Effects Of Salting Assisted By Ultrasound On Physicochemical Properties And Quality Of Salted Grass Carp And Salted-dried Grass Carp

Grass carp(Ctenopharyngodon idellus),bred with a wild area and huge production and considered as a delicacy,is one of the important economic species of freshwater fish in China and the top of four major Chinese carps.However,the processing of grass carp in China is still in a very backward stage.Nowadays,the grass carp products in the market mainly are live,secondly are semi-finished and rarely are deeply processed,which which severely restricts the development of freshwater fisheries in China.In order to reduce the process time of salting and drying,grass carp salting was treated with ultrasound in the present study to quickly prepare salted-dried grass carp.1)The effects of ultrasound treatment on the temperature,pH,density,color,UV-absorption,turbidity and free amino acid of saline and salt content,microstructure and sensory evaluation of salted grass carp were investigated.The results showed that heat effect of ultrasound was observed obviously with the temperature of saline increasing about 4-16?;the ultrasound treatment reduced the pH and density with pH and density reducing from 6.25 and 1.1166 g/mL to 6.10 and 1.1120 g/mL,but increased whiteness,turbidity and UV-absorption of saline solution with whiteness,turbidity and UV-absorption increasing from 62.35,0.202 and 0.749 to 80.76,0.689and 1.157,respectively;salting assisted by ultrasound promoted the rapid increase of salt content of salted fish.The microstructure results showed that salting assisted by ultrasound caused a certain extent to the destruction of the grass carp.2)The salted grass carp was prepared after salting assisted by ultrasound and the research was to explore the effect of the application of ultrasound on the quality and safety of salted product.The results showed that ultrasound treatment promoted the oxidation of lipid and protein in a certain extent,with POV and TBARS increasing from 0.48 meq/kg liqid and 0.22 mg MDA/kg sample to 0.83 meq/kg liqid and 0.50mg MDA/kg sample,carbonyl group content increasing from 0.69 nmol/kg protein to1.22 nmol/kg and total sulfhydryl group content decreasing from 9.34 nmol/kg protein to 7.00 nmol/kg protein,respectively;salting assisted by ultrasound improved the content of nitrate and nitrite of salted grass carp with nitrate and nitrite content increasing from 17.41 mg/kg and 12.34 mg/kg to 19.32 mg/kg and 15.72 mg/kg,respectively,and had a certain inhibitory effect on the growth of microorganism at the same time.3)The salted-dried grass carp was prepared by salted grass carp(salting time,120 min)at 30~oC for 50 h.The objective of this study was to explore the effect of salting assisted by ultrasound on water content,pH,texture,color,free amino acids,fatty acids and microstructure of salted-dried grass carp.The results showed that the application of ultrasound significantly accelerated drying rate;as ultrasound power increased,pH,elasticity,L,b showed a rising trend with pH,elasticity,L,b increasing from 6.370,0.704 g,41.307 and 7.91 to 6.775,0.836 g,55.933 and 27.11,respectively,but the hardness showed a downward trend,decreasing from 2355 N to 1582 N;salting assisted by ultrasound increased the type of free amino acids from 15 to 17 and decreased the content;the microstructure results showed that salting caused muscle tissues shrunken and salting assisted by ultrasound did a great damage to muscle tissues of salted-dried grass carp.4)The research was to explore the effect of the application of ultrasound on the quality and safety of salted-dried product.The results showed that ultrasound treatment promoted the oxidation of lipid and protein in a certain extent,with POV,TBARS and the relative content of saturated fatty acids(SFA)increasing from 0.83meq/kg liqid,0.63 mg MDA/kg sample and 28.305%to 1.47 meq/kg liqid,0.86 mg MDA/kg sample and 40.481%,the total content of monounsaturated fatty acid(MUFA)and polyunsaturated fatty acids(PUFA)decreasing from 38.087%and33.608%to 35.602%and 23.917%,carbonyl group content increasing from 1.29nmol/kg protein to 2.15 nmol/kg and total sulfhydryl group content decreasing from20.51 nmol/kg protein to 16.96 nmol/kg protein,respectively;salting assisted by ultrasound improved the content of nitrate and nitrite of salted-dried grass carp with nitrate and nitrite content increasing from 20.08 mg/kg and 16.28 mg/kg to 32.46mg/kg and 29.24 mg/kg,respectively,and had a certain inhibitory effect on the growth of microorganism at the same time.5)The results of this study showed that the application of ultrasound could significantly improve the rate of salting and drying of grass carp,inhibit some microbial growth,but also promote the oxidation of lipid and protein in a certain extent and improve the content of nitrate and nitrite.Therefore,when applying ultrasound technology,appropriate ultrasound power and time should be taken into account according to the actual situation.