L. Assistant Rawa abdul Redha Aziz
FOOD MICROBIOLOGY LAB 10
Microbiological spoilage of Sweet Foods
-Sweet food can be spoiled lower than other food because it has high
levels of sugar, and that will affect on microorganisms
growth.
- There is a normal flora in sweet food such as
Osmophilic Microorganism.
Honey
-Honey contains 80% sugar
-It can be spoiled when crystallization happens. Crystallization is the
process where sugar crystals will separate from honey leading to increase
water activity to 10-20%.
-At this Aw and increase temperature, yeast will grow causing Ethanol
production and alcoholic yeasty honey.
-Osmophillic yeast:
Saccharomyces bailli var. osmophilus
Saccharomtces bisporusvar. mellis
Saccharomyces rouxii (also spoil Pekmez)
-The surface of honey is considered to be the target of molds such as
Aspergillus , Penicillum , Mucor (Why???)
- To preserve honey from spoilage, it is prefer to pasteurize it at
60°C for 30 min.
Jam, Candies, and Nestele
***Jam:-Jam contains 70% sugar and pH of 4; therefore, bacteria can not grow
on these conditions.
- Jam can be spoiled faster because it contains the whole fruits not small
piceses. These fruits will protect spores from high temperature
pasturization.
- Spores of bacteria can not grow on this environment, but
osmophilic yeast can grow leading to alcohol, acids, and gases
production.
-Molds such as Byssochlamys fulva grow on the surface of jam;
just like with honey.
Collage of Science/ Kufa University
Fourth Level
L. Assistant Rawa abdul Redha Aziz
FOOD MICROBIOLOGY LAB 10
***Candies and Nestle:-Here, candies and nestele are seldomly spoiled;
however, nestle can be spoiled when using
contaminated plant materials or milk as a matrix for it.
-These contaminated matrixes could have Clostridium
spores or microorganisms toxins.
Lab Work
A-Safety Tests of Sweet Food:
**You can take 1 ml by pipette from sweet food if possible and
culture it on test tubes of N.A. (containing 20% sucrose). Tests
tubes then incubate at 25-30° C/ 2-5 days. After that, see
whether there is gowth or not.
** Take by loop from test tube that has M.O growth and put it
on slide and stain it. See under the microscope.
B-Microorganisms Plate Count
You can take 1 ml by pipette from sweet food if possible to 9
ml D.W to make the first dilution. Then you make the other
dilutions until 10-5. Take 1ml from each dilution and culture it
on Petri dishes of N.A. (containing 20% sucrose). Petri dishes
then incubate at 30-32°C/ 3 days. After that, read the result.
** Take by loop from D.W and put it on slide. Then take by
neddel from plates that have M. growth and stain it. See under
the microscope.
C-Isolate molds and yeast from sweet food
Make dilutions until 10-5 from sweet food sample. Take 1ml
from each dilution and culture it on Petri dishes of PDA
(containing 20% sucrose). Petri dishes then incubate at 25°C/ 35 days. After that, read the result.
** Take by loop from D.W and put it on slide. Then take by neddel from
plates that have M. growth and stain it. See under the microscope.
Collage of Science/ Kufa University
Fourth Level