Effects Of Temperature Fluctuations On Quality Of Frozen Thick Flank In Storage

The quality of frozen foods is affected by two aspects.One is the frozen product temperature which determines the water freezing ratio.Other is the temperature fluctuation of the frozen product which affects growth rate of ice crystals.Stored in constant low temperature can prolong the shelf life of frozen products.The influence of temperature fluctuations caused by inaccurate temperature control and permeation of enclosing structure in cold store on the quality of frozen foods is studied,which is of great help to the optimization of the energy-saving optimization of variable refrigerant flow constant temperature cold store and other refrigeration systems.A frozen storage system with a programmable logic controller can keep at constant low temperature and has adjustable temperature fluctuation range was built,to simulate the temperature fluctuation process in cold store.The pre-treated meat samples were placed in four different temperatures:a constant temperature set of-18?,-10?to-18?,-14°C to-18°C,-16°C to-18°C.Frozen samples were stored for 2,4,and 6 weeks and compared to fresh samples.The texture analyzer and Low Field NMR technology were used to detect the physicochemical parameters of frozen thick flank.The impact of different temperature fluctuations on the quality of frozen foods was analyzed quantitatively,and shelf-life model was established.The quality of frozen products is predicted by the temperature fluctuation amplitude and frozen storage time?temperature fluctuation frequency?,which provides a theoretical basis for the development of constant temperature cold store.The direct drying method was used to detect water content,and low-field nuclear magnetic technique was used for non-destructively test of moisture content and migration of different phases.It was concluded that the water holding capacity measured by the direct drying method decreased rapidly during the early storage period,and decreased slowly during the later storage period.With the extension of frozen storage time,the changes in the thermostatic group were smaller,and the bigger temperature fluctuation amplitude,the faster the water holding capacity decreased in temperature fluctuation group.After 6 weeks storage in the 18°C constant temperature group,the water holding capacity was kept at 73.8%,which was basically the same as fresh meat samples.The law of the variation of the holding capacity with respect to the amplitude of temperature fluctuation and the time of frozen storage was obtained.The model fitness was 0.734.The results of low-field NMR testing showed that the reduction in water holding capacity during the 6 weeks of frozen storage,was mainly caused by the content of free water and unable flow water.After 6 weeks,the constant temperature group compared with fresh meat only small change in free water was detected;the T_2b,T₂₂,and T₂₁ in the 18+4°C group were significantly lower than those in the fresh group?P<0.05?.The correlation analysis showed that the water holding capacity was significantly correlated with T_2b and T₂₁?P<0.05?.Therefore,the water holding capacity can be tested by low field nuclear magnetic technology rapidly and non-destructively.The hardness,chewiness,elasticity,and resilience of samples were detected by total texture analysis through TX.Plus Texture Analyzer.Cooperated with the HDP/BS,A/mors tool,the tenderness and freshness of meat samples were obtained by shear strength tests.Studies have shown that:With the extension of frozen storage time and temperature fluctuation amplitude,hardness,chewiness,elasticity,resilience,tenderness and freshness show a downward trend.The relationship of hardness,chewiness,tenderness,freshness with time,temperature were found through multiple linear regression.Two-way ANOVA analysis of hardness,chewiness,moisture content was used,and found that there was a significant difference?P<0.05?with storage time and temperature.So they can be used as an important indicator of temperature fluctuations on the quality of frozen foods.The determination of TVB-N and thiobarbituric acid was performed using an automatic nitrogen determination instrument.It was concluded that with the increase of frozen storage time,the changes in the thermostatic group were smaller.While in the temperature fluctuation group with the amplitude of fluctuations increased,the value increased.Especially in the late period.Analysis of the correlation between the physicochemical indicators found that pH has weak correlation between other physicochemical indicators;the correlation between the texture parameters is significant,the coefficients are greater than0.86.The water holding capacity has strongly correlation with texture parameters,TVB-N,TBARS.The values are all greater than 0.73.