Browsing by Author "Dorleku, W."
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Item Phenolic Oxidases in Gall Disease of Milicia Species(University of Ghana, 2000-08) Dorleku, W.; Gbewonyo, W. S. K.; Osei, Y. D.; Addy, M. E.; University of Ghana, College of Basic and Applied Sciences, School of Physical and Mathematical Sciences, Department of ChemistryMilicia regia and M . excelsa are inva.lua.iDle plant species in Ghana for their durable timber. Their numbers are however dwindling. Efforts by the forestry department to establish plantations have been unsuccessful due primarily to attack by Phytolyma species, resulting in gall formation. Phenols and phenolic oxidases appear to be important in the defence mechanisms of some plants as well as in wound healing and regulation of growth in these plants. Thus, they may be natural resistance factors of the Phytolyma-induced gall disease of Milicia species. The activities of phenolic oxidases, [polyphenol oxidase (PPO) and peroxidase (PRO)] and the phenolic content in galls and leaves of Milicia species differing in susceptibility to Phytolyma attack were determined. Polyphenol oxidase and peroxidase were also extracted and partially purified from acetone powders prepared from the galls and leaves. The activity of polyphenol oxidase was found to be higher in the leaves of the resistant plants than in the tolerant and susceptible plants. Galls of the seedlings also showed higher activity of the enzyme than in the normal leaves. Similar trends were also observed for the activity of peroxidase in the samples but the differences in activity were insignificant. Phenol and o-dihydroxyphenol contents of galls of seedlings were slightly lower than in the normal leaves. The resistant plants also showed slightly higher phenol content than the tolerant and susceptible plants. The susceptible plants on the other hand appeared to contain slightly higher o-dihydroxyphenol than the resistant plants. Peroxidase and polyphenol oxidase were extracted and partially purified from acetone powders prepared from galls and leaves of the samples. The peroxidase and polyphenol oxidase from the galls were purified 10 and 14-fold, respectively, using gel filtration followed by ion-exchange chromatography. The peroxidase and polyphenol oxidase from the leaves were also purified 37 and 17-fold, respectively, using ion-exchange chromatography followed by gel filtration. The activities of the two enzymes could not be separated as they co-eluted in the same fractions. The purified enzymes from both sources did not oxidize monophenolsItem Response surface optimisation of enzymatic hydrolysis of cassava peels without chemical and hydrothermal pretreatment(2022) Dorleku, W.; Bayitse, R.; Hansen, A.C.H.; Saalia, F.K.; Bjerre, A.Cassava peel is a feedstock of significant potential for bioprocessing into industrial products. Its economic utility has however not been explored despite its advantages over traditional first-generation biomass feedstock. We demonstrate in this study that cassava peel can be hydrolysed to produce glucose at very high efficiency without chemical or hydrothermal pretreatment. We evaluated the conversion efficiency of a one-step simultaneous hydrolysis of the peel with mixed enzymes. Response surface methodology was applied to optimise the hydrolysis condition for maximum glucose recovery. Glucose concentration was measured by HPLC-IR and polynomial regression models defining the process parameters fitted to predict the optimal setting of process variables for maximum glucose recovery. Maximum glucose recovery was predicted to occur at pH 4 and 54.75 °C with an enzyme mixture containing 10 FPU/g cellulase, 0.5 U/g β-glucosidase, 50 U/g amyloglucosidase, and 50 U/g α-amylase. Validation experiments confirmed that up to 95.48% glucose can be recovered from 0.06 g/ml of cassava peel in 43.15 h at these factor settings. Overall, the empirical models developed present an efficient tool for glucose recovery at high conversion efficiency. This model could be used for large-scale industrial production of glucose from cassava peel without the cost of pre-treatment.