Study On Antioxidant Properties Of Polyphenolic Compounds Of Millet Bran And Their Application In Pickering Emulsion

Millet,commonly known as cereal,is an annual herb of the family Gramineae.Millet bran is produced during the initial processing of grain,accounting for about 1/10 of the grain mass.millet bran is rich in a variety of bioactive components,among which polyphenolic compounds have great potential for development as important antioxidants.In this paper,we optimized the extraction and process of polyphenolic compounds with millet bran as raw material,studied the components and antioxidant properties of millet bran polyphenolic compounds,and used them in the preparation of Pickering emulsions stabilized by zein-polyphenol complexes to provide theoretical guidance for the functional development and application of millet bran.The main research contents and results are as follows.1.Extraction,process optimization and separation and purification of polyphenolic compounds from millet bran.The extraction and process optimization of polyphenols were carried out by single-factor test combined with response surface design method.It was found that the optimal extraction conditions for polyphenols of millet bran were:ultrasonic power 250 W,ultrasonic time 50 min,ultrasonic temperature 40℃,ethanol volume fraction 70%,at which the extraction amount was(38.02±2.15)mg/g.Four kinds of macroporous adsorbent resins(AB-8,D101,X-5,HPD-100)were selected to study the adsorption and desorption performance of different adsorbent resins on millet bran The adsorption and desorption performance of different adsorbent resins on millet bran polyphenols were studied,and the optimal macroporous adsorbent resin was selected as AB-8,and the subsequent purification test was carried out,and the purified millet bran polyphenols were lyophilized as yellow-brown powder.2.Analysis of the fractions of polyphenolic compounds of millet bran and in vitro antioxidant performance study.The fractions of polyphenolic compounds of millet bran were characterized by characteristic reaction method,infrared spectroscopy and liquid mass spectrometry(HPLC-ESI-MS).The in vitro antioxidant properties of millet bran polyphenols were evaluated by DPPH,hydroxyl radical and ABTS+ methods.The characteristic reaction method indicated that the extracts contained polyphenols,and the infrared spectroscopy analysis showed that the extracts contained characteristic functional groups of polyphenols.HPLC-ESI-MS inferred that millet bran mainly contained 10 polyphenols including p-coumaric acid,resveratrol and mucoxanthin.The in vitro antioxidant results of millet bran polyphenols were:the scavenging effect of millet bran polyphenols on DPPH radicals,ABTS+ radicals and iron reduction ability were close to that of Vc in the test range,and the scavenging effect on hydroxyl radicals was weaker than that of Vc in the test range.the results indicated that the in vitro antioxidant performance of millet bran polyphenols was strong and had great potential for development as natural antioxidants.3.Nanoparticles of maize alcoholic protein(zein)complexed with millet bran polyphenols were prepared by the inverse solvent method,and the optimum complexed mass ratio of zein to polyphenols was optimized by determining the particle size and potential of the complexes.The effects of the introduction of polyphenols on the protein structure were investigated by Fourier transform infrared spectroscopy,fluorescence spectroscopy,three-phase contact angle(θ),X-ray diffraction(XRD),and scanning electron microscopy;the in vitro antioxidant properties of zein-polyphenol complexes were also studied.The experimental results showed that the complex has a more uniform particle size distribution and possesses a larger potential at a ratio of 1:0.6.Infrared spectra showed that zein formed hydrogen bonds with millet bran polyphenols after complexation;fluorescence spectra revealed that polyphenols in zein-polyphenol complexes had a burst effect on zein;contact angle results showed that the introduction of millet bran polyphenols improved the hydrophilicity of zein;XRD results showed that polyphenols existed in the complexes in amorphous forms;scanning electron microscopy revealed that the morphology was different before and after complexation,indicating that zein-XRD results showed that the polyphenols were present in amorphous form in the complex.The in vitro antioxidant results confirmed that the introduction of polyphenols could effectively improve the antioxidant properties of zein.4.The stability of Pickering emulsions prepared from zein-polyphenol complexes under different pH conditions was investigated.The results showed that the Pickering emulsions prepared from zein-polyphenol complexes had small particle size,sharp and narrow peaks at pH=9,indicating that the emulsions were more stable,and the emulsions were prepared at pH 9 in subsequent experiments.The emulsions prepared with zein-polyphenol complex nanoparticles showed higher oxidative stability and retarded the formation of primary and secondary oxides during storage to some extent.