Studies On Chemical Composition And Antioxygenation Of Extract From Walnut Shell With Subcritical Water Treatment

Walnut shell contains a number of phenolic compounds and quinone compounds,including lignin, cellulose and hemicellulose. However as an agricultural waste, its utilization is limited. Currently, conventional extraction for walnut shell is organic solvent extacton, but there are some disadvantages, such as low extraction rate, long time of extraction, residues and pollution. While subcritical water extraction is a green, energy-saving, extraction-efficient, and time saving technology. In this study, subcritical water extraction technology was chosen to extract the walnut shell and the effect of material-solvent ratio and temperature on the components extracted by subcritical water extraction technology and the effect of temperature on antioxidant capacity of extract was studied.By studying the effect of different material-solvent ratio(w/v) that is 1%, 2%, 3% on the chemical ingredients of extract from walnut shell with subcritical water treatment, the results showed dry matter yield, total sugar yield and protein yield of extract were at peak in material-solvent ratio of 2%. While the material-solvent ratio increasing, total phenol yield of extract continuously decreased. Based on the above results, material-solvent ratio of 2% was chosen as the fellow-up experimental parameter.Then a variety of ingredients yield of extract from walnut shell with subcritical water treatment in different temperature from 120℃ to 220℃ were investigated. With the extraction temperature increased, the total sugar and protein yield kept increasing, until the temperature reached at 200℃, and the yield of sugar and protein reached the maximum. After the temperature exceeded 200℃, the yield of sugar and protein declined.With the increasing temperature, the 5-HMF yield ascended continuously, while p H value decreased; the component contents of those molecular weight were less than 100 k Da continuously increase, but the component contents of those molecular weight were more than 100 k Da decreased. Compared with the organic solvent extraction, total sugars and protein yield of subcritical water extracts in each temperature were higher than those of organic solvent extract. The total phenol yield of organic solvent extract was less than those in subcritical water extracts when the extraction temperture exceeded 180℃.Antioxidant capacity of extracts were studied and the results showed both antioxidant capacity of subcritical water extracts and the concentration of phenolic compounds were increased with the extraction temperature rising. And some chemical components of subcritical water extracts were found such as phenol 2,4-bis(1,1-dimethylethyl),phenol,2,2’-methylene-bis(1,1-dimethylethyl)-4-methyl,phenol,2-(1, 1-dimethylethyl)-(1-methyl-1-phenylethyl),phenol,4,4’-bis(methythylethyldene),phen-ol by GC-MS method.Subcritical water extraction technology can be applied on the extraction of effective components of walnut shell. Compared with the organic solvent extraction technology, besides advantages such as high efficiency, and environmenttal friendiness, subcritical water extraction technology can extract main effective components of walnut shell than organic solvent extraction. The extracts have a variety of antioxidants and antioxidant capacity.