Spoilage of canned foods, eggs and other foods

SPOILAGE OF CANNED FOODS

• Cans can undergo spoilage under certain cicumstances

• E.g. underprocessing, contamination through seams, damages to the can, preprocess spoilage.

• Spoilage and the Mos involved depend on the acidity of the food

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MICROORGANISMS INVOLVED

• A. Mesophiles

– PA

– Butyric anaerobes

– Aciduric flat sour

– Lactobacilli

– Yeasts

– Molds

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• B. Thermophiles

– Flat sour

– Anaerobes producing sulfide

– Anaerobes not producing sulfide

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Based on the level of acidity the canned foods are categorized as follows

Low acid canned foods:

• pH >4.6

• Meat and marine products

• Milk, some vegetables, meat vegetable mix

• Spoilt by thermophiles such as Bacillus stearothermophilus and coagulans

• Sulfide spoilers Cl. nigrificans and bifermentans

• Gaseous spoilers such as Cl. thermosaccharolyticum

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• Mesophilic spoilers PA 3679

• Cl. botulinum – spoilage and toxin producers

• Acidic pH 3.7-4.0

• Fruits such as tomatoes, pears

• Thermophiles such as B. coagulans

• Mesophiles such as B. macerans, C. butyricum, Lactobacilli etc.

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• High Acidic pH <3.7

• Fruits and vegetables such as grapefruit, other citrus fruits, sauerkraut, pickles, lime

• Yeasts, molds, LAB and some non-spore forming mesophiles

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Spoilage Manifestations in canned foods

Organism Manifestation Product condition

ACIDIC PRODUCTS

B. Thermodurans Flat can, no change in vacuum

Slight pH change with off odor and flavor

Butyric anaerobes Swollen cans, may burst

Fermented product with butyric odor

Nonsporeformers Can swells, may burst

Acidic odor

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LOW ACIDIC PRODUCTS

Sulfide formers Can flat, product absorbs H2S

Black appearance with rotten egg odor

Putrefactive Anaerobes

Can swells, may burst

Partially digested, pH slightly above normal

Anaerobic sporeformers

Can flat, Coagulated evaporated milk, beet turns black

Flat sour Can looks flat, slight vacuum change

pH goes down drastically, sour taste, abnormal odor

Thermophilic anaerobes

Can swells, may burst

Fermented sour, cheesey or butyric odor 9

Can Defects

• Flat – both ends concave – it remains flat even when brought down sharply on its end on a solid flat surface

• Flipper – normally appears flat, when brought down sharply on its end on a flat surface one end flips out. When pressure is applied on to this end, it flips in again and the can appears flat

• Springer – one end permanently bulged. When sufficient pressure is applied to this end it will flip in but the other end will flip out

• Soft swell – can is bulged at both ends but not so tightly – the ends can be pushed with thumb

• Hard swell – both ends bulged, can’t be pushed back with thumb – this can will burst usually at the seam

SPOILAGE OF EGGS

• Freshly laid eggs are generally sterile (inside) however, sometimes they may contain pathogens

• Lysozymes in eggs are effective against G(+) bacteria

• Avidin in egg white also contributes to reduce Mos

• Conalbumin in egg white makes Fe unavailable for MOs

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• After laying many Mos can be found on the surface which can migrate into the egg

• Pseudomonas Flavobacterium

• Acinetobacter Staphylococcus

• Proteus Acaligenes

• Aeromonas Enterobacter

• E coli Salmonella

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• Mucor Penicillum

• Hormodendron Cladosporium

• and

• Torula

• The common spoilage type is known as rotting

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Egg Rot & other spoilage conditions

Rot Organism responsible

Green Rot Pseudomonas fluorescenes

Colorless Rot Pseudomonas Spp. Acinetabacter

Black Rot Proteus, Pseudomonas, Aeromonas

Pink rot Pseudomonas

Red rot Serratia

Custard rot Proteus vulgaris Pseudomonas

intermedium

Pinspots (Mold attacks) Penicillium and Cladosporium

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• Entry is favored by high RH

• Under these conditions surface growth is high

• Inner membrane is the most resistant toward bacterial migration followed by shell and outer membrane

• More bacteria are found in association with egg yolk

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• When Mos cross the thin and thick white they reach egg yolk

• There MOs produce H2S and other by products making the yolk runny

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Cereals & Flour

• Low aw

• Rich in CHO

• Contains protein

• Due to low aw, growth of all MOs is restricted

• Bleaching agents used in flour bring MO content further down in flours

• When aw becomes favorable Bacillus, Rhizopus may grow – black spots

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Beers, Ales and Wines

• pH ranges between 4-5 with nutrients

• Spoilage of beers and ales is commonly termed ‘Beer infections’

• Four major conditions are

• Ropiness

• Sarcinae sickness

• Sourness

• Turbidity

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• In ropiness the liquid becomes thick and oily

• Acetobacter

• P. cerevisiae

• Lactobacillus and

• Gluconobactor oxydans

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• Sarcinae sickness is caused by

• P cerevisiae

• It produces a honey like odor

• Diacetyl produced by Pediococus causes the odor

• Sourness is by Acetobacter

• They oxidize ethanol to acetic acid

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• Zymomonas anaerobia and some yeasts such as Saccharomyces cause turbidity and off odors

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• Megasphaera cerevisiae

• Pectinatus cerevisiphillus and

• Zymophilus spp. are also found in association with stale beer

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Wines

• Spoilt by bacteria and yeasts

• The most common condition is known as Tourne disease caused by anaerobes that use sugars

• Volatile acidity goes up

• Cloudiness and later on a mousey odor

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• Candida valida is the most important yeast involved

• Causes ‘wine flowers’ or a thin film by growing on the surface

• They utilize ethanol and other compounds

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• Malo-lactic fermentation

• Malic acid is fermented to lactic acid and CO2

• Acidity goes down and flavor is affected Leuconostoc oenos

• Lactobacillus plantarum converts tartaric acid to LA. Acetic acid and CO2

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