The effect of commonly used techniques and solvents in the antioxidant activities of pink-flesh guava fruit were studied. The extraction techniques compared were homogenization, shaking, sonication, magnetic stirring, and maceration for 1, 2, and 3 days. The solvent systems used were methanol, ethanol, and acetone at three different concentrations (50%, 70%, and 100%) and with 100% distilled water. The antioxidant activity of the fruit was evaluated using Folin-Ciocalteu index, ferric-reducing antioxidant power assay, and 1,1-diphenyl-2-picrylhydrazyl free radical-scavenging capacity. Ultrasonic and homogenization were the best techniques to extract the antioxidant from guava fruit. Homogenization technique was found to be the most convenient exhaustive and time-saving extraction technique. Results showed that the extracting solvent significantly (P<0.05) altered the antioxidant property estimations of pink-flesh guava fruit. Pure solvents were inefficient extraction media for antioxidant. Enhanced extraction yields were obtained from solvent containing higher water concentrations and 50% acetone is a recommended solvent for extracting antioxidants compounds from pink-flesh guava fruit. High correlations between phenolic compositions and antioxidant activities of pinkflesh guava extracts were observed. High levels of antioxidant activities were detected in pink-flesh guava, indicating that the fruit may serve as an excellent dietary source of natural antioxidants.

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Root and litter biomass on carbon dynamics and its effect on other soil properties information are needed to explore in Malaysia due to rapid change of land use.Objective of this study was to determine the effect of root and litter biomass of forest and oil palmunder different soil depths on soil organic carbon and its stock,soil available water, bulk density, pH, electrical conductivity. In this regard, twoland use systems (forest and oil palm) were selected for the study. In each land use we collected litter biomass, root and soil samples from four different locations. For the characterization of soil and root three core samples were taken (0-5, 5-15, 15-30, 30-60 and 60-90 cm)from each location, and then combined and air-dried.Soil samples were air-dried for 2 weeks at room temperature, grounded and sieved (<2 mm). Soil available water content, soil organic carbon, pH and EC were determined by standard methods.Results revealed that maximum organic matter (6.75%) was found in forest soil at 0-5 cm depth of soil. SOC content was decreased with the increase of soil depth in forest. On average soil organic carbon stock was significantly higher under oil palm (3.09 t ha -1 ) than forest (2.28 t ha -1 ) up to 90 cm depth of soil. Available water content was higher in surface soil (0-15 cm) than subsurface soil due to mechanization of oil palm plantation area. Soil reaction (pH) was higher in forest soil than oil palm plantation soil.Litter biomass or droppings performed δ 13 C dilution in surface soilbut root system enriched δ 13 C in subsurface soil. 13 C isotope tracer technique confirmed that root and litter biomass of forest and oil palm plantation can greatly influence on vertical distribution of organic carbon when soils show gradual increase of δ 13 C values with depth.

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