Transcript Important Factors in Microbial Food Spoilage

MICROBIAL FOOD SPOILAGE
Dr. Ir. Eni Harmayani, M.Sc.
Important Factors in
Microbial Food Spoilage
Significance of Microbial Types
►
Raw and most processed foods normally contain many
types of
 bacteria (the first important component in spoilage due to a shorter
generation time),
 yeasts (favorable positions over molds to cause rapid spoilage of
foods),
 molds,
capable of multiplying and causing spoilage.
►
However, in food where bacteria and yeasts do not grow
favorably and the foods are stored for a relatively longer
period of time (breads, hard cheese, fermented dry
sausages, and acidic fruits and vegetables) spoilage due to
mold growth is more prevalent.
Significance of Microbial Numbers
► The
spoilage detection level can range from
106 – 108 cells/g, mL or square centimeter.
► Spoilage associated with H2S, some amines,
and H2O2 formation can be detected at a
lower microbial load, while formation of
lactic acid may be detected at a higher
microbial load.
Significance of Predominant
Microorganisms
► The
microbial profile of a food is quite different
from that of a pure culture growing in a laboratory
medium.
► An unspoiled, nonsterile food generally contains
many types of microorganisms consisting of
bacteria, yeasts, and molds (also viruses) from
different genera and may be more than one
species from the same genus.
► When the same food is spoiled, it is found to
contain predominantly one or two types, and they
may not even be present initially in the highest
numbers in the unspoiled product.
Some Important Food Spoilage
Bacteria
►
Psychrotrophic Bacteria
 Aerobic : Pseudomonas fluorescens, P. fragi, other Pseudomonas
species, Acinobacter, Moraxella, and Flavobacterium. (some molds
and yeasts)
 Facultative anaerobic : L. viidescens, L. sake, L. curvatus,
Leuconostoc mesenteroides etc.
 Thermoduric psychrotrops :
anaerobs : spores of Bacillus coagulans and Bacillus
megaterium, some strains of L. viridescens.
► Anerobes : spores of Clostridium laramie, Clo. estertheticum, Clo.
algidicarnis, Clo.putrefaciens, and unidentified Clostridium spp.
► When a food is temperature abused above 50C, some true mesophiles
(growth temperature range 15 – 45 0C, optimum 25 – 40 0C) can also
grow.
► However, at 10 – 15 0C storage temperature psychrotrophs will
generally grow much faster than these mesophiles.
► Facultative
► Thermophilic
Bacteria
 The bacteria in this group grow between 40 – 90 0C,
with optimum growth at 55 – 65 0C.
 Spores of some thermophilic Bacillus and Clostridium
spp. can be present in these heat treated foods, which
at warm temperatures germinate and multiply to cause
spoilage.
 Some thermoduric vegetative bacteria surviving low
heat processing (such as pasteurization) or
thermophiles getting in food as post-heat contamination
can also multiply in this warm foods, especially if the
temperature is close to 50 0C.
► Aciduric
Bacteria
 Bacteria capable of growing relatively rapidly in
food at pH 4.6 or below are generally regarded
as aciduric (or acidophilic).
 Spoilage of acidic food products :
►Fruit
juices, pickles, salsa, salad dressings,
mayonnaise, and fermented sausages.
 Heterofermentative LAB and homofermentative
LAB have been associated with such spoilage.
 Yeast and molds are aciduric and thus are
associated with spoilage of such foods.
Food Types
► Intrinsic
factors that can cause food
spoilage :
 Aw & pH : food with a lower Aw (0.90) or a
lower pH (5.3) is less susceptible to bacterial
spoilage than one with Aw = 0.98 or pH = 6.4.
Yeast and molds will probably grow equally well
under both conditions.
 O – R potential, nutrient content, antimicrobial
substances, protective structures.
