Title page for ETD etd-10212009-174731


Document Type Doctoral Thesis
Author Madoroba, Evelyn
Email evelyn.madoroba@gmail.com
URN etd-10212009-174731
Document Title Molecular characterization and population dynamics of lactic acid bacteria during the fermentation of sorghum
Degree PhD
Department Microbiology and Plant Pathology
Supervisor
Advisor Name Title
Dr E T Steenkamp Co-Supervisor
Prof J Theron Co-Supervisor
Prof T E Cloete Supervisor
Keywords
  • lactic acid bacteria
  • fermentation of sorghum
  • southern Africans
  • ting
Date 2009-09-02
Availability unrestricted
Abstract
Ting is a cooked fermented sorghum food that is popular amongst southern Africans for its sour taste and unique flavour. However, major challenges are associated with large-scale production and marketing of this spontaneously fermented food due to inconsistent microbiological and sensory quality. The use of starter cultures may circumvent these limitations. Prior to engaging starter cultures, detailed knowledge of the microbial diversity and dynamics during fermentation is important. Therefore, the aim of this study was to investigate microbial diversity and dynamics during sorghum fermentations, and to clarify the role of starter cultures regarding the microbiological safety and consumer acceptance of sensory characteristics of fermented ting.

A culture-independent approach, based on the use of PCR-denaturing gradient gel electrophoresis (DGGE), revealed that Lactococcus lactis, Lactobacillus curvatus, Weissella cibaria and some Enterobacteriaceae were predominant at the end of spontaneous sorghum fermentations. Culture-dependent methods indicated that Lb. fermentum, Lb. plantarum, Lb. rhamnosus, E. faecalis, E. mundtii, W. cibaria and L. lactis were predominant at the end of fermentation. These results not only indicated the predominant bacteria during sorghum fermentation, but also indicated that a combined approach is required to reveal microbial diversity and dynamics during spontaneous sorghum fermentations.

Based on the above results, L. lactis, Lb. fermentum, Lb. plantarum and Lb. rhamnosus were evaluated as starter cultures for production of ting. All the starter cultures were able to ferment sorghum, but the lowest pH and highest lactic acid was produced in naturally fermented sorghum inoculated with L. lactis. This fermentation showed an increase in the number of lactic acid bacteria and yeasts, whilst pathogen counts decreased. Ting from this fermented gruel, in contrast to naturally fermented sorghum, had sensory properties preferred by panelists. The results indicated that the use of L. lactis in starter cultures may result in ting with consistent and acceptable attributes.

2009 University of Pretoria. All rights reserved. The copyright in this work vests in the University of Pretoria. No part of this work may be reproduced or transmitted in any form or by any means, without the prior written permission of the University of Pretoria.

Please cite as follows:

Madoroba, E 2009, Molecular characterization and population dynamics of lactic acid bacteria during the fermentation of sorghum, PhD thesis, University of Pretoria, Pretoria, viewed yymmdd < http://upetd.up.ac.za/thesis/available/etd-10212009-174731/ >

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