Effects Of Thawing Methods On Protein Properties And Gel Formation Ability Of Frozen Surimi

Surimi is a kind of aquatic conditioning food material,which is produced by the process of collecting meat,rinsing,fine filtration,dehydration,packing,freezing and so on.Large amount of fishing,high water content and rich nutrition are the characteristics of aquatic products,so cryopreservation is the best way to maintain qualities.As intermediate material,thawing is an essential step in the subsequent processing and retail process for frozen surimi.In industrial production,air thawing,water thawing and so on are the most common thawing methods.Some new thawing techniques need to be introduced to improve the thawing efficiency and guarantee the quality of the thawed surimi,because these methods are time-consuming and low efficiency,and juice leakage,microbial reproduction and other phenomena occur during the process of thawing surimi.Microwave thawing?MW?and radiofrequency thawing?RF?are new options.The whole food is heated by high frequency alternating electromagnetic field to stimulate the ionic vibration and the polar rotation of water molecules.The both thawing efficiency is much higher than the traditional thawing methods,but their thawing effects need to be studied.First the basic components of frozen surimi,the dielectric properties of surimi and the distribution of the temperature in the center layer of the fish were determined,and the uniformity of microwave thawing and radio-frequency thawing was compared.And then the influence of air thawing,microwave thawing and radiofrequency thawing on frozen surimi,based on thawing water loss rate,salt-soluble protein content and Ca²⁺-ATPase activity were studied.The effects of three thawing methods on gelation characteristics of frozen surimi were further studied,including hydrogel holding,gel forming ability and SDS-PAGE gel electrophoresis experiment,and the following conclusions were obtained:?1?The basic components of frozen surimi were determined,and the results showed that the water content was 72.58%,the ash content was 1.03%,the crude protein content was 19.23%,the crude fat content was 2.61%,and the pH value was 7.2.?2?The vector network analyzer was used to determine dielectric constant and dielectric loss factor of surimi from-20?²0?at 27.12 MHz and 915 MHz frequency,and energy penetration depth of electromagnetic wave under different temperature was calculate.Results showed that the dielectric constant,dielectric loss factor and energy penetration depth of surimi under 27.12 MHz were larger than 915MHz.At two frequencies,dielectric constants of surimi increased slowly with the increase of temperature from-20?to 5?;then rapidly increased from-5?to 0?with the increase of temperature;and started slightly down from 0?to 20?with the increase of temperature.At 27 MHZ frequency,the dielectric loss factor of surimi increased from-20?to 0?with the increase of temperature,and increased rate was the highest between-5?and 0?,higher between-20?and-5?,the lowest between 0?and 20?range.At 915 MHz frequency,the dielectric loss factor of surimi increased slightly between-20?and 20?with the increase of temperature.Energy penetration depth of radio frequency?27.12 MHz?decreased rapidly during-20?⁰?with the increased of temperature,slowly during 0?²0?,while energy penetration depth of microwave?915 MHz?decreased slowly with the temperature.The whole surimi was suitable for thawing by radio frequency thawing than microwave.?3?Infrared camera was used to record the temperature distribution of the center layer of surimi after thawing by different thawing methods,and the temperature change and the time required for the center temperature of the frozen surimi from-20°C to 2°C were determined.The results showed that the center temperature of frozen surimi rose from-20°C to-2.1°C by the air thawing for 5 hours.The center temperature of frozen surimi rose from-20°C to-2.4°C by microwave thawing for 3min18s.The center temperature of frozen surimi rose from-20°C to-2.3°C by radio frequency thawing for 10minutes.The thawing efficiency of frozen surimi was microwave thawing>radio frequency thawing>air thawing.The temperature distribution of the center layer of surimi was even by air thawing,and the temperature difference between the inner and outer layers was the smallest;the temperature distribution of the center layer of surimi by radio frequency thawing was also even,but the temperature difference between the inner and outer layers was large;The temperature distribution in the center layer of surimi by microwave thawing was not even,the temperature difference between the inner and outer layers was largest,and some surimi protein were even denatured.?4?The thawing water loss rate,salt-soluble protein content,and Ca²⁺-ATPase activity were used as indexes to compare the thawing methods.The results showed that the thawing water loss rate,salt-soluble protein content and Ca²⁺-ATPase activity of the surimi were the best by air thawing,and there was no significant difference?P>0.05?between air thawing and radio frequency thawing.The thawing water loss rate,salt-soluble protein content and Ca²⁺-ATPase enzyme activity by microwave thawing were the worst,and there were significant differences?P<0.05?between microwave thawing and the other thawing methods.?5?The gel retention capacity and gel formation ability of frozen surimi were determined by measuring three thawing methods.The results showed that there were significant differences in the three thawing methods?P<0.05?.The gel retention capacity and gel formation ability by microwave thawing were the worst.There were no significant differences of gel retention capacity between air thawing and RF thawing?P>0.05?.The results of SDS-PAGE gel electrophoresis showed that the electrophoresis myosin heavy chain?MHC?band by microwave thawing was the narrowest.