436 Modern Food Microbiology
High Acid (pH < 4.0–3.7)
This category includes fruits and fruit and vegetable products—grapefruit, rhubarb, sauerkraut,
pickles, and so forth. These foods are generally spoiled by non-sporeforming mesophiles—yeasts,
molds, Alicyclobacillus spp., and/or lactic acid bacteria. Alicyclobacillus spp. can grow in and cause
spoilage of apple and tomato juice and white grape juice.
52 The fungus Byssochlamys can grow at pH
as low as 2.0, and Neosartorya fischeri can grow as low as pH 3.0.
9
Canned food spoilage organisms may be further characterized as follows:
• Mesophilic organisms
– Putrefactive anaerobes
– Butyric anaerobes
– Aciduric flat sours
– Lactobacilli
– Yeasts
– Molds
• Thermophilic organisms
– Thermophilic anaerobes producing sulfide
– Flat-four spores
– Thermophilic anaerobes not producing sulfide
The canned food spoilage manifestations of these organisms are presented in Table 17–15.
With respect to the spoilage of high-acid and other canned foods by yeasts, molds, and bacteria,
several of these have been repeatedly associated with certain foods. The yeasts Torula lactis-condensi
and T. globosa cause blowing or gaseous spoilage of sweetened condensed milk, which is not heat
processed. The mold Aspergillus repens is associated with the formation of “buttons” on the surface
of sweetened condensed milk. Lactobacillus brevis (L. lycopersici) causes a vigorous fermentation in
tomato catsup, Worcestershire sauce, and similar products. Leuconostoc mesenteroides has been found
to cause gaseous spoilage of canned pineapples and ropiness in peaches. The mold Byssochlamys fulva
causes spoilage of bottled and canned fruits, and its actions cause disintegration of fruits as a result of
pectin breakdown.
5 Torula stellata has been found to cause the spoilage of canned bitter lemon, and
to grow at a pH of 2.5.
44
Frozen concentrated orange juice sometimes undergoes spoilage by yeasts and bacteria. Hays and
Reister
23 investigated samples of this product spoiled by bacteria. The orange juice was characterized
as having a vinegary to buttermilk off-odor with an accompanying off-flavor. From the spoiled product were isolated L. plantarum var. mobilis, L. brevis, Leuconostoc mesenteroides, and Leuconostoc
dextranicum. The spoilage characteristics could be reproduced by inoculating the above isolates into
fresh orange juice.
Minimum growth temperatures of spoilage thermophiles are of some importance in diagnosing the
cause of spoiled canned foods. B. coagulans (B. thermoacidurans) has been reported to grow only
slowly at 25
◦ C but grows well between 30
◦ C and 55
◦ C. G. stearothermophilus does not grow at 37
◦ C,
its optimum temperature being around 65
◦ C with smooth variants showing a shorter generation time
at this temperature than rough variants.
17 T. thermosaccharolyticum does not grow at 30
◦ C but has
been reported to grow at 37
◦ C. For reviews on the spoilage of acid and low-acid food products, see
references 9, 38, and 52.
Also of importance in diagnosing the cause of canned food spoilage is the appearance of the
unopened can or container. The ends of a can of food are normally flat or slightly concave. When
High Acid (pH < 4.0–3.7)
This category includes fruits and fruit and vegetable products—grapefruit, rhubarb, sauerkraut,
pickles, and so forth. These foods are generally spoiled by non-sporeforming mesophiles—yeasts,
molds, Alicyclobacillus spp., and/or lactic acid bacteria. Alicyclobacillus spp. can grow in and cause
spoilage of apple and tomato juice and white grape juice.
52 The fungus Byssochlamys can grow at pH
as low as 2.0, and Neosartorya fischeri can grow as low as pH 3.0.
9
Canned food spoilage organisms may be further characterized as follows:
• Mesophilic organisms
– Putrefactive anaerobes
– Butyric anaerobes
– Aciduric flat sours
– Lactobacilli
– Yeasts
– Molds
• Thermophilic organisms
– Thermophilic anaerobes producing sulfide
– Flat-four spores
– Thermophilic anaerobes not producing sulfide
The canned food spoilage manifestations of these organisms are presented in Table 17–15.
With respect to the spoilage of high-acid and other canned foods by yeasts, molds, and bacteria,
several of these have been repeatedly associated with certain foods. The yeasts Torula lactis-condensi
and T. globosa cause blowing or gaseous spoilage of sweetened condensed milk, which is not heat
processed. The mold Aspergillus repens is associated with the formation of “buttons” on the surface
of sweetened condensed milk. Lactobacillus brevis (L. lycopersici) causes a vigorous fermentation in
tomato catsup, Worcestershire sauce, and similar products. Leuconostoc mesenteroides has been found
to cause gaseous spoilage of canned pineapples and ropiness in peaches. The mold Byssochlamys fulva
causes spoilage of bottled and canned fruits, and its actions cause disintegration of fruits as a result of
pectin breakdown.
5 Torula stellata has been found to cause the spoilage of canned bitter lemon, and
to grow at a pH of 2.5.
44
Frozen concentrated orange juice sometimes undergoes spoilage by yeasts and bacteria. Hays and
Reister
23 investigated samples of this product spoiled by bacteria. The orange juice was characterized
as having a vinegary to buttermilk off-odor with an accompanying off-flavor. From the spoiled product were isolated L. plantarum var. mobilis, L. brevis, Leuconostoc mesenteroides, and Leuconostoc
dextranicum. The spoilage characteristics could be reproduced by inoculating the above isolates into
fresh orange juice.
Minimum growth temperatures of spoilage thermophiles are of some importance in diagnosing the
cause of spoiled canned foods. B. coagulans (B. thermoacidurans) has been reported to grow only
slowly at 25
◦ C but grows well between 30
◦ C and 55
◦ C. G. stearothermophilus does not grow at 37
◦ C,
its optimum temperature being around 65
◦ C with smooth variants showing a shorter generation time
at this temperature than rough variants.
17 T. thermosaccharolyticum does not grow at 30
◦ C but has
been reported to grow at 37
◦ C. For reviews on the spoilage of acid and low-acid food products, see
references 9, 38, and 52.
Also of importance in diagnosing the cause of canned food spoilage is the appearance of the
unopened can or container. The ends of a can of food are normally flat or slightly concave. When