Effects Of Glycosylation On The Quality And In Vitro Digestion Characteristics Of Mackerel (Scomber Japonicus) Fish Floss

Mackerel（Scomber japonicus）is a typical marine pelagic fish that is mainly distributed in the Northwest Pacific Ocean,including the Sea of Japan,the Yellow Sea,and the Mediterranean Sea.In China,the annual catch of mackerel ranks fourth in the marine fish catch.However,mackerel is usually sold as fresh,resulting in low-processing utilization and low sales.The production of intensive-and deep-processing products with mackerel as a raw material is beneficial to improve its processing utilization rate,endow it with higher added value,and alleviate its overproduction.Fish floss is a kind of leisure fish product which is rich in nutrition,easy for human body to digest and absorb and easy to carry.At present,the taste of fish floss in the market is relatively single,so it is of great significance to study the preparation of mackerel fish floss with different sugar processing to promote the sales of fish floss and broaden its product types.In this study,mackerel was used as raw material to prepare dried fish floss by adding different sugar（sucrose,glucose,xylose,fructose and galactose）.The flavor,floss quality,sensitization,nutrition and antioxidant activity after in vitro digestion of fish pine were measured,and mackerel myofibrillar protein was extracted for glycosylation modification.The Maillard reaction degree,structure and antioxidant changes of glycosylated myofibrillar protein grafted products were studied to explore the reasons for the changes of fish floss flavor and quality.The main research results were as follows:1.A total of 64 volatile compounds were detected in fish floss.Hexanal,heptanal,nonanal,decanal,undecanal,tridecanal,pentadecanal,4-ethyl-benzaldehyde,dodecanal,benzene acetaltaldehyde,（E,E）-2,6-nonadienal,（E,E）-2,4-decadienal,2-undecanone,1-octen-3-ol,（E）-2-hepten-1-ol,1-heptanol,and 2-pentyl-furan were regarded as key volatile compounds.Furthermore,E-nose and partial least squares-discriminant analysis（PLS-DA）showed that there were significant differences in flavor among fish floss samples.The correlation analysis of browning index,fatty acids and key volatile compounds confirmed that MR and lipid oxidation made great contribution to the flavor formation.2.The floss quality of glycosylated fish floss decreased,but the floss content,fluffiness and fine fluffiness of galactose fish floss were the highest in the added sugar group.IMP was accumulated in fish floss,and the TAV values were all greater than 1,which contributed greatly to the umami of fish floss.And the highest IMP content of Xyl in glycosylated fish floss was 121.59 mg/100g.The free amino acid content of glycosylated fish floss decreased significantly,and the content of His in xylose fish floss was decreased to 292.35 mg/100g,which reduced the bitterness of mackerel floss.The principal component analysis of electronic tongue showed that there were significant differences in the taste among fish floss samples,and the taste profile difference between xylose fish floss and other samples was the most obvious.Western-blot analysis showed that there was parvalbumin in mackerel floss.After glycosylation,the Ig G binding ability of parvalbumin decreased significantly,and it was the lowest in xylose fish floss.3.Except xylose fish floss,the digestibility of fish floss with sugar was significantly improved.Particle size analysis showed that the molecular diameter of crude peptide solution after gastrointestinal two-step digestion was smaller than that after gastric digestion.Antioxidant analysis showed that with the increase of concentration,the antioxidant activity of fish floss digestive products also increased,and the antioxidant activity of gastric digestive products was higher than that of gastrointestinal digestive products.Among them,xylose fish floss digestive products had the strongest antioxidant activity,with DPPH free radical scavenging rate,hydroxyl radical scavenging rate and reducing power of 63.22%,19.84%and 1.06,respectively.It can be seen from the amino acid composition that the content of essential amino acids in the crude peptide products of gastrointestinal digestion was more than 35%,which had a certain nutritional value.At the same time,the antioxidant amino acids of the digestive products accounted for more than 80%,indicated that the antioxidant activity of the digestive products of fish floss was related to its amino acid composition.4.The p H value of glycosylated myofibrillar protein reaction system decreased significantly.The lowest p H value of xylose myofibrillar protein graft was 7.00.At the same time,the absorbance and grafting degree were the largest at A294 nm and A420 nm.SDS-PAGE results showed that glycosylated myofibrillar protein aggregates were mainly formed by Maillard reaction between myosin and actin and sugar molecule.FTIR analysis showed that the spectral intensity of the glycosylated protein increased near 3 350 cm^-1and 1 070-1 000 cm^-1 due to the hydroxyl group and sugar ring functional group C-O-C of the introduced sugar molecule.After heating and glycosylation,theα-helix of the protein decreased and the content of irregular curl increased,indicating that the protein structure became more loose.The result of fluorescence spectra showed that theλ_max of glycosylated protein grafts shifted red,indicating the glycosylated grafted products were in a more hydrophilic micro-environment.The results of UV spectrum showed that the absorption intensity of xylose graft was the highest in the range of 260-310 nm.From the results of antioxidant index,the antioxidant activity of xylose myofibrillar protein graft was the highest,followed by galactose graft product,indicating that the higher the degree of Maillard reaction,the higher the antioxidant activity.