ISOLATION, CHARACTERISATION AND MODIFICATION OF SOME YEAST STRAINS FROM CITRUS JUICE FOR ENHANCED FERMENTATIVE ABILITY

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dc.contributor.authorOBASI, BLESSING CHIDI
dc.date.accessioned2016-02-05T09:31:36Z
dc.date.available2016-02-05T09:31:36Z
dc.date.issued2014-12
dc.descriptionA DISSERTATION SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES AHMADU BELLO UNIVERSITY, ZARIA IN PARTIAL FULFILLMENT OF THE REQUIREMENTS FOR THE AWARD OF A DOCTOR OF PHILOSOPHY DEGREE IN MICROBIOLOGY DEPARTMENT OF MICROBIOLOGY, FACULTY OF SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA NIGERIA.en_US
dc.description.abstractABSTRACT Yeast species present in sweet orange juice were isolated from healthy fermented single strength orange juice (FSSOJ) and defective single strength orange juice (DSSOJ). The characterisation of the indigenous yeast flora was carried out using analytical profile index techniques (API AUX 20C kit), physiological characterisation and genetic modification by mutation (nitrous acid and UV light irradiation treatment). The physiological characterisation involved the testing of several parameters required for ethanol production and dough leavening ability for bakery products (bread). These parameters were temperature, ethanol concentration tolerance, flocculation rate and sugar fermentative activity. The isolation rate of different yeast strains obtained using (API kit) in this research showed that yeast varies in their morphological and physiological characteristics. A total of 51 species were identified, representing 4 genera; 32 from FSSOJ, 19 species from DSSOJ. The isolation and prevalence rate of the yeast strains were Candida krusei (29)(57%),Rhodotorula minuta(10)(20%), Candida zeylanoides (4)(8%), Candida parapsilosis (3)(6%), Geotrichumcapitatum(2)(4%), Candida lusitaniae, Candida norvegensis and Kodamea ohmeri (1)(1%) respectively. The ability of some of the isolates:Candida lusitaniae, Candida parapsilosis and Rhodotorula minuta to metabolise xylose showed that they possessed the genes responsible for xylose fermentation. Thus, these made them suitable for ethanolic fermentation of hydrolysates of cellulosic materials. All the wild yeast strains obtained in this research combined four attributes namely; flocculation ability, tolerance to ethanol 8-18% (v/v), growth at 37 - 420C, and ability to ferment 10-40% (w/v) glucose except Geotrichum capitatum. Yeast possessing such combination of attributes appeared to have considerable potential for industrial application. Based on the physiological attributes and mutagenicity of the wild yeast strains for ethanol, dough leavening ability and the evaluation of the bread quality made with them,the ix following results were obtained. The mutants of nitrous acid-induced and UV-irradiated(NAM and UVM:2F36,2F8,2F9,DS6 and DS20) selected for ethanol production showed an appreciable increase in ethanol yields which ranged from 14.78-18.18% v/v within two to five days, while the wild yeast strains(2F36,2F8,2F9,DS6 andDS20)ranged from 10.93-17.05% v/v within five to seven days of fermentation period respectively. The ethanol yields were obtained from fermentation of 5% sorghum starch after distillation, using titrimetric dichromate method. The result obtained from the dough leavening capacity showed that the mutants of sweetened dough had a better leavening ability than that of the unsweetened dough. However, some species of the wild strains, Kodamea ohmeri,Candida norvegensis, and Rhodotorula minuta obtained in this research had an outstanding dough leavening capacity both in the sweetened and unsweetened dough when compared with the commercial baker‟s yeast. The results of the hedonic rating of the bread samples showed that the panelists preferred the wheat bread made using the mutant strains of yeast in the sweetened bakery product, while those samples made using the wild strains were preferred in the unsweetened bread samples. This study enabled the acquisition of data on the basic physiological and mutagenic pattern of yeasts required for the industrial production of higher ethanol concentration and dough leavening capacity with regard to their use in bakery products.en_US
dc.identifier.urihttp://hdl.handle.net/123456789/7372
dc.language.isoenen_US
dc.subjectISOLATIONen_US
dc.subjectCHARACTERISATIONen_US
dc.subjectMODIFICATIONen_US
dc.subjectYEASTen_US
dc.subjectFERMENTATIVEen_US
dc.subjectCITRUS JUICEen_US
dc.titleISOLATION, CHARACTERISATION AND MODIFICATION OF SOME YEAST STRAINS FROM CITRUS JUICE FOR ENHANCED FERMENTATIVE ABILITYen_US
dc.typeThesisen_US
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