Study On Protein Structures And Flavor Components Of Muscle From Crisp Grass Carp During Brittle Formation Process

Grass carp(Ctenopharyngodon idellus,GC)is a common freshwater fish species in China.The costs of cultivation is lower,but the range and yield is higher.However,the meat of grass carp is soft,and taste bad.The common grass carp muscle became crisped after breeding common broadbean,which was called as “crisp grass carp(Ctenopharyngodon idellus C.et V,CGC)”.It gives people special taste,while increases the economic value.The structure changes of myofibrillar and sarcoplasmic protein had been found in muscle of CGC during brittle formation process,which were attempted to reveal the relationship between brittleness of crisp grass carp and protein structure.In addition,the volatile and fatty acid composition were measured,which were attempted to reveal flavor and development and utilization of abdominal fatty.The results included the followings:(1)The results indicated that hydrophobic amino acids and sulfur amino acids of sarcoplasmic protein were showed an increase tendency,while the hydrophilic amino acids was showed a decreasing trend.Disulfide bond content of sarcoplasmic protein from crisp grass carp showed an increase tendency with crisping and total sulfhydryl content decreased during brittle formation process.Surface hydrophobicity increased during brittle formation process and peak position of the fluorescence spectrum blueshifted.Infrared spectroscopy showed that amide A,B,I,II and III of characteristic absorption peaks were all emerged in muscle sarcoplasmic protein from crisp grass carp during brittle formation process,and the position of every peak was fluctuated.Secondary structure of sarcoplasmic protein showed that the relative contents of ?-helix decreased whereas those of ?-sheet,?-turn and random coil increased,those were accompanied by brittle formation of crisp grass carp.Both Tm and ?H of sarcoplasmic protein from crisp grass carp showed an increase tendency with crisping by DSC.(2)The results indicated that hydrophobic amino acids and sulfur amino acids of myofibrillar protein were showed an increase tendency,while the hydrophilic amino acids was showed a decreasing trend.Disulfide bond content of myofibrillar protein from crisp grass carp showed an increase tendency with crisping and total sulfhydryl content decreased during brittle formation process.Surface hydrophobicity increased during brittle formation process and peak position of the fluorescence spectrum blueshifted.Infrared spectroscopy about secondary structure of myofibrillar protein showed that the relative contents of ?-helix decreased whereas those of ?-sheet,?-turn and random coil increased,those were accompanied by brittle formation of crisp grass carp.There were 3 peaks,peak 1and peak 2 may related to myosin,and peak 3 may related to actin.Both Tm and ?H of myofibrillar protein from crisp grass carp showed an increase tendency with crisping in peak 1,peak 2 and peak 3 by DSC.(3)To study the changes in volatile components of crisp grass carp muscle during brittle formation process,samples were acquired and measured periodically by solid phase micro-extraction(SPME)and gas chromatography-mass spectrometry(GC-MS),a total of 61 volatile components were identified.The results showed that relative content of alcohols and other kinds increased at CGC1,and then decreased brittle formation process of crisp grass carp.Before CGC2,the relative content of alkanes increased,whereas aldoketones decreased and its relative content was still higher.After CGC2,the relative content of the former decreased greatly and remained in a very low level at CGC5,whereas the later increased greatly and remained in a very high level at CGC5.Aldoketones were the major effects on the flavor of crisp grass carp muscle.The higher contents of nonanal and 2,3-Octanedione were 18.18% and 32.12% in common grass carp,respectively.By the end of crispness,the contents of those decreased to 5.45% and 12.71%,respectively,while the content of hexanal was 65.52%.Besides,other kinds of volatile components were considered lower effect on flavor due to their high odor thresholds or low contents.(4)The changes of abdominal fatty acid composition extracted from abdominal adipose tissue of crisp grass carp during brittle formation process were analyzed by gas chromatography-mass spectrometry(GC-MS).The results showed that a total of 19 kinds of fatty acids,including 7 saturated fatty acid(SFA),2 monounsaturated fatty acid(MUFA)and 10 polyunsaturated fatty acid(PUFA)in abdominal adipose tissue of crisp grass carp were detected in different crisping periods.The contents of MUFA significantly increased whereas those of PUFA and n-6 PUFA significantly decreased(p <0.05)with the increase of crisping time.The fatty acid ratio of SFA:MUFA:PUFA was similar to 1:2:1 and the closest in grass carp during whole crisping process.Moreover,the content of n-3 PUFA decreased(p>0.05)at CGC1,and always lower than the common grass carp.The ratios of n-6 PUFA to n-3 SFA ranged from(3.36±0.04)to(4.10±0.04)and the highest value at CGC1.