MSCFST / Department of Food Science and Technology / Watermelon (Citrullus lanatus) juice is rich in phytochemicals that possess antioxidant properties which are known to have a positive contribution to human health. Colour, pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity are quality properties that characterise watermelon juice. However, these quality properties undergo some chemical changes throughout the stages of maturity of the fruit as well as during thermal processing. The aim of this study was to investigate the effects of maturity and filtration on the physicochemical properties (colour, pH, total soluble solids) and the phytochemicals (lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity) of fresh watermelon juice. It further investigated thermosonication effects on these quality properties using response surface methodology (RSM). RSM considering temperature (25 – 52ºC), time (2 – 10 min) and amplitude level (24.1 – 60 μm) at a constant frequency of 20 kHz were the independent variables while colour variables (L*, a* and b*, C* and h*), pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity were the dependent variables. Results showed that colour, pH, total soluble solids, lycopene, β-carotene, ascorbic acid, total polyphenolic content and antioxidants activity of watermelon fruit juice are maturity dependent. All the physicochemical and phytochemical properties increased with maturity. The combination of the CIELAB parameters (L*, a*, b*) was clearly explained by the Chroma (C*) and hue (hº). The (C*) and hº values of the watermelon fruit juice were significantly (p < 0.05) affected by the stages of maturity. The red colour was observed to be more saturated in the fully - ripe sample as indicated by the highest Chroma (7.35) values. The half - ripe sample which was observed to be pink - red had a C* of 5.88 while the lowest (4.32) value was observed from the unripe sample. The highest hº value was obtained from unripe sample (83.89), while lower value was observed from the fully - ripe (76.03) sample because of the saturation of the red colour in the fully - ripe sample. The total soluble solids also increased with stages of maturity 6.66 to 6.60 at half - ripe while at fully - ripe redness changed from 9.3 to 8.99 and TSS 8.37 to 8.02. Filtration has shown a significant (p < 0.05) on the C* and hº values. There was a higher retention of all dependent variables at lower thermosonication treatment (25ºC; 24.4 μm), especially the lycopene which increased by 127%. Model predictions for the colour properties and phytochemicals were closely correlated to the experimental results obtained. Prediction models were found to be significant (p < 0.05) with low standard errors and high coefficients of determination (R2). / NRF

MSc (Microbiology) / Department of Microbiology / Background: The medicinal value of plants lies in some chemical substances that produce a definite physiological action in the human body. The secondary metabolites help the plants to survive hash conditions and could be used by humans as supplements of their health, as foods additives or for medicinal purposes. This bioactive compounds are not always beneficial to human beings, and some of this plants bioactive compounds can be toxic or genotoxic to human cells. This study used several methods to evaluate of phytochemical constituents and mutagenic properties of Coccinia rehmanni and Jatropha zeyheri plant extracts. Methodology: Methanol was used for extraction of the bioactive compounds from the two selected plants, filtered with Whatman filter paper and evaporated with rotary evaporator. The extracts were fractionated using open column chromatography. Chemical and TLC methods were used to determine phytochemicals of the study plants extracts and fractions. The plants extracts and fractions were tested against Vero cell lines in order to evaluate cytotoxicity and genotoxicity of the plants. NucRed and LTR Hoechst 33342 dyes were used for cytotoxicity and genotoxicity respectively. For the evaluation of cytotoxicity and genotoxicity Quantification of live and dead cells for the screening assay was performed using the ImageXpress Micro XLS Widefield Microscope and acquired images analyses using the MetaXpress software and Multi-Wavelength Cell Scoring Application Module. Antimutagenicity of plants extracts was observed using PARP universal colorimetric assay kit. Acquired data was transferred to an EXCEL spreadsheet and data was analyzed. Results and discussion: C. rehmanni (12.03%) yielded more extract than J. Zeyheri (8.20%). the two plants had different compound composition and were in different stages of maturity. The study revealed the domination of Terpenoids, Cardiac glycosides, Phenolic and tannis. With an exception of two fraction fractions all the fractions was found to be toxic to an extent were genotoxicity of such fraction could not be concluded. The reason for such extreme toxicity could be due to the influence of the retained alcohol during rotary evaporation. xvi | P a g e Conclusion: this study provides and add to existing knowledge on the phytochemicals mutagenicity and anti-mutagenicity of C. rehmanni and J. Zeyheri medicinal plants. The study serves as scientific proof that extensive use of this plant in traditional medicine for treatment of various ailments may lead to some irreversible damages. / NRF

