Thermoduric & Psychrophilic Bacteria from Milk Obtained from the Addis Ababa Dairy Development -U Enterprise
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Date
1988-06
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Addis Ababa University
Abstract
An attempt has been made in this study to isolate A identify
thermoduric A psychropivilic bacteria, which are the most serious
spoilage organisms, from milk obtained from tin? Addis Ababa Oairv
Hovelpoment Enterprise (AADDE ). An effort was also made to trace the
sources A origin of these organisms so as to prevent or at least reduce
their access into milk A hence increase the shelf -life of the
pasteurized milk A milk products.
The standard plate count { SPG) ranged between 4 X 10? A
3 X 109 bactoria/ml for raw milk, between 6 X 10'* A 3 X 10^ for plant
pasteurized milk A between 3 X 103 A 2.5 X for laboratory
pasteurized milk. The high standard plate count for the plant
pasteurized milk, as compared to that of the laboratory pasteurized
milk, has been found to bo due to the ability of many organisms to gain
access to the pasteurized milk as post pasteurization contaminants.
Psychrophilic bacteria wore the most dominant organisms in
both raw (98.1%) A plant pasteurized (53.0%) milk samples. Laboratory
pasteurized milk, on the other hand, contained predominantly
thermoduric bacte.
During the course of study, bacteria belonging to 14 genera
were isolated, the most dominant being: Streptococcus ( 27% ) ,
Staphylococcus (19,5%), micrococcus (13.9%) , Bacillus ( 12.9%) A
Arthrobactor (11.3%),.
Out of the 185 representative isolates identified
50% were cocci A 40% rods.
As many as 16 species of bacteria belonging to 9 genera were
isolated from raw milk, while 20 species of bacteria belonging to 14
gonora wore isolatcd from tho plant pasteurized milk. This indicated
that bacteria , other than those found in raw milk have been introduced
into the pasteurized milk as post pasteurization contaminants from the
bulk tanks, fillers A their pipelines and the plastic bags that contain
pasteurized milk. This fact has also been supported by data from
keeping quality tests performed at different sampling sites.
Sodium hydroxide ( dnOH ) A sodium carbonate ( NaC'03) , chemicals
regularly used for rinsing A disinfecting utensils at the Addis Ababa
hairy development Enterprise , were found to be ineffective in
inactivating bacteria at concentrations as high as 1:100 at 50-90
minutes holding time. Other disinfectants tested such as Savlon , A
Chlorox, on the other hand, were found to i> effective in eliminating
the same group of bacteria at lower concentrations ( 3 :HOO ) at 15-30
minutes holding time.
Based on this study , therefore, recommendations are made by
which the Dairy Plant can improve milk handling A processing conditions
A produce milk A milk products with improved shelf -life.
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Biology