Fundamental Food Microbiology, Third Edition - Fuad Fathir

286 FUNDAMENTAL FOOD MICROBIOLOGY
1. Flat Sour Spoilage
The cans do not swell but the products become acidic because of germination and
growth of facultative anaerobic Bac. stearothermophilus. Germination occurs at high
temperature (43�C and above), but growth can take place at lower temperature (30�C
and above). The organism ferments carbohydrates to produce acids without gas but
with some off-flavor and cloudiness.
2. Thermophilic Anaerobe (TA) Spoilage
The spoilage is caused by the growth of anaerobic Clo. thermosaccharolyticum with
the production of large quantities of H 2 and CO 2 gas and swelling of cans and with
sour and cheesy odor. Following germination in the thermophilic range (43�C and
above), the cells can grow at lower temperatures (30�C and above).
3. Sulfide Stinker Spoilage
This spoilage is caused by the Gram-negative anaerobic sporeformer Desulfotomaculum
nigrificans. The spoilage is characterized by a flat container but darkened
products with the odor of rotten eggs due to H 2S produced by the bacterium. H 2S,
produced from the sulfur-containing amino acids, dissolves in the liquid and reacts
with iron to form black color of iron sulfide. Both germination and growth occur at
thermophilic range (43�C and above).
B. Spoilage Due to Insufficient Heating
Insufficient heat treatment results in the survival of mainly spores of Clostridium
and some Bacillus spp. Following processing, they can germinate and grow to cause
spoilage. The most important concern is the growth of Clo. botulinum and production
of toxins.
Spoilage can be either from the breakdown of carbohydrates or proteins. Several
Clostridium spp., Clo. butyricum and Clo. pasteurianum, ferment carbohydrates to
produce volatile acids and H 2 and CO 2 gas, causing swelling of cans. Proteolytic
species, Clo. sporogenes and Clo. putrefacience (also proteolytic Clo. botulinum),
metabolize proteins and produce foul-smelling H 2S, mercaptans, indole, skatole,
ammonia, as well as CO 2 and H 2 (causing swelling of cans).
Spores of aerobic Bacillus spp., surviving inadequate heating, do not grow in
cans. However, spores of some facultative anaerobic Bacillus spp., such as Bac.
subtilis and Bac. coagulans, grow, with the production of acid and gas (CO 2).
C. Spoilage Due to Container Leakage
Damaged and leaky containers allow different types of microorganisms to get inside
from the environment after heating. They can grow in the food and cause different
types of spoilage, depending on the microbial types. Contamination with pathogens
makes the product unsafe.