The Analysis Of Typical Sour Substances In Giant Squid(Dosidicus Gigas) Mantle Muscle And Its Mechanism Of Sourness

Giant squid?Dosidicus gigas?is an abundant cephalopod source while the unflavorable sourness perceived by consumers would discourage the potential edibleness of raw muscle and the development of related products.In this present study,sourness-related components in Dosidicus gigas mantle muscle were identified by means of taste omission tests and taste addition tests and typical sourness-active compounds were determined,the effects of different temperature on the content of sourness-related components during low-temperature storage were investigated,the mechanism of sourness in giant squid?Dosidicus gigas?mantle muscle was revealed on the basis of protonated organic acid,the molecular interaction mechanism between typical sourness-active compound and myofibrillar protein in giant squid?Dosidicus gigas?mantle muscle was studied,which would provide some theoretical support and technical reference for the development of methods of sourness-removal in giant squid?Dosidicus gigas?mantle muscle.The main research results and conclusions are as fellows:?1?The flavor difference was compared between complete synthetic extract and natural extract of Dosidicus gigas.The complete synthetic extract containing sourness-related components according to their natural concentration succeeded in reproducing the taste profile of mantle muscle natural extract of Dosidicus gigas,without significant difference?p>0.05?in the five basic tastes between these two extracts other than the stronger fishy taste and aftertaste in the natural extract.The taste profile of simplified synthetic extract was closely similar to that of complete synthetic extract?p>0.05?,with the only difference in that the astringency in simplified synthetic extract was weaker.Simplified synthetic extract,provides a better simulation environment to study the contribution of organic acids and opines to sourness in mantle muscle of Dosidicus gigas,not only reproducing the whole taste profile of mantle muscle extract but also reducing the disturbance of complicated matrixes.?2?The typical sour substances of Dosidicus gigas mantle muscle were determined through omission tests and addition tests.Characteristic flavor components including His,Lys,Arg,Glu,Cys,malic acid,meso-alanopine,?-alanopine,tauropine,AMP,K⁺,Na⁺,NH₄⁺,Cl^-,TMAO and glycine betaine were conformed.meso-alanopine,?-alanopine and tauropine were the typical sourness substances.Other components such as amine acid,organic acid,to some extent,had contribution to the sourness of mantle muscle of Dosidicus gigas while inorganic ions had effects on the appearance of sourness.?3?Sourness-related components of giant squid?Dosidicus gigas?mantle muscle during storage at 0?were determinated.The shelf-life of Dosidicus gigas mantle muscle was estimated as 13d by the means of Quality Index Method?QIM?during storage at 0?.Through the whole storage,the pH of Dosidicus gigas mantle muscle maintained the basic stability,the total volatile basic nitrogen?TVBN?gradually increased and the flavor free amino acid?FAA?increased gradually during the former storage and then decreased to the end of storage.The pyruvate appeared a similar trend as FAA while other organic acid nearly kept unchanged.The content of opines gradually increased and reached the maximum at the end of storage.?4?Sourness-related components of giant squid?Dosidicus gigas?mantle muscle during frozen storage were determinated.During the frozen storage at-18?and-33?,the pH of Dosidicus gigas mantle muscle maintained the basic stability and the TVBN gradually increased.The flavor FAA increased gradually during the former storage and then maintained stable till the end of storage.The organic acids as well as opines nearly maintained unchanged.There is no significant effect of low temperature on organic acid and opines?p>0.05?.?5?The acid formation mechanismof sour substance was studied.Hydrogen ion would produce sour taste at low pH while would not be perceived at high pH.At most food system,the contributors of sourness are organic acids and other compounds that could produce sour taste.At relatively high pH,the appearance of sourness was related mainly with the molar concentration of protonated organic acid and the intensity of sourness had a significant linear positive correlation with the concentration of protonated organic acid.At the same pH,any organic acid or opine with at least 1 protonated carboxyl group would produce the same sour taste response.The structure of organic acid would have no effect on the intensity of sourness when the concentrations of protonated organic acid and pH were kept constant at the same time.The protonated organic acids contributing to the sourness of simplified synthetic extract of Dosidicus gigas mantle muscle was mainly comprised of acid opines,which once again proved that opines were the typical sourness substances in Dosidicus gigas mantle muscle.?6?The spectral characters of myofibrillar protein of Dosidicus gigas mantle muscle were studied before and after the interaction between myofibrillar protein and meso-alanopine.The absorbance and peaks position remained unchanged in the ultraviolet-visible absorption spectroscopy of myofibrillar protein whether meso-alanopine was added to myofibrillar protein or not,which preliminarily indicated that meso-alanopine had no effect on the microenvironment of aromatic heterocyclic amino acid residues in myofibrillar protein.The fluorescence quenching reaction of meso-alanopine to myofibrillar protein without obvious regularity,which indicated that there existed interaction between meso-alanopine and myofibrillar protein,affecting the hydrophobic structure of myofibrillar protein,while the binding site was not in the hydrophobic domain.The results of circular dichroism shown that meso-alanopine would make the?-helical structure of myofibrillar protein transformed into?-sheet,making the structure of myofibrillar protein tended to be more loose and appeared a tendency of loose to relative tightness,which indicated that meso-alanopine,to some extent,had an effect on the molar structure of myofibrillar protein.?7?The chemical shifts of hydrogen atom in meso-alanopine were studied by method of nuclear magnetic resonance?NMR?before and after the interaction between myofibrillar protein of Dosidicus gigas mantle muscle and meso-alanopine.¹H-NMR spectroscopy shown that the chemical shifts of hydrogen atom of-CH-and-CH₃ in meso-alanopine shifted towards to the low-field with a narrow range,which indicated that the binding site maybe located in the hydrophilic area of the surface in myofibrillar protein.