Study On The Quality Change And Microbial Growth Model Of Prepared Beef During Storage

The prepared beef is gradually favored by consumers for its rich nutrition and easy cooking,and has become a new consumption trend.However,the prepared beef is susceptible to microbial contaminationin the process of processing,storage,sale.In addition,because the cold chainsare not complete,it is often prone to freezed and thawed repeatedly during the transport.Therefore,the quality of prepared beef is affected considerablely.In this study,the microbiological indexes and quality changes of prepared beef in packaging methods were investigated at constant temperature(room temperature,cold,freezing)storage and in the process of repeated freezing and thawing.Besides,the MATLAB software was used to simulate the growth of microorganism under different packaging conditions and storage temperatures.The growth model was established and evaluated,The main results are as follows:1.It was studied that the effects of different storage temperatures and different packaging methods(plastic box packaging,pallet cling film packaing and vacuum packaging)on the microbes from prepared beef.The results showed that,at room temperature,the microorganism of prepared beef packaged by 3 kinds of packaging methods from 0 to 3 d were rapid and the sensory quality decreased rapidly.The packaging of plastic box and pallet cling film packaing in the 1st day had a sensory score of nearly 8 points and vacuum packaging in the first 1.5 d less than 8,indicating that prepared beef has been significantly spoilage;In the cold storage conditions,the rate of sensory decline was slower than the three kinds of packaging at room temperature,the plastic box packaging and pallet cling film packaing of the total number colonies reach the maximum value(10.05 lg CFU / g and 9.37 lg CFU / g)in the 5st day The values of were beyond the acceptable range and the sensory score was nearly 8 points,while the vacuum packaging was less than 8 points on the 7th day.At freezing storage,the number of microorganisms in prepared beef by three kinds of packaging decreased first and then increased slowly.The quantity of lactic acid bacteria,moulds and yeasts in prepared beef packed by pallet cling film packaing went up with the increasing storage time,and the range was larger than the data for plastic box packaging and vacuum packaging.2.The change of L*value of prepared beef in the three kinds of packaging at room temperature and cold was not significant,and a* and b* values show a decrease trend.The L* value of the prepared beef by vacuum packaging in the freezing storage changed insignificantly,and a* and b* value increased.The L* value of prepared beef in plastic box packing also did not change significantly,but the a* and b* value decrease,Differently,the prepared beef in pallet cling film packaing displayed a decline for L* and a* value and a fluctuation for b* value.As for pH,it went up,when the prepared beef stored at room and cold temperature,and the amount of change in the order was plastic box packaging>pallet cling film packaing>vacuum packaging.On the contrary,the changes of pH of prepared beef in freezing storage were small.3.The effects of freezing-thawing frequency and thawing temperature on microbial population and quality of prepared beef were studied.The results showed that the microbes,pH,color and freezing-thawing frequency of the prepared beef did not reveal a regular changes.The higher thawing temperature and more thawing times were,the more microbial growth was.The L*value of the 4 thawing temperature was not significant with the increase of freeze-thaw cycles,the a* value decreased slowly,and the b* value increased.4.The data for 5 microbiological indicators which stored at room temperature and cold storage were simulated,and the growth model was established and validated by MATLAB 2015 a software.Compared with cold storage,the modified Gompertz equation can be used to better describe the microbial growth of different packaged beef at room temperature.