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In recent years, there has been a strong focus on beneficial foods with probiotic microorganisms and functional organic substances. In this context, there is an increasing interest in the commercial use of kefir, since it can be marketed as a natural beverage that has health promoting bacteria. There are numerous commercially available kefir based-products. Kefir may act as a matrix in the effective delivery of probiotic microorganisms in different types of products. Also, the presence of kefir’s exopolysaccharides, known as kefiran, which has biological activity, certainly adds value to products. Kefiran can also be used separately in other food products and as a coating film for various food and pharmaceutical products. This article aims to update the information about kefir and its microbiological composition, biological activity of the kefir’s microflora and the importance of kefiran as a beneficial health substance.
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REVIEW
published: 30 October 2015
doi: 10.3389/fmicb.2015.01177
Edited by:
Maria De Angelis,
University of Bari Aldo Moro, Italy
Reviewed by:
Theo Varzakas,
Technological Educational Institute
of Peloponnese, Greece
Cristiana Garofalo,
Università Politecnica delle Marche,
Italy
*Correspondence:
Carlos R. Soccol
soccol@ufpr.br
Specialty section:
This article was submitted to
Food Microbiology,
a section of the journal
Frontiers in Microbiology
Received: 22 April 2015
Accepted: 12 October 2015
Published: 30 October 2015
Citation:
Prado MR, Blandón LM,
Vandenberghe LPS, Rodrigues C,
Castro GR, Thomaz-Soccol V
and Soccol CR (2015) Milk kefir:
composition, microbial cultures,
biological activities, and related
products. Front. Microbiol. 6:1177.
doi: 10.3389/fmicb.2015.01177
Milk kefir: composition, microbial
cultures, biological activities, and
related products
Maria R. Prado1, Lina Marcela Blandón1, Luciana P. S. Vandenberghe1,
Cristine Rodrigues1, Guillermo R. Castro2, Vanete Thomaz-Soccol1and
Carlos R. Soccol1*
1Department of Bioprocess Engineering and Biotechnology, Federal University of Paraná, Curitiba, Brazil, 2Nanobiomaterials
Laboratory, Institute of Applied Biotechnology – School of Sciences, Universidad Nacional de la Plata, La Plata, Argentina
In recent years, there has been a strong focus on beneficial foods with probiotic
microorganisms and functional organic substances. In this context, there is an
increasing interest in the commercial use of kefir, since it can be marketed as a
natural beverage that has health promoting bacteria. There are numerous commercially
available kefir based-products. Kefir may act as a matrix in the effective delivery of
probiotic microorganisms in different types of products. Also, the presence of kefir’s
exopolysaccharides, known as kefiran, which has biological activity, certainly adds value
to products. Kefiran can also be used separately in other food products and as a
coating film for various food and pharmaceutical products. This article aims to update
the information about kefir and its microbiological composition, biological activity of the
kefir’s microflora and the importance of kefiran as a beneficial health substance.
Keywords: kefir, biological activity, polysaccharides, kefiran, microbial composition
INTRODUCTION
Kefir is an acidic-alcoholic fermented milk product with little acidic taste and creamy consistency
that was originated in the Balkans, in Eastern Europe, and in the Caucasus (Fontán et al., 2006;
Serafini et al., 2014). Kefir can be produced by fermenting milk with commercial freeze-dried kefir
starter cultures, traditional kefir grains, and the product that remains after the removal of kefir
grains (Bensmira et al., 2010). Kefir grains are a kind of yogurt starter, which are white to yellow –
white, gelatinous, and variable in size (varying from 0.3–3.5 cm in diameter) and are composed
by a microbial symbiotic mixture of lactic acid bacteria (108CFU/g), yeast (106–107CFU/g), and
acetic acid bacteria (105CFU/g) that stick to a polysaccharide matrix (Garrote et al., 2010;Chen
et al., 2015). After successive fermentations, kefir grains can break up to new generation grains,
which have the same characteristics as the old ones (Gao et al., 2012).
Commercial kefir is produced by two methods: The “Russian method” and the pure cultures.
