School of Biological Sciences
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Item The Effects of Different Methods of Salting on the Quality of Salted Fish(University of Ghana, 1996-06) Dowuona, S.Samples of fresh Tilapia (Tilapia species) and Redfish (Sparidae species) were salted using the pickle and kench curing methods. The salted fish were then dried using solar and air-drying methods. Standard methods were used to determine the effects of processing and dryinq methods on the chemical composition of the processed fish. With the uptake of salt by the fiah, the ash content increased significantly during processing, with resultant decreases in the fat, protein and moisture contents. Fat decrease was alao partly attributed to dripping of liquified fat during drying as well as chemical oxidation of the fat. Protein losses were also partly due to proteolysis of the protein as well as denaturation. The extent of the differences in moisture, fat and protein between the pickled and kenched samples were not significant except for ash and salt contents. Sensory evaluation using the rank method and analyaed by Analysis of Variance (ANOVA) showed that the kench cured and airdried samples are more acceptable, whiles pickle cured and solar dried samples are least acceptable with respect to texture, odour and appearance. The salted dried Tilapia samples were also found to have a longer shelf-life than the similarly treated Redfish samples.Item Development and Quality Evaluation of Pre-Gelatinized Instant Weaning Foods Based on Cereals and Legumes(University of Ghana, 1991-07) Abotsi, S.K.Item Development of Precooked Foods Process and Product Evaluation(University of Ghana, 1983-06) Masopeh, E.A pre-cooked food has developed from cornmeal and cowpead flour . The cowpea seeds were germinated and also dehulled. Control seeds of these treatments were made. Method used in the preparation of the product was steaming and traditional roasting in the earthen- ware mashing boul. Chemical analysis on the products Showed that the product developed had a higher protein content than cornmeal . Evaluation of the functional characteristics revealed that the water absorbed by the products increased with an increase in the number of germination days . The undehulled products also absorbed water and swelled more than the dehulled products. This ws attributed to the presence of the seed coat in the undehulled sead products. There was not much difference in the water absorption and swelling properties with respect to the levels of corn and cowpea. Viscoamylograph runs showed no change in the gelatinisation of the germinated seed products , however there was a little increase in the viscosity of the ungerminated seed product during the holding and cooling sections. Sensory evaluation of the corn-cowpea product showed that the product was acceptable. Anaalysis of variance calculations showed a significant (p~ 0.01) effect of dehulling and cersination on the colour, odor, flavor and tho beneral acceptability of the nroducts The panelists could detect differences in the different products subjected to the different treatments. A second product similar to the corn-cowpea product was developed from corndough. Fermented and unfermented corndough were used. Functional characteristics analysis showed a high water absorption and swelling of unfermented corndough products. Analysis on the product Showed no significant difference in the colour, odor etc . of the fermented and unfermented corndough products . However, the unfermented corndough product was more acceptable.Item Studies on the Role of the Coleopteran Species Callosobrochus Maculatus Fab., Sitophilus Zeamais Mots. And Tribolium Castaneum Herbst. In The Dispersal of Fungi among Stored Grains of Maize (Zea Mays L.) And Rice (Oryza Sativa L.) And Seeds Of Cowpea (Vigna Unguiculata Walp.) And Bambara Groundnut (Vigna Subterranea L.) Verdc](University of Ghana, 1995-12) Badu-Yeboah, K.Seven Aspergillus species, A . clavatus, A . flavus, A.fumigatus, A. niger, A . ochraceus, A. sulpl1ureus and A. ustus have been used to investigate the role of three Coleopteran insect pests, namely, Callosobrochus maculatus, sitopl1ilus zeamais and Tribolium castaneum in the persistance and spread of contaminant fungi among grains of maize (Zea mays) and rice (oryza sativa) and seeds of bambara groundnut (vigna subterranea) and cowpea (Vigna unguiculata) . The Aspergillus species were among fungi isolated from the grains and seeds. Bambara groundnut seeds on saIe at Kaneshie , La, Madina, Makola and Mallam Atta markets in Accra district contained species of Absidia, Aspergillus, Cladosporium, Fusarium, Neurospora, Paecilomyces, Penicillium