The Effect of Sodium Chloride Concentration on the Growth of Bread Mold
Khoa Tran
Department of Biological Science
Saddleback College
Mission Viejo, CA 92692
Abstract
The growth of bread mold depends on many factors: temperature, pH, water and sodium chloride
concentration. This experiment will test that the growth of fungus is decrease with the increase of sodium
chloride concentration. The use of sodium chloride at 0% concentration in the control group showed the
significant in growth of fungus after four days and almost covered the whole slice in seven days with the
average of 17.7 ± 0.617 (± S.E.M, n = 10) colonies. At 5% concentration, there was only the average
growth of 0.9 ± 0.298 (± S.E.M, n = 10) colonies after 7 days. At 10% concentration and above
concentration did not show any growth of bread mold after seven days. The ANOVA test showed a
significant different with P = 1.49x10-68 and Post Hoc (Bonferroni Correction - Multiple Comparison)
was run resulting in a significant difference between the 0% concentration and the 5% concentration, as
well as a difference between the 5% concentration and the 10% concentration and above groups.
Introduction
Mold is a disgusting organism. When people think about it, they think of a nasty yellow or green bacteria
growing on food or someone foot, however mold can be interesting to study (Gray 1970). The word mold
is a general term that is used for fungi that produce asexual spores. It is a microscopic fungus that is made
up of long tube-like strands of cells and all of these are called mycelium and these form colonies that keep
multiplying. There are approximately one hundred thousand known types of mold and scientists think that
there could be more than two hundred thousand. Molds grow on lots of food, especially foods with lots
of starch, like bread. Often, lots of preservatives are added to bread to keep mold and other organisms
from growing. There are five common food spoilage molds: Penicillium roqueforti, Trichoderma
harzianum, Paecilomyces variotii, Aspergillus niger, and Emericella nidulans (Cuppers, Henk G A
M, Oomes, Suus, and Brul, Stanley, 1997). Some molds are safe, some harmful. The molds that are
essential for food such as ones used on cheeses but the fuzzy molds that grow on some foods such as
bread can be toxic as with food poisoning (Anon, 2010). There are many factors that contribute to the
growth of mold such as: temperature, pH, and sodium chloride concentration (E Z Panagou, P N
Skandamis, and G-J E Nychas, 2005). The salt content will affect mold growth, and inhibited production
of some metabolites (Godinho and Fox, 1981). The present paper is hypothesized that the sodium chloride
concentration will slow down the growth of bread mold at low concentration and will inhibit any mold
growth at high concentration.
Materials and Methods
Eighty slices of baked bread without preservatives were divided into eight groups for the test ranging
from 0% concentration of sodium chloride which was used as control group and the sodium chloride
concentration went up with the increment of 5% to the maximum of 40%. The sodium chloride
concentration was prepared by mixing of water and table salt, the 5% concentration was mixed using 95
ml of water and 5 grams of salt; other concentrations were mixed with the same method. The slices of
bread were sprayed with the salt concentration from zero percent to forty percent and exposed to the open
air inside the living room for 30 minutes to simulate the same condition as when the consumers tried to
make sandwich. The breads were covered with nylon to prevent them from drying out and left in the
dinner table for 7 days. The temperature, pH, water of these slices of bread were kept the same for seven
days. After seven days, the nylon cover was removed and the mold colonies on each slice of bread were
counted.
Results
Numbers of colonies of mold on each slice of bread were counted after seven days. There was significant
difference in the growth of mold on the slices with zero percent concentration with the average of 17.7 ±
0.617 (± S.E.M, n = 10) colonies per slice. The average number of colonies on the five percent
concentration is 0.9 ± 0.298 (± S.E.M, n = 10). There was no growth of any mold on any slice of bread
with the concentration of ten percent or higher (Figure 1). The ANOVA test was run for 0%, 5% and 10%
and greater groups with the P = 1.49x10-68 which was less than 0.05so a Post Hoc Bonferroni Correction
was run resulting in a significant difference between the zero percent concentration and the five percent,
as well as a difference between the five percent concentration and the ten percent or greater groups.
Figure 1: There is the significant different in the average number of colonies (17.7 ± 0.617 (± S.E.M, n =
10) on the zero percent concentration compare to five percent concentration (0.9 ± 0.298 (± S.E.M, n =
10) and greater than ten percent. The growth on the five percent slice (0.9 ± 0.298 (± S.E.M, n = 10) is
also significant compare to the greater than ten percent slices (0 growth). The graph shows the average
colonies on zero, five and greater than ten percent concentration and the error bar of ± SEM, n = 10
Discussion
The data shows there was a difference in the average number of molds when the sodium chloride
concentrations used were varied. The zero percent group showed a high number of colonies (17.7 ± 0.617
(± S.E.M, n = 10), the five percent group showed some growth (0.9 ± 0.298 (± S.E.M, n = 10) but very
few compare to the zero percent group. At higher concentration (ten percent or above) showed no sign of
growth. In the case of this experiment, the hypothesis being tested was correct; the high sodium chloride
concentration will slow down or stop the growth of bread mold. The hyperosmosis environment created
by the high sodium chloride concentration will make the fungus cell tries to adjust the concentration
inside the cell equal to the concentration outside; eventually the cell will lose all the water, become
dehydrated and died. The salt content will affect mold growth (Godinho and Fox, 1981) and this
experiment showed the same results.
Literature Cited
Gray, W. D., 1970. What We Find When We Look at Molds. New York: McGraw-Hill Book Company.
Godinho, M., and P. H. Fox., 1981. Effect of NaCL on the germination and growth of Penicillium
roqueforti. Milchwissenschaft. 36:205-208.
Cuppers, Henk G A M, Oomes, Suus, and Brul, Stanley., 1997 "A model for the combined effects of
temperature and salt concentration on growth rate of food spoilage molds. " Applied and Environmental
Microbiology 63.10
Anonymous,. Hold that mold., 2010. University of California, Berkeley, Wellness Letter, 26(6), 8.
E Z Panagou, P N Skandamis, and G-J E Nychas., 2005 "Use of gradient plates to study combined effects
of temperature, pH, and NaCl concentration on growth of Monascus ruber van Tieghem, an ascomycetes
fungus isolated from green table olives. " Applied and Environmental Microbiology 71.1