In the “Russian method” kefir is produced on a larger scale, using a series fermentation process,
beginning with the fermentation of the grains and using the percolate. The other method
employs pure cultures isolated from kefir grains or commercial cultures (Leite et al., 2013). Also,
the industrial or commercial process uses direct-to-vat inoculation (DVI) or direct-to-vat set
(DVS) kefir starter cultures. In addition, Bifidobacterium sp., Lactobacillus sp. and probiotic yeast
(Saccharomyces boulardii) may be used as adjunct cultures when blended with kefir grains or kefir
Frontiers in Microbiology | www.frontiersin.org 1October 2015 | Volume 6 | Article 1177
Prado et al. Milk kefir
DVI cultures (Wszolek et al., 2006). On the other hand, whey
may be a practical base for kefir culture production, and
fermented whey has shown to be a suitable cryoprotective
medium during freeze-drying. The freeze-dried culture retains
a high survival rate and shows good metabolic activity and
fermentation efficiency, indicating a good potential for its
use as a value-added starter culture in dairy technology.
All of these studies have shown promising perspectives
for the application of kefir grains in whey valorization
strategies (Bensmira et al., 2010;Cheirsilp and Radchabut,
2011).
Traditionally, kefir is manufactured using cow, ewe, goat, or
buffalo milk. However, in some countries, animal milk is scarce,
expensive, or minimally consumed due to dietary constraints,
preferences, or religious customs. Therefore, there have been
many attempts to produce kefir from a variety of food sources
such as soy milk (Botelho et al., 2014). Historically, kefir has
been linked with health, for example, in Soviet countries, kefir
has been recommended for consumption by healthy people to
restrain the risk of some diseases (Saloff-Coste, 1996;St-Onge
et al., 2002;Farnworth and Mainville, 2003). The consumption
of this fermented milk has been related to a variety of health
benefits (Vujiˇ
ciˇ
c et al., 1992;McCue and Shetty, 2005;Rodrigues
et al., 2005a) not only linked to its microflora, but also
due to the presence of some metabolic products as organic
acids (Garrote et al., 2001;Ismaiel et al., 2011). In addition,
kefir cultures have the ability to assimilate cholesterol in milk
(Yanping et al., 2009). On the other hand, there is a growing
commercial interest in using kefir as a suitable food matrix
for supplementation with health-promoting bacteria. Kefir may
not only be a natural probiotic beverage, but also acts as an
effective matrix for the delivery of probiotic microorganisms
(Vinderola et al., 2006;Medrano et al., 2008;Oliveira et al.,
2013).
In kefir grains the main polysaccharide is kefiran, which
is a heteropolysaccharide composed by equal proportions of
glucose and galactose and is mainly produced by Lactobacillus
kefiranofaciens (Zajšek et al., 2011). It has been demonstrated
that kefiran improves the viscosity and viscoelastic properties
of acid milk gels (Rimada and Abraham, 2006), and is able
to form gels that have interesting viscoelastic properties at
low temperatures, because of that, kefiran can also be used
as an additive in fermented products. Besides, kefiran can
enhance the rheological properties of chemically acidified skim
milk gels increasing their apparent viscosity (Zajšek et al.,
2013).
Compared with other polysaccharides, kefiran has
outstanding advantages such as antitumor, antifungal,
antibacterial properties (Cevikbas et al., 1994;Wang et al.,
2008) immunomodulation or epithelium protection (Serafini
et al., 2014), anti-inflammatory (Rodrigues et al., 2005b), healing
(Rodrigues et al., 2005a), and antioxidant activity (Chen et al.,
2015).
This review presents the most recent advances about kefir
and kefiran, their production and microbial cultures involved,
biological activities and potential applications in health and food
industries.
MICROBIAL COMPOSITION OF KEFIR
GRAINS AND KEFIR
Kefir grains have a complex composition of microbial species
such as the predominance of lactic acid bacteria, acetic bacteria,
yeasts, and fungi (Jianzhong et al., 2009;Pogaˇ
ci´
c et al., 2013).
This microbial species are classified into four groups:
homofermentative and heterofermentative lactic acid bacteria
and lactose and non-lactose assimilating yeast (Cheirsilp and
Radchabut, 2011). In that way, Lactobacillus paracasei ssp.
paracasei,Lactobacillus acidophilus, Lactobacillus delbrueckii
ssp. bulgaricus,Lactobacillus plantarum,andL. kefiranofaciens
are predominant species. However, these species represent
only 20% of the Lactobacillus in the final fermented beverage,
with the remainder consisting of Lactobacillus kefiri (80%;
Yüksekdag et al., 2004;Zanirati et al., 2015). Acetobacter aceti
and A. rasens have also been isolated, such as the fungus
Geotrichum candidum. More than 23 different yeast species
have been isolated from kefir grains and from fermented
beverages of different origins. However, the predominant species
are Saccharomyces cerevisiae, S. unisporus, Candida kefyr,
and Kluyveromyces marxianus ssp. marxianus (Witthuhn
et al., 2004;Diosma et al., 2014;Zanirati et al., 2015;
Tab l e 1 ).
