Technology Research Of Crispy Shrimp Production By Vacuum Frying

Litopenaeus vannamei is abundant in our country,which is rich in nutrition,delicious in taste and popular among consumers.At present,however,the shrimp is mainly in cold chain circulation and the cost of transportation is higher.The form of shrimp products,including fresh,frozen and dried shrimp is single and the products are all in low added-value,thus unable to meet the demand of modern consumers for diversification and convenience.In order to make full use of the shrimp resources,in this paper,the smaller whole shrimp（litopenaeus vannamei）was the raw material and the vacuum frying was used to develop crispy shrimp leisure food,the circulation of which could be in normal temperature.Firstly,the vacuum frying process of shrimps was optimized.Then,the change laws of moisture loss and oil absorption in shrimp during vacuum frying process were analyzed.Furthermore,the effect of vacuum frying on quality characteristics of crispy shrimp was investigated.Finally,the packing methods and shelf life of vacuum fried crispy shrimp was researched.The main contents and results were as follows:1.Fresh litopenaeus vannamei was the raw material,and fuzzy mathematic sensory evaluation was indicator.Based on single-factor experiment,frying temperature,frying time and vacuum degree were selected as independent variables and the vacuum frying technology was optimized by Box-Bohnken experimental design of response surface methodology.The results showed that frying temperature,frying time,vacuum degree as well as interaction between frying time and vacuum degree had extremely significant effects on sensory score（P<0.01）.The effects of interactions between frying temperature and frying time,frying temperature and vacuum degree was significant（P<0.05）.The optimal condition for vacuum fried crispy shrimp was as follows:frying temperature110℃,frying time 50 min and vacuum degree 0.09 MPa.Under this condition,the sensory score of crispy shrimp was 90.09±1.27,which was close to the predictive value（94.51）.2.The moisture loss and oil absorption in shrimp during vacuum frying were fitted by two common empirical models and three fundamental function,including exponential function,power function and parabola function.The fitting results showed that the changes of moisture loss in shrimp with frying time,frying temperature and vacuum degree were well accord with exponential model,parabola model and first order kinetic model,respectively.The R²of the models were 0.992,0.980,0.978.The changes of oil absorption with frying time,frying temperature could well be described by power function model,and with vacuum degree was accurately fitted by exponential model.The R² of the three models were respectively 0.989,0.966 and 0.976.3.In order to investigate the effect of vacuum frying on the quality of crispy shrimp,the oil absorption property,astaxanthin content and sensory quality of vacuum fried shrimp was analyzed.The smell characteristics and volatile components were also respectively analyzed by electronic nose and GC-MS.The results revealed that the vacuum frying could significantly reduce the oil absorption of crispy shrimp（P<0.05）.Under the optimal frying conditions,the oil absorption of vacuum fried crispy shrimp was 30.23%,while the normal atmospheric fried shrimp reached 43.43%.The content of astaxanthin measured by HPLC in vacuum fried crispy shrimp was 10.17μg/g.Compared with fresh shrimp（23.06μg/g）,vacuum frying resulted in loss of astaxanthin in shrimp,which was more severe in atmospheric frying（4.8μg/g）.The result of sensory evaluation showed that the vacuum fried crisp shrimp was highly accepted by consumers in terms of color,shape,grease and crispy,moreover,the score of all quality indexes of the vacuum fried crispy shrimp were significantly higher than that of the atmospheric fried shrimp.The electronic nose data of vacuum fried crispy was analyzed by the method of principal component analysis（PCA）,discriminant factor analysis（DFA）and flavor radar map analysis,then the analysis results showed that the difference of flavor between vacuum fried crispy shrimp and atmospheric fried crispy shrimp was significant.94 volatile components were detected in vacuum fried crispy shrimp by GC-MS technique and the total content was 130.31μg/kg.The volatile flavor substances mainly included esters,pyrazines,alcohols,aldehydes,ketones,acids,pyrrole pyridine compounds,nitrogen compounds,hydrocarbons and oxygen heterocyclic compounds,among which esters,aldehydes and nitrogen compounds were with higher content.Compared with atmospheric fried shrimp,the vacuum fried crispy shrimp had more kinds of volatile components and its content was obviously higher.There are 91 kinds of volatile components in atmospheric fried shrimp,but the content is only56.65μg/kg where the contents of pyrrole pyridine compounds and nitrogenous compounds were relatively high.The vacuum fried crispy shrimp mainly presents the fruity aroma,fatty and oily aroma,fishy smell,and faint aroma of caramel,while aroma of caramel in atmospheric fried shrimp is intense.4.To extend the shelf life of the vacuum fried shrimps,the influence of packaging material（aluminum foil bag and PE bag）and gas proportion（100%N₂,70%N₂+30%CO₂,30%N₂+70%CO₂,100%CO₂）on total volatile basic nitrogen（TVB-N）,peroxide value（POV）,total viable count（TVC）and sensory evaluation of vacuum fried crispy shrimp was discussed.The results indicated that there was a significant difference between two packing materials,as well as gas proportion of modified atmosphere packing.The best packing condition for vacuum fried shrimps was aluminum foil bag and modified atmosphere packing with 70%CO₂+30%N₂.Then,the vacuum fried shrimps were packed with the best condition and stored at different temperatures（4,15,25,37,47℃）.Further studies were carried out to establish shelf life prediction models of TVB-N value,POV value and TVC with respect to storage time and storage temperature.The results showed that TVB-N value,POV value and TVC increased with the increase of storage time and temperature.The changes of each index were consistent with the first-order kinetics model.The prediction equations for shelf life of TVB-N value,POV value and TVC were SL=0.1e^1822.4/T,SL=1.11e¹401.5/T401.5/T and SL=0.24e^1627/Trespectively.The shelf lifes of vacuum fried crispy shrimp stored at 4,15,25℃were respectively verified and got the results that the actual shelf lifes were 75,62,50 days,which were consistent with the prediction results.