This document discusses sources of microorganisms that can contaminate foods as well as characteristics used to identify molds, yeasts, and bacteria important to the food industry. Molds are identified by features of their hyphae, spores, and sporangiophores. Yeasts are characterized by their methods of reproduction and cell morphology. Bacteria cause food spoilage through hydrolysis reactions and fermentation that produce acids, alcohols, and gases. Important microorganisms discussed include Aspergillus, Penicillium, Saccharomyces, Lactobacillus, and Salmonella.

1. Sources of microorganisms in different food
•Growing plants carry a typical flora of microorganisms on their surfaces and
may become contaminated from outside sources.
•Animals likewise have a typical sources of flora plus and intestinal one, give
off organisms in excretions and secretions, and also become contaminated from
outside sources.
Name of sources:
1. Plants and fruits
2. Animals
3. Sewage
4. Soil
5. Water
6. Air

2. Molds
1. Hyphae septate or nonseptate
2. Mycelium clear or dark
3. Mycelium colored or colorless
4. Whether sexual spores are produced and the type
: oospores, zygospores or ascospores
5. Types of Asexual spores: Sporangiospores,
conidia, arthospores
6. Characteristics of the spore head
a. Sporangia: size, color, shape, location
b. Spore heads bearing conidia: single conidia,
chains, budding conidia, or masses, shape and
arrangement of sterigmata or phialides, gumming
together of conidia

3. 7. Appearance of sporangiophores or
conidiophores: simple or branched, and if
branched the type of branching: size and shape
of columella at tip of sporangiophore; whether
conidiophores are single or in bundles
8. Microscopic appearance of asexual spores
especially of conidia; shape, size color, smooth
or rough; one two or many celled.
9. Presence of special structures solons,
rhizoids, foot cells, apophysis, chlamydospores,
sclerotia etc.
Molds

4. IndustriallyImportant Molds
Mucor:
Used in Amylo process for the sccharification of starch . Helps in ripen cheeses
and making certain oriental foods.
Zygorrhynchus:
Unequal in size. Similar to mucor.
Rhizopus:
Bread molds. Very common in spoilage of berries, fruits, vegetables, bread etc.
Absidia: like rhizopus, sporangia different. Small and pear shaped.
Thamnidium:
Elegans found in meat in chilling storage causing whiskers on meat.
Aspergillus:
Spoilage causing and sometime useful for preparation of certain foods. Helps to
produce enzymes.
Penicillium:
Rotting of citrus fruits, ripening of blue cheeses, caused trouble in canned acid
foods.
Trichothecium:
Grows on wood, paper, fruits such as apples, peaches. Vegetables such as
cucumbers and cantaloupes.

5. Geotrichum:
Yeast like fungi called by some writes or some called molds. Geotrichum candidum
called dairy mold gives white to cream colored growth.
Neurospora:
Sometimes called red bread mold. Grows on sugarcane bagasse.
Sporotrichum:
Growing on chilled meat. Caused white spot.
Botrytis:
It causes a disease of grapes.
Trichoderma:
A very common species. Bright green in color.
Scopulariopsis:
Colonies are brownish and cottony.
Cladosporium:
This mold caused black spot.
Aletrnaria:
Common cause of food spoilage. A. teuis, A. brassicae. Brown color, dirty grey
green.
Fusarium:
Appearance is different difficult to identify.

6. Yeast
Characteristics:
•Whether ascospores are formed.
•The method ascospore formation: A) without conjugation between yeast cells. B)
conjugation of ascospores C) Conjugation of small daughter cells.
•Produced after isogamic conjugation.
•Produced by heterogamic conjugation.
•Appearance of vegetative cells: shape, size, color, inclusions.
•Method of asexual reproduction: budding, fission, combined budding and fission,
Arthospores.
•Production of a mycellium, pseudomycellium or no mycellium.
•Growth as a film over surface of a liquid
•Color of microscopic growth.
•Oxidative or fermentative.
•Nitrogen and carbon sources.
•Vitamin requirements.
•Lypolysis, urease activity, acid production, formation of starch like compounds.