and PIll lularia. The dominant genera were Aspergillus and Penicillium represented by five and [our species, respectively, and the dominant species were Aspergillus flavus and Aspergillus niger . The predominant apecles of rowpea seeds from the same markets were Aspergillus £lnvus Jere Aspergillus oryzae, Cladosporium herbarum, Penicillium cl1rysogenum and Penicillium expansum. Although all the . seven As pergillus species could grow on insect body leachate agar prepared >J i th leacha te of the three insect pests, the conidia of some of them could germinate in the leacha te of only some of the insects. only A. flavus and A. ocl1raceus condidia germinated in all the three leachates. Germination of the conidia of all the species occurred , anY>Jay, in leachates containing extracts of various tissues of seeds (axis of the embryo , cotyledon and testa) and extracts of grains. Conidia of all the species germinated in solution of dissolved faecal pellets of Callosobrochus maculatus, while conidia of 11.. clavatus, A. ocl1raceus and A . sulplJureus only germinated in the solution of dissolved faecal pellets of Sitophilus zeamais and conidia of also three species, 11. . clavatus, A . flavus and A. ochraceus germinated in the solution of faecal pellets of Tribolium castaneum. Aspergillus flavus conidia adhering to the bodies of sitoplJilus zeamais and Tribolium castaneum were transported through maize grains packed in wide glass tubes. The amount of the conidia detached as the insects moved depended on the size of the spaces among the grains and the frequency of contact between the insects and the grains. s. zeamais lost 87.8, 8~.7 and 76.7 percent of the original load of conidia as the insects travelled over 100cm through grains measuring 5.3-8.3 x 4.04-7.3mm, 8.1-10.2 x 6.0-8.2mm and 9.5-12 . 2 x 7.5-9.5mm, respectively. The corresponding figures for conidia on T. castaneulll 'vere, 88.5, 87.9 and 82.8 per cent respectively. Dead insect bodies were invaded by many fungi despite the presence of large populations of sur face bacter ia. The colonyforming- units of bacteria recorded for C. lIlaculatus, S. zeamais and T. castaneum per ml of suspending medium immediately after death were 27 . 5 x 10', 281 x 10' and 104.5 x 10' respectively i and six days later they were 37.8 x 1~, 5.0 x 1~ and zero, respectively. On the sixth day, Aspergillus flavus was isolated from the bodies of all the three insect pests. In addition, Aspergillus niger, Mucor sp., Rhizopus sp. and Trichoderma Viride were isolatC2.cI ·: c_,: from C. lIlaculatus . , Aspergillus niger and Curvularia sp. from S. zeam~ is and Clasdosporiulll sp. from T. castaneulll. The mycelium growing in the bodies after death might have arisen from inoculum either on the surface of the body or in the gut . For, the gut of the insects had extensive mycoflora. Fourteen, thirteen and sixteen fungal species were isolated from the gut of C. maculatus, S. aeolllois and T. castaneum, respectively. The predominant genera were Aspergillus and Penicillium and five species, namely Aspergillus £lavus, Aspergillus fumigatus, Cladosporium herbarum, PellicilliJ.J.m citinum and Penicillium purpurogenum were isolated from the guts of all the three insect pests. Three Aspergillus species red experimentally to the insects persisted for different lengths of time in the guts. A. flavus was isolated 6,8, and 5 days respectively, after feeding the insects, from the guts of C. maculatus, s. zeamais and T. castaneum. The corresponding survival periods for A . fumigatus were 4,6 and 5 days respecti vely, and for A. oC/lraceus, 6,4 and 3 days respectively. It was concluded that products and dead bodies of the insects would contribute to the persistence of the contaminant fungi and living insects would be responsible for both persistence and dispersal of the fungi in stored grains and seeds. Persistence and dispersal of the fungi could be reduced by measures which control the insect pest popUlation, by periodic removal of dead insect bodies especially in comparatively smaller stocks kept i.n the markets and by exposure of the products to light to drive the insects to the dark base and discourage the frequent migration.Item Competition between Corcyra Cephalonica (Staint) and Ephestia Cautella (WLK.) and Study of Radiosensitivity of the Immature Stages of Corcyra Cephalonica(University of Ghana, 1982-08) Allotey, J.Competition between Corcyra cephalonica and Ephestia cautella and radiosensitivity of the immature stages of C. cephalonica was studied. Developmental periods of the two species under similar ambient conditions but different locations were determined . Competition under limited and abundance of standard medium and broken cocoa beans was studied when the two species exist alone, one before the other and when introduced together . It was concluded that in competition E cautella becomes extinct, with. cephalonica remaining as the successful species. A detai led study of oviposition preferences of the two species when given the choice of three food commodities; standard medium, broken cocoa beans and groundnut was studied. Other studies include egg-hatchability, age and effect of population on fecundity and for the first time the daily activity patterns of the larvae of C cephalonica and E cautella have been studied in a unique way. Radiosensitivity of the developmental stages: eggs, larvae and pupae of C. Cephalonica has also been investigated .Item The Bio-Ecology of Aedes Aegypti Linn., (Dipt: Culicidae) with Particular Reference to the Immature Stages, at Legon and Surrounding Areas(University of Ghana, 1982-07) Addo-Ashong, R.C.Item Studies On The Mycoflora Of Grains Of Maize (Zea Mays L.) And The Survival Of The Contaminant Aspergillus Species(University of Ghana., 1995-10) Kesse, R.E.O.Grains of Zea mays in storage at the Kaneshie and Tema warehouses of the Ghana Food Distribution corporation with atmospheric humidity fluctuating between 55 and 90% R. H. and those stored at 40°C in the Botany Department were attacked by a large number of fungi. Non-stackburn and stackburn grains at the Kaneshie warehouse contained 26 and 16 fungal species, respectively, and those in Tema warehouse had 32 and 19 species, respectively. Aspergillus was the dominant genus of the mycoflora and Aspergillus flavus was the predominant species occurring at very high levels. The moisture content of the grains stored in the warehouses showed, an average rise of 6.9 per cent within the six months of storage. During this period the percentage occurrence of A.flavus consistently rose to a peak at the end of the 4th month and declined. Paecilomyces puntonii and Paecilomyces variotii were consistently present in the early months of storage and then disappeared. The rest of the species taking all four batches of grains together, did not show a consistent pattern of occurrence. The air spora of the Kaneshie and Tema warehouses consisted of 26 and 27 fungal species, respectively, with the same difference in the dominant species. The most abundant species recorded in the Kaneshie warehouses in descending order were Aspergillus flavus, Ciadosporium herbarum, Aspergillus flavus-oryzae, Mucor sp., Aspergillus fumigatus, Rhodotorula sp . , Penicillium expansum, Aspergillus niger and Penicillium chrysogenum. On the other hand, the most abundant species in the Tema warehouse in descending order were Cladosporium herbarum, Aspergillus flavus, Penicillium expansum, Penicillium chrysogenum, Rhodotorula sp., Rhizoctonia solani, Aspergillus parasiticus and Paecilomyces puntonii. Grains of Abeleehi, Mixed White, Obatanpa and Yellow maize varieties stored at 40°C had 15, 16, 18 and 18 contaminant fungal species despite marked average loss of 41 .4 per cent moisture content over the storage period of 4 months. Aspergillus flavus, under those conditions, was again the predominant species. Experiments which investigated growth, sporulation, conidial germination capacity, and conidial survival in Aspergillus clavatus, Aspergillus flavus, Aspergillus niger and Aspergllus tamarii, showed significant physiological differences among the species. A. clavatus grew best at 38°C and sporulated best at 26˚C; it also grew best at 62 .4 - 7 3.4% R. H., and sporulated best at 85.2 - 100%- R.H . , conidia formed at 62 4 - 100% R. H. showed 90.0 - 99 .5 per cent germination in Potato Dextrose Broth and more than 69.6 per cent germination in 1 .0 Dextrose, 1 .0 .Sucrose and 1 .0 Peptone solutions, and more than 22.2 per cent ln exudates of grains of three maize varieties, but did not germinate ln water. The conidia of the other three species did not also germinate in water. The humidity at which the conidia were formed did not affect their rate of loss of vigour in storage. The conidia survived best at 0,60 and 100% R.H. and lost vlabl1lty quickest at 20 and 80% R.H. A flavus grew and sporulated best at 34°C; grew best at the humidities of 73 .4 - 92.8% R.H. and sporulated at 100% R.H. Conidia formed at 62.4 - 100% R.H . showed 80.7 - 94.3 per cent germination in Potato Dextrose Broth and more than 11 per cent germination in maize grain exudates but did not germinate in 1.0% Dextrose, 1.0% Sucrose and 0.1% Peptone solutions. The humidity at which the conidia were formed did not affect their rate of loss of vigour