Should yoghurt cultures be considered probiotic?
Francisco Guarner1*, Gabriela Perdigon2, Ge ´rard Corthier3, Seppo Salminen4, Berthold Koletzko5and
1Digestive System Research Unit, University Hospital Vall d’Hebron, Barcelona, Spain
2Centro de Referencia para Lactobacilos (Cerela), Facultad de Bioquı ´mica, Quı ´mica y Farmacia, Universidad Nacional de Tucuma ´n,
3Institut National de la Recherche Agronomique, Unite Ecologie Physiologie Systeme Digestif, Jouy-en-Josas, France
4Food Development, Health Biosciences Program, Functional Foods Forum, University of Turku, Finland
5University of Munich, Metabolic Diseases and Nutrition, Munich, Germany
6Universita Cattolica Del Sacro Cuore (UCSC), Fac Agraria Istituto Microbiologia, Piacenza, Italy
(Received 8 July 2004 – Revised 17 January 2005 – Accepted 17 January 2005)
Probiotics are live micro-organisms that when administered in adequate amounts confer a health benefit on the host. Consumption of yoghurt has been
shown to induce measurable health benefits linked to the presence of live bacteria. A number of human studies have clearly demonstrated that yoghurt
containing viable bacteria (Streptococcus thermophilus and Lactobacillus delbrueckii sp. bulgaricus) improves lactose digestion and eliminates symptoms
of lactose intolerance. Thus, these cultures clearly fulfil the current concept of probiotics.
Bacteria: Functional Food: Probiotic definition: Market regulation
Fermented milks and yoghurts have been used throughout the
history of mankind. A proposal by the European Commission for
a council regulation laying down additional rules on the common
organization of the market in milk and milk products for yoghurt
and yoghurt-like products was presented recently (AGRI/38743/
2003rev3). Article 2 and Annex of the proposal establish that
delbrueckii sp. bulgaricus. The term ‘yoghurt-like product’ is
defined as alternative culture yoghurt (i.e. when L. bulgaricus is
substituted by other Lactobacillus species for the fermentation of
milk) or yoghurt containing probiotic bacteria (when probiotic
bacteria are added to the yoghurt or alternative cultures). Article 4
of the proposal declares that ‘probiotic bacteria’ are live food
supplements, which benefit the health of the consumer.
These statements and definitions seem to fit well with the
common knowledge and use of the terms by scientists, industry
and the general public. The proposal clearly differentiates
between yoghurt starter cultures (S. thermophilus and L. bulgar-
icus) and probiotic bacteria that may be added (see Article 2 and
Annex), but the distinction does not exclude S. thermophilus
and L. bulgaricus from the category of probiotic bacteria. The
starter cultures can also be probiotics as long as they comply
with the definition of probiotic. For instance, if some of the
health benefits achieved by consumption of yoghurt are linked
to the presence of live bacteria, then these bacteria are probio-
tics (defined by the proposal as ‘live food supplements which
the notion of probiotics, and to analyse whether the usual yoghurt
cultures (S. thermophilus and L. delbrueckii sp. bulgaricus) qualify
for this notion according to our current concepts. If the starter cul-
tures are probiotics, products that have been heat-treated after fer-
mentation would lack the probiotic benefit of yoghurt, even if
other nutritional properties are unchanged by heat treatment. As
mentioned by the council regulation (see Point 9 in the Preamble),
legislation of most EU member states establishes that the presence
of living bacteria in large quantities is a characteristic of yoghurt,
and the notion of yoghurt should therefore be reserved to this kind
mented milk product in which the starter micro-organisms are
viable, live and abundant (Codex Standard for Fermented Milks,
Probiotics: historical evolution of the concept
The origin of the term ‘probiotic’ is credited to Werner Kollath as
related in a publication by the German scientist Ferdinand Vergin
*Corresponding author: Dr Francisco Guarner, fax þ 34 93489 4456, email firstname.lastname@example.org
(1954). Kollath proposed the term ‘Probiotika’ to designate
‘active substances that are essential for a healthy development
of life’. The Greek meaning of the term (‘for life’) is opposed
to ‘antibiotics’ (‘against life’), at that time a very well recognized
‘hit’ of science. In a paper published in Science a few years later,
Lilly & Stillwell (1965) described probiotics as substances
secreted by one micro-organism that stimulate the growth of
another. Other US scientists later used the term probiotic with
the same meaning: factors that stimulate growth (Sperti, 1971;
Nutini et al. 1982). However, Parker (1974) made a different
use of the term, which was applied to describe animal feed sup-
plements specifically designed to improve health. He introduced
a new definition: ‘organisms and substances which contribute to
intestinal microbial balance’. The success of the new concept is
mainly due to the subsequent work of Roy Fuller in Reading
(UK), who revised Parker’s definition by removing the reference
to ‘substances’. Thus, a probiotic is ‘a live microbial feed sup-
plement which beneficially affects the host animal by improving
its intestinal microbial balance’ (Fuller, 1989). The concept was
also applicable to human nutrition and medicine (Fuller, 1991).
