture content and sensory scores were gradually reduced, pH valueincreased first and then decreased. According to Arrhenius equation, using TVB-N andtotal number of colonies as an indicator, a dynamic model which forecast the shelf life ofthe steamed stuffed bun was establish. The activation energy Ea and pre-exponential factork0of each index respectively were15.868kJ/mol,56.549kJ/mol and309.482,1.8×109.5.Effect of different thawing conditions on quality of cooked bun fillings The food was easy to happen all kinds of changes, these changes would lead reduction oftaste and quality. The experiment thawed using six methods including normal temperature,cold water, microwave,100Mpa high-pressure,150Mpa high-pressure and200Mpahigh-pressure. Determination of physical indicators included thawing time, thaw mass loss,tenderness, texture, color and chemical indicators included pH, fat oxidation, volatile basicnitrogen. We could get the effect of different thawing conditions on quality of cooked bunfillings. The results showed that: the thawing time and qualitative loss of microwavethawing and super high pressure thawing were low. The tenderness were high in addition to200MPa high-pressure; Different thawing methods and fresh meat had significantdifference (P<0.05) in terms of texture results.and hardness and chewiness were high(P<0.05) under200MPa condition. Other thawing methods had no significant difference(P>0.05) in hardness, springiness, chewiness, resilience.Six kind of thawing methods couldimprove the brightness values (L*) in color; Natural thawing and200MPa high pressurethawing had significant difference (P <0.05) during the first thaw cycle on pH,and six kindof thawing methods had no significant difference（P>0.05）in other thaw cycles. Super highpressure thawing and microwave thawing both could effectively inhibit fat oxidation andthe corruption of meat products with the increase of number of freezing and thawing. |
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