| Carvacrol(Car)is a plant-derived natural antiseptic with broad-spectrum antibacterial activity and antioxidant properties,and is permitted to be added to food products.But carvacrol has poor water solubility,poor stability and special aroma,which limits its application in food system.Nano embedding technology through delivery carrier can make up for the defects to a certain extent and enhance the practical application value of carvacrol.Ovalbumin has high nutritional value and good emulsification,foaming and gelling properties.As the base material of protein based delivery system,it has the advantages of non-toxic and self-assembly,so it can be used to develop various delivery systems.At the same time,pH shifting and ultrasound technology can be used to modify proteins,and can also be widely used as excellent nano embedding technology.Therefore,the effect of ultrasound-assisted pH shifting treatment on the structure and emulsification properties of ovalbumin was studied in this paper.On this basis,ovalbumin-carvavol nanoparticles were prepared successfully,and the characterization structure and antibacterial properties were investigated.Finally,the practical application effect of ovalbumin-carvavol nanoparticles in refrigerated Marine fish was evaluated.The main research contents and results are as follows:(1)Study on the influence of ultrasound-assisted pH shifting treatment on the structure and emulsification characteristics of ovalbumin:The ultrasound-assisted pH shifting treatment modified ovalbumin was prepared,and the effect of ultrasound-assisted pH shifting treatment on physicochemical properties,molecular structure and emulsification properties of ovalbumin was investigated.The results showed that after ultrasound-assisted pH shifting,the turbidity of ovalbumin decreased,the particle size and PDI decreased,but the potential increased.With the increase of ultrasound time,the content of free sulfhydryl group and surface hydrophobicity increased by 149.1%and 435.4%,respectively.The maximum fluorescence intensity of the fluorescence spectrum increased and the maximum emission wavelength redshifted,indicating that ultrasound-assisted pH shifting treatment effectively changed the tertiary structure of oobumin,exposing the internal sulfhydryl and hydrophobic groups.Circular dichroism analysis showed that the molecular spatial structure of ovalbumin was changed after treatment,and the protein conformation tended to be flexible.The secondary structure analysis showed that the content of α-Helix decreased from 42.2%to 35.1%,and the content of β-Turn and Random coil increased from 13.20%and 31.90%to 17.20%and 33.10%,respectively.The particle size of the emulsion prepared by ultrasound-assisted pH shifting treatment decreased,the emulsion potential increased,and the emulsion had good dispersion.Emulsifying activity and stability increased by 33.08%and 113.6%,respectively.The emulsion does not delaminate within 48 h and has better storage capacity.The results showed that ultrasound-assisted pH shifting treatment could effectively change the molecular structure of ovalbumin and improve its emulsifying property.(2)Study on the construction and antibacterial properties of ovalbumin-carvavol nanoparticles regulated by ultrasound-assisted pH shifting treatment:Ovalbumin-carvavol nanoparticles(SU-OVA-Car)nanoparticles were prepared by ultrasound-assisted pH shifting treatment,and their physicochemical properties,structural characterization and bacteriostatic performance were investigated.The results showed that the encapsulation rate of SU-OVA-Car nanoparticles reached 88.94 ± 1.87%when the protein concentration was 10 mg/mL,pH=12.0,the mass concentration ratio of ovalbumin to carvavol was 4:1,the ultrasound time was 10 min and the ultrasound power was 500 W.The particle size,PDI and potential of SU-OVA-Car nanoparticles were 105.3 ± 1.95 nm,0.16 ± 0.037 and-26.7 ±0.851 mV,respectively.The determination of fourier transform infrared spectrum(FTIR),differential scanning calorimeter(DSC)and X-ray diffraction(XRD)showed that the secondary and tertiary structures of ovalbumin changed to some extent in terms of chemical structure and thermodynamic properties,hydrogen bonding and hydrophobic action were the main binding forces of SU-OVA-Car nanoparticles,and the thermal properties changed due to the formation of nanoparticles with good crystallinity.At the same time,it also proved that ovalbumin successfully encapsulated Car into nanoparticles.Scanning electron microscope(SEM)showed that SU-OVA-Car nanoparticles were spherical particles with uniform size distribution.The antibacterial diameter of SU-OVA-Car nanoparticles for S.aureus and E.coli was 27.25± 1.16 mm and 26.49± 0.69 mm,respectively.The MIC values were 38.125 μg/mL and 76.25 μg/mL,respectively,and the MBC values were 76.25μg/mL and 152.5 μg/mL,and the growth of S.aureus and E.coli was completely inhibited within 24 h.(3)Study on the preservation effect of ovalbumin-carvavol nanoparticles on sea bass:The preservative and preservation effects of Car,simple mixed sample(OVA+Car)and SU-OVA-Car nanoparticles on refrigerated sea bass were studied.The results showed that both Car and OVA+Car could inhibit the rot of fish.SU-OVA-Car nanoparticles had the best effect on the preservation of refrigerated sea bass.Car has good antibacterial and antioxidant properties.However,due to its lack of stability and insolubility in water,Car is easy to be affected by environment and has limited effect on inhibiting fish spoilage.OVA+Car has no effective embedding and preparation of Car nanoparticles,and its inhibition effect on fish corruption is almost no significant difference with Car.SU-OVA-Car nanoparticles could significantly slow down the decay of fish.On the 10th day of storage,the total number of colonies,volatile base nitrogen and TBARS were 7.48 lg CFU/g,21.94 mg/100 g and 0.63 mg/kg,respectively,which were significantly lower than the blank control group.SU-OVA-Car nanoparticles soak can effectively inhibit the decomposition of protein and microbial growth in fish,so that fish in sensory evaluation,the total number of colonies and volatile base nitrogen indicators are better than other groups,so that fish has a better preservation effect. |
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