(c) "Sulfide stinker" spoilage is characterized by a flat container in
which the contents are darkened and have the odor for rotten eggs. This type of
spoilage is caused by the sporeforming, anaerobic obligately thermophilic
microorganism, Clostridium nigrificans. No swelling of the container is produced
because the hydrogen sulfide is very soluble in the food. However, it does react with
any iron present to form black iron sulfide.
b. Spoilage in Acid Foods. Micro-biological spoilage in acid foods is caused
by microorganisms capable of growing at pH 4.6 or lower. Clostridium botulinum does
not grow in these products unless abnormal conditions first produce a pH in excess of
4.6. Groups of microorganisms that may be associated with spoilage in acid foods (pH
4.6 or lower) are described as follows.
(1) Sporeforming microorganisms. A variety of acid-tolerant, sporeforming
microorganisms may survive processing. They are as follows.
(a) Butyric anaerobes, such as the mesophilic, sporeforming anaerobe
Clostridium pasteurianum, which produces butyric acid as well as carbon dioxide and
(b) Aciduric flat sours, especially Bacillus coagulans, in tomato
(c) Heat-resistant molds, particularly in the case of the contamination
of juice concentrates and fruits by these fungi prior to processing. The causative
microorganisms are usually Byssochamys fulva and related or similar species which
produce very heat-resistant spores. Spoilage is evidenced by a moldy taste and odor,
color fading, the presence of mold mycelia in the product, and sometimes slight swelling
of the container lid.
(d) Yeasts and bacteria that do not reproduce by spores
(asporogenous) may cause spoilage in cases of grossly insufficient processing. This
type of spoilage may be indistinguishable from leaker spoilage unless the containers are
thoroughly examined for leakage and structural defects.
(2) Thermophilic microorganisms. Thermophilic (high-temperature) spoilage
may occur in acid foods, especially tomato products.
(3) Bacteria, yeast, and/or mold contaminants. Pure or mixed cultures of
acid-tolerant bacteria, yeast, and mold contaminants are commonly found in leaker
spoilage of acid products. The containers may be swollen or flat. Gas and swelling of
the can is commonly produced by bacteria or yeasts and sometimes by molds.
Spoilage in flat cans is caused by bacteria (rods and/or cocci) which do not produce
gas. A slight lowering of the pH usually occurs. Mold spoilage usually is evidenced by
the presence of mycelia and fungal spores in flat containers having a leak large enough
to permit entrance of oxygen.