| Apple is the fruit of plants belonging to Rosaceae Malus, which is the first big fruit and is one of the agricultural products with competitive advantage in the international market in China. The main processing of it is pretreating. In the actual production life, the apple pomace tend to be thrown away or abandoned, resulting in a lot of waste. Apple polyphenols have properties in oxidation resistance, anticancer, liver protection and blood pressure control and so on. There have been some studies on apple polyphenols; the most focus in the free phenols of skin and flesh at home and abroad. But the bound phenols are rarely reported.In this paper, 70% ethanol aqueous solution was used to extract the free phenol from the high quality red Fuji apples. After that, the bound phenols in the residue were released by alkaline degradation, acid degradation, and enzymatic hydrolysis respectively. The high performance liquid chromatography(HPLC – DAD) method was applied to detect the types and contents of individual phenolic in free phenol and three kinds of bound phenols. The antioxidant capacity of polyphenols was evaluated by different antioxidant activity method,and antibacterial activity was studied as well. The obtained major results are as follows:(1) 70% ethanol aqueous solution with hot reflux extraction was applied for free phenols from apple pomace, and the content of free phenols was 4199.692 mg/kg DP. Under the condition of 40 degrees, the optimum alkaline degradation time was 4 h, and the NaOH concentration was 3 mol/L, and the optimum acid degradation time was 15 h, and the methanol / concentrated sulfuric acid concentration was 13: 1(v / v), and the optimum enzymatic degradation time was 20 h, and the tannase activity was 1000 U.(2) Hyperoside, chlorogenic acid, phlorizin, catechin, quercetin, phloretin and gallic acid were the major polyphenols of apple pomace. Catechin, quercetin, phloretin, gallic acid,protocatechuic acid and caffeic acid were mainly in bound form. The highest content of gallic acid, protocatechuic acid, caffeic acid and phloretin by enzymatic hydrolysis were 16.122μg/g, 18.574 μg/g, 13.030 μg/g and 69.934 μg/g respectively, and the highest content ofcatechin and quercetin by acid degradation were 148.909 μg/g and 66.396 μg/g respectively.Acid degradation and enzymatic hydrolysis are more suitable than alkaline hydrolysis for the extraction of bound phenols of apple pomace.(3) Free phenols had high values of reducing ability(1427.910 μmol/100 g DP) and ABTS radical scavenging ability(518.022 μmol/100 g DP). And the DPPH value was 40.991μmol/100 g DP. Bound phenols extracted by alkaline hydrolysis possessed the highest value of reducing ability(959.911 μmol TE/100 g DP), and the enzymatic and acid method values were 734.000 μmol TE/100 g DP and 841.94 μmol TE/100 g DP respectively. Bound phenols extracted by alkaline hydrolysis possessed the highest value of DPPH(82.900 μmol TE/100 g DP), which was 3 times higher than enzymatic hydrolysis and nearly 2 times higher than acid degradation. Bound phenols extracted by enzymatic hydrolysis had the highest value of ABTS(996.742 μmol TE/100 g DP). And alkaline and acid method values were 715.342 μmol TE/100 g DP and 681.801 μmol TE/100 g DP respectively.(4) Free phenols and bound phenols had certain protective effect on AAPH-induced and Cu2+/H2O2-induced bovine serum albumin(BSA), and the protective activity of bound phenols by acid degradation was stronger than enzymatic hydrolysis and alkaline hydrolysis.The protective activity increased with the increase of free phenols concentration at concentration of 75-1200 μg/mL.(5) When the sample concentration was 0.5 g/mL, free phenols exhibited the strong antibacterial activities on Salmonella with an inhibition zone diameter of 5.7 mm, but inhibition of Escherichia coli was not very obvious. Bound phenols by acid degradation had the highest antibacterial activities on Escherichia coli and Salmonella with an inhibition zone diameter of 7.7 mm and 3.7 mm, respectively. |
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