The microbial composition may vary according to kefir origin,
the substrate used in the fermentation process and the culture
maintenance methods. Tibetan kefir, which is used in China, is
composed of Lactobacillus, Lactococcus, and yeast. Additionally,
acetic acid bacteria have been identified in Tibetan kefir,
depending on the region in China from where it was obtained
(Gao et al., 2012), additionally, Tibetan kefir composition differs
from that of Russian kefir, Irish kefir, Taiwan kefir, Turkey
fermented beverage with kefir; however, it is known that
this microbial diversity is responsible for the physicochemical
features and biological activities of each kefir (Jianzhong et al.,
2009;Kabak and Dobson, 2011;Gao et al., 2012;Altay et al.,
2013).
Wang et al. (2012) examined a section of a whole kefir
grain and found in the outer layer of the grain, lactococci,
and yeasts, and, in the inner layer of the grain, the quantity
of lactobacilli were much higher and more yeasts cells were
found. There are little information about the mechanism of grain
formation, so the same authors, proposed a hypothesis to explain
that. “Initially, Lactobacillus kefiranofaciens and Saccharomyces
turicensis start to auto-aggregate and co-aggregated to small
granules.” The aggregation is enhanced when the pH drops. The
biofilm producers, Lactobacillus kefiri,Kluyveromyces marxianus
HY1, and Pichia fermentans HY3 then adhere to the surface of
these small granules due to their cell surface properties and their
strong aggregation ability, which gives rise to thin biofilms. After
biofilm formation, the kefir yeasts and Lactobacillus continue to
co-aggregated with the granule strains and associate with the
granule biofilm to become a three dimensional microcolony.
As the cell density due to the growth of kefir yeasts and
Lactobacillus increases, cells and milk components that are
present in the liquid phase accumulate on the granule surface
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Prado et al. Milk kefir
TABLE 1 | Microbial compositions found in kefir and kefir grains of different origins.
Microorganism Source – Country Reference
Lactobacillus kefir, Lactobacillus kefiranofaciens, Lactobacillus paracasei,
Lactobacillus plantarum, Lactococcus lactis ssp. lactis, Kluyveromyces
marxianus, Lactobacillus parakefir, Saccharomyces cerevisiae,
Saccharomyces unisporus, Leuconostoc mesenteroides, Acetobacter sp.,
Saccharomyces sp., Lactococcus lactis ssp. lactis biovar diacetylactis,
Lactococcus lactis, Lactobacillus kefiri, Lactobacillus parakefiri
Kefir grains and beverage
Argentina
Garrote et al., 2001;Londero
et al., 2012;Hamet et al., 2013;
Diosma et al., 2014.
Lactobacillus kefiri, Lactobacillus kefiranofaciens, Leuconostoc mesenteroides,
Lactococcus lactis, Lactococcus lactis ssp. cremoris, Gluconobacter frateurii,
Acetobacter orientalis, Acetobacter lovaniensis, Kluyveromyces marxianus,
Naumovozyma sp., Kazachastania khefir
Kefir grains and beverage
Belgium
Korsak et al., 2015
Lactobacillus kefiri, Lactobacillus kefiranofaciens, Leuconostoc mesenteroides,
Lactococcus lactis, Lactobacillus paracasei, Lactobacillus helveticus,
Gluconobacter japonicus, Lactobacillus uvarum, Acetobacter syzygii,
Lactobacillus satsumensis, Saccharomyces cerevisiae., Leuconostoc sp.,
Streptococcus sp., Acetobacter sp., Bifidobacterium sp., Halococcus sp.,
Lactobacillus amylovorus, Lactobacillus buchneri, Lactobacillus crispatus,
Lactobacillus kefiranofaciens ssp. kefiranofaciens, Lactobacillus kefiranofaciens
ssp. kefirgranum, Lactobacillus parakefiri
Kefir grains – Brazil Miguel et al., 2010;Leite et al.,
2012;Zanirati et al., 2015
Lactobacillus brevis, Lactobacillus delbrueckii ssp. bulgaricus, Lactobacillus
helveticus, Streptococcus thermophilus, Lactobacillus casei ssp.
