| Squid is a popular seafood because of its high nutritional value and functional properties.However,the shelf-life of fresh squid is very short,and squid allergy is one of the most common,severe,and long lasting food allergies.Tropomyosin and hemocyanin have been identified as the major allergens from squid.Changes in the secondary and tertiary structure of food allergens are crucial to their allergenic potential.Therefore,it is important to seek an alternative preservation technology for fresh squid,not only for controlling the growth of microorganisms,but also for reducing the allergenicity of squid allergen proteins.High hydrostatic pressure(HHP),a valuable non-thermal food processing and preservation technology,provides potential benefits for solving these two problems.This study investigated the effect of HHP treatments on the physicochemical property,microbial growth,and protein quality of squid(Todarodes pacificus),and analyzed the changes in structural properties and allergenicity of HHP treated squid allergen proteins.The squid samples were subjected to single-or two-cycle HHP treatments for a same total holding time of 20 min.Single-cycle treatments were applied at 200,400,or 600 MPa for 20 min,and two-cycle treatments consisted of two 10 min cycles at 200,400,or 600 MPa,respectively.The sample held at ambient pressure without HHP treatment was used as a control.The four parts research contents were mainly completed as follows:1.The effects of HHP on physical and chemical qualities of squids were investigated.The impact of HHP treatments at different pressure levels on shelf life indicators(Total plate count,total volatile basic nitrogen and pH),water properties,color and texture profile analysis of squids during refrigerated storage were studied.Results showed that HHP is an effective preservation technology for fresh squids.After 4°C storage for 10 days,for HHP treated samples,the total plate count,total volatile basic nitrogen and the hardness was reduced by 34%-76%,28%-65%,14%-63%,respectively,compared with control.HHP treatments also delayed browning discoloration,and destroy the fibers of the squids during storage.It is worth pointing out that water properties were highly relevant to total volatile basic nitrogen,L*,hardness and cohesiveness of squids(P<0.001).2.The influences of HHP on protein quality,in vitro antioxidant and anti-inflammatory of squids were studied.For HHP treated samples,the soluble protein nitrogen content,in vitro protein digestibility,antioxidant and anti-inflammatory was increased 0.81%-3.39%,2.93%-16.02%,0.02-0.07 and 0.04-0.20 respectively,compared with control.The two-cycle 600 MPa HHP treatments resulted in the highest values of soluble protein nitrogen content for 7.59%,in vitro protein digestibility for84.42%,reducing power ability for 0.13 and DPPH scavenging activity;1.80,1.19,2.17 and 1.27 times of control,respectively.The SDS-PAGE indicated that HHP caused severe damage to squid proteins;the 280 kDa,172 kDa,102 kDa,43 kDa and 38 kDa protein were weaken after HHP treatments in SDS-PAGE,and higher pressure caused more disruption of protein than lower pressure.~1H nuclear magnetic resonance showed that the main spectral changes associated to the in vitro antioxidant and anti-inflammatory properties of proteins following HHP treatment were in the range of 3.00-3.19 and 3.60-3.79 ppm.3.The impacts of HHP treatments on the protein structure and allergenicity of squid tropomyosin were also investigated.For HHP treated samples,?-helix content and free sulfhydryl content was reduced by16%-51%,1.86-19.41,respectively;surface hydrophobicity index and maximum height of atomic force microscopy was increased by 16-149 and1.89-5.23 times,respectively;and the IgE and IgG-binding capacities of squid tropomyosin were reduced by 33%-48%,compared with control.~1H nuclear magnetic resonance showed that the main ranges of the characteristic regions for the allergenic properties were 0.99–1.03,1.19-1.24,1.44-1.49,1.79-1.84,2.85-2.90,3.36-3.39 and 3.40-3.43 ppm4.The secondary,tertiary and quaternary structures and allergenicity of squid hemocyanin were characterized.Electrophoresis analysis revealed that HHP treatment significantly decreased the band intensity of hemocyanin when increasing pressure from 200 MPa,400 MPa to 600MPa.The protein structure analysis of squid hemocyanin showed that peptide segments information was changed by HHP and hemocyanin peptide segments(DVQNLMSALKR,EGSHFSVLGGSTEMPWAFDR and GHNAIHSWVGGPS)were changed by HHP.For HHP treated samples,the?-helix content and particle gyration radius HHP treatment was decreased by 3.47%-8.70%and 6%-21%,respectively;the surface hydrophobicity index and guinier aggregation number was increased by18-47 and 17%-57%,respectively.HHP treatment decreased the IgE and IgG-binding capacities,decrease the allergenicity(P<0.05)of squid hemocyanin by 29-63%.The HHP-reduced allergenicity model can be described as this y=A×e~x(where y was the pressure,x was the allergenicity index,and A was the constant,respectively).This study provided valuable information on the application of HHP for controlling microbial growth and quality deterioration,improving functional properties of squids,modifying the protein structure,and reducing the allergenicity of squid allergen proteins.This information is valuable for developing industrial applications of this novel non-thermal processing technology in fresh seafood processing. |
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