Experimental and numerical studies of droplet impact on flowing liquid films

Droplet impact on flowing liquid films constitutes an important research area due to its manifold applications both in industry and day-to-day living. Previous studies have, however, ignored the contributions of stochastic waves to the drop impact dynamics. In this project, an experimental study of droplet impact on controlled flowing liquid films is carried out. The aim of the study is to provide an understanding of the contributions of the spatial structures of waves to drop impact dynamics on flowing films. The experimental facility consists of a falling film rig which comprises film flow, film control, and droplet-generation units, as well as a high-speed imaging system. In a preliminary study, the effect of film control on the dominant wave propagation modes is investigated. Two classes of waves are identified, namely the gamma I and II wave families, which are characterised both qualitatively and quantitatively and confirmed to be in good agreement with previous studies in the literature. Studies on the interaction patterns between doubly-excited planar pulse waves on an uncontrolled flowing film surface are then carried out to provide insight into the interaction patterns of waveforms on flowing liquid films. Distinct interaction modes are found to be of central importance to understanding the complex wave interactions which could lead to interfacial ‘turbulence’. The effect of film control on the impact dynamics of both low and high-inertia drops is then studied. In both studies, the impact surface is divided into the “wave hump”, “flat film”, and “capillary waves” regions. For low-inertia drop impacts, film control is observed to have a qualitative and quantitative effect on the length of liquid columns formed in a partial coalescence outcome, the pinch-off time, as well as the size of the ejected daughter droplets. Qualitative differences included a complete change of the outcome, with other outcomes such as ‘bouncing’, ‘sliding’, and ‘total coalescence’ observed in the low-inertia drop impact scenario. For high-inertia drop impacts, the effect of film control is studied in the morphology of the crown produced in a splash outcome as well as the distinctive attributes of the ejected droplets. Significant quantitative differences are observed in the features of the crown such as its structure, diameter, height, wall thickness, facing-direction, coalescing time, and baseline propagation modes, as well as the number and size distribution of the ejected secondary droplets. Finally, numerical studies of the flow situations investigated experimentally are also carried out using two novel codes, one using interface-capturing and adaptive, unstructured meshes, the other employing a hybrid interface-tracking/level-set technique on structured meshes. The numerical results obtained show very good agreement with the experimental studies both qualitatively and quantitatively.Open Acces

Screening of Microorganisms Isolated from Different Environmental Samples for Extracellular Lipase Production

Lipases are hydrolytic enzymes that hydrolyse triglycerides to free fatty acids and glycerol and those from microbes have occupied a prominent position as industrial biocatalysts. Microorganisms isolated from oil polluted environmental samples were screened for their lipase producing ability. A total of thirty seven bacteria and seventeen fungal strains belonging to the genera Trichoderma (16 spp.) and Aspergillus (1 sp.) were obtained from the samples. Acinetobacter sp. had the highest frequency of occurrence (37.8%). The lipolytic activity of the bacteria when screened on solid agar ranged within 3.0m - 15.5amm, 3.0n - 15.5amm and 3.0 - 16a mm at 24, 48 and 72 hours of incubation, respectively. Acinetobacter sp. (OG3) had the highest activity at different hours of incubation. Eight isolates did not show any activity throughout the incubation period. On submerged fermentation, the growth of the lipolytic bacteria ranged within 0.093 - 1.003 in which Acinetobacter sp. had the highest growth while Bifidobacterium sp. had the lowest. Lipase production ranged within 1.25 U/ml - 8.65 U/ml in which Acinetobacter sp. had the highest production. During submerged fermentation, the growth of the selected fungal isolate ranged within 0.00 - 0.200a , 0.00 - 0.25a and 0.00 - 0.3190a in which T. FISO1 had the highest at 3 and 7 days of incubation while T. virens FSU/AW3 had the highest at 14 days of incubation. There was a significant difference in lipase production by the fungi, it ranged within 0.70n - 12.35a U/ml, 1.8k - 19.15a U/ml and 2.50n - 19.8a U/ml in which Hypocrea patella FAD1, T. stromaticum FSUAW1 and T. virens FSU/AW3 had the highest at day 3, 7 and 14, respectively. The study has shown that the bacteria and Trichoderma strains isolated are potential lipase producers

Phytochemical analysis, antioxidant, antibacterial potentials and chemical composition of methanol extract of Oscillatoria sp.