in storage. The conidia survived best at 0, 20, 40, and 100% R.H. and lost viability quickest at 80% R.H. A. niger grew and sporulated best at 34°C; grew best at the humidities of 92.8 and 100% R.H. and sporulated best at 62.4 - 92.8% R.H. Conidia formed at 62.4 - 100% R.H. showed 83.4 - 98.4 per cent germination in Potato Dextrose Broth but did not germinate in maize grain exudate, and in 1.0% Dextrose, 1.0% Sucrose and 0.1% Peptone solution. Conidia formed at 73.4 - 85.2% R.H. apparently had a greater potential for survival than those formed at the other humidities. A. niger conidia survived longest at 100% R. H. and longevity decreased with decreasing relative humidity. A· tamarii grew and sporulated best at 30°C; grew best at 62.4 - 73.4% R.H. and sporulated best at 62.4% R.H. Conidia formed at 62 . 4 - 100% R.H. showed 87.7 - 98.6 per cent germination in Potato Dextrose Broth but did not germinate in maize grain exudate nor in 1.0% Dextrose, 1.0% Sucrose and 0.1% Peptone solutions. Conidia formed at 65.0 85.2% R.H. seemingly had a greater potential for survival than those formed at the other humidities. A. tamarii survived longest at 0, 20, 40, and 60% R.H. and lost viability quickest at 100% R.H. Conidia of all the four species which were swollen prior to germ tube development and were then air-dried died within 1-6 hours. It was concluded that because of the variation in response of the fungl to temperature and humidity, warehouses held at a set temperature and relative humidity would not be able to control fungal contamination of the grains. More resistant fused pericarp and testa which could emerge from breeding programmes may be one of the more efficient ways by which invasion of the gralns could controlled.Item Sensitivity of Asexual Blood Stages Of . Plasmodium Berghet (Nk 65) to Chloroquine(University of Ghana., 1994-03) Aryee, N.A.The erythrocytic developmental cycle of Plasmodium berghei can be conveniently divided into the ring, tropho-zoite and schizont stages based on morphology. The sensitivity and effect of chloroquine on density-gradient isolated fractions of each of these stages was investigated using the plasmodial strain P.berghei (NK65), a rodent model as an experimental tool. This plasmodial strain was found to be routinely lethal in infected mice in the absence of administered therapeutic levels of chloroquine. P.berghei infected blood was separated into the various developmental stages using discontinuous Percoll gradient centrifugation. The various stage-isolated fractions were found to be infective and sensitive to these same levels of chloroquine. However chloroquine was found to show insignificant differential sensitivity with regards to the developmental stage of berghei (NK 65) strain.Item Biology And Ecology Of The Predatory Mosquito, Culex (Lutzia) Tigripes Grandpre And Charmoy (Diptera:Culicidae) In South-Eastern Ghana.(University of Ghana., 1990) Appawu, M.A.Culex (lutzia) tigripes Grandpré and charmoy is a larvivorous mosquito with all instars of the larvae feeding primarily on the immature stages of other mosquito species found in their habitats. They breed in a wide range of water bodies but seem to prefer those already containing larvae of other mosquito species. The fluctuations in the population of the larval instars and pupae were studied by weekly sampling throughout the year. It breeds throughout the year and the population peaks either coincide with or follow that of the preys; with both fluctuating with the rainfall. The larval densities of c. (L) tigripes were very small compared with those of other mosquito species; thus only 392-952 larvae of the predator were collected in the peak periods of May to July compared to 2786-8676 larvae of the prey mosquitoes. No significant correlation was noted between variations in the numbers of C. (L) tigripes and the following physical and chemical properties of the breeding water: pH, Temperature, Chloride, Dissolved Oxygen and Total Alkalinity. Life-table studies showed the existence of high mortalities in the later stages of the predator. Starting from egg rafts collected from the field and providing C. quinguefasciatus larvae as the larval food and chicken as a source of blood, a colony of C. (L) tigripes was started but poor insemination appeared to be the major obstacle to successful and permanent colonization. vi Artificial insemination and copulation were also not successful.The optimum larval developmental temperature was 30°C, and 32°C for the pupae. Even though more prey larvae were consumed between 30-32°C than between 20-26°C, there was a reduction in weight of the final instar larvae and pupae at the