Separation And Purification Of Polyphenols From Walnut Seed Coat And Preparation Of Microcapsules

Walnut is an important woody grain and oil tree in China,accounting for more than 50%of the woody oil tree planting area.Walnut kernel has high nutritional value,and as the by-product of walnut kernel processing,the walnut seed coat is rich in a variety of polyphenols.Polyphenol are having many functions,including anti-oxidation,anti-cancer,lowering blood lipid and so on.In actual production,the walnut seed coat is mostly discarded after hot alkali treatment and high pressure water washing.The walnut seed coat obtained by the dry separation is used as raw material,and adopt suitable for industrialized production technology to extraction polyphenols from the walnut seed coat and improve the stability of polyphenols.They are of great significance to the development of polyphenols products in walnut seed coat and the value of utilization of walnut processing by-products.Therefore,the study aimed to base on the dry separation of walnut seed coat as raw material,and research on the extraction and purification process of polyphenols in walnut seed coat,and analyze the composition of polyphenols.Next,the preparation process of polyphenol microcapsules in walnut seed coat was discussed,and the structure characteristics,polyphenol composition,antioxidant activity and stability of microcapsule are studied.The main results are as follows:1.Optimization of the optimum extraction and purification process parameters for polyphenols from walnut seed coat.Using walnut seed coat obtained by dry method as raw material and polyphenol extraction amount as an index,the extraction process of polyphenols was optimized by response surface methodology.The results showed that the optimal parameters were as follows:ratio of material to solvent for 1:74(g/mL),ultrasonic temperature 40℃,ultrasonic time 50 min,pH 5.4,and the content of polyphenols from walnut seed coat was(111.76±2.32)mg/g.The effects of ultrafiltration and macroporous resin purification methods on the purity of polyphenols were compared.The macroporous resin static and dynamic test were used to purify the polyphenols of walnut kernel pellicle.The adsorption/desorption test conditions were as flow:polyphenol concentration 1.5 mg/mL and eluent ethanol concentration 60%;The adsorption/desorption test parameters were:sample flow rate 1.0 mL/min,eluent volume 5 BV,and the elution rate of 1.0 mL/min.Under these conditions,the purity of the polyphenols obtained increased from 33.63%to 77.53%.but the purity of the polyphenols only increased to 54.85%after ultrafiltration.Taking purity as the evaluation index,the resin was selected to purify polyphenols in this experiment.2.Study on the composition change of polyphenols before and after resin purification and the antioxidant activity of polyphenols after purification.The composition and content of phenolic before and after purification was analyzed by liquid chromatography-mass spectrometry(LC-MS),and ten compounds were identified.The main compounds polyphenols before purification were gallic acid(136.96 mg/100g BP).gentiolic acid(3.19 mg/100g BP).protocatechuic acid(2.81 mg/100g BP).chlorogenic acid,(2.57 mg/100g BP),ferulic acid(1.07 mg/100g BP),vanillic acid(0.85 mg/100g BP).The polyphenol components with higher polyphenol content after purification,and the results were as follow:gallic acid,28.99 mg/100g AP;vanillic acid,2.88 mg/100g AP;ferulic acid,2.55 mg/100g AP;chlorogenic acid,1.44 mg/100g AP;p-Coumaric acid,1.13 mg/100g AP;protocatechuic acid,0.95 mg/100g AP;gentisic acid,0.85 mg/100g AP.The purified walnut kernel pellicle polyphenols have higher DPPH radical scavenging capacity,and the IC50 was 7.66 μg/mL.The hydroxyl radical(·OH)scavenging capacity of walnut kernel pellicle polyphenols was significantly lower than Vc,and the IC50 values were 371.17 μg/mL for walnut kernel pellicle polyphenols and 166.95 μg/mL for Vc.3.Study on the microencapsulation of polyphenols in walnut inner seed coat and analysis of the characteristics of microcapsules.Using the purified polyphenol concentrate,and maltodextrin and gum Arabic,as the wall material and core material respectively.The spray drying method was used to optimize the process parameters of microcapsules through single factor and orthogonal experiments.The orthogonal optimization of process parameters are:the complex wall material concentration 5%,wall material ratio 4:1(g/g),core to wall ratio 1:13(g/g).and the embedding rate of microcapsules reaches 90.17%.The microcapsules displayed a spherical shape,partially recessed,and no cracks,typical of spray-dried products.The Fourier Transform Infrared Spectroscopy(FITR)experiments proved that the polyphenol was embeded.The phenols in the microcapsules were detected by LC-MS.and the results showed that the higher polyphenol content was gallic acid(4.26 mg/100g PM),vanillic acid(0.86 mg/100g PM).chlorogenic acid(0.41 mg/100g PM),and gentisic acid(0.38 mg/100g PM),and caffeic acid and erucic acid could not be detected.The microcapsule had scavenging ability to DPPH· and OH·,with IC50 values of 84.16 μg/mL,4.6 mg/mL,which indicated that the microcapsules have good DPPH scavenging ability.4.The thermal stability of microencapsulated polyphenols and the changes in their antioxidant activity in solution.The retention rate and antioxidant activity changes of microcapsules under different heating temperature and heating time conditions were measured.The results showed that with the increase of temperature,the retention rate of microencapsulated polyphenols and DPPH radical scavenging rate decreased slowly compared with unembedded polyphenols.At heating temperature is 100℃,the microcapsules showed that an increment of the retention rate for 8.86%and the scavenging rate of DPPH for 17.31%;with the extension of heating time,compared with unembedded polyphenols,the retention rate of microcapsules and the scavenging rate of DPPH decreased slowly,when the heating time was 7 h,the retention rate of the microcapsules and the scavenging rate of DPPH· were increased by 48.17%and 36.46%,respectively.The results show that microcapsules can improve the thermal stability of polyphenols.