Microbiology Of Cereals And Cereal Products

Microbiology of Cereals and cereal products. Spoilage of cereals and their products and preservation techniques.

1. MICROBIOLOGY OF CEREALS
AND CEREAL PRODUCTS
PRESENTED BY :-
MD KAMIL
DEPT. OF FOOD SCIENCE AND TECHNOLOGY
MAKAUT, WEST BENGAL

2. CONTENTS
✓INTRODUCTION
✓SOURCES OF CONTAMINATION
✓SPOILAGE OF CEREALS
✓SPOILAGE OF CEREAL PRODUCTS
✓ROPINESS OF BREAD
✓PRESERVATION OF CEREALS

3. INTRODUCTION
• Cereal grains, such as wheat, corn, rye, oat, rice, etc., are important nutrients and energy sources for humans.
• Cereal grains are the most commonly consumed food group worldwide and they are grown on about 60% of the cultivated
land in the world.
• Cereals are consumed in various forms in the food industry.
• Cooked cereals are eaten directly after cooking (rice, maize).
• Flours are made by grinding cereals (such as wheat, maize, rice, and rye) and products processed from them, e.g. biscuits,
cookies, etc.
• Bread is usually made from flours of wheat and rye by yeast fermentation.
• Manufactured dried cereal products produced from wheat, maize, oats, and rice.
• However, cereals are also used to produce dough, batter, pasta, noodles, pastries, cake, etc.
• These products are subject to physical, chemical, and microbiological spoilage that affects the taste, aroma, leavening,
appearance, and overall quality of the end consumer product.

4. SOURCES OF CONTAMINATION
• The exteriors of harvested grains retains some of the natural flora they had while
growing plus contamination from soil, insects & other sources.
• There then is possibility of contamination during other procedures such as
blending & conditioning.
• Freshly harvested grains contain loads of a few thousand to million of bacteria
/gm and mold spores.
• Bacteria are mostly in the families Pseudomonas, Micrococci, Lactobacilliand
Bacilli.
• Scouring & washing the grains remove some of the microorganisms, but most of
the microorganisms are removed with the outer portions of the grains during
milling. The milling processes especially bleaching reduce no. of organisms.

5. SOURCES OF CONTAMINATION
• Corn meal and flour contain several hundred to several thousand bacteria and
mold per gram. Species of Fusariumand Penicilliumare dominant molds.
• The surface of freshly baked bread is free of viable microorganisms 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 such as Fusaria&
Penicilliumhas become a significant concern because of the presence of mycotoxin.
•Bacteria in wheat flour include spores of Bacillus, coliformbacteria ,and few
representatives of the genera Achromobacter, Flavobacterium, Sarcina,
Micrococcusand Serratia. Mold spores are of Aspergillus, penicillium, Alternaria&
Cladosporium. patent flours usually give lower counts than straight or clear & no.
Decreases with storage of flour.

6. SPOILAGE OF CEREALS
• Spoilage is the term used to describe the deterioration of food
texture, color, odour or flavor to the point where it is unappetizing or
unsuitable for human consumption.
• Cereals usually contain 70–75% carbohydrates, 8–15% protein, fat,
fiber, vitamins, and minerals with near-neutral pH and hence are
susceptible to microbial growth leading to spoilage.
• Microbial growth is normally prevented due to sufficiently low
water activity (i.e. Below 0.70).
• Moldis considered the primary organism for causing spoilage in
cereal.
• Bacteriacan also cause spoilage of cereals, but yeastscause few
spoilage problems.

7. SPOILAGE OF CEREALS
• The most commonly associated bacterial families with cereals
are Bacillaceae, Micrococcaceae, Lactobacillaceae, and
Pseudomonadaceae .
• Yeast that is found in cereal includes Candida, Cryptococcus,
Pichia, Sporobolomyces, Rhodotorula, Trichosporon.
• Mold spores in cereals and flour are chiefly Aspergillus,
Penicillium, Alternaria, Mucor, Cladosporium, Fusarium,
Helminthosporium, Cladosporium, and Rhizopus.
• Mycotoxins are the toxic secondary metabolites produced by
mold that is found in cereal crops under favorable growth
conditions. The genera of molds producing mycotoxins are
Aspergillus, Penicillium, and Fusarium.

8. SPOILAGE OF CEREALS
MOLDS MYCOTOXINS
Aspergillus Parasiticus Aflatoxins B1,B2, G1, G2
Aspergillus Flavus Aflatoxins B1, B2
Penicillium Islandicum Islanditoxin, Luteoskyrin
Fusarium Sporotrichioides Trichothecenes : T-2 toxin
• Some examples of mycotoxins and the mold that produce them are :

9. SPOILAGE OF CEREALS
MICROORGANISMS DEFECTS IN CEREALS
Alternaria, Fusarium, Drechslera,
Cladosporium and Botrytis
Blights and Blemishes
Aspergillus fumigatus, A. Penicillioides,
A. ochraceus
Discolored germs
A. candidus Powdery white patches
A. flavus Greenish discoloration
Eurotium Discolored germs, green eye
Fusarium Red streaking, particularly on maize
Penicillium Blue coloration
Alternaria Darkening
Fusarium or Alternaria Pink or black tips on wheat
• Some of the microorganisms and the defects caused by them in cereals are :

10. SPOILAGE OF CEREAL PRODUCTS
(FLOUR SPOILAGE)
• The moisture content of flour is less than 13% that prevents the growth
of microorganisms.
• However, the addition of water to flour tends to make it susceptible
to microbial growth in flour.
• The molds found in flours are mostly Eurotiumspecies and Aspergillus
candidus. The molds produce typical mycelium in flour.
• The spoilage flour contains many psychrotrophs, flat sour bacteria,
and thermophilic spore-forming bacteria such as Acetobacter spp,
Bacillus spp, Lactic acid bacteria.
• If acid-forming bacteria are present in flour, acid fermentation
occurs followed by alcoholic fermentation by yeasts and then acetic
acid by Acetobacter spp.
• Bacillus spp is known for producing lactic acid, gas, and acetoin in
flour.

