Study On Preparation And Emulsifying Properties Of Citrus Dietary Fiber

Citrus peel,a by-product of citrus processing industry,is a source of high-quality dietary fiber.Citrus dietary fiber has excellent physical and chemical properties and physiological functions.Most of the citrus peels in China have not been effectively used,so it is of great significance to explore a method to produce high-quality dietary fiber from citrus peels.In this study,pectin-rich dietary fiber AHP-CF and H-CF was prepared from citurs peel by alkaline hydrogen peroxide treatment and homogenization treatment.Its composition,structure,physicochemical properties and micromorphology were systematically analyzed and compared with citrus peel and a commercial citrus fiber FS.Besides,the application of AHP-CF and H-CF in emulsion was further studied.The ability and mechanism of stabilizing emulsion under different conditions were analyzed,which provided theoretical basis for the application of AHP-CF and H-CF in emulsion.The results are as follows:(1)Through single factor experiment,the optimal extraction conditions of AHP-CF were as follows:Under the conditions of reaction time of 3 h,reaction temperature of 50?,H₂O₂volume fraction of 1.0%,liquid to solid ratio of 1:20 and 1mol/L Na OH solution dosage of 2m L,the yield of AHP-CF was 67.79%and the water holding capacity was 21.32 g/g.The optimal extraction conditions of H-CF were as follows:shear time of 9 min,liquid-solid ratio of 1:25,shear speed of 6000 r/min and p H 7.0.Under these conditions,the yield of H-CF was59.81%,water holding capacity was 18.26 g/g,and swelling capacity was 24.65 m L/g.The results indicated that the citrus fiber with higher yield and better hydration ability could be obtained by using these two methods.(2)The results of composition analysis and physicochemical properties determination showed that both alkaline hydrogen peroxide treatment and homogenization treatment could prepare citrus fibers which are rich in pectin and increase the content of TDF,SDF and hemicellulose.Both treatments could significantly improve the physical properties of citrus fibers.AHP-CF has the best water holding capacity,water swelling capacity and cation exchange capacity,which may be related to its larger surface area and more suitable ratio between SDF and IDF.The two treatments had little effect on oil holding capacity,but significantly increased the absolute value of Zeta potential of citrus fiber.(3)The structure and microstructure of AHP-CF and H-CF were analyzed by Fourier transform infrared spectroscopy,thermogravimetric analysis,X-ray diffraction,scanning electron microscopy.The results showed that the two treatments did not change the basic chemical structure of citrus fiber,but there were differences in the infrared absorption characteristic bands.The crystallinity of orange peel powder,AHP-CF,H-CF and FS were33.35,35.63,29.50 and 28.29%,respectively.In addition,AHP-CF had the best thermal stability,followed by orange peel powder,H-CF and Fiberstar.AHP-CF showed more folds,while H-CF had more holes and cracks on the surface.FS was stripe like and more regular than other citrus fibers.The two treatments exposed the hydrogen bonds in the cellulose and promoted the connection between pectin and cellulose microfibers through hydrogen bonds,forming a more stable network structure and improving the physical properties of citrus fibers.(4)AHP-CF and H-CF were used to construct oil-in-water emulsion with good stability.The average particle size,Zeta potential and storage stability of the emulsion were used to analyze the ability of AHP-CF and H-CF to stabilize the emulsion under different conditions.The results were compared with that of the orange peel powder and FS.It was found that the emulsion prepared by high-speed shear had good stability under the conditions of fiber content higher than 3.0%,oil mass fraction of 30%and p H 4.0.When the citrus fiber content was more than 2.0%and the homogenization pressure was 40 MPa,the emulsion prepared by high pressure homogenization had good stability.The stability of the emulsion increased with the increase of the content of citrus fiber and the decrease of the mass fraction of oil.The stability of the emulsion was low under the condition of strong acidity,and increasing the homogenization pressure was beneficial to improve the stability of the emulsion.The rheological properties of the emulsions stabilized by citrus fiber showed that they had the properties of gel,and the emulsion stabilized by AHP-CF,H-CF and FS had great thermal stability and freezing recovery.The three citrus fiber stabilized emulsion mainly by forming gel network structure and increasing steric hindrance.