This definition stressed the importance of viable microbial cells
as an essential requirement, but kept the concept restricted to a
particular mechanism of action: improvement of the intestinal
microbial balance, as in Parker’s definition. Shortly thereafter,
Havenaar & Huis In’t Veld (1992) broadened the definition to
include the microflora of other habitats different from the intesti-
nal, such as the upper respiratory tract or the urogenital tract. Pro-
biotics are ‘a mono- or mixed culture of live microorganisms
which applied to animal or man, affects beneficially the host by
improving the properties of the indigenous microflora’. Remark-
ably, the concept was still restricted to micro-organisms able to
influence the indigenous microbial balance.
The notion of probiotic as introduced by Fuller was attractive
and successful. Subsequent scientific approaches aimed at the
identification of the ideal probiotic, and discussed the character-
istics and properties required for a micro-organism to qualify as
a probiotic. Many scientific publications and reviews listed a
series of essential requirements to be checked by in vitro methods
in the screening of micro-organisms with a probiotic value. It was
suggested that only strains shown to possess these essential traits
should be tested in vivo. The list of essential requirements based
on theoretical considerations included the following:
(1) Human origin (as a token of safety for human use);
(2) Resistance to gastric acidity and bile toxicity (these properties
would predict good survival during gastrointestinal transit);
(3) Adhesion to gut epithelial cells (as a requirement for
successful colonization in vivo – the term colonization
describes the ability of a particular bacteria strain to
permanently establish in the host over time without the
need for periodic reintroduction of the bacteria; see Bezkor-
(4) Production of antimicrobial substances or bacteriocins (for
(5) Ability to modulate immune responses and ability to
influence metabolic activities of faeces (for prevention of
Several bacteria strains successfully qualified by passing through
all the in vitro tests, and thus received the ‘full title’ of being a
probiotic, in some cases without any proof of a beneficial
health effect demonstrated in human studies.
On the other hand, most recent scientific developments have
challengedthe validity and
criteria for a full definition of probiotic. For instance, the Nissle
Escherichia coli strain, isolated in 1917 for therapeutic purposes
in the pre-antibiotic era, is not resistant to acid or bile toxicity.
This strain is given in enteric-coated capsules and has proved
useful for the prevention and treatment of human disease in
well-designed human studies (see for instance the Lancet paper
on a clinical trial in ulcerative colitis; Rembacken et al. 1999).
There is no proof so far that supports or substantiates the claim
linking human origin and safety for human use, or human
origin and efficiency in human studies. It is also well known
that many pathogens exert their deleterious effect through
adhesion to gut epithelial cells (Hoepelman & Tuomanen,
1992), and again this fact has cast some doubts about the meaning
of this property by itself in the definition of a strain as probiotic
Taken together, these observations suggested that the proposed
list of in vitro properties could no longer be accepted as criteria
for definition of a probiotic. Most common views about the
in vitro tests for probiotics among the scientific community are
well reflected in the report by the Joint Food and Agriculture
Organization/World Health Organization Working Group (2002):
usefulnessof the suggested
‘In vitro tests are useful to gain knowledge of strains and the
mechanism of the probiotic effect. However, it was noted that the
currently available tests are not fully adequate to predict the
functionality of probiotic microorganisms in the human body. It was
also noted that in vitro data available for particular strains are not
sufficient for describing them as probiotic. Probiotics for human use
will require substantiation of efficacy with human trials.’
Hence, in vitro studies are and will be a very useful tool for the
selection of bacteria for a particular probiotic use, but are not
essential requirements for a strain to qualify as a probiotic. In
addition to this consensus about the in vitro tests, some important
evidence obtained in human studies has challenged Fuller’s con-
cept of probiotics. First, many bacteria able to transit alive
through the entire human gastrointestinal tract are devoid of a
measurable health effect, and second, a persistent change in the
indigenous flora by consumption of a probiotic has never been
demonstrated (Bezkorovainy, 2001). According to these obser-
vations, induction of changes in the indigenous flora should not
be considered as a primary target of probiotics. Thus, newer defi-
nitions of the probiotic concept have omitted the need to induce
changes in the microbial balance, as health benefits can be pro-
duced through other mechanisms as well.
The current concept of probiotics
Definitions proposed in recent years are listed below.
(1) ‘Oral probiotics are living micro-organisms, which upon
ingestion in certain numbers, exert health benefits beyond
inherent basic nutrition’. LABIP consensus definition (Guar-
ner & Schaafsma, 1998).
(2) ‘A live microbial food ingredient that is beneficial to health’.
Proposed by Salminen et al. (1998) and adopted as consen-
sus definition by the FUFOSE Concerted Action sponsored
by the European Commission (Diplock et al. 1999).
(3) ‘Live microorganisms which when administered in adequate
amounts confer a health benefit on the host’. Definition by
the Joint Food and Agriculture Organization/World Health
Organization Working Group (2002). The International
Scientific Association for Probiotics and Prebiotics recently
adopted this definition (Reid et al. 2003).
(4) ‘Probiotic bacteria are live food supplements which benefit
the health of the consumer’, as defined in the legal proposal
by the European Commission referred to earlier.
