| Loach(Misgurnus anguillicaudatus)is widely distributed in the fields of rice fields,ponds,ditches,rivers and lakes in China except Qinghai,Tibet and other few areas.Due to high protein,low fat and delicious meat,loach is widely loved by consumers.In recent years,weak loach processing industry has been unable to meet the growing market demand,fresh loach sales model will be eliminated gradually by the market.However the slaughtered fresh loach can make up the market vacancies,but the quality changes and preservation technology after its slaughter remain to be studied.This paper used the slaughtered fresh loach as raw material,studied its changes of physicochemical properties in the storage process.Then combined with biological antioxidant—tea polyphenols to investigate the effects of different concentrations of tea polyphenols treament on the physic-chemical properties,functional properties of myofibrillar proteins,gel properties of surimi and volatile off-odors of partial-frozen loach,so as to provide a theoretical basis for the preservation and deep processing of loach.1.The slaughtered loach was stored at 4 ?,-2.5 ? and-18 ?,and the storage temperature had a significant effect on the quality of loach.With the prolonging of storage time,the sensory score,L * value,a * value and shear value of each test group showed a decreasing trend;TVB-N value,TBA value,b* value,juice loss and cooking loss showed a significant increasing trend;pH decreased firstly and then increased;The total bacterial count showed a significant increasing trend during cold storage,decreased firstly and then increased during partial-frozen and frozen storage;Histamine did not reach the effective detection.During a certain period of time,the physical indexes such as sensory score,color,thawing juice loss and cooking loss of-2.5 ?partial-frozen storage samples were better than those of-18?frozen samples.Loach's shelf life at 4? and-2.5? was 6 d and 20 d,at the same time,the sensory score,total bacterial count and TVB-N value were 21.00 points,5.82 lgcfu/g,15.40mg/100g;15.33 points,5.83 lgcfu/g,19.04 mg/100 g.Compared with the method of cold storage,partial-frozen preservation can greatly prolong the shelf life of loach.Compared with the deep freezing method,partial-frozen can not only save energy,but also ensure the physical quality of loach during the shelf life.The main factors that affect the shelf life of loach are the growth of microbes and the oxidation of fat.If combined with a certain suppression measures under partial-frozen conditions,it's possible to further extend the shelf life.2.The tea polyphenols had a significant inhibitory effect on the quality degradation of partial-frozen loach during storage,and the higher the concentration,the more obvious the effects.Compared to the control group,the degradation rate of sensory score,L *value,a * value,shear value,juice loss and cooking loss of loach after tea polyphenols treatment were obviously inhibited;The total bacterial count,TVB-N value,TBA value increasing trend slowed significantly;TBA values remained at a low level;Histamine did not reach the effective detection.After storage for 25 d,control group and 0.1% TP treatment group's sensory score,total bacterial count and TVB-N value were 13.83 points,6.39 lgcfu/g,20.16 mg/100g;14.43 points,5.33 lgcfu/g,17.92 mg/100 g,at this point the 0.1%TP treatment group still met the quality requirements.After storage for 30 d,0.1%,0.2%,0.3%TP treatment groups' sensory score,total bacterial count and TVB-N value were 13.95 points,6.12lgcfu/g,20.05 mg/100g;14.52 points,5.91 lgcfu/g,19.01 mg/100g;14.31 points,5.86 lgcfu/g,17.88 mg/100 g,at this point 0.1%TP treatment group sample quality indicators had exceeded requirements,while 0.2%,0.3%TP treatment group samples still met the index requirements.0.1% TP treatment could extend the shelf life to 25 d,0.2%,0.3% TP treatment shelf life could be up to 30 d.3.Different concentrations of tea polyphenols had a significant effect on the functional properties of loach myofibrillar protein.The test results showed that the solubility,emulsifying activity,emulsifying stability and thiol content of myofibrillar protein in the control group and 0.1%,0.2%,0.3%TP treatment groups showed a decreasing trend in the storage process,surface hydrophobicity showed a significant increasing trend,storage elastic modulus(G ')of rheological properties characteristic index decreased,but the functional characteristics of myofibrillar protein in tea polyphenols treatment group decreased slowly,and the effect of myofibrillar protein was improved with the increase of TP concentration.4.Tea polyphenols treatment also had a significant effect on the partial-frozen storage loach's myofibrillar protein and surimi gel properties.The test results showed that the myofibrillar protein and surimi heat-induced gel water retention,hardness,elasticity and whiteness of each test sample of partial-frozen loach decreased significantly,teapolyphenols treatment could significantly slow down the declining speed of myofibrillar protein and surimi heat-induced gel retention,hardness,elasticity and whiteness,improve the surimi gel properties,the best treatment concentration was 0.3%.5.The results of GC-MS analysis showed: The main volatile component substances detected in control group were 10 kinds of aldehyde,3 kinds of ketone,11 kinds of alcohol,6 kinds of acid,6 kinds of ester,10 kinds of hydrocarbon,4 kinds of other species,and a total of 50 kinds of species;The tea polyphenols treatment groups were mainly detected 12 kinds of aldehyde,3 kinds of ketone,12 kinds of alcohol,7 kinds of acid,7 kinds of ester,25 kinds of hydrocarbon,6 kinds of other species,mainly a total of 72 kinds of species;Aldehydes and alcohols were the main volatile components of loach.With the storage time extended,the control group's aldehydes decreased firstly and then increased,alcohols decreased firstly then decreased and finaly decreased,ketones decreased,acids and amines increased,others fluctuated.The relative content of aldehydes detected in the tea polyphenols group was significantly lower than that in the control group,the alcohols reduced more significantly,the proportion of the acid substances increased more,the growth rate of the amines was significantly more slowed down,and the hydrocarbon species were more rich.Tea polyphenols treatment could significantly improve the flavor of partial-frozen loach. |
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