pseudoplantarum, Kluyveromyces marxianus var. lactis, Saccharomyces
cerevisiae, Candida inconspicua, Candida maris, Lactobacillus lactis ssp. lactis
Kefir grains and beverage
Bulgaria
Simova et al., 2002
Lactobacillus paracasei, Lactobacillus parabuchneri, Lactobacillus casei,
Lactobacillus kefiri, Lactococcus lactis, Acetobacter lovaniensis,
Kluyveromyces lactis, Kazachstania aerobia, Saccharomyces cerevisiae,
Lachancea meyersii
Kefir beverage – Brazil Magalhães et al., 2011
Lactobacillus kefiranofaciens, Leuconostoc mesenteroides, Lactococcus
lactis, Lactobacillus helveticus, Kluyveromyces marxianus, Saccharomyces
cerevisiae, Pseudomonas sp., Kazachstania unispora, Kazachstania exigua,
Lactobacillus kefiri, Lactobacillus casei, Bacillus subtilis, Pichia kudriavzevii,
Leuconostoc lactis, Lactobacillus plantarum, Acetobacter fabarum, Pichia
guilliermondii, Lactococcus sp., Lactobacillus sp., Acetobacter sp.,
Shewanella sp., Leuconostoc sp., Streptococcus sp, Acinetobacter sp.,
Pelomonas sp., Dysgonomonas sp., Weissella sp., Shewanella sp.
Kefir grains (Tibet)– China Jianzhong et al., 2009;Gao et al.,
2012, 2013a
Acetobacter acetic, Enterococcus faecalis, Enterococcus durans, Lactococcus
lactis ssp. cremoris, Leuconostoc pseudomesenteroides, Leuconostoc
paramesenteroides, Lactobacillus brevis, Lactobacillus acidophilus,
Saccharomyces sp., Brettanomyces sp., Candida sp., Saccharomycodes sp.,
Acetobacter rancens
Kefir beverage – China Yang et al., 2007
Lactobacillaceae and Streptococcaceae Kefir grains and beverage –
Ireland
Dobson et al., 2011
Lactobacillus kefiranofaciens, Dekkera anomala, Streptococcus thermophilus,
Lactococcus lactis, Acetobacter sp., Lactobacillus lactis, Enterococcus sp.,
Bacillus sp., Acetobacter fabarum, Acetobacter lovaniensis, Acetobacter
orientalis
Kefir grains – Italy Garofalo et al., 2015
Leuconostoc sp., Lactococcus sp., Lactobacillus sp., Lactobacillus plantarum,
Zygosaccharomyces sp., Candida sp., Candida lambica, Candida krusei,
Saccharomyces sp., Cryptococcus sp.
Kefir grains and beverage
South Africa
Witthuhn et al., 2005
Lactobacillus sp., Leuconostoc sp., Lactococcus sp., Zygosaccharomyces
sp., Candida sp., Saccharomyces sp.
Kefir grains – South Africa Witthuhn et al., 2004
Lactobacillus kefiri, Lactobacillus kefiranofaciens, Leuconostoc mesenteroides,
Lactococcus lactis, Escherichia coli, Pseudomonas sp., Saccharomyces
turicensis,
Kefir grains – Taiwan Wyder et al., 1999;Chen et al.,
2008;Wang et al., 2012;
Lactobacillus kefiri, Leuconostoc mesenteroides, Lactococcus lactis,
Streptococcus thermophilus, Lactobacillus kefiranofaciens, Lactobacillus
acidophilus
Kefir grains and beverage
Tur k e y
Guzel-Seydim et al., 2005;
Kesmen and Kacmaz, 2011
Lactobacillus helveticus, Lactobacillus buchneri, Lactobacillus kefiranofaciens,
Lactobacillus acidophilus, Lactobacillus helveticus, Streptococcus
thermophilus, Bifidobacterium bifidum, Kluyveromyces marxianus
Kefir grains – Turkey Kok-Tas et al., 2012;Nalbantoglu
et al., 2014
Lactococcus cremoris, Lactococcus lactis, Streptococcus thermophilus,
Streptococcus durans
Kefir beverage – Turkey Yüksekdag et al., 2004
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Prado et al. Milk kefir
TABLE 2 | Kefir microorganisms and their biological activities.
