Quality Improvement Of Circulating Water Starvation Treatment On The Muscle Of Blunt Snout Bream

Blunt snout bream（Megalobrama amblycephala）,also known as Wuchang fish,was one of the main freshwater fish species in China,with high yield and good breeding efficiency.Because of Chairman Mao Zedong’s verse“has to drink Changsha water and eat Wuchang fish”,which was well-known at home and abroad.Its unique side flat and wide body type,moderate size,delicious taste and high meat content were suitable for making dishes such as steamed fish.The high-density culture mode of ponds was the main breeding method of blunt snout bream in China.It was usually caused by the accumulation of silt at the bottom of ponds and large amounts of algae in the aquaculture water,resulting in poor flesh quality,flavor,food quality and consumer acceptability declined.The subject intended to use blunt snout bream as the experimental object,which depurated through the circulating water filtration system and studied the depuration conditions（water temperature,fish water density,water flow displacement amount and treatment time）on the physical and chemical properties,flavor and taste of muscle.The effects of depuration process were optimized by orthogonal test,circulating water depuration and upgrading technology was established to improve flesh quality to meet high quality fresh-processed aquatic products.The main research contents and results were as follows:1.Study on the effect of circulating water depuration time on the flesh quality of blunt snout bream.The circulating water depuration device was used to depurate blunt snout bream,the techniques such as texture analyzer,colorimeter,odor analyzer,HPLC,GC-MS and sensory evaluation were used to study depuration time（0～10 d）on biological indicators of blunt snout bream and muscle chemical composition,protein composition,pH value,water retention,color,TPA parameters,taste components,odor characterwastics and volatile flavor components.The results showed that treatment time had significant effects on physical and chemical components,texture,flavor,taste and sensory quality.With the prolonged depuration time,the contents of crude fat,total sugar,energy,water-soluble protein,volatile base nitrogen（TVB-N）,carbonyl value（COV）and thiobarbituric acid（TBA）content of muscle were significantly decreased,the contents of lactic acid,free amino acid,ash and salt-soluble protein were significantly increased（P<0.05）,lactic acid could play a role on flavor enhancing of muscle.The results of texture,color and sensory evaluation showed that depuration treatment can significantly increase the springiness,chewiness and sweetness and improve whiteness of muscle.The electronic nose and headspace solid phase microextraction gas chromatography-mass spectrometry（SPME-GC-MS）showed significant differences about volatile flavors at different treatment times,and aldehydes with fishy smell,grassy,and unpleasant odors of hexanal,heptaldehyde,nonanal,ketones,hydrocarbons,etc.were significantly decreased,while olefins,alcohols,and acids with mild odors increased.Before depuration content of TVB-N,COV and TBA from muscle were 12.73%,20.35%and 35.13%by lower than that undepurated samples,and free amino acid content was 43.83%higher than undepurated samples.The taste ATP（adenosine triphosphate）related compounds,the content of AMP（adenosine monophosphate）and IMP（inosinic acid）with sweet,salty and umami increased,while HxR（inosine）and Hx（hypoxanthine）with bitter taste decreased,K value decreased significantly,freshness increased.Before processing,combined with starvation of blunt snout bream for 8 days,the flesh quality can be significantly improved.2.Study on effects of circulating water depuration conditions on the flesh quality of blunt snout bream and optimized depuration treatment conditions.The circulating water depuration device was used to depurate blunt snout bream,studied fish water density（1:5,1:10,1:15,1:20,1:25,m:V）,water temperature（6,13,18,25,°C）,water flow displacement(0,50,100,200,250,double fish weight.d^-1)on the survival rate of blunt snout bream,physical and chemical properties（chemical composition,water holding capacity,color,pH,and TPA parameters）of muscle by techniques such as physical and chemical analysis instruments,texture analyzers,colorimeter.And optimized the treatment conditions by orthogonal test.Depuration conditions had great influences on water-soluble protein,free amino acid,volatile base nitrogen,ash,crude fat,total sugar content,springiness,cohesiveness and adhesiveness,but had little effect on other indicators.The results of orthogonal test showed that suitable treatment conditions for blunt snout bream were fish water density of 1:25,depurated water temperature of 18°C,water flow displacement of 200 times fish weight.d^-1,and depuration time of 10 days.Depuration treatment had little effect on protein and sugar,but significantly reduced fat content.The contents of ash,water-soluble protein and free amino acid of muscle before depuration were1.08%,3.85%and 1.58 mg/g,respectively,and the contents after depuration were 1.56%,4.39%and 2.89 mg/g,respectively,which increased by 44.44%,14.03%,and 82.91%.The salt nitrogen content of muscle after depuration was 6.44 mg/100 g,which was 18.07%lower than that before depuration（7.86 mg/100 g）.The springiness and cohesiveness of the depurated flesh were significantly improved.3.Study on changes of volatile flavor and taste substances before and after depuration.Taking blunt snout bream before and after depuration treatment as the object,the taste analyzer（electronic tongue）,odor analyzer（electronic nose）,comprehensive two-dimensional gas chromatography-time of flight mass spectrometry（GCxGC/TOFMS）,amino acid automatic analyzer,high performance liquid chromatography（HPLC）,inductively coupled plasma optical emission spectrometry（ICP-OES）and other technical means,comparative studied on the taste characterwastics,odor characterwastics,free amino acids,nucleotide metabolites,organic acids,minerals and volatile flavor substances composition and content changes before and after depuration treatment to detect circulating water depuration on flesh improvement of blunt snout bream.The electronic nose data analysis showed that there were significant differences in the odor characterwastics of muscle before and after the depuration treatment.The results of comprehensive two-dimensional gas chromatography-time of flight mass spectrometry showed that The contents of aldehyde,ketone and ester with fishy smell,grassy and fatty taste were reduced by 50.13%,43.07%and 82.51%,respectively,while the alcohol,acid,alkene and aromatic hydrocarbons showed an increase on the quantity and content of flesh with sour,sweet and aromatic odor characterwastics,and contents were increased 10.57%,29.53%,1.59 times and 3.08 times,respectively.Compared with undepurated samples,the content of umami,sour and sweet amino acids on the depurated muscle increased,the content of bitter and astringency amino acids decreased;the content of saturated and monounsaturated fatty acids of muscle decreased,the content of polyunsaturated fatty acids increased,especially EPA and DHA increased significantly,the total amount increased by 87.59%;the content of tartaric acid,malic acid and lactic acid increased;the content of potassium,sodium,calcium,phosphorus and chromium ions with salty of inorganic ions increased,magnesium,iron,manganese,copper and zinc ion content decreased,the potassium,iron and zinc ions among them were significantly different before and after depuration;In the nucleotide metabolites,adenine,guanine and guanosine,uridine,thymine and uracil reduced,while adenosine and inosine increased,and the purine logarithm value was related to freshness of muscle.After depuration,the umami,sour and sweetness of muscle was enhanced,while bitterness,astringency and salty taste was weakened.