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Fruits of two jujube (Ziziphus jujuba Mill.) cultivars were collected at four stages of ripening and analyzed in terms of chemical compounds. The cultivars were grown under the climatic conditions of the Sub-Carpathian area Ramnicu-Valcea in Romania (45°6′17″N, 24°22′32″E). Total phenols content, total flavonoids content, organic acids from jujube fruits and related antioxidant activities were investigated during the ripening stages. The antioxidant activity of alcoholic extracts was investigated by the 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging method. Total phenolic content was determined by using the Folin-Ciocalteu assay, while determination of flavonoids was done by aluminium nitrate colorimetric method, and organic acids were separated by reversed phase chromatography. The results obtained have indicated significant differences (p < 0.05) found in bioactive compounds and antioxidant activity, depending on cultivars and ripening stage. Total phenolic content ranged from 1634.44 to 472.38 mg GAE/100g in methanolic extracts of the two varieties studied, while total flavonoids content ranged from 19.9 to 48.5 mg QE/100 g. As regards the influence of ripening stage, the results show that the highest antioxidant activity was recorded in the stage of white maturity. The impact of maturity stage was significant on organic acid distribution of jujube extracts, and ascorbic acid is the major organic acid found in jujube fruits, followed by malic acid and lactic acid. Jujube fruits are rich in bioactive compounds and can be a complement in human's healthy eating.

Papaya fruits (Carica papaya L.) are valuable both as food, including concentrates and mixed beverages and in traditional medicine. The goal of the study was to evaluate the antioxidant activity of various parts of unripe and ripe papaya fruit from the DPPH· kinetics point of view. Peel, pulp, seed, and seed-pulp of unripe and ripe papaya fruits (¼ and >¾ level of ripening) were extracted with ethanol and monitored at 517 nm in the presence of DPPH·. The radical scavenging capacity (RSC) at various time ranges and DPPH· reaction rates for specific time intervals were determined. The highest RSC values were obtained for papaya pulp extracts, consistently higher for the ripe samples in comparison with the unripe ones (86.4% and 41.3%). The DPPH· rates significantly differ for the unripe and ripe papaya extracts, especially for the first time range. They are more than double for the ripe papaya. These values were 2.70, 4.00, 3.25, 2.75 μM/s for the peel, pulp, seed, seed-pulp extracts from the ripe papaya and only 1.00, 1.65, 1.40, 1.80 μM/s for the unripe samples. DPPH· kinetic approach can be useful for a fast and simple evaluation of the overall antioxidant properties of fruit extracts.

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