Research On Rf Thawing Technology Under Different Conditions

In addition to the pre-slaughter,pre-cooling,transportation,quick-freezing and selling processes,meat needs to be thawed before cooking.RF defrosting is a relatively new method of defrosting meat,the principle of this defrosting method is similar to microwave,using its strong penetration,can easily defrost frozen meat and temperature uniformity is good,but also to ensure that the quality of the meat after defrosting almost no loss.The meat chosen for this paper is mutton,and the dielectric properties of mutton were measured,the following thawing experiments were carried out on frozen mutton:(1)mutton of different thicknesses(2cm,2.5cm,3cm)was thawed by RF at 15°C and 90%ambient relative humidity(40.68 MHz,400W);(2)mutton of 2cm thickness was thawed at0°C and different ambient relative humidity(50%,90%)for RF thawing(40.68 MHz,400W);(3)2cm thickness of mutton at 15℃ and different ambient relative humidity(50%,90%)for RF thawing(40.68 MHz,400W);(4)Put the 2cm thickness of mutton into a refrigerator thawing chamber to thaw;(5)Put the 2cm thickness of mutton in a microwave oven with the thawing setting on.The temperature of the mutton before thawing is-15°C for each defrosting method and six thermocouples were placed inside the mutton with an external temperature monitor connected to obtain the temperature trend of mutton throughout the thawing process.The colour(a*,b*,L*)and p H of the mutton were also measured after each thawing and sensory evaluation was carried out.The following conclusions were drawn:(1)The dielectric constant and dielectric loss factor of mutton increase with increasing temperature and the depth of RF energy penetration decreases with increasing temperature at a frequency of 40.68 MHz and in the range of-20 to 10°C;(2)For RF thawing of meat blocks of different thicknesses(2cm,2.5cm,3cm),The smaller thickness(2cm),the more uniform temperature will be when thawing,and the difference in quality after thawing is not significant;(3)For RF thawed meat blocks at different ambient temperatures(0°C,15°C)and different ambient relative humidity(90%,50%),the low temperature condition(0°C)can effectively alleviate local overheating,improve temperature uniformity and is also beneficial to the quality(colour and sensory quality)of the thawed meat;although the high relative humidity condition(90%)makes temperature at the edges of meat blocks rise,the quality of meat thawed under high relative humidity conditions(juice loss rate,organoleptic quality)is significantly improved.Overall,the benefits outweigh the disadvantages of thawing meat,and meat blocks thawed under low temperature and high humidity conditions(0°C ambient temperature,90% ambient relative humidity)have the best temperature uniformity and best quality after thawing;(4)As a comparison experiment to RF thawing,air thawing had good temperature uniformity after thawing,with a temperature difference of only about 3°C between the centre of the meat block and the outer edges.However,compared to RF thawing,air thawing takes longer and cannot guarantee the thawing quality.Thawing in the refrigerator increases the rate of juice loss of meat,and there is also the problem of bacterial growth during the thawing process,which makes it difficult to ensure the safety of food.Microwave thawing time is shorter,the central temperature of meat block from-15℃ to-3℃ only takes about 90 s,but the temperature uniformity of the meat block after thawing is significantly reduced,and the temperature difference between cold and hot spots can reach 17℃.