Spoilage On Canned Foods BAM
Spoilage On Canned Foods BAM
Spoilage On Canned Foods BAM
January 2001
The incidence of spoilage in canned foods is low, but when it occurs it must be investigated
properly. Swollen cans often indicate a spoiled product. During spoilage, cans may progress
from normal to flipper, to springer, to soft swell, to hard swell. However, spoilage is not the
only cause of abnormal cans. Overfilling, buckling, denting, or closing while cool may also
be responsible. Microbial spoilage and hydrogen, produced by the interaction of acids in
the food product with the metals of the can, are the principal causes of swelling. High
summer temperatures and high altitudes may also increase the degree of swelling. Some
microorganisms that grow in canned foods, however, do not produce gas and therefore
cause no abnormal appearance of the can; nevertheless, they cause spoilage of the product.
Spoilage is usually caused by growth of microorganisms following leakage or
underprocessing. Leakage occurs from can defects, punctures, or rough handling.
Contaminated cooling water sometimes leaks to the interior through pinholes or poor seams
and introduces bacteria that cause spoilage. A viable mixed microflora of bacterial rods and
cocci is indicative of leakage, which may usually be confirmed by can examination.
Underprocessing may be caused by undercooking; retort operations that are faulty because
of inaccurate or improperly functioning thermometers, gauges, or controls; excessive
contamination of the product for which normally adequate processes are insufficient;
changes in formulation or handling of the product that result in a more viscous product or
tighter packing in the container, with consequent lengthening of the heat penetration time;
or, sometimes, accidental bypassing of the retort operation altogether. When the can
contains a spoiled product and no viable microorganisms, spoilage may have occurred
before processing or the microorganisms causing the spoilage may have died during
storage.
Underprocessed and leaking cans are of major concern and both pose potential health
hazards. However, before a decision can be made regarding the potential health hazard of a
low-acid canned food, certain basic information is necessary. Naturally, if Clostridium
botulinum (spores, toxin, or both) is found, the hazard is obvious. Intact cans that contain
only mesophilic, Gram-positive, sporeforming rods should be considered underprocessed,
unless proved otherwise. It must be determined that the can is intact (commercially
acceptable seams and no microleaks) and that other factors that may lead to
underprocessing, such as drained weight and product formulation, have been evaluated.
The preferred type of tool for can content examination is a bacteriological can opener
consisting of a puncturing device at the end of a metal rod mounted with a sliding triangular
blade that is held in place by a set screw. The advantage over other types of openers is that
it does no damage to the double seam and therefore will not interfere with subsequent seam
examination of the can.
Table 1. Useful descriptive terms for canned food analysis.
Exterior can condition
leaker
dented
rusted
buckled
paneled
bulge
use separate presterilized can openers for each can. Make opening in
sterilized end of can large enough to permit removal of sample.
3. Removal of material for testing. Remove large enough portions from
center of can to inoculate required culture media. Use sterile pipets, either
regular or wide-mouthed. Transfer solid pieces with sterile spatulas or other
sterile devices. Always use safety devices for pipetting. After removal of
inocula, aseptically transfer at least 30 ml or, if less is available, all
remaining contents of cans to sterile closed containers, and refrigerate at
about 4C. Use this material for repeat examination if needed and for
possible toxicity tests. This is the reserve sample. Unless circumstances
dictate otherwise, analyze normal cans submitted with sample
organoleptically and physically (see 5-b, below), including pH determination
and seam teardown and evaluation. Simply and completely describe product
appearance, consistency, and odor on worksheet. If analyst is not familiar
with decomposition odors of canned food, another analyst, preferably one
familiar with decomposition odors, should confirm this organoleptic
evaluation. In describing the product in the can, include such things as low
liquid level (state how low), evidence of compaction, if apparent, and any
other characteristics that do not appear normal. Describe internal and
external condition of can, including evidence of leakage, etching, corrosion,
etc.
