A Study Of Antioxidative Activity Of Extracts From Leaves Of Psidium Guajava Linn

The long history of guava's use has led modern-day researchers to study guava extracts with its use as medicines goes back to early man. Guava has many different properties that contribute to the nutrition and the prevention of oxidative reactions that lead to many chronic diseases. In this study, our attention was much paid to polyphenolic compounds contained in Psidium guajava Linn leaf and their antioxidative capacity. Dried ground leaves of Psidium guajava L. (guava) were extracted by deionized water and aqueous ethyl alcohol 50% (1:10) ratio at 40 oC. The extracted liquid was partially concentrated by evaporation under reduced pressure to 10% of the original volume and the concentrate was freeze-dried. The total phenolic content in the extracts was determined spectrophotometrically according to Folin-Ciocalteu's phenol method and calculated as gallic acid equivalent (GAE). Remarkably high total phenolic content 575.3 ( 15.5 and 511.6 ( 6.2 mg of GAE/ g of dried weight material (for ethanol guava leaf extracts and water guava leaf extracts, respectively) were obtained. The optimization of the yield of the total polyphenolic by using other solvents such as methanol has increased the yield up to 10%. Phenolic compounds were separated by reversed phase high performance liquid chromatography (RP-HPLC) using formic acid and methanol (1:4) ratio. Compounds were identified by comparison with authentic standards. Six phenolic compounds with elution time profiles identical with the authentic phenolic compounds were found in guava leaf extracts. These are tannic, procatechuic, ferulic and caffeic acids and flavonoids- quercetin dihydrate and rutin trihydrate. These compounds were yielded in the range comprised between 0.3-48.6%. The antioxidant activity of guava leaf extracts, compared with that of ascorbic acid (natural antioxidant) was determined at ambient temperature by means of a 2,2-diphenyl-1-picrylhydryzyl (DPPH.) colorimetry with detection scheme at 515 nm. The activity was evaluated by the decrease in absorbance as the result of DPPH. color change from purple to yellow. The higher the sample concentration used, the stronger was the free radical-scavenging effect. The results showed that guava leaf had high antioxidant activity, which was comparable to that of ascorbic acid, green tea and black tea. On the other hand, the commercial guava leaf extracts and ethanol guava leaf extracts showed almost the same antioxidant power whereas water guava leaf extracts showed lower antioxidant activity. A strong association between antioxidant activity and total phenolic content was highly correlated with the following coefficients 0.8694 and 0.9643 respectively for water extracts and ethanol extracts. The parameters EC50 (efficient concentration) and the time needed to reach the steady state to EC50 concentration (TEC50) were studied and found to affect the antiradical capacity of the guava leaf extracts. The antiradical efficiency (AE) has been found to be a more adequate parameter for selecting antioxidants than the widely used EC50. Our study revealed that guava leaf extracts comprise effective potential source of natural antioxidants and can therefore be used to extend the shelf life of foodstuffs, to reduce wastage and nutritional losses by inhibiting and delaying oxidation. With its high antioxidative activity, it can be used as potential health benefits.