| Papaya(Carica papaya Linn.)is rich in nutrients,it not only has a sweet taste but also contains a large number of biologically active compounds,which is popular among consumers.However,the papaya peel,which is a by-product of the papaya processing industry,is often disposed as waste,which not only causes huge waste of resources but also brings environmental pollution.At present,papaya peel is mainly used for the production of animal feed or as a source of pectin,protease,etc.However,a few researches have been conducted on how to use papaya peel for deep processing and utilization.In particular,the development of antioxidant soluble dietary fiber(ASDF)in papaya peel has not been reported in the literature.Therefore,in this paper,ASDF were extracted from papaya peel by different extract methods(acid,alkali,conventional and ultrasonic assisted extraction).On this basis,the main nutritional components,structural characterization,physicochemical properties and antioxidant activity of ASDF were compared.The main research contents and conclusions are as follows:(1)The optimum conditions for acid extraction of papaya peel ASDF by single factor and orthogonal experiments:the temperature was 80 ?,the pH value was 1,the extraction time was 90 min,the ratio of solid to liquid was 1:25.The optimum conditions for alkaline extraction of papaya peel ASDF were as follows:the temperature was 75 ?,the NaOH mass fraction was 1.4%,the time was 80 min,the solid-liquid ratio was 1:20.The optimum conditions of ultrasound-assisted extraction of papaya peel ASDF by single factor and response surface analysis:the extraction time was 31 min,the ultrasonic power was 175 W,the ratio of liquid to material was 16.6:1.The yield of ASDF obtained by the acid test was 20.7%,alkaline ASDF yield was 9.17%,ultrasound ASDF was 36.99%.(2)The main nutritional components of papaya peel ASDF were determined using the national standard method.The results showed that the contents of polysaccharide in papaya peel ASDF were higher than 200 mg/g and the protein contents were less than 18 g/100g.And the four kinds of ASDF contain 18 amino acids and 15 minerals.(3)Fourier transform infrared spectroscopy(FTIR),scanning electron microscopy(SEM),X-ray diffraction(XRD),thermodynamic properties(TGA)and high performance liquid chromatography(HPLC)were used to characterize the structure of ASDF and determine its monosaccharide composition.The results showed that ASDF obtained by four different extraction methods belonged to heteropolysaccharides and the main components were all neutral sugars,namely glucose(Glc)and arabinose(Ara).Through structural characterization,it was found that the typical structures of polysaccharide compounds and cellulose I crystal structures existed in all four ASDFs.The patterns of several ASDFs were similar.It shows that ultrasound-assisted and acid-base coupling does not change the crystal type of ASDF but can destroy the crystal structure of ASDF to varying degrees.Compared with conventional ASDF,the initial degradation temperatures of the other three ASDFs are higher,which indicates that the other three ASDFs have higher thermal stability.(4)The physical properties and of papaya peel ASDF were studied by water-and oil-holding capacities,swelling,combined hydraulic and emulsification.The results showed that ultrasonic ASDF,acid ASDF and alkali ASDF were superior to conventional ASDF in terms of water-and oil-holding capacities,swelling,combined hydraulic.Analyzed and compared the emulsification properties of papaya peel ASDF.The results showed that the interfacial tension of alkaline ASDF(7.199±0.01 mN/m)was much lower than that of sugar beet pectin and gum arabic,which indicated the emulsification performance of alkaline ASDF was the best.The average particle size of sugar beet pectin and alkali ASDF was much smaller than that of gum arabic,and the light absorption ratio(SRI)was much higher than that of gum arabic,which indicated that the stability of alkaline ASDF is better than that of gum arabic.At the same time,the optical microscope observation diagram and the latex analysis showed that the alkali ASDF emulsion particles was larger in size and evenly distributed.It showed that alkaline ASDF was good in storage stability.(5)Using oxygen radical absorbance capacity(ORAC),ABTS,DPPH and reducing power method were used to evaluate the antioxidant activity of ASDF in papaya peel.HPLC-MS was used to determine the composition of polyphenols in papaya peel.The experimental results showed that there was no significant correlation between antioxidant capacity and total phenol content in papaya peel ASDF,and the polyphenols contained in all four ASDFs was catechins.Among them,the acid ASDF had the best resilience and scavenging ability of DPPH free radicals,while the alkaline ASDF had better scavenging ability of ABTS free radicals and total antioxidant capacity. |
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