Background: Algae contains some useful phytochemicals and Oscillatoria sp. is a green microalga which has various applicationsObjectives: Phytochemicals, antioxidant, antibacterial potential and chemical composition of methanol extract of Oscillatoria sp. were evaluated.Materials and Methods: Extraction of bioactive compound from Oscillatoria sp., determination of phytochemicals, antioxidant, antibacterial potential and chemical composition of the methanol extract.Results: Saponin, alkaloids and flavonoids were detected in the methanol extract while glycosides and phenols were absent. The scavenging assay for the antioxidant increased in a dose dependent (100 -1000 μg/mL) manner. The DPPH scavenging activity, Total phenolic content, Ferric Reducing Antioxidant Power Assay (FRAP) and hydrogen peroxide scavenging activity ranged from 21.8 - 44.9%, 9.09 -21.46%, 0.43 - 42.49% and 19.4 - 74.4% respectively. The methanol extract had inhibitory activity against the test pathogens in which Pseudomonas aeruginosa ATCC 27853 (24.0 mm) had the highest susceptibility. GCMS chromatogram of the methanol extract of Oscillatoria sp. shows fifteen major peaks which indicated the presence of Oleic acid, stearic acid, aracidic acid, methyl laurate, methyl myristate, oxirane and palmitic acid.Conclusion: Oscillatoria sp. methanol extract contain some phytochemicals and some heterocyclic compounds. The extract had good antioxidant capability and appreciable antibacterial activity against the test pathogens.Keywords: Oscillatoria sp.; methanol extract; Phytochemical; Antioxidant; GC-MS; Antibacteria

Microbiological, proximate analysis and sensory evaluation of processed Irish potato fermented in brine solution

The microflora, proximate analysis and sensory evaluation of Irish Potato (Solanum tuberosum) slices fermented in 2.0% brine solution under micro-aerophilic condition for five days at room temperature were studied. The Nutritive qualities of the brined- fermented samples were analyzed and organoleptic parameters were accessed through trained panelist. There was an increase in microbial load of the brined-fermented samples especially within the first three days of fermentation as a result of hydrolysis of carbohydrate and subsequent conversion to sugars and minerals by the fermenting microorganisms. The organisms isolated from the fermentation set up include Bacillus, Flavobacterium, Micrococcus, Lactobacillus and Staphylococcus species. Decrease in microbial counts at the latter stages of fermentation was attributed to the high total acidity of the medium with reduction in pH from 7.50 to 5.03, while the lactic acid bacteria increased continuously throughout the period of fermentation. The results of the proximate analysis showed that there was a reduction in the crude fiber content from 28.96 to 20.04 mg/g, reducing sugar from 127 to 72 mg/g and ash content from 8.01 to 4.08 mg/g. The fried fermented chips were more desirable and preferred to the unfermented control

Screening of Lactic Acid Bacteria Isolated from Fermented Food for Bio-molecules Production

Production of bio-molecules is an important factor in assuring the proper consistency and texture of fermented foods. Lactic acid bacteria (LAB) isolated from fermented food were screened for lactic acid, diacetyl, hydrogen peroxide, pH development and Exopolysaccharide (EPS) production. Thirty-five strains of LAB were isolated and characterized from fermented dairy and non-dairy foods. The LAB species identified include: Lactobacillus fermentum, Lactobacillus plantarum, Lactobacillus brevis, Lactobacillus cellobiosus, Lactobacillus delbruekii, Lactobacillus coryniformis, Lactobacillus casei, and Leuconostoc messenteroides. The most predominant species was Lactobacillus plantarum (34.29%). All the isolates were screened for lactic acid, hydrogen peroxide, diacetyl and pH and EPS production. Lactic acid production ranges within 0.11-1.96 mg/l in which the highest was produced by L. plantarum LPF2. L. plantarum LPF2 also produced the largest amount of diacetyl (1.92 mg/l). Hydrogen peroxide produce by the isolates ranges within 0.0002-.35 mg/l and L. fermentum LFBO1 produced the highest. The pH ranged within 3.2-6.5 in which L. plantarum LPF2 had the least. L. plantarum LPW7 and LPBO9, Leu. messenteroides LMWO2 and LMW4 bring the reduction of the pH of the fermentation medium to 3.8 at 36 hours. All the isolates were screened for EPS production on solid medium. The isolates were all creamy; four were highly mucoid, eight were mucoid while twenty-three were slightly mucoid. All the isolates are EPS producers, EPS production ranged within 120-1,390 mg/l in which the highest was produced by L. fermentum LF6

Mycological, toxigenic and nutritional characteristics of some vended groundnut and groundnut products from three Northern Nigerian ecological zones