PhD (Microbiology) / Department of Microbiology / Background: Currently, Human Immunodeficiency Virus/ Acquired Immune Deficiency Syndrome (HIV/AIDS) is one of the deadliest diseases in the world. In Gabon, the prevalence is estimated at 4.1%. Because of the several side effects of highly active antiretroviral therapy on the health of people living with HIV, an emphasis on the utilization of based plant treatments have been noticed highlighted with testimonies of patient health improvement. That led researchers to conduct ethnobotanical surveys aiming at reporting medicinal plants used to treat HIV related opportunistic infections. From the outcomes, 20 plants have been selected based on the frequency of their use but also on the absence of papers in the literature related to HIV research conducted in Gabon. This study aims at evaluating the cytotoxicity, antioxidant, antimicrobial, anti-HIV and immunomodulatory activities of the 20 selected plants and to establish the phytochemical profile of these plants. Methodology: The plants were extracted using absolute methanol and distilled water. Qualitative (phytochemical screening) and quantitative (TPC and TFC) analysis were performed on the 40 extracts obtained. The extracts were assessed for cytotoxicity on Vero and HeLa cells using MTT and dual staining/fluorescence microscopy. The antimicrobial activity of the extracts was evaluated using well diffusion assay and micro-broth dilution assay. DPPH free radical scavenging assay and ferric reducing power were used to determine the antioxidant potential of the extracts. The anti-HIV effect was evaluated on HIV infected blood using reverse transcriptase inhibitory assay and p24 antigen inhibitory assay. The immunomodulatory effects of the extracts were evaluated on HIV infected blood using IL-2, IL-6 and TNF-α ELISA. Coula edulis and T. iboga methanol extracts were selected for fractionation using column chromatography. LC-MS was used to establish the phytochemical profile of the two selected extracts. Results: The results revealed that saponins, alkaloids, terpenoids, phenols, tannins, steroids, flavonoids and cardiac glycosides were detected in almost all the plant extracts. The extracts were found to contain more phenolics than flavonoids especially the methanolic extracts. Both alcoholic and aqueous extracts of C. edulis, M. cecropioides, S. ochocoa, S. kamerounensis, U. guineensis and C. religiosa, the methanolic extract of A. hirtella and R. vomitoria and the aqueous extracts of U. klainei presented IC50 significantly lower (p<0.05) than ascorbic acid (38.87±1.54 μg/ml). Both Coula edulis methanolic and aqueous extracts, methanolic extracts of S. kamerounensis, S. gabonensis, M. monandra, U.guineensis and A. klaineana showed antioxidant activity significantly xii | P a g e (p<0.01) higher than Ascorbic acid whose EC50 was 152.16±1.09 μg/ml. For the fluorescence microscopy the extracts of interest for Vero cells inhibition were A. klaineana, T. iboga, U. klainei and C. edulis while for Hela cells the cytotoxic activity was significant (p<0.05) for the following extracts: U. klainei, U. guineensis, P. soyauxii, A. klaineana, V. conferta, M. monandra, R. vomitoria, R. africanum, C. edulis and S. ochocoa. The extracts of C. edulis, M. cecropioides, S. ochocoa, S. gabonensis, A. hirtella, R. vomitoria, S. kamerunensis, P. soyauxii, U. guineensis and T. iboga displayed the highest antimicrobial activity against all the selected bacteria. For the anti-HIV the extracts of interest were V. conferta (47%), C. lucanusianus (47%), C. religiosa (44%), A. hirtella (42%), S. kamerunensis (41%), M. puberula (41%) as well as both aqueous and methanolic extracts of T. iboga (48% and 45% respectively), U. guineensis (46% and 41% respectively) and A. klaineana (41% and 44% respectively). The results for RT inhibition assay revealed that out of 24 selected plant extracts selected only C. edulis, C. religiosa, C. lucanusianus, R. africanum, P. soyauxii and V. conferta were able to decrease RT by more than 50%. The modulatory effect of the extracts on the secretion of IL-2, IL-6 and TNF-α by HIV infected cells was found to be insignificant (p>0.05). The fractionation of T. iboga and C. edulis methanol extracts eluted 4 fractions each. The LC-MS analysis revealed at negative ionization the presence of phenolic compounds (Ellagic acid, Gallic acid, and quercetin) in C. edulis samples while alkaloids (ibogaine, ibogaline, voacangine) were mainly found in T. iboga samples at positive ionization. The two crude extracts and the fractions showed some levels of antimicrobial, antioxidant, anti-HIV and anti-inflammatory activities. Conclusion: The present study has validated the use of the selected plants in the management of AIDS in Gabon and provided an explanation of the improvement in HIV individual’s life reported. Some of these plants could constitute good candidate for promising anti-HIV molecules. / NRF

No description available.

