Studies On Green Extraction Of Polyphenols From Processed Areca Nut Seeds And Characterization Of The Extraction/chitosan

Processed areca nut seed is a byproduct in the manufacturing of chewable areca nut products.At present,about 35 000 tons of processed areca nut seed are produced annually,and most of them are directly discarded or even incinerated,causing a waste of resources and environmental pollution.On the other hand,common plastic packaging of fruits and vegetables has many disadvantages of high temperature resistance/relatively expensive cost/release of toxic and harmful substances,especially difficulty in degradation.With the development of technology and need for healthy living,the use of plastic packaging is gradually replaced by biodegradable materials.Chitosan has excellent performance in film-forming,degradation and safety.The research of chitosan films has been a noticeable focus for research and utilization.Natural plant polyphenols can be grafted with chitosan to improve the film characterization.In this study,seventeen deep eutectic solvents(DES)were used to extract polyphenols from processed areca nut seed.Total polyphenol contents and polyphenol composition were determined in the extractions to evaluate the extraction efficiency of different DES.All the polyphenol extractions containing DES solvents were mixed with chitosan solution to prepare composite films.A polyphenols extraction was chosen according to the film characterization for follow-up research.The best dosage of polyphenol extraction was optimized according to their physical and chemical properties.A scanning electron microscope(SEM)and a fourier infrared spectrometer(FTIR)were used to investigate the interior structure of the films.Free radical scavenging capacities and the preservative properties on composite films fresh-cut apples were explored preliminarily.Specific contents and conclusions of this study are listed following.(1)Three hydrogen bond acceptors(choline chloride,betaine and proline)and eight hydrogen bond donors(such as glycerol,citric acid,glucose and urea)were used to prepare DES.A total of seventeen DESs were successfully synthesized.(2)Seventeen DES were used to extract polyphenols from processed areca nut seed,respectively.Total contents of polyphenols(TPC),flavonoids(TFC)and anthocyanidins(TAC)were determined.The results indicated that TPC,TFC and TAC in the extractions by DES(DES-ANE)were significantly higher than those in the extraction by water and 75%ethanol solution(p<0.05).Eight of the DES-ANEs contained more of the three components than the 75%ethanol solution extraction,and six DES-ANEs contained more of polyphenols and anthocyanidins than the 75%ethanol solution extraction.The polyphenols extraction efficiency of deep eutectic solvents was much higher than those of water and 75%ethanol solution.According to the quantitative analysis of polyphenols in DES-ANE,it was found that there were significant differences in the contents of different polyphenol components in different DES-ANEs.(3)Seventeen DES-ANEs were added to chitosan solution to prepare DES-ANE/chitosan composite films(CS-DES-ANE).Five parameters including appearance color,thickness,water vapor transmission rate,tensile strength and elongation at break were used to evaluate the characterization of the composite films.Results showed that addition of different DES-ANE could alter appearance color and thickness of the laminated films.CS-DES5-ANE showed the strongest tensile strength and elongation at break,which were significantly different from the rest of the groups(p<0.05),and its water vapor transmission rate was also lower than most of other films.Comprehensively considered,DES5-ANE was selected for the follow-up experiments.(4)Additive amounts of DES5-ANE were optimized in this section.2.5%,5.0%,10%,20%and 30%of DES5-ANE were added into chitosan solution to prepare composite films,respectively.Differences of the films in appearance,color,thickness,microstructure,transparency,water vapor transmission rate,mechanical properties and antioxidant activities were evaluated.According to the SEM photographs,we found that the addition of DES5-ANE could significantly improve roughness of the composite films.Comparing the FTIR spectra of each composite films,DES5-ANE also could alter the absorbance.The visibal color of composite films with more CS-DES5-ANE was significantly different compared with the films of less addition.Among the tested five composite films,the films added with 20%DES5-ANE had the best tensile strength,elongation at break and scavenging ability of ABTS~+and DPPH radicals.Although its water vapor barrier value was not better comparing to the films adding less DES5-ANE,it was also significantly lower than that of the CS film(p<0.05).In the experiment on the preservation effect of fresh-cut apples,the CS-DES5-ANE composite film acted better on reducing water loss,maintaining soluble solid content and inhibiting the formation of malondialdehyde than the CS-DES one(p<0.05).In conclusion,DES was a good alternative solvent to extract polyphenols from processed areca nut seed.The phenolic extraction coulud be used to improve the characterization of chitosan film and the composite product had a potential complication in fruit preservation.