4. Physical examination. Perform net weight determinations on a
representative number of cans examined (normal and abnormal). Determine
drained weight, vacuum, and headspace on a representative number of
normal-appearing and abnormal cans (1). Examine metal container integrity
of a representative number of normal cans and all abnormal cans that are not
too badly buckled for this purpose (see Chapter 22). CAUTION: Always
use care when handling the product, even apparently normal cans, because
botulinal toxin may be present.
5. Cultural examination of low-acid food (pH greater than 4.6). If there is
any question as to product pH range, determine pH of a representative
number of normal cans before proceeding. From each container, inoculate 4
tubes of chopped liver broth or cooked meat medium previously heated to
100C (boiling) and rapidly cooled to room temperature; also inoculate 4
tubes of bromcresol purple dextrose broth. Inoculate each tube with 1-2 ml
of product liquid or product-water mixture, or 1-2 g of solid material.
Incubate as in Table 2.
Table 2. Incubation times for various media for examination of low acid foods (pH >
4.6).
Medium
Chopped liver (cooked meat)
2
2
2
55
55
35
24-72
24-48
96-120
After culturing and removing reserve sample, test material from cans (other than those
classified as flat) for preformed toxins of C. botulinum when appropriate, as described in
Chapter 17.
a. Microscopic examination. Prepare direct smears from contents of each
can after culturing. Dry, fix, and stain with methylene blue, crystal violet,
or Gram stain. If product is oily, add xylene to a warm, fixed film, using a
dropper; rinse and stain. If product washes off slide during preparation,
examine contents as wet mount or hanging drop, or prepare suspension of
test material in drop of chopped liver broth before drying. Check liver
broth before use to be sure no bacteria are present to contribute to the
smear. Examine under microscope; record types of bacteria seen and
estimate total number per field.
b. Physical and organoleptic examination of can contents. After removing
reserve sample from can, determine pH of remainder, using pH meter. DO
NOT USE pH PAPER. Pour contents of cans into examination pans.
Examine for odor, color, consistency, texture, and overall quality. DO
NOT TASTE THE PRODUCT. Examine can lining for blackening,
detinning, and pitting.
Table 3.Schematic diagram of culture procedure for low-acid canned foods
LVA, liver-veal agar; NA, nutrient agar; CMM, cooked meat medium; BCP, bromcresol
purple dextrose broth.
Table 4. Incubation of acid broth and malt extract broth used for acid foods (pH 4.6)
Medium
Acid broth
Acid broth
Malt extract broth
No. of tubes
Temp. (C)
2
2
2
55
30
30
48
96
96
G.
Table 7. Spoilage microorganisms that cause high and low acidity in
various vegetables and fruits
Spoilage type
Thermophilic
pH groups
Examples
Flat-sour
Thermophilic(a)
Sulfide spoilage(a)
Mesophilic
Putrefactive anaerobes(a)
Butyric anaerobes
Aciduric flat-sour(a)
>5.3
>4.8
>5.3
Corn, peas
Spinach, corn
Corn, peas
>4.8
>4.0
>4.2
Corn, asparagus
Tomatoes, peas
Tomato juice
Lactobacilli
Yeasts
Molds
4.5-3.7
<3.7
<3.7
Fruits
Fruits
Fruits
H.
Table 8. Spoilage manifestations in low-acid products
Group of
organisms
Classification Manifestations
Flat-sour
Can flat
Product
Thermophilic
anaerobe
Can swells
May burst
Product
Sulfide
spoilage
Can flat
Product
Putrefactive
anaerobe
Can swells
May burst
Product
Aerobic
sporeformers
Can flat or
swollen
I.
Table 9. Spoilage manifestations in acid products
Type of organism
Classificatio Manifestation
n
Bacillus thermoacidurans
(flat, sour tomato juice)
Can flat
Product
Can swells
May burst
Product
Nonsporeformers (mostly
lactic types)
Can swells
Product
Acid odor
J.
