Browsing by Author "Wickramarachchi, P. A. S. R."

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Exploring bioactive compounds in the endolichenic fungus, Xylaria feejeensis, inhabiting the lichen, Graphis librata, collected from Negombo lagoon, Sri Lanka
(Institute of Chemistry Ceylon Adamantane House, Rajagiriya, Sri Lanka., 2020) Gunawardhana, M. H. A. Y.; Wickramarachchi, P. A. S. R.; Weerasinghe, W. R. H.; Paranagama, P. A.
The accelerating pharmaceutical problem of bacteria growing resistant to existing antibiotics forces the scientific community to search for new antibacterial compounds for antibiotic drug development. Literature reveals that Sri Lankan mangrove inhabiting endolichenic fungal (ELF) population is rich in many such bioactive compounds. Previously isolated and cultured ELF, Xylaria feejeensis; from the lichen Graphis librata inhabiting in the mangrove plant Rhizophora mucronata was cultured on 60 large potato dextrose agar medium containing petri dishes and incubated for 14 days at room temperature. After extracting secondary metabolites to ethyl acetate (EA) the resulted crude extract was tested for its antibacterial and antioxidant activity. EA crude extract showed negligible antioxidant activity in DPPH radical scavenging assay hence this assay was not proceeded further. The activity of crude extract (5 mg/ml) against Escherichia coli (ATCC25922), Staphylococcus aureus (ATCC25923) and Bacillus subtilis (ATCC6051) was tested using agar well diffusion antibacterial assay. An inhibition zone diameter of 1.9 cm, 2.2 cm, and 2.2 cm against three bacterial strains with Azithromycin positive control (5 mg/ml) 2.2 cm, 2.2 cm and 2.3 cm was observed respectively. By partitioning of EA crude extract resulted two antibacterial active hexane and chloroform fractions and one antibacterial inactive 60% methanol in water fraction. Hexane fraction showed the highest antibacterial activity with inhibition diameter zone of 2.6 cm against E.coli with 2.6 cm diameter of inhibition zone for positive control. Further purification of hexane fraction was performed by normal phase column chromatography and 4 fractions were resulted. The highest polar fraction showed 1.4, 2.1 and 1.7 cm diameter inhibition zones of growth of E.coli, S. aureus and B. subtilis comparable with 2.2 cm Azithromycin. The other 3 fractions showed no antibacterial activity against these bacterial strains. Results suggest that further purification of active fraction and structure elucidation might result in new antibiotic lead compounds.
Growth patterns of Aspergillus sp. in stored rice during the post-harvest storage and their in-vivo growth control by cinnamon oil-chitosan microcapsules
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Rajapaksha, R. P. S. P.; Kumarathunga, P. G. J. D.; Wickramarachchi, P. A. S. R.
Rice (Oryzae sativa L.) is the most important staple food crop in Sri Lanka. Inadequate storage conditions for rice can result in fungal infestation, leading to the presence of micotoxin that pose significant health risks to humans. A common storage fungus, Aspergillus sp. is responsible for producing Aflatoxins in stored grains. The use of cinnamon leaf oil (CNO) as an antifungal agent has garnered attention due to its low toxicity to mammals, high effectiveness, and wide availability. However, the direct application of CNO presents challenges such as volatilization, degradation of active compounds, and imparting unpleasant taste and odor to food products. To overcome these limitations and achieve controlled release, microencapsulation is an effective technique. Understanding and controlling the growth of aflatoxigenic fungi, specifically Aspergillus sp. on stored rice is of paramount importance to ensure food safety. In this study, a comprehensive investigation was conducted to assess the in-vivo growth dynamics of Aspergillus sp. colonies over a six-month period during the post-harvest storage. The rice samples were carefully stored in separate poly bags and rice packets to monitor any variations in fungal colonization. Microcapsules (MCs) containing cinnamon leaf oil were prepared by inotropic gelation of chitosan crosslinking with sodium tripolyphosphate (STPP 1%). Monthly observations of Aspergillus sp. in rice were performed by growing in potato dextrose agar (PDA) media and subsequent spore quantification was carried out using a haemocytometer. The results demonstrated that the spore counts exhibited slight variations throughout the six-month duration. Notably, the highest spore count of 3.02 x 107 mL-1 was observed in the sixth month, suggesting a potential accumulation of viable spores during prolonged storage. To investigate the efficacy of growth control measures, rice grains were inoculated with the spores of Aspergillus sp. and assessed the minimum inhibitory dose (MID) of cinnamon oil loaded chitosan microcapsules (CNO-CS-MCs). Remarkably, the Aspergillus sp. fungus exhibited growth when exposed to 1 - 5 mg of cinnamon oil within the microcapsules, indicating their role in facilitating fungal proliferation. However, a noticeable inhibition of fungal growth was observed when the oil dose in MCs was increased to 7.5 mg. And free CNO mixed rice grains showed 100 % growth inhibition of Aspergillus sp. at 2 mg of oil (MID). Upon further incubation in PDA media, fungal growth was detected in the 7.5-12.5 mg CNO range. And treatments with 15 mg and higher doses exhibited no fungal growth after incubation in PDA media. Therefore, the minimum lethal dose (MLD) of CNO-loaded chitosan microcapsules against Aspergillus sp. was determined to be 15 mg. These findings emphasize the promising potential of CNO-CS microcapsules as a mean to control the growth of aflatoxigenic fungi on stored rice
Potential of using leaf extract of Annona glabra as a novel, green source for the synthesis of silver nanoparticles
(4th International Research Symposium on Pure and Applied Sciences, Faculty of Science, University of Kelaniya, Sri Lanka, 2019) Paragodaarachchi, Y. L.; Wickramarachchi, P. A. S. R.
