Date of Award

2010

Thesis Type

Masters

Document Type

Dissertation

Divisions

Faculty of Science

Department

Institute of Biological Sciences

Institution

Universiti Malaya

Abstract

An understanding of the postharvest parameters is essential for the successful market introduction of red-fleshed dragon fruit, Hylocereus polyrhizus, which has been recently developed as fruit crop. In this study, fruit at three different harvest maturities were evaluated in terms of physiological and biochemical aspects. Fruit which were harvested at complete red stage maintained their quality for up to one week. On the other hand, fruit harvested at early maturity attained the physical properties of fruit ripened on the plant (firmness reduced, peel colour changes, pH increased) but they contained noticeably lower concentrations of soluble sugars suggesting that fruit can be harvested earlier but there is a cut off point to be considered. As part of extending the studies, activities of cell wall degrading enzymes on the fruit were carried out. Activities of the fruit softening-related enzymes were detected in all different harvest maturity fruit. The enzymes chosen to represent their pectin and hemicellulose modifying potentials that cause loss in firmness are polygalacturonase, pectin methylesterase and cellulase. Furthermore, the optimum storage temperature at which the fruit will have the longest marketable life with minimal loss of quality was determined. Thus, the effect of storage temperatures on the fruit at three different harvesting maturities showed storage at 6˚C had maintained the fruit quality in terms of peel colour and as well as organoleptic properties. However, storage at 16˚C showed the highest loss and faster deterioration. This could be observed in terms of the appearance of sunken areas, discolouration and also declined in organoleptic properties. As one of the atmosphere modifying methods, fruit were stored under film packaging conditions. Eventually, film packaging successfully prolonged the shelf life while maintaining the fruit quality of H. polyrhizus when kept at 6˚C for two weeks. Thus, these research findings showed that the quality of H. polyrhizus are affected by factors such as different maturity and the ability of the fruit to tolerate different storage temperature and also atmosphere conditions.  Photodynamic therapy (PDT) involves the intravenous administration of a photosensitiser that preferentially localises in cancerous tissues more than the surrounding normal tissues. Subsequent illumination of photosensitiser generates reactive oxygen species that cause irreversible photo-damage to the cancer cells. To date, most photosensitisers that have been approved for clinical use or are currently in clinical trials are cyclic tetrapyrroles which are derived or inspired by naturally occurring chlorophyll and its degradation products. Some non-tetrapyrrolic photosensitisers have also been found in nature suggesting that there are potential photosensitisers with interesting structures in nature. To this end, this thesis outlines the collection of fourteen species of seaweeds from Cape Rachado, Port Dickson, where their methanolic extracts were screened for cytotoxicity at 20 μg/mL with promyelocytic leukemia cell-line, HL60 in dark and light-treated conditions. Five of these extracts showed varying degrees of cytotoxicity in light-treated condition. A Pheophyta (brown), namely Turbinaria conoides and a Chlorophyta (green), namely Cladophora patentiramea were selected for further chromatographic separation guided by MTT-bioassay due to the availability of raw materials. The isolation process yielded a total of nine compounds with > 50% photo-cytotoxicity at 5 and 10 μg/mL. Pheophorbide-a methyl ester (1), 132-hydroxypheophorbide-a methyl ester (2) and pheophorbide-a (3) were among the major products isolated. Furthermore, several other minor compounds were also identified in the study, including purpurin-18 methyl ester (4) and 132-methoxyl pheophorbide-a methyl ester (5) from Turbinaria conoides; as well as 151-methoxypurpurin-7-lactone methyl diester (6), isomers of 132- hydroxypheophorbide-b methyl ester (7 and 8) and 7-formyl-151-methoxy-7-lactone methyl diester (9) from Cladophora patentiramea. There are also a number of potentially novel compounds with mass values and UV-Vis profiles that are not similar to known compounds. To conclude, seaweeds are good sources of photosensitisers

Initial

khm

Additional Information

Dissertation (M.A.) – Faculty of Science, Universiti Malaya, 2010.

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