| Silver carp(Hypophthalmichthys molitrix)has gained increasing popularity in food production and with customers due to its high levels of protein and unsaturated fatty acids,along with this fish being a rapid grower,resistant to disease,and inexpensive.It plays an important role in meeting the needs of people’s life and enriching dietary structure.However,silver carp also easily produces fishy odor compounds due to physiological conditions and living environment,which can lessen the acceptability of customers and restrict the devoplement of silver carp processing industry.Hence,it is necessary to find an effective way to deal with this problem.The current deodorization methods have some limitations such as chemical residues,changes in physicochemical properties of fish products,and generation additional odors.Applications of spice extracts to remove the fishy odors have gained growing attention due to their safety,efficacy,and simple operation.However,most of reports have focused on deodorizing effect of spice extracts,and researches on industrialized deodorization of spice extracts remain poorly studied.It remains unclear which active substances contribute to the deodorizing effect of spice extracts.Furthermore,little information is available on the mechanism of removal of fishy odor compound by spice extracts.Therefore,the study first explored the effect of different spice extracts on deodorizing effect for silver carp,and applied the response surface principle to optimize the deodorizing conditions for rosemary,zanthoxylum bungeanum,and kaempferi extracts on silver carp.On this basis,rosemary extract showed the best eodorizing effect,and then determinated its deodorizing components.Finally,the effect of interactions between protein of silver carp and deodorizing active compounds on fishy odor compounds was used to elucidate the deodorizing mechanism.The main findings are as follows:(1)Influence of deodorizing effect for spice extracts on silver carpThis study used thiobarbituric acid(TBA)value,trimethylamine(TMA)value,and sensory evaluation score as indices to evaluate the deodorizing effect of different spice extracts on silver carp.On this basis,The single factor test and the response surface principle were used to optimize the deodorizing conditions of spice extract with stronger deodorizing ability.Meanwhile,after the deodorizing conditions were optimized,the effect of volatile compounds of silver carp was analysed.Results showed that the best deodorizing conditions for rosemary extract on silver carp were: rosemary extract solution concentration and the material-liquid ratio were 0.17% and 1:3.40(g:m L),respectively with the soaking for 41 min.After deodorizing under above conditions,TBA value,TMA value and the sensory evaluation score were 0.35 ± 0.02 mg MDA/kg,1.55 ± 0.06 mg/kg,and 1.81 ± 0.07,respectively.The best deodorizing conditions for zanthoxylum bungeanum extract on silver carp were: zanthoxylum bungeanum extract solution concentration and the material-liquid ratio were 0.17% and1:3.40(g:m L),respectively with the soaking for 31 min.After deodorizing under above conditions,TBA value,TMA value and the sensory evaluation score were 0.34 ± 0.01 mg MDA/kg,1.56± 0.04 mg/kg,and 1.85 ± 0.08,respectively.The best deodorizing conditions for kaempferi extract on silver carp were: kaempferi extract solution concentration and the material-liquid ratio were 0.12% and1:4.30(g:m L),respectively with the soaking for 31 min.After deodorizing under above conditions,TBA value,TMA value and the sensory evaluation score were 0.37 ±0.01 mg MDA/kg,1.55 ± 0.01 mg/kg,and 1.95 ± 0.15,respectively.The headspace solid-phase microextraction and gas chromatography-mass spectrometry analysis showed that application of spice extracts could significantly reduce the contents of fishy odor compounds(hexanal and1-octen-3-ol,etc.).The degree of decrease of volatile compounds was the largest in rosemary extract(2)Determination of deodorizing active compounds in rosemary extractProteins,polysaccharides,and polyphenols of rosemary extract were removed to obtain different samples,which were used to evaluate the deodorizing effect on silver carp by changes in volatile compounds and sensory evaluation.The phenolic compounds in rosemary extract were qualitatively assayed using an ultra-HPLC(UPLC)in tandem with quadrupole time of flight mass spectrometry(Q-TOF-MS).Based on the results of UPLC-Q-TOF-MS qualitative assays,RA,CA,and CS were quantified and used to perform deodorizing experiment.Results showed that the OAVs of seven volatile compounds(hexanal,heptanal,octanal,nonanal,E-2-octenal,1-octen-3-ol,and decanal)contributing to the fishy odor were greater than 1.Thus,these seven volatile compounds were considered the main fishy odor-active compounds of silver carp.Sensory detection results and changes of contents of volatile showed that the lower the total phenolic content of rosemary extract,the poorer deodorizing effects against silver carp,suggesting that the deodorizing effect was primarily driven by polyphenols.The removal of proteins or polysaccharides did not diminish the deodorizing effect of rosemary extract.Meanwhile,RA,CA,and CS of rosemary extract could reduce the contents of fishy odor-active compounds and fishy odor scores,suggesting that RA,CA,and CS were active deodorizing ingredients.(3)Mechanism of phenolic compounds on interactions of myofibrillar protein(MP)with fishy odor compoundsFluorescence spectrum,ultraviolet spectrum,circular dichroism,and molecular docking were employed to investigate the effects of RA,CA,and CS on volatile compound binding sites and MP conformation.Meanwhile,the deodorizing mechanism of phenolic compounds was investigated.Results showed that phenolic compounds form complexes with MP,inducing changes in the conformation of MP and enhancement of protein-protein interactions,which leads to a decrease in hydrophobic binding sites.The endogenous fluorescence intensity,absolute value of Zeta potential,and total sulfhydryl content were decreased,and particle size was increased and secondary structures(α-helix,β-sheet,β-turn,and randomly coiled)was changed.The previous experimental results(fluorescence spectroscopy,surface hydrophobicity and molecular docking)showed that the main forces between phenolic compounds and MP was hydrophobic interaction forces.The hydrophobic interactions was found to be involved in the bingind of MP and fishy odor compounds after application of different bond-disrupting agents.Therefore,the addition of phenolic compounds promotes the release of fishy odor compounds by changing the structure of and competing for hydrophobic binding sites in MP,inducing fishy odor release and increase in fishy odor scores.RA was the strongest promoter of fishy odor compounds release,followed by CA and CS.Conclusion: in this study,the deodorizing conditions of spice extracts(rosemary,zanthoxylum bungeanum,and kaempferi)for silver carp has been established.Meanwhile,polyphenols are the main deodorizing components of rosemary extract,and RA,CA,and CS are the main active deodorizing ingredients in rosemary extract.The deodorizing mechanism of RA,CA,and CS was further investigated.It was found that the addition of phenolic compounds promotesd the release of fishy odor compounds by changing the structure of and competing for hydrophobic binding sites in MP,thereby achieving the effect of deodorization. |
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