This study aims at investigating the potential of using the leaf extract of Annona glabra for the green synthesis of silver nanoparticles (AgNPs) and optimization of process parameters to obtain nanoparticles with narrow size range. A. glabra is a very troublesome invasive species, where it grows in estuaries and stifles mangroves. Phytochemicals present in plant extracts are capable of acting as reducing and stabilizing agents during the synthesis of nanoparticles. The active ingredient responsible for the reduction of Ag+ ions and stabilization of silver nanoparticles varies depending on the plant extract used. Aqueous leaf extracts of A. glabra were prepared by heating chopped leaves (20.0 g) with water (100.0 mL) at different temperatures (60 – 100 °C) for 1 hour. AgNPs were synthesized by incubating silver nitrate (20.00 mL), as the precursor, with the plant extract, as the reducing agent. The mixture was incubated for 3 hours under slow agitation and dark conditions. Amount of plant extract (2 – 10 mL), concentration of silver nitrate (1 – 10 mM) and incubation time (0.5 - 24 hours) were changed to find the optimum conditions for the synthesis of AgNPs. Formation of silver nanoparticles were confirmed by the color change of the mixture from faint yellow to light brown and the surface plasmon resonance band around 420 nm. The size of the nanoparticles formed were measured by dynamic light scattering (DLS).The surface plasmon resonance peak maxima was detected at 417 nm for the biofabricated AgNPs using A. glabra leaf extract. With the increase of plant extract, size of AgNPs increased from 206 – 314 nm. Particle size increased from 183 – 224 nm with increase of silver nitrate concentration. The plant extract made at 100 °C produced the smallest nanoparticles. The size of AgNPs were polydispersed in a range of 10 – 190 nm displaying a narrower size range which falls within the general nanoscale. The optimum formulation was obtained at 100 °C extraction temperature for the leaf extract, 2 mL of plant extract, 1 mM silver nitrate and 7 hours of incubation. Leaf extract of A. glabra can be used for the synthesis of AgNPs and only low concentrations of leaf extract of A. glabra are needed to synthesize silver nanoparticles.
Qualitative analysis of heavy metal adsorption by the green synthesized silver nanoparticles
(Institute of Chemistry Ceylon Adamantane House, Rajagiriya, Sri Lanka., 2020) Ramanayake, R. A. D. J.; Wickramarachchi, P. A. S. R.
Silver nanoparticles (AgNPs) have attracted high research interest because of their important applications in antimicrobial, catalysis, and water treatment plants. They display totally new and enhanced properties compared to larger bulk material particles and these novel properties are due to the difference in specific characteristics such as particle size, distribution, morphology and higher surface area-to-volume ratio. The aim of this research was to determine the Pb(II) and Cu(II) adsorption of synthesized AgNPs using natural polymer, chitosan as both reducing and capping agent. AgNPs were formed in an autoclave at 15 psi and 131 0C by varying the AgNO3 and chitosan concentrations and autoclaving time. AgNPs solution thus obtained was mixed with Pb(II) and Cu(II) (0.05, 10, 100, 200, 500 ppm) solution separately and kept overnight. The removal of metal ions from the solution was monitored by the shift and intensity variation of the surface plasmon resonance (SPR) band of the AgNPs. The green synthesized silver nanoparticles were characterized using ultra violet visible (UV-Vis) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscope (SEM) and particle size analyzer. UV-Vis peak at the 430 nm confirmed the formation of chitosan stabilized silver nanoparticles. The dynamic light scattering (DLS) measures confirmed that the average size of synthesized AgNPs was 818.4 nm with the polydispersity index of 0.243 revealing the uniform size and good dispersion of the nanoparticles. The optimum concentrations of AgNO3 and chitosan were recorded as 50 mM and 2% respectively. The maximum yield of nanoparticles was obtained at 60 minutes of autoclaving, which was decided as the optimum time of autoclaving. After addition of metal ions, AgNPs solutions showed a color change and a shift and variation in intensity of the SPR band at lower metal ion concentrations while at higher metal concentrations SPR band disappeared indicating the adsorption of metal ions onto the AgNPs. Hence this has the potential to be developed as a heavy metal removal technique in water.