Graduate Thesis Or Dissertation

The role of ascorbic acid on discoloration of strawberry juice and concentrate

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  • The purpose of this.investigation was to determine how enzymes and oxygen influence the role ascorbic acid has on pigment degradation and browning during storage for strawberry juice and concentrate. The ascorbic and dehydroascorbic acid content of blanched and unblanched, nitrogen-treated and air-exposed samples of strawberry juice and concentrate was measured periodically during storage. The ascorbic acid retention was higher for the blanched strawberry juice and concentrate. The nitrogen treatment retarded the degradation of ascorbic acid. There appeared to be a relationship between the degradation of ascorbic acid and the degradation of anthocyanin and the development of browning. Due to the complexity of the natural strawberry juice and the multiple possible pathways leading to browning, a model system was designed to determine how color deterioration during storage is affected by the interaction of ascorbic acid, catechin (flavanol), and anthocyanin pigment under either anaerobic or oxygenated environment. Ascorbic acid treatment showed a statistically significant effect on such parameters as anthocyanin content, browning index, level of polymeric color, color density, Hunter "a" value, and Hunter "L" value, suggesting that ascorbic acid can bleach the anthocyanin pigment and also contribute to browning, either directly or indirectly. Two different patterns were observed in ascorbic acid browning for the model system. When oxygen was present, an induction period proceeded the development of browning, suggesting that the oxidative degradation product of ascorbic acid is responsible for much of the browning. In the absence of oxygen, however, this induction period did not occur. A gel filtration technique for the measurement of polymeric color in strawberry juice was also developed in this study. The polymeric pigment formed during storage was resistant to bisulfite bleaching.
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