Spoilage of bread, cake and breakfast cereals

1. Contamination, Preservation, and Spoilage of
Cereals and Cereal Products
A.Poshadri
Asst.Professor – Food Technology

2. Introduction
• Cereals and Cereal products are important human food resources
and live stock feeds world wide
• The exteriors of harvested grains retains some of the natural
flora they had while growing plus contamination from soil ,
insects & other sources
insects & other sources.
• Freshly harvested grains contain loads of a few thousand to
million of bacteria /gm and mold spores
• Excess moisture in cereals, grains, flours and other cereal based
food stuff permits the growth of molds but more moisture will
the growth of yeasts and bacteria.

3. • The most commonly found spoilage bacteria are Pseudomonas,
Micrococci, Lactobacilli and Bacilli.
• Scouring and washing of the grains remove some of the
microorganisms
• Most of the microorganisms are removed with the outer portions of
the grain during milling.
grain during milling
• The milling processes especially bleaching reduce no. of organisms.
• Recontamination may take place during blending and conditioning

4. • Bacteria in wheat flour include spores of Bacillus, coliform
bacteria, and a few representatives of the genera Achromobacter
*, Flavobacterium, Sarcina, Micrococcus, Alcaligenes, and
Serratia.
• Mold spores are chiefly those of aspergilli and penicillia, with also
some of Alternaria, Cladosporium, and other genera
Alternaria, Cladosporium, genera
• Aspergillus flavus and A. parasiticus produces aflatoxin.

5. • Corn meal and flour contain several hundred to several thousand
bacteria and mold per gram. Species of fusarium & penicillum are
dominant molds.
• Because of the incubation in a moist conditions , malts contain high
numbers of bacteria , usually in the millions per gram.
• The surface of freshly baked bread is free of viable microorganisms
but is subject to contamination by molds from the air during
but is subject to contamination by molds spores from the air during
cooling & before wrapping. cakes are similarly subject to
contamination.
• spores of bacteria able to cause ropiness in bread will survive the
baking process.
• The contamination of cereals grains products with molds has become a
significant concern because of the presence of mycotoxin.

6. Preservation
• Most cereals and cereal products have such a low moisture
content that there is little difficulty in preventing the growth of
microorganisms as long as the foods are kept dry.
• The storage temperature of about 4 4 to 7 2°C is recommended
• The storage temperature of about 4. 4 to 7. 2°C is recommended
for the dry products.
• Many bakery products eg. bread , rolls, cakes, pastries &canned
mixes contain enough moisture to be subject to spoilage unless
special preservative methods are employed.

7. Methods
• Asepsis:improperly sanitized equipments
may be source of rope bacteria and the
acid –forming bacteria that cause
sourness of dough.
• Bread , cakes and other baked products
may be subject to spoilage by molds
should be protected against
contamination by mold spores.

8. Methods
Use of Heat:
• Bakery products may be sold unbaked ,
partially baked or fully baked.
• The complete baking process destroys all
the bacterial cells, yeasts mold but
the bacterial cells, yeasts , mold spores but
not spores of rope –forming bacteria.
• Spores can survive during heat so unbaked
products are kept for short period or kept
cool during longer storage of time.

9. Methods
Use of low temp.
baked products should be kept under cool
conditions or refrigerated in home for the
prevention of food spoilage.
These can be stored for months in the frozen
conditions.
Unbaked or partially baked products, waffles,
cheesecake, ice cream pie, and fish, poultry,
and meat pies are usually frozen.
Bread and rolls can be stored successfully for
months in the frozen condition.

10. Methods
Use of Chemicals.
A large no. of preservatives have been
employed , particularly as mold
inhibitors , in breads , rolls , cakes.
Sodium and calcium propionate ,
sodium diacetate and sorbates are
used extensively.
Acidification of dough with acetic acid
has been used to combat rope.

11. Methods
Use of irradiation
In bakeries , ultraviolet rays have been to destroy or reduce
numbers of mold bacteria in dough and proof rooms, on the
knives of slicing machine on the surface of breads cakes
knives of slicing machine , on the surface of breads , cakes.
Ionizing radiations , gamma and cathode rays have been applied
experimentally for the preservation of baking goods.
• Low-level irradiation can also be used to destroy insects in
stored grains.

12. SPOILAGE
• Cereals grains , meals &flours made from them should not be subject
to spoilage if are stored or kept properly because their moisture
content is too low to support even the growth of molds.
• The major factors involved in the spoilage of grain by molds include
microbial load, moisture levels above 12 to 13 %, physical damage and
storage temperature
• The microbial contribution of cereal grains and flours to convenience
foods is an important consideration from a public health aspect and as
a source of possible spoilage agents.

13. Spoilage
Flours
Dry cleaning , washing and the milling of grains and sifting of flour
reduce the content of microorganisms
White wheat flour, however, usually is bleached by an oxidizing agent,
such as an oxide of nitrogen, chlorine, nitrosyl chloride, or benzoyl
peroxide, and this process serves to reduce microbial numbers and
kinds.
A moisture content of flour of less than 13 percent has been reported
to prevent the growth of all microorganisms. Other workers claim
that 15 percent permits good mold growth and over 17 percent the
growth of both molds and bacteria

14. • If acid-forming bacteria are present, an acid fermentation begins,
followed by alcoholic fermentation by yeasts if they are there
and then acetic acid by Acetobacter species.
• In the absence of lactics and coliforms, micrococci have been
found to acidify the paste, and in their absence species of
Bacillus may grow, producing lactic acid, gas, alcohol, acetoin,
and small amounts of esters and other aromatic compounds.
• It is characteristic of most flour pastes to develop an odor of
acetic acid and esters.

