| Summary: | 碩士 === 靜宜大學 === 食品營養研究所 === 95 === The peels, pulps, seeds and latex of papaya (Carica papaya var. Tainung No.2) fruits were used as materials in this study. After lyophilization, these four portions were extracted with water for antioxidant capacity investigation. The antioxidant capacities included reducing power, ferrous ion chelating power, α,α-diphenyl-β-picrylhydrazyl (DPPH) radical scavenging activity, 2’-azino-bis (3-ethylbenzthiazoline-6-sulfonic acid) (ABTS) radical scavenging activity and superoxide anion radical scavenging activity. The results showed that the antioxidative activity increased with increasing papaya water extract concentration. When the antioxidative capacity was expressed as the reducing rate constant, antioxidative activity constant or the half-inhibition concentration (IC50), the water extract of mature papaya seeds had the highest reducing power (reducing rate constant = 5.20 ± 0.14 mL/mg) and DPPH radical scavenging activity (IC50 = 182.94 ± 14.31μg/mL), while the water extract of immature papaya seeds had the highest ABTS radical scavenging activity (IC50 = 22.92 ± 1.22μg/mL) and superoxide anion radical scavenging activity (IC50 = 131.21 ± 6.86μg/mL). Incubation of the water extract of papaya seeds at 100℃ for 30 min revealed that ABTS radical scavenging capacity was almost retained, but superoxide anion radical scavenging capacity was completely lost. Therefore, the ABTS free radical scavenging activity was related to thermostable substances, whereas the superoxide anion radical scavenging activity could be attributed to thermolabile substances. There was no detectable superoxide dismutase (SOD) activity in the water extract of papaya seeds, as analyzed by PhastGel isoelectrofocusing electrophoresis and SOD activity staining. Consequently, the superoxide anion scavenging activity was linked to SOD-like substances. From the above results, the papaya seeds consisted of powerful antioxidant substances, and had high potential applications for natural antioxidant preparation.
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