Extraction,Purification And Application Of Tannins From Almond Skin

Armeniaca sibirica is also named as Siberian apricot,which belongs to Armeniaca genus of Rosaceae.It is a good variety of drought and cold resistance,which is produced in the north of China.The almond has a wide range of applications,it can be used for medicine,oil extraction and edible.However,a large number of almond skin are produced during almond processing.At present,almond skin has much lower utilization rate,and it is usually discarded as solid waste,which not only leads to serious waste of resources but also causes certain pollution to the environment.Tannins are the secondary metabolites of polyphenols with a molecular weight of 500-3000.It can precipitate with polysaccharides,proteins and alkaloids,and has anti-inflammatory,anti-cancer,anti-asthma and other pharmacological activities.Tannins have been widely used in leather,adhesive,beverage manufacturing,animal feed and other industries,and its market demand is increasing year by year.Through the preliminary test of our research group,we found that almond skin is rich in tannins.If the waste resource of almond skin can be developed and utilized,it will bring great economic and social benefits.Therefore,the tannins extraction process,purification process and tanning effect of the purified tannins from almond skin were studied.The main research contents are as follows:1.The extraction of tannins from almond skin was carried out by the method of water bath reflux.Taking the yield of tannins from almond skin as an index,the effects of four factors,i.e.solid to liquid ratio,extraction time,extraction temperature and ethanol volume fraction,on the extraction effect of tannins from almond skin were investigated.On the basis of single factor,response surface method was used to optimize the extraction process of tannins from almond skin.The results showed that the extraction process model of almond skin tannins was very significant.The optimal experimental conditions were as follows:the solid to liquid ratio was 1:22(g/mL),the extraction time was 89 min,the extraction temperature was 70?,the volume fraction of ethanol was 50%,and the yield of almond skin tannins was 2.13%.2.The static adsorption and desorption experiments were used to investigate the adsorption and desorption properties of five macroporous adsorption resins for almond tannins and the best macroporous adsorption resin was determined.The effects of loading concentration,loading flow rate,loading amount on adsorption performance,ethanol volume fraction,elution flow rate and eluent dosage on desorption performance were investigated.The results showed that the best purification conditions were as follows:HP-20 macroporous adsorption resin,tannins concentration of sample solution was 1.20 mg/mL,the loading flow rate was 1 BV/h,the loading amount was 4 BV,and the eluent was 70%ethanol solution,elution flow rate was 1.5 BV/h,eluent dosage was 3 BV.Under these conditions,the purity of almond skin tannins increased from 9.97%to 32.58%.After the second purification,the tannins purity reached 67.20%,which was increased by 6.74 times compared with that before purification.The results show that HP-20 macroporous adsorption resin was reliable and effective in the purification of almond skin tannins.3.The purified almond tannins were used to determine the index of the extract.The effect of blue wet leather retanning was compared between almond skin tannins and commercially available BA tannins and valonea tannins.After that,the almond skin tannins were combined with three different metal salts for tanning research.The results showed that the properties of almond skin tannins were excellent.The shrinkage temperature,thickening rate,and elongation at break of almond skin tannins retanned leather were higher than those of BA tannins and valonea tannins,but the tear strength and tensile strength were slightly lower than the other two.In the combination tanning process of almond tannins extract combined with metal salt,the optimal dosage of almond tannins extract was 16%,and the most suitable metal salt for tannins extract tanning was aluminum salt,the optimal dosage of aluminum salt was 8%.Under these conditions,the shrinkage temperature of leather was 108.3?,the thickening rate was 87.72%,the tensile strength was 10.80 N·mm-2,the tear strength was 36.72 N·mm-1,and the elongation at break was 86.86%.Compared with the combined tanning performance of commercial tanning extracts,the tensile strength of almond tannins extract and aluminum combined tanning leather was lower,the tear strength and elongation at break were higher,and the shrinkage temperature and thickening rate were equal.