Effect Of Different Drying Methods On The Flavor Of Takifugu Obscurus

Takifugu obscurus(T.obscurus)is popular among consumers because of its unique flavor.The production of puffer fish has increased year by year since the opening of circulation policy in 2016.However,the processing industry of puffer fish has been in a relatively poor stage due to the short development time.Therefore,it is of great significance to explore suitable drying technology for T.obscurus to adjust the industrial structure of pufferfish,diversify the consumption mode,so as to promote the development of processing industry.In this study,T.obscurus was dried by hot air drying(HAD),hot air assisted radio frequency drying(HARFD)and microwave vacuum drying(MVD)to explore the effect of different drying methods on the flavor of T.obscurus.Then,a drying method which can obtain great flavor and suitable for industrial application was selected to provide theoretical basis for puffer fish processing industry.(1)The proximate analysis,color,rehydration ratio,free amino acids,5'-nuclotides,organic acids and inorganic ion of HAD,HARFD and MVD T.obscurus were investigated.The taste activity value(TAV)was used to determine the taste active components of dried T.obscurus,and the taste synergistic effect of amino acids and 5'-nucleotides was evaluated by the equivalent umami concentration value(EUC).No significant decrease was found in crude protein,ash,lipid contents(dry matter weight)of three dried groups when compared with the fresh group.The color retention and rehydration were best in MVD group.The highest contents of umami amino acids,sweet amino acids,bitter amino acids and total free amino acids were found in HAD group,followed by HARFD group,and the lowest in MVD group.5'-IMP was the predominant5'-nucleotide in all three dried groups.According to the TAVs of each taste components,the common taste active components of the three dried T.obscurus included 5'-IMP,Ala,Arg,Lys,Na~+,K~+.The EUC values of HARFD and HAD groups were 19.81 g MSG/100g and 17.32 g MSG/100 g,respectively,which was about twice that of MVD group.The electronic tongue(E-tongue)could effectively distinguish the taste profiles of the three dried T.obscurus.(2)SPME-GC-TOFMS was used to study the volatile compounds of three different dried T.obscurus.The odor active components of three dried T.obscurus were identified according to the odor activity value(OAV).The sensory evaluation of dried T.obscurus were carried out by sensory quantitative descriptive analysis(QDA).A total of 150volatile compounds were identified,including 8 aldehydes,15 alcohols,10 ketones,9esters,2 phenols,7 nitrogen,oxygen and sulfur compounds,20 aromatics,9 terpenes and61 hydrocarbons.The common odor active components of three dried T.obscurus included 3-methylbutanal,2-methylbutanal,hexanal,heptanal,nonanal,acetone,trimethylamine,pyridine,toluene,o-xylene,p-xylene,1-methylethyl-benzene,p-cymene,1,2,3,5-tetramethyl-benzene,caryophyllene and humulene.The differences in the contents of(E)-2-nonenal,1-penten-3-ol,2-ethyl-1-hexanol,myrtenol,tetramethyl-pyrazine,styrene,mesitylene,heptanal,acetone,trimethylamine and caryophyllene may lead to the difference of flavor among three dried T.obscurus.QDA results showed that the intensities of fish fragrance and crab roe-like and coasted aroma of HARFD and HAD groups were higher than those of MVD group,and PCA analysis results showed that there was a positive correlation between MVD and fishy,earthy,and rubbery.In addition,the electronic nose(E-nose)could effectively distinguish the odor profiles of the three dried T.obscurus.(3)The color,TBA and total volatile basic nitrogen(TVBN)content of HAD T.obscurus at three different storage temperatures(37°C,45°C and 55°C)were investigated.With the extension of storage time,L*values of HAD T.obscurus decreased,other indexes such a*value,?E,TBA and TVBN content increased.The shelf life prediction model was established using Arrhenius equation based on TVBN contents,and the shelf life of HAD T.obscurus was estimated to be 36.22 and 32.18 days at 0°C and 4°C,respectively.The HAD T.obscurus at different storage time was discriminated by linear discriminant analysis(LDA)based on E-nose and E-tongue fusion data.The back propagation neural network(BPNN)algorithm was used to establish the prediction model for storage time,TBA and TVBN contents.The model parameters were as following:the input layer contained 38 neurons,the hidden layer contained 30 neurons,and the output layer contained 1 neuron.In the three prediction models,the root mean square error(RMSE)and determination coefficient(R~2)of validation set and calibration set were close.Therefore,the established BP neural network models could accurately predict the storage time,TBA and TVBN contents of HAD T.obscurus stored at 37°C.