Table 10. Laboratory diagnosis of bacterial spoilage
Underprocessed
Leakage
Can
Product
appearance
Sloppy or fermented
Frothy fermentation;
viscous
odor
pH
Wide variation
Microscopic
and cultural
History
Spoilage scattered
Leakage may be due not to can defects but to other factors, such as
contamination of cooling water or rough handling, e.g., can
unscramblers, rough conveyor system.
K.
Table 11. pH range of a few selected commercially canned foods
Food
pH range
Food
pH range
Apples, juice
3.3 - 3.5
Jam, fruit
3.5 - 4.0
Apples, whole
3.4 - 3.5
Jellies, fruit
3.0 - 3.5
Asparagus, green
5.0 - 5.8
Beans
Lemon juice
2.2 - 2.6
Lemons
2.2 - 2.4
Baked
4.8 - 5.5
Lime juice
2.2 - 2.4
Green
4.9 - 5.5
Loganberries
2.7 - 3.5
Lima
5.4 - 6.3
Mackerel
5.9 - 6.2
Soy
6.0 - 6.6
Milk
5.1 - 5.8
Cow, whole
6.4 - 6.8
5.5 - 6.0
Evaporated
5.9 - 6.3
Beets, whole
4.9 - 5.8
Molasses
5.0 - 5.4
Blackberries
3.0 - 4.2
Mushroom
6.0 - 6.5
Blueberries
3.2 - 3.6
Olives, ripe
5.9 - 7.3
Boysenberries
3.0 - 3.3
Orange juice
3.0 - 4.0
Oysters
6.3 - 6.7
Bread
White
5.0 - 6.0
Peaches
3.4 - 4.2
5.1 - 5.6
Pears (Bartlett)
3.8 - 4.6
Broccoli
5.2 - 6.0
Peas
5.6 - 6.5
Carrot juice
5.2 - 5.8
Pickles
Carrots, chopped
5.3 - 5.6
Dill
2.6 - 3.8
Sour
3.0 - 3.5
Cheese
Parmesan
5.2 - 5.3
Sweet
2.5 - 3.0
Roquefort
4.7 - 4.8
Pimento
4.3 - 4.9
Cherry juice
3.4 - 3.6
Pineapple
Chicken
6.2 - 6.4
Crushed
3.2 - 4.0
6.2 - 6.7
Juice
3.4 - 3.7
Chop suey
5.4 - 5.6
Sliced
3.5 - 4.1
Cider
2.9 - 3.3
Plums
2.8 - 3.0
Clams
5.9 - 7.1
Potato salad
3.9 - 4.6
Cod fish
6.0 - 6.1
Potatoes
Corn
Cream style
5.9 - 6.5
Mashed
5.1
White, whole
5.4 - 5.9
On-the-cob
6.1 - 6.8
Prune juice
3.7 - 4.3
Whole grain
Pumpkin
5.2 - 5.5
Brine-packed
Raspberries
2.9 - 3.7
Vacuum-packed
6.0 - 6.4
Rhubarb
2.9 - 3.3
3.3 - 3.7
Salmon
6.1 - 6.5
Sardines
5.7 - 6.6
Cranberry
Juice
2.5 - 2.7
Sauerkraut
3.1 - 3.7
Sauce
2.3
Juice
3.3 - 3.4
Currant juice
3.0
Shrimp
6.8 - 7.0
Dates
6.2 - 6.4
Soups
Duck
6.0 - 6.1
Bean
5.7 - 5.8
Figs
4.9 - 5.0
Beef broth
6.0 - 6.2
Frankfurters
6.2 - 6.2
Chicken noodle
5.5 - 6.5
Fruit cocktail
3.6 - 4.0
Clam chowder
5.6 - 5.9
Gooseberries
2.8 - 3.1
Duck
5.0 - 5.7
Mushroom
6.3 - 6.7
Grapefruit
Juice
2.9 - 3.4
Noodle
5.6 - 5.8
Pulp
3.4
Oyster
6.5 - 6.9
Sections
3.0 - 3.5
Pea
5.7 - 6.2
Grapes
3.5 - 4.5
Spinach
4.8 - 5.8
Ham, spiced
6.0 - 6.3
Squash
5.0 - 5.8
Hominy, lye
6.9 - 7.9
Tomato
4.2 - 5.2
Huckleberries
2.8 - 2.9
Turtle
5.2 - 5.3
Vegetable
4.7 - 5.6
Strawberries
3.0 - 3.9
Miscellaneous products
Sweet potatoes
5.3 - 5.6
Beers
4.0 - 5.0
Tomato juice
3.9 - 4.4
Ginger ale
2.0 - 4.0
Tomatoes
4.1 - 4.4
Human
Tuna
5.9 - 6.1
Blood plasma
7.3 - 7.5
Turnip greens
5.4 - 5.6
Duodenal contents
4.8 - 8.2
Vegetable juice
3.9 - 4.3
Feces
4.6 - 8.4
Vegetables, mixed
5.4 - 5.6
Gastric contents
1.0 - 3.0
Vinegar
2.4 - 3.4
Milk
6.6 - 7.6
Youngberries
3.0 - 3.7
Saliva
6.0 - 7.6