Groundnut (Arachis hypogaea L.) and groundnut products are important, street-vended, energy-rich sources of protein and oils useful in human and animal diets although fraught with microbial contaminations. Fungi associated with vended samples of roasted groundnut, Kulikuli, Donkwa, peanut butter and Yaji obtained from Kano, Kaduna, Minna and Ibadan were isolated using pour-plate method. These were qualitatively screened for presence of mycotoxin on palm kernel agar medium and the concentrations of aflatoxin and deoxynivalenol content in the samples quantified through immunoassay. The fungal load of the samples was highest between 1.3X103 and 1.6X104 TFU/g while the frequency of occurrence of Aspergillus, Fusarium, Rhizopus and Penicillium species in the samples were 36%, 33%, 20% and 11%, respectively. Qualitatively, the highest aflatoxin intensity producers were two strains of Aspergillus flavus from a Yaji and Kulikuli sample. The highest aflatoxin concentration (115ppb) was recorded in the Kaduna Yaji sample and 65% of the samples had aflatoxin concentration above the FDA-prescribed 20ppb. The highest deoxynivalenol concentration (0.7ppm) was recorded in Kaduna Donkwa sample which was still lower than the 1.0ppb prescribed recommendation. Kano Yaji and Kaduna Kulilkuli had the highest protein content (60% and 44% respectively) while all samples were high in calcium and potassium (725.16-1292.75 and 325-1280mg/100g) respectively. There was fungal contamination of vended groundnut product samples and the detection of mycotoxins in all the samples. Regulatory bodies, especially in developing countries, need to set quality standards and ensure compliance of the same in street vended food products for product and consumer safety.Keywords: Groundnut products, Mycotoxigenic properties, Deoxynivalenol, Aflatoxin, Nutritional compositionAfr. J. Biomed. Res. Vol. 22 (January, 2019); 65- 7

Moulds, Proximate Mineral Composition and Mycotoxin Contamination of Banda (“kundi”/ “tinko”) Sold in Ibadan, Oyo State, Nigeria

Mycotoxin is an important toxin whose consumption could cause foodborne diseases. The moulds, proximate mineral composition and mycotoxin contamination of Banda samples purchased from different markets in Ibadan, Oyo state, were investigated. A total of 90 samples were collected during July - September and a total of 69 fungi isolates were obtained. The fungal isolates found in samples were Aspergillus niger, A. flavus, A. fumigatus, A. candidus and A. piperis among which A. niger had the highest frequency of occurrence (36.23%) followed in order by A. flavus (30.23%), A. fumigatus (13.04%), A. candidus and A. piperis (10.14%). The samples were found to contain adequate amount of proximate mineral contents. Proximate and mineral analysis carried out showed that the percentage crude protein in Banda samples collected in July is higher than that of August and September. The percentages of most of the mineral elements are higher in samples collected in August. It was observed from the analysis that the proximate and mineral composition in the dried meat was higher than that of the control (Raw meat sample). Mycotoxin analysis revealed that the samples were heavily contaminated with aflatoxins B1, B2, fumonisin (FB1 and FB2) and ochratoxin (OTA). There was a significant difference (P ≤ 0.05) in mycotoxin concentration among the samples. The AFB1 and AFB2 were found in 10% and 90% of the dried meat samples, while 10% were contaminated with FB1 and FB2, respectively. 13.3% were contaminated with OTA. AFB1 was not detected in all of the samples except samples J1, A1 and S4, respectively. For the samples collected in the month of July, the AFB2 concentration ranged within 0.00 - 201.50, FB1, FB2 and OTA concentrations ranged within 0.00i - 1.909a, 0.00i - 1.037a, and 0.00i - 2.00a, respectively. For the samples collected in August, the AFB2, FB1, FB2 and OTA concentrations ranged within 0.00i - 234.20a, 0.00i - 2.327a, 0.00i - 1.003a, and 0.00 - 1.600a in which sample A7 had the highest concentration. The AFB2 concentration ranged within 0.00 - 167.20a in which sample S1 had the highest concentration. The FB1, FB2 and OTA concentrations ranged within 0.373h - 2.199a, 0.167h - 1.965a, and 0.00f - 2.133a for the samples collected in September. The levels of mycotoxin contamination in all the samples exceeded the maximum limit permitted in most countries. The detection of AFB1 and AFB2 in the dried meat samples could be of public health significance and hence there is an urgent need for concerned regulatory bodies to impose necessary measures to safeguard health of consumers. Conclusively, the presence of mycotoxin producing fungi and the level of AFB1 and AFB2 in the dried meat samples call for serious attention in the country and there is a need for some form of quality control and proper preservation before usage

Influence of Different Nutrient Sources on Exopolysaccharide Production and Biomass Yield by Submerged Culture of Trametes versicolor and Coprinus sp.