11. SPOILAGE OF CEREAL PRODUCTS
(SPOILAGE OF BAKERY PRODUCTS)
• There are a wide variety of bakery products including leavened and
unleavened bread, rolls, buns, croissants, muffins, cakes, doughnuts,
pastries, pancakes, waffles, biscuits, cupcakes, and sweet rolls.
• The nutrient content of bakery products includes carbohydrates, proteins,
lipids, vitamins, and minerals.
• Therefore, bakery products are susceptible to microbial growth
due to their high nutrient content and also because the most
common factor of these products is water.
• The most famous bakery product that is consumed worldwide for a very
long period is bread.
• The ambient temperatures, product pH levels between 5.4 and
7.5, and water activity in the range of 0.75–0.98 promote spoilage
of baked cereal foods with mold, yeast, and rope bacteria.

12. SPOILAGE OF CEREAL PRODUCTS
(SPOILAGE OF BAKERY PRODUCTS)
• The most common source of microbial spoilage of bread is mold growth. The
bacterial spoilage condition is known as ‘rope’ caused by the growth of the
Bacillus species. The least common of all types of microbial spoilage in bread is
that caused by certain types of yeast.
• Typical genera of mold involved in spoilage are Penicillium, Aspergillus,
Cladosporium, Fusarium, Monilia, Endomyces, Rhizopus, and Mucor.
• Yeasts that can cause surface spoilage of bakery products include
Saccharomyces, Debaryomyces, Kluyveromyces, Pichia, Candida, and
Zygosaccharomyces.
• Pastry spoilage is similar to bread, but the pastry filling or topping is more
susceptible to microbial growth.
• However, due to high sugar concentration, pastries are rarely spoiled by bacteria.
• The most common spoilage is caused by mold. They cause sugar fermentation and make them
sour in taste with an alcoholic odor.

13. SPOILAGE OF CEREAL PRODUCTS
(ROPINESS OF BREAD)
• Ropiness of bread is fairly common in home baked bread,
especially during hot weather ,but it is in commercially baked bread
because of preventive measures now employed.
• Ropiness is caused by a mucoid variant of Bacillus subtilis.
• The spores of these species can withstand the temperature of the
bread during baking , which does not exceed 100̊C , can
germinate and can grow in the loaf if conditions are favorable.
• The area of ropiness is yellow to brown in color & is soft, sticky to
touch. In one stage the slimy material can be drawn out into long
threads when the bread is broken and pulled apart first the odour is
evident ,then discoloration and finally softening of the crumb , with
stickness and stringiness.

14. SPOILAGE OF CEREAL PRODUCTS
MICROORGANISMS DEFECTS IN BREAD
Rhizopus stolonifer
(bread mold)
White cottony
mycelium & black rot
Penicillium expansum Green colour
Aspergillus niger
Greenish or purplish-
brown to black color
Monilia sitophila
Pink or reddish colour
on bread
Aspergillus glaucus
Green and gray-
green colour
Aspergillus flavusOlive green colour
MICROORGANISMS DEFECTS IN BREAD
Mucor Gray colour
Endomycopsis fibuliger
Trichosporon variable
Chalky defect
Bacillus subtilis, Bacillus
mesentericus, Bacillus
licheniformis, Clostridium
spp, Lactobacillus spp,
Leuconostoc spp.
Ropiness
Serratia marsescens Red or bloody bread
Saccharomyces
cerevisiae
Alcoholic off-flavour
• Some defects observed on bread due to microbial spoilage are :

15. SPOILAGE OF CEREAL PRODUCTS
(PASTA AND NOODLE SPOILAGE)
• Both pasta and noodle manufacture includes no cooking step,
microbial contamination may occur during the mixing and
drying process.
• They are stored and distributed in dry form so spoilage is rare.
• During the manufacturing process, it may spoil from bacterial
or fungal growth.
• For example, Enterobacter (Aerobacter) cloacae have been
found in pasta and noodle that causes gas production.
• Cooked and fresh homemade pasta should be stored in the
refrigerator to slow mold growth and preserve its freshness as
long as possible. Most pastas last in the fridge for 3–5 days.

16. PRESERVATION OF CEREALS
• There are several methods of preservation of cereals :
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.
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 spores but not spores of rope –forming
bacteria.they can survive during heat so unbaked products
are kept for short period or kept cool during longer storage of
time.

17. PRESERVATION OF CEREALS
USE OF LOW TEMPERATURE :
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.
USE OF CHEMICAL PRODUCTS :
A large number 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.
USE OF IRRADIATION:
In bakeries, ultraviolet rays have been used to destroy or reduce the
numbers of mold, bacteria in dough and proof rooms, on the 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.

18. THANKYOU