Organism of interest Origin Biological activity Reference
Lactobacillus plantarum MA2 Tibetan kefir Hypocholesterolemic effect Yanping et al., 2009
Lactobacillus plantarum Lp27 Tibetan kefir Inhibited cholesterol absorption Ying et al., 2013
Lactobacillus plantarum CIDCA 83114 Kefir grains –
Argentina
Inhibit the growth of Shigella sonnei in vitro and
also the cytotoxicity of C. difficile toxins on
eukaryotic cells
Bolla et al., 2013
Lactobacillus kefir CIDCA 8348 Kefir grains –
Argentina
Inhibit the growth of Shigella sonnei in vitro and
also the cytotoxicity of C. difficile toxins on
eukaryotic cells
Bolla et al., 2013
Lactobacillus plantarum ST8KF Kefir grains –
South Africa
Bactericida effect against: Lactobacillus casei,
Lactobacillus salivarius, Lactobacillus curvatus,
Listeria innocua
Powell et al., 2007
Lactobacillus kefiranofaciens K1 Kefir grains –
Taiwanese milk
Antiallergenic effect Chen et al., 2008;Wei-Sheng et al., 2010
Lactobacillus kefiranofaciens M1 Kefir grains –
Taiwanese milk
Immunoregulatory effects – anticolitis effect Hong et al., 2009;Chen et al., 2012
Lactobacillus lactis CIDCA 8221 Kefir grains –
Argentina
Inhibit the growth of Shigella sonnei in vitro and
also the cytotoxicity of Clostridium difficile
toxins on eukaryotic cells
Bolla et al., 2013
Kluyveromyces marxianus CIDCA 8154 Kefir grains –
Argentina
Inhibit the growth of Shigella sonnei in vitro and
also the cytotoxicity of Clostridium difficile
toxins on eukaryotic cells
Bolla et al., 2013
Saccharomyces cerevisiae CIDCA 8112 Kefir grains –
Argentina
Inhibit the growth of Shigella sonnei in vitro and
also the cytotoxicity of Clostridium difficile
toxins on eukaryotic cells
Bolla et al., 2013
Lactobacillus lactis ssp. cremoris Kefir grains –
India
Activity against food spoilage bacteria Raja et al., 2009
Source: Soccol et al., 2014.
TABLE 3 | Biological activity of kefiran.
Exopolysaccharide Biological activity Reference
Kefiran Reduction of blood pressure induced by hypertension Maeda et al., 2004
Favors the activity of peritoneal macrophages
Increase in peritoneal IgA Duarte et al., 2006
Antitumoral activity Liu et al., 2002
Antimicrobial activity Rodrigues et al., 2005a
Modulation of the intestinal immune system and protection of epithelial cells against
Bacillus cereus exocellular factors
Medrano et al., 2008;Piermaria et al., 2010
and the kefir grains are formed. There is a symbiotic relation
between the microorganisms present in kefir grains, wherein
the bacteria and yeast survive and share their bioproducts as
power sources and microbial growth factors. This microorganism
association is responsible for lactic and alcoholic fermentation
(Witthuhn et al., 2005; Wang et al., 2012;Hametetal.,
2013).
After receiving its actual/present denomination, some
of the microorganisms isolated and identified in kefir
cultures were classified using the product name, as in
Lactobacillus kefiri, L. kefiranofaciens, L. kefirgranum,
Lactobacillus parakefir,andCandida kefyr (Wyder et al.,
1999;Kwon et al., 2003;Yang et al., 2007;Kok-Tas et al.,
2012). Tab l e 1 demonstrates the microbial composition, which
has been isolated from kefir and kefir grains of different
origins.
BIOLOGICAL ACTIVITY OF KEFIR
Due to its composition, kefir is mainly considered a probiotic
resource (Nalbantoglu et al., 2014). “Probiotics are microbial cell
preparations or components of microbial cells with a beneficial
effect on the health of the host” (Lopitz et al., 2006). Some
studies suggest that probiotic bacteria in kefir consumers’ gut are
abundant and are correlated with health improvement (Ahmed
et al., 2013;Zheng et al., 2013); in that way, it had been
demonstrated that the cell-free fraction of kefir enhances the
ability to digest lactose relieving symptoms (Farnworth, 2005;
Rizk et al., 2009).
Another reason for the increased interest in probiotic strains
from kefir is its capacity to lower cholesterol levels. There are
different ways in which bacteria can alter serum cholesterol: (i)
through the binding to and absorption into the cell before it can
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Prado et al. Milk kefir
FIGURE 1 | Kefiran structure.
be absorbed into the body; (ii) producing free and deconjugating
bile acids; (iii) inhibiting the enzyme HMG-CoA reductase
(Yanping et al., 2009).
