Study On The Effect Of Pre-treatment Process On The Flavor Precursors And Flavor Of Fried Tilapia

The tilapia is a kind of high-quality freshwater fish,no inter muscular thorns,rich in a variety of unsaturated fatty acids.It is recognized as a healthy food.In this paper,sensory evaluation,electronic nose(E-nose),headspace solid-phase microextraction(GC-MS),and gas chromatography-ion mobility spectrometry(GC-IMS)were used to study the effect of pretreatment(pickling and drying)on the flavor of fried tilapia,and the flavor precursors associated with flavor substances were analyzed by detecting free amino acids,fatty acids and nucleotides to provide a good foundation for further exploring the formation mechanism of fried fish flavor and improve the flavor quality of fried fish.The contents and results of the study are as follows:The sensory evaluation method was used to analyze the odor changes of fried tilapia during the salting treatment,and electronic nose and principal component analysis were used to evaluate the differences of different samples.Combined with GC-IMS and GC-MS techniques,the changes of flavor composition and characteristics of fried tilapia were analyzed during the salting treatment.The sensory evaluation showed that the meat flavor and fat taste of fried tilapia were significantly enhanced and the fishy smell was weakened after salting.Methyl groups and aldehydes and ketones are important aroma substances in fried tilapia by electronic nose.Nonanal,3-methyl pyrazine,2-dimethyl pyrazine,3-methyl pyrazine,and other substances were detected only in fried tilapia after salting by GC-IMS.Combined with GC-MS and ROAVs,it is worth knowing that 3-methyl butyraldehyde,hexanal,(E)-2-decenal,(E)-2-decenal and 1-octene-3-ol are the key flavor substances of fried tilapia before salting.After salting,the ROAV value of(E,E)-2,4-heptadienal in fried tilapia increases,the meat flavor increases,and the ROAV value of 1-octen-3-ol and hexanal decreases.The smell of earth and grass weakened.Studies have shown that salting helps to enhance the aroma of fried tilapia and reduce unpleasant odors.The free amino acids,fatty acids and flavor nucleotides of the main flavor precursors of fried tilapia before and after salting were determined.The results showed that salting had a significant effect on the flavor and flavor components of tilapia.After salting treatment,the salinity of tilapia increased significantly,the activity of endogenous protease increased,glycogen was degraded,and the content decreased,resulting in pyrazine compounds.The contents of fat and protein decreased significantly,and the contents of unsaturated fatty acids and free amino acids increased significantly.Combine with the changes in volatile components of fried tilapia before and after salting,it is found that the increase of pyrazine aroma substances in fried tilapia is related to the increase of the Maillard reaction substrate-sugar and protein degradation products after salting;Hydrolysis of fats into free fatty acids promotes(E,E)-2,4-heptadienal,(E)-2-decenal,(E,E)-2,4-decadienal and other aroma substances.At the same time,salting also promotes a significant increase in flavored amino acids and GMP content that provides umami flavor.Studies have shown that salting treatment can cause the degradation of macromolecular substances to produce small-molecule flavor precursors,and then a series of chemical reactions occur,producing pleasant odors and promoting the flavor of fried tilapia.The effects of sun drying,hot air drying and vacuum freeze drying on the flavor of fried tilapia were analyzed by electronic nose,gas chromatography-ion transfer spectrometry(GC-IMS)and gas chromatography-mass spectrometry(GC-MS)combined with sensory evaluation.Electronic nose analysis showed that the nitrogen oxides,alkanes,sulfides and aldol ketones in the dried fried tilapia were significantly increased.The principal component analysis of the electronic nose showed that the fried fish after drying was different from those without drying.Among them,natural drying and hot air drying have similar contours,and the degree of discrimination is low.GC-IMS and GC-MS analysis showed that the drying treatment significantly increased frying tilapia alcohols,aldehydes and pyrazines.The main volatile flavors are hexanal and2-ethyl-5-methylpyrazine,which Provide grassy and nutty flavor.However,2-ethyl-6-methylpyrazine was only detected in hot-air dried samples,providing roasting flavor for fried tilapia.Studies have shown that drying treatment significantly enhances the roasting taste and meat aroma of fried tilapia,among which hot air drying is the most significant.The fatty acids,amino acids,flavor nucleotides,TVB-N values,POV values and TBA values of fried tilapia under different drying treatments were detected.Combined with the changes in the volatile components of fried tilapia after dehydration and drying,it is found that the increase of pyrazine aroma substances in dried fried tilapia is related to the Maillard reaction;the same fat hydrolysis into free fatty acids promotes(E,E)-2,4-Heptadienal,(E)-2-decenal,(E,E)-2,4-decadienal and other aroma substances are improved.The results showed that the contents of fatty acids and amino acids in the samples treated by sun drying and hot air drying changed significantly,and the change of flavor of fried tilapia under drying treatment was related to the thermal degradation of fatty acids,amino acids and flavor nucleotides.The effects of sun drying and hot air drying on the flavor of fried tilapia come from protein spoilage and fat oxidation.Among them,the protein deterioration of fried tilapia treated by sun drying was more significant,and the fat oxidation of fried tilapia flavor treated by hot air drying was more significant.Its TVB-N value,POV value and TBA value are all in line with the national regulations.