Study On The Extraetion,Purification,Antioxidant And Antibacterial Activities Of Polyphenols From Peanut Shells

Polyphenols is a large class of plant secondary metabolites in plant. It is confirmed that polyphenols have various physiological properties and are helpful to human health. Peanuts (Arachis hypogaea L.), an annual herbaceous plant, are an important crop in China and many other countries. China ranks first in peanut production in the world and the annual production of peanut is more than14.5million tons with approximately4.5million tons of peanut shells producted. Peanut shells have many bioactive components with effects on preventing and curing diseases and are rich in polyphenols. In the background of that the disease prevention and cure functions of natural bioactive components are being increasing concerned, study on the peanut shells polyphenols will not only deepen people’understanding of the value of peanut shells, but also lay basis for the rational development and use of peanut shells.In this study, peanut shells as the research object, the extraction and purification methods, and the antioxidant and antibacterial activities in vitro of polyphenols in peanut shells had been researched. This is a relatively comprehensive and systematic study. The main experimental results in this paper were listed as follows, respectively.1. The Box-Behnken design (BBD) combined with response surface methodology (RSM) was employed to optimize three different extraction methods for total polyphenols from peanut shells. The results indicated that the highest extraction yield of polyphenols by heat reflux extraction (HRE) could arrive1.77%using69%ethanol as solvent and1:50solid to liquid ratio for3.0h at the temperature of93℃, which was higher than that by microwave-assisted enzymatic extraction (MAEE) and ultrasonic-assisted extraction (UAE).2. The separating and purifying purpose of the polyphenols from peanut shells was studied and compared with seven kinds of macroporous resins including D4020, X-5, S-8, D101, AB-8, NKA-9and NKA-Ⅱ. The results showed that the polar NKA-9macroporous resin was good sorbent of the polyphenols, its adsorption rate and desorption rate were69.47%and89.55%, respectively. The optimum conditions for separating and purifying the polyphenols by NKA-9resin were based on adsorption at35℃of sample solution with an initial concentration of1.0mg/mL at pH6.0, followed by desorption using90%(v/v) ethanol at pH6.0with a ratio of sample solution volume to resin weight of15:1(mL/g). After one run treatment with NKA-9resin, the purity of polyphenols could reach the height of62.73%, which is approximately4.15times higher than the previous15.57%, while the recovery of polyphenols could reach92.9%.3. The antioxidant activities of the purified polyphenols were evaluated in vitro by scavenging capability of DPPH free radical, superoxide anion free radical and hydroxyl free radical, total antioxidant capability, reducing power and β-carotene bleaching test. The results showed that the purified peanut shells polyphenols have significant antioxidant activities, which could be used as a source of potential antioxidant.4. Six pathogenic bacteria(Escherichia coli, Salmonella typhimurium, Shigella lexneri, Staphylococcus aureus, Listeria monocytogenes, Bacillus subtilis) were selected to in bacteriostasis experiments in vitro. The effect of inhibiting the bacteria was determined by the inhibition zone diameter, MIC and MBC test. The results showed that the purified polyphenols had the strong inhibition on Staphylococcus aureus with a MIC and MBC of0.125mg/mL,4mg/mL, respectively. It had significant inhibition of Listeria monocytogenes, Salmonella typhimurium, and Shigella lexneri, for all MIC and MBC were0.125mg/mL and8mg/mL, respectively. However, the effect of inhibiting Escherichia coli and Bacillus subtilis were not obvious and both MIC and MBC were0.25mg/mL and8mg/mL, respectively. The peanut shells polyphenols were potential preservative which could inhibit some microorganisms.