► Extrinsic
factors : storage conditions
Metabolism of Food Nutrients
Carbohydrates
Food nutrients
Lipids
Proteinaceous and
NPN compounds
CO2, H2, H2O2, lactate,
acetate, formate,
butyrate, isobutyrate,
isovalerate, ethanol,
propanol, butanol,
isobutanol, diacetyl,
acetoin, butanediol,
dextran, levans.
CO2, H2, NH3, H2S,
amines, keto acids,
mercaptans, organic
disufides, putrescine,
cadaverine, skatole
Fatty acids, glycerol,
hydroperoxides,
carbonyl compounds
(aldehydes, and
ketones), nitrogenous
bases.
Preference for Utilization of Food
Nutrients
► In
general, microorganisms prefer to use
carbohydrate first, followed by NPN and
proteinaceous compounds, and then lipids.
 It again depends on whether or not a particular
species has the ability to use specific
carbohydrate.
► In
mixed microbial population, as normally
present in food, availability and amount of
metabolizable carbohydrates greatly affect
the spoilage pattern.
Microbial Growth in Succesion
► The
intrinsic factors or environments of a
food dictate which, among the mixed
microbial species normally present, will
multiply rapidly and become predominant to
cause spoilage.
► If sufficient time is given, the predominant
microbial types and the nature spoilage of a
food can change.
Spoilage of Specific Food
Groups
Prevention of spoilage
► Knowing
types of microorganisms
associated with spoilage of specific foods is
essential for developing preventive
measures
► Intrinsic and extrinsic factors can be
manipulated to prevent microbial growth
Fresh and Ready to Eat Meat Products
► Raw
Meat
 From animals and birds contain a large group of
spoilage bacteria
 The predominant spoilage flora in a meat is determined
by :
► the
nutrient and oxygen availability,
► storage temperature,
► pH,
► the storage time of the product
► generation time of the spoilage microorganisms under a given
environment.
► Meat
are more perishable than other food
commodities
 Abundance all nutrients required for growth of bacteria,
yeasts and molds
 All of these nutrients readily available
 Carcasses and cuts may be spoiled by bacteria or by
molds
(Mucor, Rhizopus), black or green spots
(Cladosporium, Penicillium)
► Whiskers
 Ground meats and steaks are almost exclusively spoiled
by bacteria
► Storage
temperature selects for psychrotropic spoilage
organisms
 Pseudomonas, Moraxella, Acinetobacter, Psychrobacter
 Steaks tend to undergo surface spoilage
► Ready
to Eat Meat Products
 High heat processed uncured and cured meat
products (heat treatment to make them
commercially sterile)
 Low heat processed uncured and cured meat
products
 Sources of microorganisms :
►Raw
meat
►Spices and other ingredients
►Natural casings
► Spoilage
in ready to eat meat products :
 Slimy spoilage
► Occurs
on the outside of casing
 Yeast, LAB, B. thermosphacta
 Souring
► Occurs
underneath the casing
 Due to growth of LAB
 Greening
to H2O2 production (Lactobacillus)
► Due to H2S production
► Due
 Reacts with myoglobin to form sulphmyoglobin
 Pseudomonas mephitica
Eggs and Egg Products
► Rotting






Green rots (Pseudomonas fluorescens)
Colorless rots (Pseudomonas, Acinetobacter)
Black rots (Proteus)
Pink rots (Pseudomonas)
Red rots (Serratia)
Custard rots (Proteus vulgaris, P. intermedium)
► Pinspots
(molds, Penicillium, Cladosporium,
Mustiness, P. graveolans, Proteus)
► Hen’s
egg structure includes barriers against
microbial entry and growth :
 External
►Outer
waxy shell membrane
►Shell
►Inner
shell membrane
 Internal (white)
►Lysozyme
►Avidin
(chelates biotin)
►High pH (~ 9.3)
►Conalbumen (chelates iron)
 Yolk is an excellent medium for bacterial growth
Milk and Milk Products
► Raw
Milk
 Microbiota of milk from healty cows
► Micrococcus,
Staphylococcus, Lactic acid cocci (Lactococcus and
Streptococcus)
 Microbiota of milk from cows with mastitis
► Staphylococcus
