Submitted in complete fulfilment for the Degree of Master in Food Science and Technology, Durban University of Technology, 2017. / Hibiscus sabdariffa is an under-utilised plant that has been reported to have great potential in the pharmaceutical and nutraceutical industries. The vibrant red pigment indicates a source of anthocyanins that could be produced into a food colourant with additional nutritional benefits however stability is a hindering factor. The crude anthocyanins were extracted from dried calyces by means of four different acidified ethanol and methanol solvent systems to determine the maximum crude anthocyanin yield. The crude extracts were analysed under the following parameters; heat, light, pH stability and degradation kinetics, which included thermal degradation and DPPH radical scavenging ability. Two synthetic colourants were analysed based on the stability parameters; heat, light and pH and compared with the natural H. sabdariffa crude extracts. Each of the four crude extracts were analysed for the total phenolic content using Folin Ciocalteu’s method. The DPPH and FRAP assays were used to determine the radical scavenging activity of the extract with the highest yield. The identification and quantification of the crude anthocyanins were carried out using HPLC-DAD. The highest crude anthocyanin yield of 19.92% was observed by HCl acidified ethanol extract Acetic acid/water/methanol extract produced the lowest yield of 8.72%. The stability results showed that pigment retention of samples heated at 80˚C had a greater decrease over time than those heated at 50˚C. The pH stability of samples incubated for 7 days indicated that crude anthocyanins degraded slower at acidic pH, which is in keeping with reported literature therefore this extract, should be added to foods with lower pH. Light stability showed slower degradation in dark incubated samples resulting in 84% pigment retention after a 10 day period. Synthetic colourants proved to be superior, as they had showed better stability than the natural colourant under the same conditions. Half-life of thermally treated samples showed a decrease upon heating, colour was also affected as samples became dull and murky. DPPH of thermal treated samples showed a decline in radical scavenging activity from 70 to 85˚C and thereafter an increase was observed between 85 and 90˚C, this could be due to the release of degradation products that have antioxidant capability. Solvent systems did not have an effect on the total phenolic content of crude extracts as no significant difference was observed by each of the H. sabdariffa crude extracts contained an average of 54.67 mg/ml GAE. The radical scavenging ability assessed by the DPPH and FRAP assays showed 53.75% and 57.51% radical scavenging ability respectively. Although the synthetic colourants showed better stability, a natural food colourant from H. sabdariffa can still be beneficial as it has potential to be applied into foods that contain low pH such as jelly and yoghurt. The additional benefits that natural food colourants possess aid in the marketability of the product. / M

Submitted in fulfillment of the requirements for the award of the degree of Master of Health Sciences: Dental Technology, Durban University of Technology, Durban, South Africa, 2017. / The poor mechanical properties of denture base acrylic resins can cause dentures to fracture either through impact or stress fatigue. Various metal reinforcing materials such as powders, nets, plates and wires together with synthetic fibres are therefore used to improve the strength properties of denture base acrylic resins. Despite their benefits, they are difficult to apply during fabrication, are costly, non-recyclable, and not environmentally friendly. The suitability of Hibiscus sabdariffa (H. sabdariffa) as a fibre reinforcement material for denture base acrylic resins was therefore investigated. A quantitative research paradigm and a two-phased experimental research design was used. The preliminary study used Fourier transform infrared (FT-IR) spectroscopy, thermogravimetric analysis (TGA) and field emission scanning electron microscope (FE-SEM) to assess the characteristics of, and the effect of, mercerisation on H. sabdariffa fibres. In determining the suitability of H. sabdariffa fibres, fibre diameter, fibre density, moisture content and absorption were examined. The main study investigated the mechanical and physical properties of two sample groups namely: the unreinforced (control) group and the H. sabdariffa fibre-reinforced (test) group denture base acrylic resins. The flexural strength, impact strength, specific wear rate, hardness and water absorption behaviour were determined in line with ASTM D 790 and D 256, G 99, D 2583 and D 570 methods of testing, respectively. Parametric and non-parametric tests were used to analyse the mean differences (p = 0.05) between the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins. The preliminary study revealed that H. sabdariffa fibres favourably compared to other lignocellulosic fibres in terms of fibre diameter, fibre density, water content and absorption behaviour. In the main study, a t-test revealed that there were significant differences in flexural strength at 0oC (p < 0.0001) and at 65oC (p < 0.0025) between the two sample groups. Similarly, there were significant differences in the impact strength between the two sample groups at 0oC (p < 0.031) and at 65oC (p < 0.0001). In contrast to the 200g load, there were significant differences (p < 0.044) in the specific wear rate of the unreinforced and the H. sabdariffa fibre-reinforced denture base acrylic resins at the 500g load. The hardness values revealed no significant differences (p > 0.707) between the two sample groups. There were however, significant differences (p < 0.041) in the water absorption rate between the two sample groups. Overall, the prominent features of this study showed that H. sabdariffa fibre is a suitable reinforcement fibre material for denture base acrylic resins and is in compliance with ISO 1567: 1999. Although this study found that H. sabdariffa fibres can be used as reinforcement material for denture base acrylic resins, the results cannot be generalised to clinical conditions, therefore in vitro and in vivo investigations are recommended. / M