Influence of different nutrient sources on Exopolysaccharide (EPS) production and Biomass yield by submerged culture of Trametes versicolor and Coprinus sp. was investigated. The best EPS production by Trametes versicolor and Coprinus sp. was stimulated by sucrose. EPS production ranged within 1,011-17945 mg/l and 200-18,765 mg/l, respectively. The least EPS production was recorded in xylose and glucose, respectively. Xylose and sorbitol supported the highest biomass yield (1.9 gdryw/l and 2.0 gdryw/l) by Trametes versicolor and Coprinus sp., respectively. Yeast extract induced the highest EPS production (7,835 mg/l) by T. versicolor. The EPS ranged within 701-7,835 mg/l. Casein stimulated the highest production of EPS by Coprinus sp. and it ranged within 563-7,474 mg/l. Yeast extract and NaNO3 induced the highest biomass yield by Trametes versicolor and Coprinus sp., respectively. Biomass yield ranged within 1.0-1.6 gdryw/l and 2.0-1.9 gdryw/l. The highest EPS production by the strains was stimulated by glutamic acid and it ranged within 272-3,684 mg/l and 209- 8,899 mg/l, respectively. The least stimulatory amino acids were alanine and glutamate, respectively. The best amino acids for biomass production by the isolates were aspartic acid and asparagines, respectively, and it ranged within 1.0-15.0 gdryw/l and 1.0-16.0 gdryw/l

Phycosynthesis of Silver Nanoparticles Using Chlorella vulgaris Metabolites: Its Antibacterial, Anti-Biofilm and In-Vitro Cytotoxicity Potential and Effect of Optimized Conditions on Biosynthesis.

The adverse effects of multidrug resistant and biofilm forming microbes on human health is of major concern; therefore a search for potential alternative in nanoparticles is required. Green phycosynthesis of silver nanoparticles (SNP) using The Clear Supernatant (TCS) of blue-green algae, Chlorella vulgaris (Cv) was investigated. The greenly synthesized Chlorella vulgaris TCS SNPs (CvTCSSNPs) were characterized using UV-Vis spectrophotometry, SEM, TGA, DLS, EDX and XRD. The antibacterial, antibiofilm and in vitro cytotoxicity against brine shrimp was evaluate. Colour change from light green to chocolate brown indicate CvTCSSNPs biosynthesis and surface Plasmon resonance peak was observed at 300 nm. CvTCSSNPs was 10 μm in size, spherical in shape, and can withstand high temperature without totally losing its weight. DLS shows the particle diameter average of 82.19 nm and 505.3 nm with a polydispersity index of 0.505. The EDX analysis confirmed a strong signal of silver element. The CvTCSSNPs had strong antibacterial activity and profoundly antibiofilm activity against Citrobacter sp., S. aureus ATCC 29213, E. coli ATCC 35218 and Pseudomonas aeruginosa ATCC 27853. CvTCSSNPs toxicity to Artemia salina (brine shrimp) LC50 was 1256. 69 μg/mL, it was observed to be insignificant with the highest mortality rate at 2000 μg/mL and the lethality was dose dependent. pH 10, 37˚C, 40 mL extract, 5 mM AgNO3 supported optimum CvTCSSNPs production. In conclusion, the phycosynthesized CvTCSSNPs had strong antibacterial and antibiofilm activity against the test pathogens. CvTCSSNPs may be used as safe and alternative to antibiotics against MDR biofilm producing pathogens

Screening of Some Basidiomycetes for Bio-polymers and Biomass Production in Submerged Cultivation

Twenty-one species of edible and non-edible basidiomycetes were screened for bio-polymers and biomass production in submerged cultivation. All the basidiomycetes produced bio-polymers and there was variation in quantities of bio-polymers produced by the strains at different incubation times. The bio-polymers production ranged within 44 - 9,177 mg/l, 63 - 14,525 mg/l and 69 - 6,367 mg/l at days 2, 7 and 14, respectively. Coriolus versicolor produced the highest yield at day 7. The biomass production at days 2, 7 and 14 ranged within 0.12 - 0.23g dry w/l, 0.13 - 0.25g dry w/l and 0.13 - 0.30g dry w/l in which C. versicolor also had the highest yield. The highest biomass production was recorded on day 14