Browsing by Author "Ratnatilleke, A. A. L."

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Evaluation of different methods for modifying starch obtained from Manihot esculenta MU51 (Cassava MU51) to develop an effective food thickener
(Faculty of Science, University of Kelaniya Sri Lanka, 2024) Sathsarani, W. D. N.; Ratnatilleke, A. A. L.
Cassava is a low-cost crop cultivated in tropical countries for food and as a rich source of starch that is amenable to value addition. Native cassava starch, however, is undesirable for many industrial applications because of its poor structural properties. In order to improve these properties, native starches are often modified. Modification can improve these limitations by tailoring them to a specific industrial need. This study aimed to evaluate various starch modification methods used to modify cassava starch obtained from the cassava MU51 variety in order to produce an effective food thickening agent for the food industry. The MU 51 variety is readily available and has a high starch content relative to other local varieties. Native cassava starch extracted from cassava MU51 tubers was acetylated to three distinct degrees of substitution: 0.08, 0.12, and 0.17. Cassava starch was subjected to acid treatment to prepare acid-modified starch, while physical treatment of raw starch produced pregelatinised starch. Both native and modified starch samples were then analysed for total starch content, amylose content by colorimetry, viscosity by a viscometer, solubility, and swelling power by the Leach method. Viscosity is the major parameter for determining the thickening property of starch, followed by amylose content, swelling power, solubility, and total starch content. The results showed that acetylated starch with a 0.17 degree of substitution exhibited the highest viscosity (1.42 Pa at 15% w/v) compared with other modified samples, indicating its strong potential as a thickening agent. Other acetylated starch samples also showed higher viscosities than native starch at 5%, 10%, and 15% w/v concentrations. Pre-gelatinised starch had the highest amylose content (19.83%), compared to native starch and the other modified starch samples. Swelling power increased with temperature for all the native and modified starch types. An acetylated sample with a 0.17 degree of substitution demonstrated the highest solubility (51.8%) at 80 °C, outperforming native starch (40.0%). Solubility of acidmodified samples increased with temperature up to 80 °C and decreased at 90 °C, whereas pregelatinised starch solubility increased up to 90 °C without a decrease at 80 °C. In terms of total starch content, native starch had the highest amount (75.78 µg/mL), with pre-gelatinised, acetylated, and acidmodified samples showing progressively lower values. These results highlight that while total starch content is important, viscosity, amylose content, and solubility are the key factors influencing thickening performance. The ANOVA results indicated that there is a significant difference (p < 0.001) between the native and modified samples. The modified starch samples were compared with a commercially available sample, with the acetylated starch at a 0.17 degree of substitution exhibiting the closest performance, and by comparison, this sample emerged as the most suitable for use as an effective food thickening agent. Therefore, the acetylation method is better than the other two methods that can be used to modify MU51 cassava starch as a food thickener.
Evaluation of Mimosa pudica and Mimosa pigra as green manure for agricultural Production
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Faiz, F. F.; Ratnatilleke, A. A. L.
Due to the ongoing energy crisis and rising fertilizer input cost, there is renewed interest in organic manuring for agricultural production. Commonly used organic manure sources include farmyard manure and green manure prepared from nitrogen-fixing legumes. This work investigates two nitrogen fixing shrubs for N accumulation, N release patterns upon soil incubation and their effect of released N on plant growth. The two plants used belong to genus Mimosa namely M. pudica and M. pigra. The selection of these leguminous plants was based on their ability to form symbiotic relationships with nitrogen-fixing bacteria and capability to convert atmospheric nitrogen into ammonia, a valuable source of nitrogen that can be used as green manure. Mimosa plants were cut and separated into leaves, stems, and roots. The available ammonium N and nitrate N content in each plant part was determined by Kjeldahl method and nitrate ion selective electrode. Their capacity to release usable N into the soil was determined by incubating plant parts with soil in litter bags under aerobic conditions. The efficacy of the green manure on plant growth was determined by pot experiments and the data were statistically analyzed. The leaves of M. pudica showed the highest amount of ammonium nitrogen (2.05 ± 0.40%), while the roots of M. pigra showed the highest amount (0.79 ± 0.13%). The leaves of M. pudica (0.03 ± 0.01%) and roots of M. pigra (0.03 ± 0.01%) showed the highest amount of nitrate nitrogen. When the plant parts were cut, separated, and incorporated into the soil for a period of 24 weeks, the rate of N mineralization increased the ammonium and nitrate nitrogen availability. M. pudica showed an increase of ammonium N from (0.190 ± 0.032% to 0.66 ± 0.10%), while M. pigra showed an increase from (0.12 ± 0.03% to 0.73 ± 0.04%). The incorporation of these plant parts into soil planted with Capsicum annuum (Chilli plant) in a pot experiment bioassay showed a discernible effect on plant growth. Notably, the incorporation of M. pudica leaves (34.3 ± 0.5 cm) and M. pigra leaves (30.5 ± 0.2 cm) resulted in greater plant heights compared to the control group (16.2 ± 0.1 cm), which resulted in significant differences (p value, 0.024 < 0.05) in plant growth. The findings of the study suggest that the plant segments of M. pudica and M. pigra possess a substantial quantity of nitrogen that can be effectively utilized. Hence, these plants possess the potential to serve as a viable green manure resource.