aureus, Streptococcus agalactiae, Coliforms,
Pseudomonas, and other streptococci
► Count
> 103 in the bulk tank (if not separated)
 Spoilage of refrigerated milk consists usually of bitter,
rancid, fruity flavors due to putrefaction and caused by
psychrotrophs
 Spoilage of milk at room consists usually of souring due
to fermentation and LAB
► Pasturized
Milk
 Usually associated with Gram-negative
psychrotrophs
►Bitter,
rancid, fruity, or unclean flavor
 Gram-positive, psychrotrophic sporeformers
(Bacillus spp.), can grow and cause spoilage
(sweet curdling)
Vegetables and Fruits
► Widely
varied products (raw, frozen, canned,
dehydrated, fermented)
► Sources of m.o in fresh vegetables and fruits
 Soil (Bacillus, Clostridium, fungi)
 Wide distribution in nature (Lactobacillus, Leuconostoc,
Streptococcus)
 Fertilizers (non-fermented manure)
 Water (irigation, solvent, washing)
 Dust (air)
 Animals, insects, humans
 Harvesting equipment and utensils
 Packing equipment
 Ice, transporting vehicles, inadequate storages, cross
contamination, handling previous to consumption
►
Types of spoilage on
vegetables and fruits
 Bacterial soft rot
► Soft,
mushy product,
sometimes with off-odors
 Souring by LAB
 Gray mold rot (Botrytis sp.),
Rhizopus soft rot (Rhizopus
sp.) and many other rots
caused by species of molds
 Bacteria are of less
impotance in the spoilage of
fruits because of the lower
pH
Fish, Crustaceans, and Mollusks
► Fish
 Microbial spoilage is determined by the microbial types,
their level, fish environment, fish types, methods used
for harvest, and subsequent handling
► Crustaceans
 Microbial spoilage in shrimp is more prevalent than that
of crabs and lobsters because crabs and lobsters remain
alive until they are pocessed
► Mollusks
 As compared to fish and crustaceans, oyster, clam, and
scallop meats are lower in NPN compounds but higher
in carbohydrates
 The mollusks are kept alive until processed; thus,
microbial food spoilage occurs only after processing
Soft Drink, Fruit Juices and Preserves,
and Vegetable Juices
► Among
the microorganisms that can be present in
these products, only aciduric molds, yeasts, and
bacteria (Lactobacillus, Leuconostoc, and
Acetobacter) are able to cause spoilage if
appropriate preservation methods are not used
► To prevent of these potential spoilage
microorganisms, several additional preservation
methods are used, include :
 heat treatment, to kill vegetative microorganisms in
tomato juices,
 freezing,
 refrigeration,
 addition of specific chemical preservatives.
(Harmayani & Sumedi, 2006)
Cereals and Their Products
►
Cereal grains
 If the Aw increase above 0.6, some species of fungi (Aspergillus,
Penicillium, and Rhizopus) can grow and cause spoilage
 Yeats are common on all cereals, although they represent only a
minority of the microbial flora
►
Refrigerated Dough (biscuits, roles, and pizza)
 Susceptible to spoilage (gas formation) from the growth of
psychrotrophic heterolactic species of Lactobacillus and
Leuconostoc then the gas can blow the containers, especially when
the storage temperature increases to 100C or above
►
Breads
 A specific type of bread spoilage, designated as ropiness and
characterized by soft, stringy, brown mass with fruity odor, caused
by the growth of some mucoid variants of Bacillus subtilis
► Pastas
 Anaerobic packing and refrigeration storage can prevent
mold growth and slow down the growth of yeasts,
anaerobic and facultative anaerobic psychrotrophic
bacteria
► Pastries
 They can spoilage by microorganisms coming with the
ingredients that are added after baking such as icing,
nuts, toppings, and cream
 Due to low Aw, most products will allow only molds to
grow
Liquid Sweeteners and Confectioneries
► Most
of these products have an Aw of 0.8 or
below and are normally not susceptible to
bacterial spoilage.