7. Important Yeasts
Schizosaccharomyces:
Found in tropical fruits, molasses, soil, honey. Common species S. pombe.
Sachharomyces:
Common S. cerevisiae. Leavening of bread. Ale, wines, production of
alcohol, glycerol, invertase. Ability to ferment lactose.
Zygosaccharomyces:
Notable ability to grow on high concentration of sugar, involved in spoilage
of honey, siruos and molasses. Fermentation of soy sauce and some wines. Z
nussbaumeri grows in honey
Pichia:
P membranaefaciens grows on beers or wines.
Debaryomyces:
D kloeckeri grows on cheese and sausage.
Torulopsis:
Spoil milk products, fruit juices, condensed milk, acid containing foods.
Candida:
Able to spoil in high salt and acid. C lipolytica able to spoil butter and
oleomargarine.

8. Bacteria
Bacteriologists are concerned with the growth and
activity of bacteria in foods and with the accompanying
chemical changes.
Form of Changes:
Hydrolysis of complexes carbohydrates to simple ones.
Hydrolysis of proteins to polypeptides, amino acids,
ammonia or amines.
Hydrolysis of fats to glycerol and fatty acids.
O-R reaction utilized by bacteria to obtain energy from
foods.
 Yields organic acids, alcohols, aldehydes, ketones and
gases.

9. Important Bacteria
Acetobacter:
Oxidize ethyl alcohol to acetic acid. A definite issue of alcoholic beverages
spoilage.
Aeromonas:
Gram negative facultative anaerobe, psychrophilic. A human pathogen and
pathogenic to fish, frogs, other mammals.
Alcaligens:
Ropiness in milk, slimy growth on cottage cheese.
Bacillus:
Manufacture lactic acid, spoil canned vegetables. Mesophiles, Thermophiles.
Proteolytic.
Brevibacterium:
B. Linens produce surface smear of certain cheeses e.g. brick, Limburger, create
orange red pigment and helps ripening.
Clostridium:
Putrefaction of foods, ferment carbohydrates, produce acids and gases. Stormy
fermentation of milk caused by C. perfringens.
Corynebacterium:
Can be found in aseptically drawn milk, caused bovine mastitis.

10. Enterobacter:
Widely distributed in nature and coliform group of bacteria.
Escherichia:
Found in feces. Coliform group bacteria, pathogenic to humans.
Flavobacterium:
Yellow to orange pigmented sp. Cause discoloration on the surface of meat, spoilage
of shellfish, eggs, butter, poultry, milk.
Klebsiella:
Commonly associated with respiratory and intestinal tracts of humans. K.
pneumoniae is the causative organism for a bacterial pneumonia in humans.
Mycobacterium:
Use in production of vitamins. Able to spoil pasteurized of milk, dairy product,
market milk and dry milk.
Pseudomonas:
Resistant to many disinfectant used in food industry, utilized variety of carbohydrate,
aerobic, grow well at low temperature, pigment produce by some sp., proteolytic and
lipolytic activity. Affects flavor, utilize simple nitrogenous foods.
Salmonella:
Enteric pathogens, grow in foods and transported by foods.
Shigella:
Causing bacillary dysenteries. Transported by foods.

11. Staphylococcus:
Yellow to orange growth. Produce enterotoxins causes food
poisoning.
Streptococcus:
Causes mastitis in cows, human septic sore throat, scarlet fever.
Streptomyces:
Musty/ earthy odors.
Vibrio:
In fresh and salt water, in soil, in alimentary canal of humans and
animals. Some pathogenic to human.
Yersinia:
Causative organisms of plague in human and in rat, other rodents.
Y. enterocolytica causative agents of food-borne outbreak.
Proteus:
Spoilage of meats, seafood, eggs. Large in no present in
unrefrigerated foods and made suspect of food poisoning.