Effect And Control Of Pre-steaming And Microwave Controlled-pressure Heating On Quality Of Frozen Cantonese Crystal Shrimp Dumpling

Cantonese crystal shrimp dumpling is Chinese pastry with wheat-starch-made dumpling skin,which has the characteristics of thin skin,rich filling,rich juice,and low elasticity.It is prone to deterioration such as cracking and leakage of juice in the process of freezing,storage,transportation and heating.To solve the above problems from the perspective of process control,this study adopted pre-steaming treatment of shrimp dumplings before freezing,and explored how different pre-steaming degrees affect shrimp dumplings during freezing and thawing.The impact of cracking rate,moisture characteristics and sensory quality.On the other hand,aiming at the problem that the quality of shrimp dumplings is not easy to control during heating and curing process,the effects of 4 heating methods are compared,and targeted analyzed of the mechanism of heating on starch aging.Based on the study of the single factor action law of shrimp dumplings loading,bag heat sealing temperature and microwave heating time,the packaging-heating combination conditions suitable for shrimp dumplings were optimized through response surface experiments,which provides theoretical support and practical guidance for the quality improvement of frozen Cantonese crystal shrimp dumplings.Specific conclusions are as follows:（1）In order to solve the problem of high freezing crack rate in the process of frozen storage,the shrimp dumpling was pre-steamed before frozen storage and compared the differences in freezing performance,sensory quality and edible safety of shrimp dumplings without pre-steaming and pre-steaming for 2-8 minutes after freezing and thawing.Pre-steaming can effectively reduce the occurrence of freeze cracking and increase the specific volume of shrimp dumplings after repeated freezing and thawing.With the extension of the pre-steaming time,the water content in the shrimp dumplings show an upward trend under the same freezing-thawing time.The low-field NMR results show that the pre-steaming is beneficial to increase the relative content of hard-to-flow water,the uniformity of water distribution and protons in the shrimp dumplings,but no obvious effect on the internal moisture freedom（T2）.In addition,pre-steaming can effectively improve the sensory quality of the frozen-thawed shrimp dumplings in terms of shape,surface smoothness and color.However,with the extension of the pre-steaming time,the frozen-thawed shrimp dumplings are prone to peculiar smell,fat oxidation and microbial reproduction are obvious.Based on the above and referring to the requirements of the national standard for frozen foods,it is believed that pre-steaming for 2 to4 minutes is a better condition to reduce the rate of frozen cracking of shrimp dumplings and optimize the quality.（2）In view of the problem that frozen shrimp dumplings are prone to quality deterioration under heating condition,the shrimp dumplings was packaged and microwave heated in pressure-controlled steam-expendable packing bags.The effects of steaming heating（SH）,microwave heating（MH）,microwave steaming atmospheric heating（MSAH）and microwave steaming pressure-controlled heating（MSPH）on the quality of shrimp dumpling were compared.The heating rate of shrimp dumplings under different heating methods is MSPH>MH>MSAH>SH;SH and MSPH are significantly better than MSAH and MH in terms of water holding capacity,uniformity of water distribution and proton strength.In terms of texture properties,it also has lower hardness,chewiness,shear force and higher springness;In addition,the starch in the shrimp dumplings shows a typical A-type diffraction peak,and the highest starch crystallinity is in MH（23.27%）,followed by MSAH（15.58%）,MSPH（4.75%）and SH（3.68%）are the lowest.Steaming heating and microwave steaming pressure-controlled heating are beneficial to delay the starch gelatinization process and reduce the occurrence of starch aging.Based on the above,it is believed that microwave steaming pressure-controlled heating has obvious advantages in shortening procedures and saving processing time.The shrimp dumplings after heating have a moist taste similar to traditional steaming heating.（3）Aiming at the new processing of microwave steaming pressure-controlled heating,the influence and law of factors such as loading capacity（3～6）,bag heat sealing temperature（115～160℃）and microwave heating time（60～180 s）on the quality of shrimp dumplings were discussed by single factor experiment combined with response surface optimization,which shows thatⅠ.The moisture content,free water content and moisture distribution uniformity in the shrimp dumplings are positively correlated with the loading capacity,while the hardness,chewiness,shear force and peroxide value are negatively related to the loading capacity;increasing the loading density is beneficial to promote the overall acceptability of shrimp dumplings;Ⅱ.Heat sealing temperature（steam-exhausted pressure control point）has a significant impact on the quality of shrimp dumplings.The critical steam-exhausted pressure value of the packaging bag under the heat-sealing condition of 115～130℃is reduced to0.112～0.125 MPa.Exhausting steam too fast is not conducive to the maintenance of the water holding capacity and fluidity of the shrimp dumplings;increasing heat the sealing temperature is beneficial to increase the moisture content of the shrimp dumplings and improve the sensory quality such as color and taste,and the texture indicators such as hardness and shear force will also decrease.However,high heat-sealing temperature will cause the humidity in the bag to increase and promote the fat oxidation of shrimp dumplings;Ⅲ.The moisture content,elasticity of shrimp dumplings shows a downward trend with the extension of heating time,while hardness,shear force,peroxide value shows an upward trend;appropriately increasing heating time is beneficial to improve the sensory score of shrimp dumplings,but the sensory quality of shrimp dumplings decreases after heating more than 120 s.Ⅳ.The regression square of fuzzy comprehensive evaluation value Y for each factor（loading capacity A,heat sealing temperature B and microwave heating time C）was obtained by response surface experiment is Y=0.94+0.10×A+0.075×B-0.080×C+1.884×10^-3×AB+0.048×AC+0.052×BC-0.12×A²-0.12B²-0.24C².The packaging-heating condition corresponding to the optimal solution of the model is loading 5.4,heat sealing temperature 147.7℃,heating time 115.1 s,and the maximum response value is 0.977.The experimental value verified under the conditions of loading capacity of 5,heat sealing temperature of 148℃,and heating time of 115 s is 0.968,showing that the model fits well.