Physicochemical assessment of microbial communities of fermented olives in Namibia using culture dependent and independent methods
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Date
2019
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Publisher
University of Namibia
Abstract
Wild olives are native to the Mediterranean area, sub-tropical and central Asia, and
parts of Africa. Table olives are prepared from the raw fru it of the European or
domesticated olive Olea europaea L. Hoff. Table olives are one of the lesser known
fermented fruits in Namibia with naturally associated lactic acid bacteria (LAB) and
yeast. These microorganisms are responsible for the development of aroma and
flavour in the final olive product. The aim of this study was to document processing
methods of table olive production, determine the physicochemical parameters which
affect microbial growth and identify the microbial communities associated with olive
fermentation in Namibian table olives using culture dependent and independent
methods. Untreated table olives in Namibia are produced mostly by spontaneous
fermentation . A total of 30 olive samples were collected from two different sites
(Noab and Shalom) from February to October 2018. Total plate count, total phenolic
content, total LAB and total yeast and mould count were also determined over 5
months to study the kinetics and dynamics of microbial populations during this
fermentation. DNA was extracted using a culture dependent method and the culture
independent method of metagenomic analysis was also used. Total phenol content
ranged from 2.323 x 10-4 g Gallic Acid Equivalent (GAE) /mL at day 0 to 8.691 x
10-4 GAE/mL on day 150. Olive samples had an alkaline pH (8 .9) which was then
decreased and stabilized to around 4.5 after day 30 and remained constant up until
day 150. Titratable acidity ranged from 0.29 g/L at day 0 to 2.85 g/L at day 150, and combined ac idity from 0.008 Mol NaOH/L at day 0 to 0.128 Mol NaOH/L at day
150. NaCI content of both sites ranged from 8.24 to 10.54% NaCl. Total count plate
showed that LAB (3.9814 ± 0.25494 log10 CFU/ mL) and yeast (4.1098 ± 0.23534
log1o CFU/ mL) had similar counts for both sites. Phyla including Rozellomycota,
Chytridiomycota, Mucoromycota, Cercozoa, Rotifera, Glomeromycota,
Calcarisporiellomycota, Mortierellomycota, Basidiomycota, Ascomycota,
Neocallimastigomycota, Fusabacteria, Acidobacteria, Chlorojlexi, Deferribacteres,
Verrucomicrobia, Actinobacteria, Bacteriodetes, Proteobacteria, Firmicutes and
Cyanobacteria for 16S sRNA, 18S rRNA and ITS were identified through
metagenomic analysis. This study is the first attempt to use metagenomics analysis
on Namibian table olives and confirming the presence of probiotic LAB and yeast
which might be responsible for the special organoleptic properties of this product.
Description
A mini thesis submitted in partial fulfillment of the requirements for the Degree of Master of Science ( Microbiology)