MOLECULAR CHARACTERIZATION OF LACTIC ACID BACTERIA ISOLATED FROM SOURDOUGH AND THEIR BAKING POTENTIALS
MOLECULAR CHARACTERIZATION OF LACTIC ACID BACTERIA ISOLATED FROM SOURDOUGH AND THEIR BAKING POTENTIALS
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Date
2016-10
Authors
DASHEN, MICHAEL MACVREN
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Abstract
This study was aimed at determining the lactic acid bacteria composition of Nigeria‘s type II sourdough, their baking potentials and the type of exopolysaccharides genes they carry. Doughs made from three different brands of Nigeria‘s widely used wheat flour were fermented spontaneously to produce sourdough. Microbial counts, pH and titratable acidity of the sourdoughs were determined. Lactic acid bacteria were isolated from the sourdoughs and identified. Selected lactic acid bacteria from the sourdoughs and selected sourdough were used to bake bread and doughnuts. The lactic acid bacteria were also screened for exopolysaccharides (EPS) production ability. Molecular characterization and sequencing of the exopolysaccharide genes were also carried out. The results obtained revealed that the lactic acid bacteria were the dominant population in all the sourdough samples. The highest total mean counts were log 6.826±0.68, 6.551±0.57 and 6.414±0.59 for lactic acid bacteria, fungal count and aerobic plate count respectively at room temperature. At 400C, the highest total mean counts were log 7.051±1.04, 4.925±0.64 and 4.968±0.88 for lactic acid bacteria count, fungal count and aerobic plate count respectively. Significant difference exists between these counts at P≤0.05. The pH values decreased with increase in fermentation time; it ranged between 6.73 ±0.05 and 4.20 ±0.29 while the TTA values increased with increase in fermentation time; it ranged between 0.168±0.00 and 0.676±0.01. A total of seventy-nine (79) isolates of lactic acid bacteria were obtained. The lactic acid bacteria isolated from the sourdough samples included Lactobacillus plantarum (34.17%), Lactobacillus brevis (29.11%), Lactobacillus pentosus (17.72%), Pediococcus pentocaseus (8.86%), Lactobacillus buchneri (2.53%), Lactobacillus collinoides (2.53%), Lactobacillus fermentum (2.53%) and Pediococcus acidilactici (2.53%). Nineteen (24.05%) out of the total of seventy-nine (79) lactic acid bacteria isolates produced exopolysaccharides. Sixteen (84.21%) of the nineteen EPS positive isolates phenotypically expressed their EPS in form of mucoid and ropy
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colonies while three (15.79%) produced only mucoid colonies. Fourteen (73.68%) of the nineteen EPS positive isolates were heterofermenters. The best gas producers were Lactobacillus plantarum SP2 and Lactobacillus brevis SP5. The highest dough leavening was obtained from the combination of Lactobacillus plantarum and baker‘s yeast which was 108.00±2.00cm3 compared to 92.00±1.00cm3 for baker‘s yeast alone both at 180 minutes of dough leavening. Significant difference exists between the dough leavening at P≤0.05. All the lactic acid bacteria based bread and doughnuts also compared favourably with the baker‘s yeast bread and doughnuts and commercial bread and doughnuts in terms of organoleptic quality. All the lactic acid bacteria based bread and doughnuts had longer minimum mould free shelflife than the baker‘s yeast and commercial bread and doughnuts. All the bread and doughnuts were within standard with respect to moisture content and protein contents. Seven (36.84%) of the nineteen (19) exopolysaccharides producing lactic acid bacteria were levansucrase (LevV) gene positive while none was glucansucrase gene positive. Molecular Phylogenetic analysis indicated close relationship between the isolates. Therefore the lactic acid bacteria isolated from the type II sourdough have the potentials for use as starter culture in baking for the improvement of the organoleptic quality and shelflife of bakery products in Nigeria.
Description
A THESIS SUBMITTED TO THE SCHOOL OF POSTGRADUATE STUDIES, AHMADU BELLO UNIVERSITY, ZARIA, IN PARTIAL FULFILLMENT FOR THE AWARD OF DOCTOR OF PHILOSOPHY IN MICROBIOLOGY DEPARTMENT OF MICROBIOLOGY, FACULTY OF SCIENCE, AHMADU BELLO UNIVERSITY, ZARIA
Keywords
MOLECULAR,, LACTIC ACID,, BACTERIA,, SOURDOUGH,, BAKING POTENTIALS,