Studies On The Phenolics In Guava Leaf

Guava leaf has been used for centruries as a herb for the treatment of diarrhea, cough andother diseases. Phenolics have been thought to be the main active compounds in guava leafwhich contribute to these pharmaceutical characters. In this study, our attention was much paidto the extraction, separation, identification of the phenolic compounds in guava leaf as well astheir antioxidative and antimicrobial activity.Firstly, the extraction processes of polyphenolic compounds from dry guava leaf includingsolvent extraction, enzymatic assisted extraction were discussed. It was found that the extractionrecovery was greatly impressed by different solvents, solvent concentration, extractingtemperature, extracting time and particle size of guava leaf. After one single test and a L9(34)orthogonal test, the optimum extracting condition were obtained 50% acetone solution,extraction temperature 60℃, extraction time 1hr, 40 Mu and the total phenols was 143 mg GAE(gallic acid equivalent)/g.Secondly, phenolics in guava leaf extract were purified and then identified. Several resinsincluding polyamide, silica gel, DA201, NKA, NKA-9, D3520, D4020 were investigated bycomparing their absorption and desorption rate. It was found that DA201 was proper for crudepurificating phenols in guava leaf extract. After first being separated through DA201 column, thecollection extract was further purified through polyamide coloumn. By UV screening, fraction Aand B were obtained. Identification of flavonoids and flavonoid glycosides in A and B wascarried out by means of HPLC-UV and HPLC-MS analysis. By using HPLC-UV, two knownphenolics (gallic acid and quercetin) and five new reported ones (procatechuic acid, chlorogenicacid, caffeic acid, kaempferol, ferulic acid) were identified in guava leaf extract. By usingLC-MS, two flavonoids (quercetin and kaempferol) and four flavonoid glycosides (three knowncomponents, quercetin 3-O-alpha-L-arabinoside, quercetin 3-O-beta-D-glucoside, quercetin3-O-beta-D-galactoside, along with one novel compound, kaempferol-glycoside) and three otherunknown compounds have been identified in the fractions.Finally, the antioxidant activity of guava leaf extracts was determined at ambienttemperature by means of a 2, 2-diphenyl-1-picrylhydryzyl (DPPH.) colorimetry with detectionscheme at 515 nm. It's shown that guava leaf had high antioxidant activity, which wascomparable to that of ascorbic acid and quercetin (natural antioxidant). Crude acetone guava leafextract has higher antioxidative activity than water, alcoholic extract. What's more, antimicrobialactivity of the guave leaf extract was also studied, and the result was shown that it was effectivein inhibiting the growth of Escherichia coli, Staphylococcus aureus, Salmonella.