The microorganisms in the kefir grains produce lactic acid,
antibiotics and bactericides, which inhibit the development
of degrading and pathogenic microorganisms in kefir
milk (Liu et al., 2002). Kefir acts against the pathogenic
bacteria Salmonella, Helicobacter, Shigella, Staphylococcus,
Escherichia coli, Enterobacter aerogenes, Proteus vulgaris,
Bacillus subtilis, Micrococcus luteus, Listeria monocytogenes,
Streptococcus pyrogenes,(Lopitz et al., 2006), Streptococcus
faecalis KR6, Fusarium graminearum CZ1 (Ismaiel et al.,
2011), and the fungus Candida albicans. On the other
hand, it has been demonstrated that a mixture of kefir
isolated bacteria and yeast is able to prevent diarrhea and
enterocolitis triggered by Clostridium difficile (Bolla et al.,
2013). Besides, kefir showed good efficacy in inhibiting spore
formation and aflatoxin B1 produced by the fungus Aspergillus
flavus, which is a toxic compound formed either in the
field or during food storage. Therefore, kefir appears as a
promising safe alternative natural food preservative offering
protection against intoxication with aflatoxin B1 (Ismaiel et al.,
2011).
It had been proved that many species of lactobacilli
present in kefir have S-layer proteins. Surface layers (S-
layers) can be aligned in unit cells on the outermost surface
of many prokaryotic microorganisms (Mobili et al., 2009).
It has been demonstrated that these S-layer proteins can
apply a protective action inhibiting the grown of Salmonella
enterica serovar Enteritidis in Caco-2 cells, and also have the
ability to antagonize the effects of toxins from Clostridium
difficile on eukaryotic/eukaryotic cells in vitro (Carasi et al.,
2012).
However, there are other important bioactivities that have
been tested with kefir grains, the cell-free fraction of kefir or
acid lactic bacteria isolated from kefir, such as antitumoral
(Gao et al., 2013b), anti-inflammatory (Diniz et al., 2003),
antimicrobial (Anselmo et al., 2010) immunoregulatory
(Hong et al., 2009), antiallergenic (Wei-Sheng et al., 2010),
wound healing (Huseini et al., 2012), antidiabetic (Young-In
et al., 2006) antimutagenic (Guzel-Seydim et al., 2006), and
antigenotoxic (Grishina et al., 2011). In that way, it had been
demonstrated that kefir cell-free fraction has antiproliferative
effects on human gastric cancer SGC7901 cells (Gao et al.,
2013b), colon adenocarcinoma cells (Khoury et al., 2014),
HuT–102 malignant T lymphocytes, sarcoma 180 in mice,
Lewis lung carcinoma and human mammary cancer (Rizk
et al., 2009), and reduce oxidative stress (Punaro et al.,
2014). Another study has shown that suspensions after 24 h
fermentation and mechanically disintegrated kefir grains cause
a significant inhibition of granuloma tissue formation and
a 43% inhibition of the inflammatory process (Diniz et al.,
2003).
Nevertheless, there are other important studies performed
with some microorganisms isolated from different types of kefir.
Some microorganisms with their biological activities and origin
are shown in Tab l e 2 .
KEFIRAN, A POTENTIAL
EXOPOLYSACCHARIDE
The increased search for natural polysaccharides has been very
significant due to their use in the food, pharmaceutical, and
cosmetic industries as additives, bio-absorbents, metal removal
agents, bioflocculants, and medicine delivery agents, among other
functions (De Vuyst et al., 2001;Welman and Maddox, 2003;
Badel et al., 2011). Many microorganisms, such as bacteria, fungi,
and weeds, have the capacity/ability to synthesize and excrete
extracellular polysaccharides, and these polysaccharides can be
either soluble or insoluble (Wang et al., 2010;Badel et al., 2011).
The polysaccharides that are commonly used as food
additives are xanthan, dextran, gellan, and alginates, while
the exopolysaccharides (EPSs) produced by lactic acid bacteria
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Prado et al. Milk kefir
TABLE 4 | Marketed kefir-based products and their information.
Companies Product General information
Lifeway
United States
Canada
Great Britain
Low Fat Kefir
Non-Fat Kefir
Veggie Kefir
All-natural
99% lactose-free
Gluten-free
12 probiotic cultures
High in protein and calcium
Kefir Oats All-natural
99% lactose-free
Gluten-free
12 probiotic cultures
Oat fiber enriched
High in protein and calcium
Perfect 12 Kefir
Traditional Kefir
Greek Style Kefir
All-natural
99% lactose-free
Gluten-free
12 probiotic cultures
No added sugar
High in protein and calcium
Low Fat Kefir (Organic) USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
12 probiotic cultures
High in protein and calcium
Whole Milk Kefir
(Organic)
USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
12 probiotic cultures
No added sugar
Helios Kefir (Organic) USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
Seven probiotic cultures
Contains Inulin
Green Kefir (Organic) USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
12 probiotic cultures
Phytoboost =1serving of
vegetables
ProBugs (organic) USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
12 probiotic cultures
No-spill pouch
ProBugs Blast (Organic) USDA Certified Organic
Oregon Tilth Certified Organic
99% lactose-free
Gluten-free
12 probiotic cultures
High in protein and calcium
Frozen ProBugs
(Organic)
All-natural
99% lactose-free
Gluten-free
10 probiotic cultures
High in protein and calcium
Frozen Kefir All-natural
99% lactose-free
(Continued)
TABLE 4 | Continued
Companies Product General information
Gluten-free
10 probiotic cultures
90 calories per serving
1goffat
Frozen Kefir Bars All-natural
99% lactose-free
Gluten-free
10 probiotic cultures
60 calories per serving
0.5goffat
BioKefir All-natural
20 Billion units of probiotics
12 probiotic cultures
99% lactose-free
Gluten-free
High in protein and calcium
Farmer Cheese 99% lactose-free
Gluten-free
High in protein and calcium
Evolve Kefir
United States
Evolve Kefir 11 probiotic cultures.