Spinal fluid
7.3 - 7.5
Urine
4.8 - 8.4
Magnesia, milk of
10.0 -10.5
Water
Distilled, CO2
6.8 - 7.0
Mineral
6.2 - 9.4
Sea
8.0 - 8.4
Wine
2.3 - 3.8
Cultures come from intact cans that are free of leaks and have
commercially acceptable seams. (Can seams of both ends of can
must be measured; visual examination alone is not sufficient.)
2. Examination of acid foods (pH 4.6 and below) by cultivation. From each
can, inoculate 4 tubes of acid broth and 2 tubes of malt extract broth with 12 ml or 1-2 g of product, using the same procedures as for low-acid foods,
and incubate as in Table 4. Record presence or absence of growth in each
tube, and from those that show evidence of growth, make smears and stain.
Report types of organisms seen. Pure cultures may be isolated as shown in
Table 5.
F Interpretation of results (see Tables 6-11)
1. The presence of only sporeforming bacteria, which grow at 35C, in cans
with satisfactory seams and no microleaks indicates underprocessing if their
heat resistance is equal to or less than that of C. botulinum. Spoilage by
thermophilic anaerobes such as C. thermobutylicum may be indicated by gas
in cooked meat at 55C and a cheesy odor. Spoilage by C. botulinum, C.
sporogenes, or C. perfringens may be indicated in cooked meat at 35C by
gas and a putrid odor; rods, spores, and clostridial forms may be seen on
microscopic examination. Always test supernatants of such cultures for
botulinal toxin even if no toxin was found in the product itself, since viable
botulinal spores in canned foods indicate a potential public health hazard,
requiring recall of all cans bearing the same code. Spoilage by mesophilic
organisms such as Bacillus thermoacidurans or B. coagulans and/or
thermophilic organisms such as B. stearothermophilus, which are flat-sour
types, may be indicated by acid production in BCP tubes at 35 and/or 55C
in high-acid or low-acid canned foods. No definitive conclusions may be
drawn from inspection of cultures in broth if the food produced an initial
turbidity on inoculation. Presence or absence of growth in this case must be
determined by subculturing.
2. Spoilage in acid products is usually caused by nonsporeforming lactobacilli
and yeasts. Cans of spoiled tomatoes and tomato juice remain flat but the
products have an off-odor, with or without lowered pH, due to aerobic,
mesophilic, and thermophilic sporeformers. Spoilage of this type is an
exception to the general rule that products below pH 4.6 are immune to
spoilage by sporeformers. Many canned foods contain thermophiles which
do not grow under normal storage conditions, but which grow and cause
spoilage when the product is subjected to elevated temperatures (50-55C).
B. thermoacidurans and B. stearothermophilus are thermophiles responsible
for flat-sour decomposition in acid and low-acid foods, respectively.