15. Spoilage
Bread
The fermentation taking place in the dough for various kinds is due to
microorganisms are desirable and even necessary in making certain kind of
bread.
The acid fermentation by lactics and coliform bacteria that is normal in
flour pastes or dough may be too extensive if too much time is permitted
flour pastes or dough may be too extensive if too much time is permitted ,
with the result that the dough bread made from it may be too ‘sour’.
Excessive growth of proteolytic bacteria during this period may destroy
some of the gas –holding capacity so essential during the rising of the dough
& produce a sticky dough.
The chief types of microbial spoilage of baked bread have been moldiness
and ropiness , usually termed “mold” & “rope”.

16. • Molds are the most common and hence the most important cause of the
spoilage of bread and most bakery products.
• The temp. attained in the baking procedures usually are high enough to kill all
the molds spores in and on the loaf.
• Chief molds involved in the spoilage of bread are
- bread mold”, Rhizopus tolonifer (syn., R. nigricans) with its white cottony
mycelium and black dots of sporangia ;
-Green –spored- Penicillium expansum;
-Aspergillus Niger with its greenish or purplish –brown conidial heads and
yellow
yellow pigment
pigment diffusing into the bread.
- Monilla (Neurospora) sitophila, whose pink conidia give a pink or reddish color
to its growth.
Species of Mucor or Geotrichum or any of a large number of species of other
genera of molds may develop.

17. Mold spoilage is favored by
1. Heavy contamination after baking, due, for example, to air
heavily laden with mold spores, a long cooling time,
considerable air circulation, or a contaminated slicing machine,
2. Slicing, in that more air is introduced into the loaf
3. Wrapping, especially if the bread is warm when wrapped, and
4. Storage in a warm, humid place.
• There is little growth of commercial importance on bread crust in
a relative humidity below 90 percent.

18. Preventive methods for moldiness of bread:
I. Prevention of contamination of bread with mold spores in so
far as practicable.
The air about the bread is kept low in spores by removal of possible
breeding places for molds, such as returned bread, or walls and
equipment.
equipment.
Spore-laden flour dust from other parts of the bakery has been
incriminated in causing increased moldiness of bread.
Filtration and washing of air to the room and irradiation of the room
and more especially the air by means of ultraviolet rays cut down
contamination.

19. • Prompt and adequate cooling of the haves before wrapping to
reduce condensation of moisture beneath the wrapper.
• Ultraviolet irradiation of the surface of the loaf and of slicing
knives.
• Destruction of molds on the surface by electronic heating.
Keeping the bread cool to slow mold growth or freezing and
• Keeping the bread cool to slow mold growth or freezing and
storage in the frozen condition to prevent growth entirely.
• Incorporation in the bread dough of some mycostatic chemical.
– Sodium or calcium propionate - 0.1 and 0.3 percent
– Sorbic acid, up to 0.1 percent
– Sodium diacetate, up to 0.32 percent

20. • Rope: Ropiness is caused by a mucoid variant of Bacillus subtillis or B.
licheniformis, formerly called B. mesentericus*, B. panis*, and other
species names.
• The spores of these species can withstand the temperature of the
bread during baking, which does not exceed 100°C, and can germinate
and grow in the loaf if conditions are favorable.
• The ropy condition apparently is the result of capsulation of the
• The ropy condition apparently is the result of capsulation of the
bacillus, together with hydrolysis of the flour proteins (gluten) by
proteinases
• of the organism and of starch by amylase to give sugars that encourage
rope formation
• The area of ropiness is yellow to brown in color and is soft and sticky
to the touch.

21. • Red Bread: The red color results from the growth of pigmented
bacteria, usually Serratia marcescens, an organism that often is
brilliantly red on starchy foods
• Molds, such as Monilia (Neurospora) sitophila - impart a pink to
red color to bread.
• A red color in the crumb of dark bread has been caused by
Geotrichum aurantiacum (syn.Oidium aurantiacum).
• Chalky bread: The defect has been blamed on the growth of
yeast like fungi, Endomycopsis fibuligera and Trichosporon
variable.

22. Spoilage
Cakes and Bakery Products
• The deterioration of breads, cakes, pies, and other bakery products
that is referred to as staling is due mostly to physical changes during
holding and not to microorganisms.
• Usually the toppings or fillings are more prone to microbial spoilage
Usually toppings fillings prone spoilage
than is the actual baked portion.
• It is not unusual for the fillings of many pasteries to support the
growth of microorganisms.
• Frostings, because of their high sugar content, are quite stable but
may be spoiled by molds or yeast upon storage

23. Spoilage
Pasta, Macaroni, and Tapioca
• Pasta is delivered and stored dry; therefore, there are seldom reports
of spoilage in these products.
• The swelling of moist macaroni has been reportedly caused by gas
production by bacteria resembling Enterobacter colacae.
production by resembling
• During the drying of macaroni on paper a mold of the genus Monilia
has been found responsible for purple streaks at contact points with
the paper.
• Tapioca, prepared from the root starch of cassava, will spoil if
moistened.

24. Microbiological Profile of Cereal Grains and Cereal Products