Miscellaneous Food Products 203
odor of butyric acid may precede emulsion separation. The spoilage organisms apparently attack the
sugars fermentatively. It appears that the pH remains low, thereby preventing the activities of most
proteolytic and lipolytic bacteria. It is not surprising to find yeasts and lactic acid bacteria under
these conditions. In a study of 17 samples of spoiled mayonnaise, mayonnaise-like, and blue cheese
dressings, Kurtzman et al.
31 found high yeast counts in most samples and high lactobacilli counts in
two. The pH of samples ranged from 3.6 to 4.1. Two-thirds of the spoiled samples yielded Z. bailii.
Common in some samples was L. fructivorans, with aerobic spore formers being found in only two
samples. Of ten unspoiled samples tested, microorganisms were in low numbers or not detectable at
all.
It is well established that foodborne pathogens will not grow in commercially produced mayonnaise
or dressings that have a pH of 4.4 and water-phase titratable acidity of at least 0.43 for acetic acid.
53
Foodborne pathogens typically die-off in these products, but some studies have found that E. coli
0157:H7 can persist for several weeks (see reference 53). Home-made mayonnaise has been the
source of several food poisoning outbreaks typically associated with the use of contaminated raw eggs
and the lack of sufficient organic acid to produce a safe pH level to destroy S.Enteritidis. It has been
recommended that with pure lemon juice [citric acid concentration ≥5% (w/v)], the pH should be
3.30 or below, or at least 20 ml of pure lemon juice/egg yolk.
67 It is recommended that a product of
this composition should be held at least 72 hours at 22
◦ C or above. Pathogenic strains of E. coli from
mayonnaise are covered in Chapter 27.
CEREALS, FLOUR, AND DOUGH PRODUCTS
The microbial biota of wheat, rye, corn, and related products may be expected to be that of soil,
storage environments, and those picked up during the processing of these commodities. Although
these products are high in proteins and carbohydrates, their low a w is such as to restrict the growth
of all microorganisms if stored properly. The microbial biota of flour is relatively low, as some of the
bleaching agents reduce the load. When conditions of a w favor growth, bacteria of the genus Bacillus
and molds of several genera are usually the only ones that develop. Many aerobic spore formers are
capable of producing amylase, which enables them to utilize flour and related products as sources of
energy, provided that sufficient moisture is present to allow growth to occur. With less moisture, mold
growth occurs and may be seen as typical mycelial growth and spore formation. Members of the genus
Rhizopus are common and may be recognized by their black spores.
The spoilage of fresh refrigerated dough products, including buttermilk biscuits, dinner and sweet
rolls, and pizza dough, is caused mainly by lactic acid bacteria. In a study by Hesseltine et al.,
19 92%
of isolates were Lactobacillaceae, with more than half belonging to the genus Lactobacillus, 35% to
the genus Leuconostoc, and 3% to “Streptococcus.” Molds were found generally in low numbers in
spoiled products. The fresh products showed lactic acid bacterial numbers as high as 8.38 log 10 /g.
BAKERY PRODUCTS
Commercially produced and properly handled bread generally lacks sufficient amounts of moisture
to allow for the growth of any organisms except molds. One of the most common is Rhizopus stolonifer,
often referred to as the “bread mold.” The “red bread mold,” Neurospora sitophila, may also be seen
from time to time. Storage of bread under conditions of low humidity retards mold growth, and this
type of spoilage is generally seen only when bread is stored at high humidity or when wrapped while
odor of butyric acid may precede emulsion separation. The spoilage organisms apparently attack the
sugars fermentatively. It appears that the pH remains low, thereby preventing the activities of most
proteolytic and lipolytic bacteria. It is not surprising to find yeasts and lactic acid bacteria under
these conditions. In a study of 17 samples of spoiled mayonnaise, mayonnaise-like, and blue cheese
dressings, Kurtzman et al.
31 found high yeast counts in most samples and high lactobacilli counts in
two. The pH of samples ranged from 3.6 to 4.1. Two-thirds of the spoiled samples yielded Z. bailii.
Common in some samples was L. fructivorans, with aerobic spore formers being found in only two
samples. Of ten unspoiled samples tested, microorganisms were in low numbers or not detectable at
all.
It is well established that foodborne pathogens will not grow in commercially produced mayonnaise
or dressings that have a pH of 4.4 and water-phase titratable acidity of at least 0.43 for acetic acid.
53
Foodborne pathogens typically die-off in these products, but some studies have found that E. coli
0157:H7 can persist for several weeks (see reference 53). Home-made mayonnaise has been the
source of several food poisoning outbreaks typically associated with the use of contaminated raw eggs
and the lack of sufficient organic acid to produce a safe pH level to destroy S.Enteritidis. It has been
recommended that with pure lemon juice [citric acid concentration ≥5% (w/v)], the pH should be
3.30 or below, or at least 20 ml of pure lemon juice/egg yolk.
67 It is recommended that a product of
this composition should be held at least 72 hours at 22
◦ C or above. Pathogenic strains of E. coli from
mayonnaise are covered in Chapter 27.
CEREALS, FLOUR, AND DOUGH PRODUCTS
The microbial biota of wheat, rye, corn, and related products may be expected to be that of soil,
storage environments, and those picked up during the processing of these commodities. Although
these products are high in proteins and carbohydrates, their low a w is such as to restrict the growth
of all microorganisms if stored properly. The microbial biota of flour is relatively low, as some of the
bleaching agents reduce the load. When conditions of a w favor growth, bacteria of the genus Bacillus
and molds of several genera are usually the only ones that develop. Many aerobic spore formers are
capable of producing amylase, which enables them to utilize flour and related products as sources of
energy, provided that sufficient moisture is present to allow growth to occur. With less moisture, mold
growth occurs and may be seen as typical mycelial growth and spore formation. Members of the genus
Rhizopus are common and may be recognized by their black spores.
The spoilage of fresh refrigerated dough products, including buttermilk biscuits, dinner and sweet
rolls, and pizza dough, is caused mainly by lactic acid bacteria. In a study by Hesseltine et al.,
19 92%
of isolates were Lactobacillaceae, with more than half belonging to the genus Lactobacillus, 35% to
the genus Leuconostoc, and 3% to “Streptococcus.” Molds were found generally in low numbers in
spoiled products. The fresh products showed lactic acid bacterial numbers as high as 8.38 log 10 /g.
BAKERY PRODUCTS
Commercially produced and properly handled bread generally lacks sufficient amounts of moisture
to allow for the growth of any organisms except molds. One of the most common is Rhizopus stolonifer,
often referred to as the “bread mold.” The “red bread mold,” Neurospora sitophila, may also be seen
from time to time. Storage of bread under conditions of low humidity retards mold growth, and this
type of spoilage is generally seen only when bread is stored at high humidity or when wrapped while