MSc (Microbiology) / Department of Microbiology / BACKGROUND: Antibiotic resistance amongst microbial pathogens has become a challenge over past decades, bringing about genuine and frequently deadly contaminations that can't be dealt with by ordinary means. This has led to a search on developing solutions to this problem by searching for new source of antimicrobial agents or chemically altering the existing ones. Traditional medicinal plants and nanoparticles are highly targeted as promising agents to address the challenge. Pyrenacantha grandiflora Baill from Icacenaceae family possess pharmaceutical activities and is used by Vhavenda people to cure gastrointestinal related infections, diarrhea and tooth pain. OBJECTIVES: The present study aimed to synthesize, characterize and evaluate the efficacy of Pyranacantha grandiflora extracts alone and when conjugated with selected nanoparticles against pathogenic microorganisms. Furthermore, this study investigated the efficacy of selected antibiotics when conjugated with nanoparticles against selected pathogenic microbes. METHODS: Pyrenacantha grandiflora Baill (tubers) were collected from Masisi area. Bioactive compounds were extracted using different solvents such as methanol, acetone, hot water, dichloromethane and chloroform. Preliminary phytochemical screening was done to identify different phytochemicals in the extracts and their functional groups were identified by Fourier Transform Infrared spectroscopy (FTIR). Extracts were further assessed for their total phenolic and flavonoids content. Thin layer chromatography was used to separate the compounds from the plant extracts and active compounds/group of compounds were identified by bioautography. The antioxidant ability of the extracts to scavenge free radical DPPH was also determined. Silver and gold nanoparticles were synthesized using chemical and biological methods, characterized by Ultraviolet-Visible Spectrophotometry (UV-VIS), Transmission Electron Microscopy (TEM) and Energy dispersive X-ray analysis (EDX). Plant extracts, nanoparticles and antibiotics were xix conjugated differently, and conjugates were analyzed by FTIR and their antimicrobial activities were evaluated against different bacteria and fungi. The conjugates were tested for antimicrobial activity against extended beta-lactamase producing Escherichia coli (ATCC 35218), Escherichia coli (ATCC 25922), methicillin-resistant Staphylococcus aureus (ATCC 25923), methicillin-susceptible Staphylococcus aureus (ATCC 33591) and beta-lactamase producing Klebsiella pneumonia (ATCC 700603) using agar diffusion assay and the minimum inhibitory concentrations (MIC) were determined using the microdilution method. The minimum bactericidal concentration (MBC) and minimum fungicidal concentration (MFC) were determined by sub-culturing from the MIC plates on Mueller-Hinton Agar. RESULTS: Pyrenacantha grandiflora was found to contain phenolics, saponins, alkaloids, tannin, steroids, terpenoids and flavonoids. FTIR spectroscopic studies revealed different characteristic peak values with various functional compounds similar in most extracts but differed with transmittance values. The total phenolic contents in the examined extracts ranged from 14.167 to 19.02 mg GA/g. The total flavonoid content in the examined extracts ranged from 26.603 to 34.621 mg QE/g. Thin-layer chromatography revealed various Rf values and when analyzed with bioautography, well-defined inhibition zones within the Rf value of 0.236 was identified against E. coli and K. pneumonia. The MICs of the extracts were determined, and all the extracts showed some antimicrobial activity against all tested strains ranging from 0.06-7.5 mg ml/g. Some extracts appeared to be fungicidal and hot water extracts were more active against Cryptococcus neoformans with the MFC value of 0.06 mg/ml. The methanol extract was also active against most tested strains including Candida tropicalis with the minimum fungicidal concentration value of 3.75 mg/ml. Pyrenacantha grandiflora tuber extracts conjugated with silver or gold nanoparticles exhibited a good antibacterial activity against all bacterial strain used and very few were able to exhibit bactericidal activity. Penicillin showed improvement of antibacterial activity xx when conjugated with compounds from the acetone extracts and vancomycin was found to be more effective when conjugated with silver nanoparticles and water extracts. CONCLUSION: The present study validated the efficacy of conjugated P. grandiflora tuber extracts which is used in traditional medicine. The results revealed that water extracts which are generally used by the traditional healers are active against most microorganisms tested as well as methanol and acetone extracts and the synergistic effect was observed when they were conjugated to gold and silver nanoparticles. The results of the present investigation clearly indicate that antimicrobial activity of Pyrenacantha grandiflora Baill tuber when conjugated with selected nanoparticles and antibiotics vary with test strain and the type of solvent used during extraction, thus giving hope for future development of drug leads. / NRF