Milk, Fermentation, and Fermented and Nonfermented Dairy Products 161
During cold storage of pasteurized milk, psychrotrophic Bacillus weihenstephanensis causes “sweet
curdling” due to its production of proteases and peptidases. The spoilage of UHT-treated milk can
result from the actions of heat-resistant proteases and lipases that are produced by some psychrotrophs
in raw milk, and more on this can be found in reference 17.
Ropiness is a condition sometimes seen in raw milk that is caused by Alcaligenes viscolactis.
Its growth is favored by low-temperature maintenance of raw milk for several days. The “rope”
consists of a slime-layer material produced by the bacterial cells, and it gives the product a stringy
consistency.
PROBIOTICS AND PREBIOTICS
The definition of a probiotic that dates back to the mid-1960s has been modified during the past
decade. In general, it is a consumable product that contains live organisms that are or are believed to
be beneficial to the consumer. The ingestion of live organisms such as those in yogurt or fermented
milk is critical to the original concept. The term has been applied to consumable products that produce
a number of clinical benefits, but which do not contain viable cells. One example of this is the easing
of symptoms of lactose intolerance by the ingestion of heated yogurt (for a review, see reference 53).
A definition of probiotic that encompasses the above has been proposed by Salminen et al.
61 In the
absence of viable organisms, the term “abiotics” has been suggested.
37,67 To make the definition of a
probiotic even wider, the term has been applied to bacteria that act as control agents in an aquaculture
environment.
77 For a more detailed review of probiotics, see reference 37.
Yogurt appears to be the most widely consumed of probiotic products (especially in the United
States) and while it is consumed by some because it is a fermented dairy product, it is consumed by
others because of its real or presumed health benefits. Although the typical starter cultures for yogurt are
Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, some
preparations are made by the addition of bifidobacteria. Regarding the number of viable cells that
should exist in probiotic and probiotic-like products, the Swiss Food Regulation and the International
Standard of FIL/IDF require that such products contain at least 10
6 cfu/ml while the Fermented Milks
and Lactic Acid Beverages Association in Japan requires at least 10
7 cfu/ml of viable bifidobacteria
(see reference 66). It is unclear whether viable cell numbers can be of both lactic acid bacteria and
bifidobacteria, or only one of these groups. When bifidobacteria are involved in the yogurt fermentation,
they tend to die out during storage. These organisms are anaerobes that require negative Eh conditions
and a pH near neutrality.
66 The effect of a whey protein hydrolysate on some probiotic bacteria in milk
was investigated and while the hydrolysate initially increased the growth of Bifidobacterium longum
along with two lactobacilli, after 28 days at refrigerator temperatures, the probiotic organisms were at
about the same level as in the control milk.
44
Live Bacillus spp. spores are used as probiotics and the three species most often used are B. clausii,
B. pumilus, and B. cereus at levels of ca. 10
9 /g. Positive effects have been demonstrated and they
appear to be due to the immunogenic properties of the spores, not the vegetative cells.
The effect of three starter cultures on the survival of Yersinia enterocolitica in yogurt is shown
in Figure 7–3 where the rapid acid-producing starter effected a log-5.0 reduction in 72 hours, and a
slow acid-producing strain effected a log-5.6 reduction in 96 hours.
7 Inhibitory efforts of this type
by probiotic-type products against foodborne pathogens have been demonstrated for a number of
pathogens, and while pH reduction is one factor in the inhibition, factors such as bacteriocins and
organic acid toxicity are undoubtedly involved, and this is discussed further in Chapter 13. The cause
of lactose intolerance and its detection are described below.
During cold storage of pasteurized milk, psychrotrophic Bacillus weihenstephanensis causes “sweet
curdling” due to its production of proteases and peptidases. The spoilage of UHT-treated milk can
result from the actions of heat-resistant proteases and lipases that are produced by some psychrotrophs
in raw milk, and more on this can be found in reference 17.
Ropiness is a condition sometimes seen in raw milk that is caused by Alcaligenes viscolactis.
Its growth is favored by low-temperature maintenance of raw milk for several days. The “rope”
consists of a slime-layer material produced by the bacterial cells, and it gives the product a stringy
consistency.
PROBIOTICS AND PREBIOTICS
The definition of a probiotic that dates back to the mid-1960s has been modified during the past
decade. In general, it is a consumable product that contains live organisms that are or are believed to
be beneficial to the consumer. The ingestion of live organisms such as those in yogurt or fermented
milk is critical to the original concept. The term has been applied to consumable products that produce
a number of clinical benefits, but which do not contain viable cells. One example of this is the easing
of symptoms of lactose intolerance by the ingestion of heated yogurt (for a review, see reference 53).
A definition of probiotic that encompasses the above has been proposed by Salminen et al.
61 In the
absence of viable organisms, the term “abiotics” has been suggested.
37,67 To make the definition of a
probiotic even wider, the term has been applied to bacteria that act as control agents in an aquaculture
environment.
77 For a more detailed review of probiotics, see reference 37.
Yogurt appears to be the most widely consumed of probiotic products (especially in the United
States) and while it is consumed by some because it is a fermented dairy product, it is consumed by
others because of its real or presumed health benefits. Although the typical starter cultures for yogurt are
Streptococcus salivarius subsp. thermophilus and Lactobacillus delbrueckii subsp. bulgaricus, some
preparations are made by the addition of bifidobacteria. Regarding the number of viable cells that
should exist in probiotic and probiotic-like products, the Swiss Food Regulation and the International
Standard of FIL/IDF require that such products contain at least 10
6 cfu/ml while the Fermented Milks
and Lactic Acid Beverages Association in Japan requires at least 10
7 cfu/ml of viable bifidobacteria
(see reference 66). It is unclear whether viable cell numbers can be of both lactic acid bacteria and
bifidobacteria, or only one of these groups. When bifidobacteria are involved in the yogurt fermentation,
they tend to die out during storage. These organisms are anaerobes that require negative Eh conditions
and a pH near neutrality.
66 The effect of a whey protein hydrolysate on some probiotic bacteria in milk
was investigated and while the hydrolysate initially increased the growth of Bifidobacterium longum
along with two lactobacilli, after 28 days at refrigerator temperatures, the probiotic organisms were at
about the same level as in the control milk.
44
Live Bacillus spp. spores are used as probiotics and the three species most often used are B. clausii,
B. pumilus, and B. cereus at levels of ca. 10
9 /g. Positive effects have been demonstrated and they
appear to be due to the immunogenic properties of the spores, not the vegetative cells.
The effect of three starter cultures on the survival of Yersinia enterocolitica in yogurt is shown
in Figure 7–3 where the rapid acid-producing starter effected a log-5.0 reduction in 72 hours, and a
slow acid-producing strain effected a log-5.6 reduction in 96 hours.
7 Inhibitory efforts of this type
by probiotic-type products against foodborne pathogens have been demonstrated for a number of
pathogens, and while pH reduction is one factor in the inhibition, factors such as bacteriocins and
organic acid toxicity are undoubtedly involved, and this is discussed further in Chapter 13. The cause
of lactose intolerance and its detection are described below.