Pueraria phaseoloides and Croton laccifer as sources for green manure formulations in Sri Lanka
(Faculty of Science, University of Kelaniya Sri Lanka, 2023) Gammudaly, H. M.; Ratnatilleke, A. A. L.
One of the critical problems that Sri Lanka is facing today is the inorganic fertilizer problem, which has severely affected the economy and agriculture in the country. For this crisis, a potential and a profitable solution can be obtained using local green manures. Green manures are the plants that are incorporated into the soil while still green. They facilitate the plant growth by enhancing the soil health and fertility. In Sri Lanka, several plant species, Gliricidia sepium, Pora wel (Pueraria phaseoloides), Kappetiya (Croton laccifer L.), Ipil ipil (Leucaena leucocephala) and Gansooriya (Thespesia populnea) are used as green manures since the past. This study evaluated the effectiveness of Pueraria phaseoloides and Croton laccifer L. as local green manures. In this research, experiments have been done on total nitrogen content, nitrogen release into the soil, impact of green manure on a selected plant growth (Capsicum annuum) and changes in soil parameters after the application of green manure. For the determination of nitrogen amount, the Kjeldahl method and Ion selective nitrate probe were used. Results indicated that Pueraria phaseoloides leaves contained the highest amount of nitrogen as ammonium nitrogen (0.63%), while its stems contained the highest amount of nitrogen as nitrate nitrogen (0.11%). Similar observations were also made with Croton laccifer, where its leaves showed the highest amount of nitrogen as ammonium nitrogen (3.05%). Nitrogen release experiments showed that the nitrogen levels in soil increased over the time after the incorporation of plant materials. Incorporation of Pueraria phaseoloides, into soil increased the ammonium nitrogen percentage from 0.11% to 0.7% and the nitrate percentage in soil was increased from 0.005% to 0.09%. Similarly, incorporation of Croton laccifer into soil increased ammonium nitrogen percentage from 0.11% to 0.92%. In the growth experiment, Pueraria phaseoloides and Croton laccifer plant materials were incorporated into soil, in pots, where chilli was used as the test plant. Results showed a 49.1% and 43.4% increase in height for Pueraria and Croton, respectively and a significant difference in plant height (P < 0.001) when compared to the control. Furthermore, the water holding capacity of soil was tested to study the changes of soil parameters after the incorporation of green manure. The results indicated that there was a significant increase, 20.9% and 16.5% for Pueraria and Croton, respectively in the water holding capacity of soil with and without the incorporation of Pueraria phaseoloides and Croton laccifer plant materials. The overall results indicated that Pueraria phaseoloides and Croton laccifer can be used as a potential solution for the fertilizer problem.
Strain improvement to enhance phosphate solubilizing ability of bacteria by random mutagenesis
(Research Symposium on Pure and Applied Sciences, 2018 Faculty of Science, University of Kelaniya, Sri Lanka, 2018) Gunasinghe, L. K. G.; Ratnatilleke, A. A. L.
Rock phosphate is a cheap source of phosphorous fertilizer. However, low solubility of rock phosphate makes it agronomically less effective. Combined application of rock phosphate with phosphate solubilizing bacteria (PSB) is an attractive solution to this issue. PSB produce organic acids and lower the pH of the medium which solubilise insoluble phosphates. Phosphate solubilizing abilities of wild strains, however, is considerably low. Qualitative improvement and quantitative enhancement of the phosphate solubilisation ability require genetic improvements of wild strains. Therefore, the aim of the present work is to enhance phosphate solubilizing ability of a wild strain EP11 by mutagenesis. EP11 was subjected to random mutagenesis by exposing to UV (254 nm) at varying time periods, Sodium azide (0.05 mg/L) and Ethidium bromide at varying concentrations. Amount of phosphate solubilised by each strain was determined in the PVK liquid medium supplemented with Eppawala rock phosphate (12.5 g/L) and aliquots were taken for 8 days. Aliquots withdrawn during this period were subjected to the ammonium molybdate assay. Among the mutants produced, the mutant, UV4EP11 generated by UV irradiation showed the highest phosphate solubilizing activity (135%) than the wild strain. Mutant SA5EP11 generated by exposure to sodium azide, exhibited 163% higher activity, whereas the ethidium bromide mutant, EB2EP11 showed 139% phosphate solubilizing activity compared to wild strain. All mutant strains were tested further for three generations to confirm that the mutations are stable and there is no statistically significant difference in the phosphate solubilizing ability between the generations. RP-HPLC analysis of the culture supernatants of the mutant strains UV4EP11, SA5EP11, and EB2EP11 showed that the cultures reached 50 mg/L, 84 mg/L, and 32 mg/L acid concentrations respectively. These values were substantially higher than that produced by the wild strain which was only 22 mg/L. These values correlate well with the amount of phosphate solubilized suggesting that phosphate solubilisation by mutant strains proceeds through acidification of the medium. It can be concluded that, new rock phosphate solubilising mutant strains were successfully created by exposing to mutagens and those mutants showed a qualitative improvement in organic acid production leading to enhancement of rock phosphate solubilisation.