higher temperatures. Depending on temperature each predator consumed between 160-229 larvae of C.quinguefasciatus during its entire larval development. With this rate of prey destruction, the predator can have big impact on the prey population despite the low proportion (1:7-9) of predator to prey.When larvae of C. (L) tigripes were reared on three non living diets namely; Cerelac infant cereal, dog biscuit and milk casein, the developmental period of all instars was greatly prolonged and only one larva, reared on milk casein developed into adult mosquito. The weights of the final instar larvae reared on non-living diets were significantly lower than those reared on larvae of C. quinquefasciatus. Culex (L) tigripes has well developed mandibles and serrated mouthbrushes for effective predation. The effect of the following factors on prey capture were studied: mobility, size, posture, the density and the extent to which prey and predator occur simultaneously in the same habitat. Ae. aegypti which moves more frequently was more preyed upon than An. gambiae and C. quinquefasciatus, and similarly, C.quinquefasciatus was selected more than chironomid. The strong integument of the pupae together with their large vii sizes, spherical shape, posture in the water and ability to move quickly afforded them a better chance of escaping predation by C. (L) tigripes. The effect of prey stage, predator stage and prey density on the predation rate was investigated using (C. quinquefasciatus) as prey.It was shown that the rate of predation increased with increase in the size of the predator and the density of the prey but decreased with increase in prey size. The functional response of the predator to changing prey densities followed Hollings type II model. The handling time of the predatory larvae on preys decreased as the length of time in which they were deprived of food was increased but the daily prey consumption was not affected. Cannibalism occurred in all larval stages of the predator. The rate was higher among the early instars; was lower in the presence of mosquito prey and increased with crowding.Item Studies On The Powdery Mildew Disease Of Galphimia Glauca Ca V. Caused By Leveillula Taurica (Lev.) Arn. And The Effect Of Water Stress Imposed On The Host Plant On The Fungus.(1998-09) Owusu, M.ABSTRACT The morphology of the isolate of Leveillula taurica parasitizing Galphimia glauca at Legon and the effect of water stress imposed on the host plant and on the fungus and infection rate were studied. L. taurica forms dimorphic conidia, conical or primary conidia and cylindrical or secondary conidia. The cylindrical conidia of this isolate were longer than the conical conidia. The two types of conidia were, however, physiologically identical. The conidia germinated from zero to 100% RH. Percentage germination in 24 hours of conidia from plants watered daily and with highest Relative Water Content (R.W.C.) was 20.8%. Percentage germination then decreased with decreasing atmospheric relative humidity. Conidia germination was better in light of 76 lux and the germ tubes produced were longer than in dark. Furthermore, conidia formed in light had greater vigour than those formed in dark. Greater germination was stimulated on surfaces of host leaves watered daily. Percentage of conidia obtained from plants watered daily which germinated in 24 hours was 40.0,38.4 and 22.4 percent when inoculated onto host leaves of 80.6, 74.4 and 66.7 percent RW.C., respectively. Water stress imposed on the host plant affected the morphology of the fungus and germination capacity of the conidia. Of the four levels of R.W.C. (80.6, 78.4, 74.4 and 66.7%) maintained in the host leaves, diameter of haustoria, length of unbranched conidiaphores, branching, size of the conidia, level of water content of the conidia, and the germination capacity of the conidia decreased with increasing water stress. Both the R.W.C. of the leaf on which the conidia were formed and the RW.C. of the leaf inoculated with the conidia influenced infection rate. The best combination was a high R.W.C. of source plant and a high R.W.C. of the inoculated plant. Infected leaves became chlorotic with 'green islands' and were shed prematurely. The flowers were not infected and no mycelium was detected in the stem. It was concluded that the G. glauca isolate was different in some aspects from the Capsicum sp. isolate. Also, because weaker conidia were produced on leaves with greater water stress, infection rate could be reduced by imposing water stress on the plants to a level, which may not unduly harm the plants, but result in the formation of less effective infection propagules.