Natural fruit flavors.
Fiber.
Protein and calcium
Wallaby
Organic
Australia
Lowfat Kefir 12 different strains of Live and
Active Kefir cultures.
CocoKefir
United States
CocoKefir
App
le Cinnamon CocoKefir
Citrus CocoKefir
CocoYo
Body Ecology Coconut
Kefir
Dairy, gluten, soy, and fat free
Low calorie
Contains valuable nutrients
such as potassium,
manganese, and magnesium.
Beneficial probiotic strains
show good physicochemical characteristics for their use as food
additives. In addition to these characteristics, EPSs are obtained
from microorganisms classified as GRAS (generally recognized
as safe), such as lactic acid bacteria (Wang et al., 2008;Saija et al.,
2010;Badel et al., 2011).
Many reports have demonstrated that the quantity and
properties of EPSs depend on the microorganisms used in the
fermentation process and on the fermentation conditions and
the composition of the culture media (Kim et al., 2008). EPSs
have physicochemical and rheological properties that make them
suitable as additives, which can be used as stabilizers, emulsifiers,
gelling agents, and viscosity improvers. Additionally, EPSs
possess biological properties suggesting their use as antioxidants,
antitumor agents, antimicrobial agents, and immunomodulators,
among other roles (Suresh Kumar et al., 2008;Bensmira et al.,
2010;Piermaria et al., 2010).
The EPS kefiran is produced by Lactobacillus kefiranofaciens
(Kooiman, 1968;Wang et al., 2010) from kefir grains, which are
composed of proteins, polysaccharides, and a complex symbiotic
microbial mixture (Witthuhn et al., 2005;Jianzhong et al., 2009).
These microorganisms grow in kefiran, which is a polysaccharide
matrix consisting of glucose and galactose. Despite good kefiran
production by L. kefiranofaciens alone, it has been observed that
Frontiers in Microbiology | www.frontiersin.org 6October 2015 | Volume 6 | Article 1177
Prado et al. Milk kefir
the addition of Saccharomyces sp. to the culture improves the net
quantity of kefiran, illustrating the importance of the symbiosis
between the bacteria and yeast that are present in kefir (Cheirsilp
et al., 2003).
Lactic acid bacteria can synthesize homopolysaccharides or
heteropolysaccharides. The synthesized homopolysaccharides
are glucans or fructans, which are composed of only one type
of monosaccharide (glucose or fructose, respectively; Van H i j u m
et al., 2006;Badel et al., 2011), whereas the heteropolysaccharides
contain different types of monosaccharides in different
proportions (mainly glucose, galactose, and rhamnose), (De
Vuyst and Degeest, 1999;Ruas-Madiedo et al., 2002).
Similarly to lactic acid bacteria, Lactobacillus sp. also
produces glucan and fructan. The homopolysaccharides show a
much higher performance compared with heteropolysaccharide
production (Welman and Maddox, 2003;Badel et al., 2011).
The heteropolysaccharides excreted by Lactobacillus
delbrueckii,Lactobacillus bulgaricus,Lactobacillus rhamnosus,
and Lactobacillus helveticus contain galactose, glucose,
and rhamnose as the main monosaccharides, with other
monosaccharides being present in smaller concentrations. They
are also highly branched with different types of linkages, and
their denominations are complex and generally dependent on
the main monosaccharide (De Vuyst and Degeest, 1999;Badel
et al., 2011).
Lactobacillus plantarum isolated from Tibetan kefir excretes
EPS classified as heteropolysaccharides composed of galactose,
glucose, and mannose. This EPS has the capacity/ability to reduce
blood cholesterol and form a biofilm shape (Zhang et al., 2009;
Wang et al., 2010).
