Quality And Storage Characteristics Assessments Of Caviar Based On NMR And MRI Techniques

Caviar,awarded as black gold,is the salt-cured and pre-served eggs of sturgeon that have been separated from the supporting connective ovarian tissue.Caviar is rich inproteins,high unsaturated fatty acids such as eicosapent aenoic(EPA),inorganic salt,vitamin A,B and D,and trace elements such as selenium et al.Due to its high nutritional value,caviar has become one of the most popular and expensive animal products in world trade.The nutritional compositions and nutritional quality of different levels of hybrid sturgeon caviar were firstly evaluated and compared in this study.The result showed that the content of moisture in caviar R+ was significantly higher than that of caviar R++.However,a numerically higher content of crude protein,crude fat was found in caviar R++(p>0.05).The content of essential amino acids or delicious amino acids in caviar R++ was higher than caviar R+ as well,but with no significant difference(p>0.05).There was a significant higher relative amount of EPA,DHA,EPA+DHA,or ∑n-3PUFA in caviar R++ than that of in caviar R+(p<0.05),respectively.Besides,a nuclear magnetic resonance(LF-NMR)and principal component analysis(PCA)combined method was developed to discriminate the caviar and raw sturgeon eggs based on the hydrogen protons originating from different environments with various salt concentrations.Moreover,the siberian sturgeon and hybrid sturgeon caviar,the hybrid sturgeon caviar R+ and R++ could be ditiguished as well.Secondly,a rapid,accurate analysis method of water,fat and protein contents was set up in caviar and raw sturgeon eggs through 1H LF-NMR relaxometry combined with partial least squares regression(PLSR)models and principal component regression(PCR).For PLSRpredictive model,the correlation coefficients(RCv2)of water,fat and protein were 0.9930,0.9698 and 0.9783 with root mean square error of cross-validation(RMSECV)of 0.0760,0.0308 and 0.0566,respectively.For PCA predictive model the Rcv2 were 0.9932,0.9592 and 0.9770,and the RMSECV were 0.1098,0.0878 and 0.0917,respectively.Thirdly,a noninvasive LF-NMR method was developed to monitor proton dynamics on caviar stored at-4℃ for 11 months.T2 relaxation spectra revealed three peaks at 0.54-0.75,20.61-30.78,and147.24-307.37 ms,respectively,whereas Ti showed only one peak around 167.16-217.31 ms.The T21 and T22 components remained unchanged during the storage period,while T23 was irregularly changed.NMR analysis demonstrated the moisture migrated through the extracellular spaces as free water under the action of osmotic pressure gradient during the salting treatment.Moisture and fat contents in caviar remained unchanged during the overall storage time.There was a trend for increased TVB-N values over the 11 months.Color measurement was also carried out to evaluate the quality change of the caviar.The NMR parameters clearly showed good correlation with moisture contents.