Fabrication Of Zein-Carboxymethyl Chitosan Nanocomplexes And Applications In Polyphenol Encapsulation And Preservation

Natural polyphenols are widely present in plant organs,and they have certain effects on antioxidant,anti-inflammatory,antibacterial and other aspects,which make them have the potential to be used as natural bacteriostatic agents.However,polyphenols have poor light and thermal stability and are easily inactivated under acid-base conditions,which limit their application range.Therefore,it is necessary to adopt some suitable delivery systems to improve the stability of polyphenols.Zein and carboxymethyl chitosan（CMCS）have become good materials for preparing nanocomposites because of their wide source,good biocompatibility,and strong affinity.In this paper,Zein/CMCS composites were prepared by the method of anti-solvent precipitation,and the effects of p H,ionic strength and mass ratio on the turbidity of the complexes were studied.The formation mechanism of the composites was also discussed.Zein/CMCS complexes were used to encapsulate hydrophobic polyphenol curcumin（CUR）and hydrophilic polyphenol epigallocatechin gallate（EGCG）,respectively.The physicochemical properties of Zein/CMCS-CUR and Zein/CMCS-EGCG were determined.The application of these two ternary nanocomposites in food preservation was explored,which could provide an important theoretical basis for the wide application of protein-polysaccharide-polyphenol nanocomposites in the fields of food and medicine.The main results of this paper are as follows:（1）Zein/CMCS composites were prepared by anti-solvent precipitation method,and the parameters including p H,ionic strength,and Zein/CMCS mass ratio were optimized based on turbidity and three-phase diagrams.The turbidity titration of Zein/CMCS complexes with different mass ratios（1:4,1:2,1:1,2:1,4:1）showed that the critical p H values(p H_φ1)for the formation of insoluble complexes were 4.6,4.8,5.0,5.2,5.6,respectively.The electrophoretic mobility of zein and CMCS in the range of p H 4～5.5 was determined,and the charge density（ZN）of Zein and CMCS was calculated using soft particle theory.The results showed that the charge density ratio of Zein/CMCS was close to 1 for all the above p H_φ1 values.The charges of Zein and CMCS were equal when the Zein/CMCS complex formed insoluble complexes.（2）Zein/CMCS-EGCG nanocomposites were constructed using zein and CMCS as wall materials.The encapsulation mechanism of Zein/CMCS complexes to EGCG was investigated,and the preservation effect of Zein/CMCS-EGCG nanocomposites on fish meat was studied.When the mass ratio of Zein/CMCS and EGCG is 8:1,the encapsulation rate of EGCG reached a maximum value of 79.93%with a loading capacity of 4.70%,the particle size of 121.97 nm,and theζ-potential of-36.80 m V.The Zein/CMCS-EGCG nanocomposites presented as adhered granules.The results of Fourier transform infrared（FTIR）showed that interaction between Zein,CMCS,and EGCG might include electrostatic,hydrogen bonding and hydrophobic interactions.X-ray diffraction（XRD）experiments showed that EGCG was successfully encapsulated in Zein/CMCS complexes.Differential scanning calorimetry（DSC）experiments showed that Zein/CMCS-EGCG had better thermal stability than that of Zein-EGCG complexes.In vitro simulated digestion results showed that the sustained release effect of Zein/CMCS-EGCG_8:1nanocomposite on EGCG was better than that of Zein-EGCG complex.Antibacterial experiments showed that Zein/CMCS-EGCG_8:1 nanocomplex had inhibitory effect on both Gram-positive and Gram-negative bacteria,and the relative growth rates of the two spoilage bacteria were 79.31%and 55.54%after incubation of 12 h,respectively.The antioxidant activity test found that Zein/CMCS-EGCG_8:1 nanocomposites had strong ability to scavenge free radicals and showed good antioxidant activity.Zein/CMCS-EGCG_8:1 nanocomposites were used as coating preservative to study its preservation performance for mackerel.The total number of colonies and p H values of Zein/CMCS-EGCG group were lower than thoseof other treatment groups when stored up to 6 days,indicating that Zein/CMCS-EGCG nanocomplexes had effects of inhibiting microbial reproduction,delaying protein decomposition,and reducing the production of alkaline substances.The volatile salt-based nitrogen（TVB-N）and thiobarbituric acid（TBA）values of mackerel increased continuously during the storage,and the Zein/CMCS-EGCG group maintained a higher freshness compared with the control group.Thus,the coating treatment can delay the oxidative rancidity of fish,inhibit the softness of fish,and prolong the sensory quality of fish.（3）Zein/CMCS-CUR nanocomposites were prepared using zein and CMCS as wall materials.The encapsulation mechanism of Zein/CMCS complexes to CUR and the effect of Zein/CMCS-CUR nanocomposites on banana preservation was explored.When the ratio of Zein/CMCS to CUR was 10:1,the prepared Zein/CMCS-CUR nanocomposites had smaller particle size of 95.37 nm,ζ-potential values of-21.70 m V,and encapsulation rate of 96.63%and loading capacity of 4.55%.The Zein/CMCS-CUR nanocomposites were smooth and spherical,and distributed evenly.FTIR results showed that hydrogen bonding,electrostatic and hydrophobic interactions occurred between Zein,CUR,and CMCS.XRD and DSC results showed that CUR was successfully encapsulated in Zein/CMCS complex as an amorphous form.In vitro simulated digestion experiments showed that Zein/CMCS-CUR_10:1nanocomposite had a better sustained release effect on CUR than that of Zein-CUR.The fresh-keeping index of bananas during storage was determined.After 10 days of storage,the rot rate and weight loss rate of the control group were 89.01%and 19.53%,respectively,and those of the experimental group were 49.07%and 14.60%,respectively.The coating treatment can obviously slow down the rot rate of bananas,and the coating can better maintain the original appearance of the fruits.After 10 days of storage,the pulp hardnessof the treated group（1.12 N）was greater than that of the experimental group（0.76 N）,indicating that the Zein/CMCS-CUR nanocomposites could inhibit the softening of pulp and delay the ripening of bananas to a certain extent.The soluble solids（TSS）of banana fruits increased gradually duringstorage,while the titratable acid（TA）and vitamin C（V_C）decreased.Compared with the control group,coating treatment can keep the fruits with higher TA and V_C content,so that the nutrition of banana fruits can be better maintained.