All these definitions require that the term probiotic should only be
applied to microbes administered alive having a demonstrated
beneficial effect (Reid et al. 2003). The similarities between
these new definitions clearly reflect the consensus of scientists
all over the world on this issue. The concept is now open to
many different applications in a large variety of fields relevant
for human and animal health. The concept is generic and covers
many different aspects that may be addressed by specific strains.
Yoghurt cultures are probiotic
According to current scientific concepts, yoghurt cultures are pro-
biotics if a beneficial physiological effect can be obtained by con-
sumption of the live cultures and the benefit has been
substantiated appropriately in human studies.
All S. thermophilus and most L. bulgaricus strains have a high
lactase activity (Sanders et al. 1996). It is well recognized that
yoghurt consumption improves lactose digestion and eliminates
symptoms of lactose intolerance. The physiological effects have
been clearly demonstrated in a large number of human studies
in which consumption of yoghurt (with live cultures) has been
compared with consumption of a pasteurized product (with
heat-killed bacteria; Gilliland & Kim, 1984; Savaiano et al.
1984; McDonough et al. 1987; Dewit et al. 1988; Lerebours
et al. 1989; Pochart et al. 1989; Marteau et al. 1990; Varela-
Moreiras et al. 1992; Rizkalla et al. 2000; Labayen et al. 2001;
Pelletier et al. 2001). All studies have shown better lactose diges-
tion and absorption in subjects who consumed yoghurt with live
cultures, as well as reduction of gastrointestinal symptoms. The
benefit on lactose absorption was also demonstrated in healthy
subjects without lactose maldigestion (Rizkalla et al. 2000). All
these studies highlight the essentiality of live bacteria for the
beneficial effect on lactose digestion (not excluding that other
beneficial effects can be due to non-viable bacteria). There are
no major scientific discrepancies on this issue fully established
by human intervention studies.
The functional properties of yoghurt are consistent with further
evidence obtained in important ancillary studies that confirmed
viability and metabolic activity of yoghurt bacteria in the
human intestine (Martini et al. 1987; Pochart et al. 1989; Marteau
et al. 1990), as well as in in vivo animal models (Lick et al. 2001;
Drouault et al. 2002). Yoghurt bacteria can also be detected in
faeces of human subjects consuming yoghurt (Brigidi et al.
2003; Callegari et al. 2004).
Yoghurt is also being used in the management of acute diar-
rhoeal disorders, as recommended by World Health Organization
(1995). This recommendation is based on the traditional approach
in many countries all over the world, as well as on evidence
gained in human intervention studies (Boudraa et al. 1990,
2001). Yoghurt feeding in children with acute watery diarrhoea
decreased stool frequency and shortened the duration of diar-
rhoeal episodes (Boudraa et al. 2001).
Other studies have addressed the role of yoghurt on the immune
system. Yoghurt consumption may enhance the immune response
particularly in immunocompromised populations, such as the
elderly (Meydani & Ha, 2000). The role of yoghurt in the
modulation of the immune system was further demonstrated by
Van de Water et al. (1999) in a randomized controlled trial
with human subjects. Long-term consumption of yoghurt, as com-
pared with either the same product heat-treated after fermentation
or exclusion of yoghurt products from the diet during the length
of the study (1 year), was associated with a significant decrease
in allergic symptoms.
In agreement with the demonstration of probiotic efficacy, sev-
eral consensus documents have acknowledged the probiotic
nature of yoghurt cultures. These include the report of the Joint
Food and Agriculture Organization/World Health Organization
Working Group (2002), the International Scientific Association
for Probiotics and Prebiotics workshop consensus document
(Reid et al. 2003), the Lancet review on gut flora in health and
disease (Guarner & Malagelada, 2003) and the official web
page of the Ministry of Agri-culture and Agri-Food in Canada
The concept of ‘probiotic’ has evolved to a simple and straight-
forward notion: probiotics are ‘live micro-organisms which
when administered in adequate amounts confer a health benefit
on the host’. Consumption of yoghurt has been shown to induce
measurable health benefits linked to the presence of live bacteria,
as compared with products with heat-killed bacteria. Thus, yoghurt
starter cultures clearly fulfil the current concept of probiotics at
least for its beneficial effect on lactose digestion in vivo. Some
yoghurt cultures were shown to induce other health benefits
such as reduction in severity and duration of acute diarrhoea, or
prevention of allergic disorders. Whether all yoghurt cultures
canlead tothese healthbenefits
Conflict of interest
F. G. is a member of the Beneo Scientific Committee sponsored
by Orafti (Tienen, Belgium). L. M. served as coordinator of a
research project ‘Detection in faecal samples of yoghurt cultures’,
which was co-funded by the Groupe Danone (Paris, France). B. K.
serves as the coordinator of a multi-centre research project ‘Child-
hood Obesity – Programming by Infant Nutrition’, funded by the
European Commission (QLK1-2001-00389) and co-funded by
the Groupe Danone (Paris, France). S. S. is holder of the
Bristol-Myers Squibb Foundation Unrestricted Nutrition Research
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