Effects of drying conditions on drying kinetics, product quality and retention of carpaine in papaya leaves (Carica papaya Linn.)

Yap, Jing Ying (2022) Effects of drying conditions on drying kinetics, product quality and retention of carpaine in papaya leaves (Carica papaya Linn.). PhD thesis, University of Nottingham.

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Dengue fever causes mortality and morbidity worldwide which is a major concern to governments and the World Health Organization (WHO). It was reported that carpaine, the major active compound extracted from papaya leaves, contributes to the anti-thrombocytopenic activity. Hence, carpaine plays an important role in treating dengue patients by raising the platelet count in the patients’ blood. However, carpaine in papaya leaves could degrade easily when exposed to heat and sunlight during processing and storage. There is no literature reporting on the processing aspects (e.g., preparation, drying and storage) of papaya leaves and the leaves extract to date. This could possibly be due to papaya leaves have no commercial value and the leaves are usually treated as waste. Therefore, this thesis will focus on the effects of drying conditions on drying kinetics, product quality and retention of carpaine in papaya leaves.

Extraction and quantification of carpaine from different parts of papaya leaves (young and old) and stalks were carried out. Pale yellow carpaine crystalline powders were successfully extracted and confirmed to have high purity (>95%) by 1H and 13C NMR analyses. Unblended freeze dried samples from young papaya leaves extract showed the highest amount of carpaine, total polyphenol content and DPPH free radical scavenging activities. It is thus recommended to use young leaves to extract carpaine for future drug development in dengue treatment.

The drying kinetics and drying rates of papaya leaves using different drying techniques such as hot air drying (60°C, 70°C and 80°C), shade drying and freeze drying were investigated. Typical exponential falling trends were observed, which can be best explained by Fick’s second law of diffusion. The fastest drying rate was observed at high temperature (80°C), followed by at lower temperatures (hot air drying at 60°C and 70°C, and shade drying at averagely 27°C). By using the general solution of Fick’s second law and Arrhenius equation, the effective diffusivities were determined in the range of 2.09 × 10-12 m2/s to 2.18 × 10-12 m2/s, and the activation energy required to initiate moisture diffusion was determined at 2.11 kJ/mol in hot air drying within 60°C to 80°C.

Besides, the effects of drying techniques on carpaine retention and antioxidant properties of papaya leaves were investigated to develop a preparation protocol that produces papaya leaves extract with high carpaine retention. Hot air drying at 60°C, 70°C and 80°C are not recommended for the preservation of carpaine in papaya leaves as carpaine is a heat sensitive bioactive compound. Results showed that the carpaine retention in hot air dried samples were significantly lower (p<0.05) than freeze dried and shade dried samples. It is recommended to use freeze drying to remove the moisture in the papaya leaves as it showed the highest retention of carpaine and antioxidant activities.

The knowledge on the stability of carpaine during storage is vital as the raw materials used would be mainly in dried form which will be stored in bulk quantity during commercial operation. Studies show that the Weibull model produced the best graphical fit in describing the degradation kinetics of carpaine in all dried samples (freeze dried samples, hot air dried samples at 60°C and 70°C, and shade dried samples), except for hot air dried samples at 80°C, which could be best described by the first order model. Freeze dried samples showed the highest half-life (51.20 months) among all the dried samples. It is thus recommended to select freeze dried samples for extended storage purpose as it is more stable as indicated by the lowest rate constant and the highest half-life.

Item Type: Thesis (University of Nottingham only) (PhD)
Supervisors: Hii, Ching Lik
Ong, Sze Pheng
Keywords: Carica papaya Linn., carpaine, antioxidant, dengue fever
Subjects: T Technology > TP Chemical technology
Faculties/Schools: University of Nottingham, Malaysia > Faculty of Science and Engineering — Engineering > Department of Chemical and Environmental Engineering
Item ID: 68753
Depositing User: Yap, Jing Ying
Date Deposited: 24 Jul 2022 04:40
Last Modified: 24 Jul 2022 04:40
URI: https://eprints.nottingham.ac.uk/id/eprint/68753

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