► Under aerobic conditions, some xerophilic
molds can produce visible spoilage
► Osmophilic yeasts Zygosaccharomyces
rouxii, Saccharomyces cerevisiae, Torulopsis
holmii, and Candida valida can ferment
these products
Mayonnaise, Salad Dressing, and
Condiments
► Zygosaccharomyces
bailii
► Lactobacillus fructivorans
► Bacillus vulgatus (Thousand Island dressing)
Canned Foods
► Thermophilic
sporeformers
 Can cause some types of spoilage of low acid (high pH)
foods (such as corn, beans, peas) when the cans are
temperature abused at 430C and above, even for short
duration
► Spoilage
due to insufficients heating
 Clostridium and some Bacillus spp.
► Spoilage
due to container leakage
 Damage and leakly containers will allow different types
of microorganisms to get inside from the environment
after heating
Fermented Foods
► Fermented
meat products
 If the acid production of homofermentative LAB is slow,
undesirable bacteria can grow (Clostridium, Bacillus,
and other mesophilic bacteria have been reported to
cause spoilage in such conditions.
 Products with pH < 5.0 but Aw 0.92 or above and
vacuum packaged can be spoiled by heterofermentative
Leuconostoc and Lactobacillus spp. with accumulation of
gas and liquid inside the package and creamy white
growth of bacterial cells
 If they are not vacuum packaged and have low Aw
(0.72-0.90), yeast and molds can grow on the surface,
resulting in slime formation, discoloration, and
undesirable flavor of the products.
Yeast In Specific Types of Foods
► Yeast
will actually grow to the extent that spoilage
will result depends on intrinsic and extrinsic
factors
► Many yeast species are associated with plant and
animal products and can also be found in foodprocessing environments
► Yeast are most likely to cause spoilage in products
such as fruits and soft drinks, which contain
fermentable sugars, and in those types of food,
e.g., alcoholic beverages and high-sugar and/or
high-acidity products, which restrict the growth of
competing bacteria
Food fermented with mixed cultures
of bacteria and fungi
Products
Molds
Yeasts
Bacteria
Substrate
Use
Ragi
Amylomyces rouxii
Endomyces spp.
Pichia burtonii
Pediococcus pentosaceus
Steptococus faecalis
Uncoked rice
Inoculum
Peuyem
A.rouxii
P.Burtonii
Endomycopsis fibulinger
P.Pentosaceus
Enterococcus faecalis
cassava
Snack
Miso
Aspergillus oryzae
A.sojae
Zygosaccharomyces
rouxii
T.versatilis
P.Halophilus
E.faecalis
Soybean
+ rice/barley
Flavoring
Soy
sauce
A.Oryzae
A.Sojae group
Zy.rouxii, Zy.sojae,
Zy.major, Ha. Spp.,
Torulopsis spp.,
C.etchellsii, C.versatilis
Lactobacillus delbrueckii
P.halophilus
P.damnosus
Soybean
+wheat
+salt
Flavoring
Sake
A.oryzae
Ha.anomala
S.Cerevisiae (sake)
Lactobacillus mesenteroides
var.sake
Lactobacillus sake
Rice
Liquor
Tempe
Rhizopus oligosporus
R.chinensis
R.Oryzae
Mucor indicus
Trp.beigelii
Cla.lusitaniae
C.maltosa
C.intermedia
Ya.lipolytica
Klebsiella pneumoniae
Enterobacter cloacae
Lactobacillus spp.
Mostly
soybeans
Protein
food
snack
(Deak dan Beuchat, 1996)
► Pustaka
:
 Deak, T. dan Beuchat, L.R. 1996. Handbook of
Food Spoilage Yeast. CRC Press, New York.
 Ray, B. 1996. Fundamental Food Microbiology.
CRC Press, New York.
 Nickerson, J.T. dan Sinskey, A.J. 1974.
Microbiology of Food and Food Processing.
American Elsevier Publishing Co., Inc.