The purposes of the present study were: to investigate the influence of oxygen, copper (Cu) concentration, buffer, pH and temperature on the rate of oxidation of ascorbic acid (AA) in sucrose solutions; and to define the physical and chemical roles of sucrose on AA stability. Investigations were conducted both in opened and closed systems. In the opened system the oxygen supply was manipulated by the surface to volume ratio of sample plus different speed of shaking. The parameter monitored was residual AA determined by titration with 2,6-dicholoro-phenolindophenol. In the closed system the oxygen uptake kinetics were studied at different temperature (26.5(DEGREES)C, 30(DEGREES)C, and 33(DEGREES)C) and pH levels (3.2, 4.25 and 5.0). Cupric ion activity of added copper in sucrose solutions was measured using a cupric electrode. / The results of the first system showed that if the viscosity effect could be eliminated, sucrose actually enhanced the oxidation of AA, especially in the Cu-catalyzed reactions. Cupric ion activity was greater in sucrose solutions than in the absence of sucrose. The destructive effect of sucrose on AA in Cu-catalyzed reactions was mainly due to the increased activity of Cu in sucrose solutions. The destructive effect of sucrose was lower in acetate buffered solutions than in unbuffered solutions at the same pH level (3.2) due to the Cu-complexing power of buffer salts. Observations from the second system generally agree with that of the first one. The pseudo-first order and second-order rate constants of AA oxidation in various solutions are presented and activation energies were calculated by Arrhenius equation. Both in Cu-catalyzed and non-catalyzed oxidation of AA, Approximately one mole of oxygen was used per mole of AA. / Source: Dissertation Abstracts International, Volume: 48-03, Section: B, page: 0609. / Thesis (Ph.D.)--The Florida State University, 1987.
| Identifer | oai:union.ndltd.org:fsu.edu/oai:fsu.digital.flvc.org:fsu_76090 |
| Contributors | HSIEH, YUN-HWA PEGGY., Florida State University |
| Source Sets | Florida State University |
| Detected Language | English |
| Type | Text |
| Format | 151 p. |
| Rights | On campus use only. |
| Relation | Dissertation Abstracts International |
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