Incubation at 55C will not cause a change in the appearance of the can, but
the product has an off-odor with or without a lowered pH. Spoilage
encountered in products such as tomatoes, pears, figs, and pineapples is
occasionally caused by C. pasteurianum, a sporeforming anaerobe which
produces gas and a butyric acid odor. C. thermosaccolyticum is a
thermophilic anaerobe which causes swelling of the can and a cheesy odor
of the product. Cans which bypass the retort without heat processing usually
are contaminated with nonsporeformers as well as sporeformers, a spoilage
characteristic similar to that resulting from leakage.
3. A mixed microflora of viable bacterial rods and cocci usually indicates
leakage. Can examination may not substantiate the bacteriological findings,
but leakage at some time in the past must be presumed. Alternatively, the
cans may have missed the retort altogether, in which case a high rate of
swells would also be expected.
4. A mixed microflora in the product, as shown by direct smear, in which there
are large numbers of bacteria visible but no growth in the cultures, may
indicate precanning spoilage. This results from bacterial growth in the
product before canning. The product may be abnormal in pH, odor, and
appearance.
5. If no evidence of microbial growth can be found in swelled cans, the
swelling may be due to development of hydrogen by chemical action of
1. Fisher Model 1200 Gas Partitioner, with dual thermal conductivity cells and
dual in-line columns. Column No. 1 is 6-1/2 ft x 1/8 inch, aluminum packed,
with 80-100 mesh ColumpakTM PQ. Column No. 2 is 11 ft x 3/16 inch,
aluminum packed, with 60-80 mesh molecular sieve 13X (Fig. 1).
NOTE: Other gas chromatograph instruments equipped with the appropriate
columns, carrier gas, detector and recorder or integrator may also be suitable
for this analysis.
Operating conditions: column temperature, 75C; attenuation, 64/256;
carrier gas, argon, with in-let pressure of 40 psig; flow rate, 26 ml/min
through gas partitioner and 5 ml/min through flush line; bridge current, 125
mA; column mode, 1 & 2; temperature mode, column; injector temperature,
off.
NOTE: Installation of flush system. Injection of gas samples through
either sample out port or septum injection port may lead to damaged
filaments in detector and excessive accumulation of moisture on columns
due to bypassing the sample drying tube. To avoid this, make all injections
in the sample in port. To avoid cross-contamination, install a flush line off
the main argon line (Fig. 2), and flush sample loop between injections.
2. Strip chart recorder, with full scale deflection and speed set at 1 cm/min, 1
mv
3. Can puncturing press (Fig. 3)
4. Sterile stainless steel gas piercers (Fig. 4)
5. Miniature inert valve, with 3-way stopcock and female luer on left side
(Popper & Sons, Inc., 300 Denton Ave., New Hyde Park, NY 11040), or
equivalent (Fig. 5)
6. Plastic disposable 10-50 ml syringes, with restraining attachment for
maximum volume control (Fig. 6). Syringes may be reused.
7. Gas chromatograph and caps, for capping syringes (Alltech Associates, Inc.,
202 Campus Drive, Arlington Heights, IL 60004), or equivalent (Fig. 6)
8. Beaker, 1 liter, glass or metal
9. Plastic gas tubing, 3 ft x 1/8 inch id, for exhaust tubing
10. Soap solution, for detecting gas leaks ("SNOOP" Nuclear Products Co.,
15635 Saranac Road, Cleveland, OH 44110), or equivalent
hydrogen peak to be retained on scale. After hydrogen peak returns to base line,
switch attenuation back to 64. After instrument has separated gases (about 6 min),
determine retention time and peak height for each gas recovered from unknown
sample and percent determined from standard graph by comparing retention times
and peak heights with known gases, usually associated with headspace gases from
abnormal canned food products. Mount chromatogram on mounting paper and
identify properly as in Fig. 10. For each sample examined, inject control gases for
each type of headspace gas recovered.
Figure 7. Calibration graph for gas chromatography of headspace gas, using pure and
unknown mixtures.