Kefiran is an EPS classified as a heteropolysaccharide
comprising glucose and galactose in high concentrations, and
it is classified as a water-soluble glucogalactan, which makes it
suitable to be used as an additive (Wang et al., 2008, 2010).
Kefiran has excellent rheological properties and can significantly
improve the viscosity of lacteous products by favoring and
maintaining gel properties and avoiding the loss of water during
storage (Rimada and Abraham, 2006). With respect to the
biological activity of kefiran, several studies have demonstrated
that this EPS can be used as a nutraceutical, as described in
Tab l e 3 .
The first study about kefiran structure was published by
Kooiman (1968), who proposed a structure composed of two
units: kefiran (polysaccharide) and kefirose (pentasaccharide).
Then, some authors analyzed the polysaccharide structure
with current techniques such chromatography and infrared
spectroscopy (Wang et al., 2008;Chen et al., 2015)and
nuclear magnetic resonance (NMR; Ghasemlou et al., 2012).
The kefiran structure, according to them, is shown in
Figure 1.
KEFIR-BASED PRODUCTS
Nowadays, the interest in developing functional foods is
increasingbecausepeoplewanttoimprovetheirhealthand
prevent diseases. Keeping in mind that kefir is a beverage
with high probiotic activity, among other bioactivities, new
companies are emerging around the world. One of the biggest
kefir companies known is Lifeway, which started in 1986; their
products can be obtained in the United States, Canada, and
Great Britain, all of them based in kefir beverages, frozen, and
cheese.
Other companies are Evolve Kefir with its principal product,
a smoothie; Wallaby Yogurt Company with Low Fat Kefir;
and CocoKefir LLC, which provides drinks/beverages based
mainly on coconut water cultured with a comprehensive blend
of probiotics. Tabl e 4 summarizes the products provided
these companies with some general information about each
one.
CONCLUSION
Kefir, the traditional beverage, is now recognized as a potential
source of probiotics and molecules with highly interesting
healthy properties. The careful and detailed characterization
of kefir composition has helped the scientific community to
find new possibilities for its application. Kefiran, the EPS
of kefir, has very important physicochemical and rheological
properties. Besides, its biological properties suggest its use
as antioxidant, antitumor agent, antimicrobial agent, and
immunomodulator, among other roles. Research is constantly
being conducted to consolidate kefir and kefiran properties
for the development of new important products to preserve
consumer’s health.
ACKNOWLEDGMENT
Authors want to thank CNPq and CAPES for the financial
support.
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Conflict of Interest Statement: The authors declare that the research was
conducted in the absence of any commercial or financial relationships that could
be construed as a potential conflict of interest.
Copyright © 2015 Prado, Blandón, Vandenberghe, Rodrigues, Castro, Thomaz-
Soccol and Soccol. This is an open-access article distributed under the terms of
the Creative Commons Attribution License (CC BY). The use, distribution or
reproduction in other forums is permitted, provided the original author(s) or licensor
are credited and that the original publication in this journal is cited, in accordance
with accepted academic practice. No use, distribution or reproduction is permitted
which does not comply with these terms.
Frontiers in Microbiology | www.frontiersin.org 10 October 2015 | Volume 6 | Article 1177
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Kefir is a fermented milk product that is well known and widely used in eastern Europe. Although the scientific literature is not extensive, there appears to be evidence about the beneficial effects of consuming kefir that go beyond oral tradition. Problems that must be overcome before kefir can receive official approval as being good for health include a clear definition of what kefir is, sound scientific studies in humans to demonstrate its efficacy and identification of active ingredients.
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Kefir grains were inoculated into sterilized skim milk and incubated at 25degreesC. The kefir supernatant (pH 3.5) showed strong antibacterial activities against both Gram positive and negative bacteria, such as Escherichia coli, Enterobacter aerogenes, Proteus vulgaris, Bacillus subtilis, Micrococcus luteus, and Staphylococcus aures. Most microorganisms were identified from kefir as lactic acid bacteria and yeast. Two times as many yeast as lactic acid bacteria were detected. The predominant microorganisms were Lactobacillus lactis subsp. lactis in lactic acid bacteria and Candida kefyr in yeast, making up 90% of each respective group. The biochemical properties of the isolated L. lactis subsp. lactis were nearly the same as a reference strain, L. lactis subsp. lactis ATCC 21051. However, while the isolated C. kefyr could decompose sorbitol, ribose, raffinose, and mannitol, the reference strain C. kyfer IFO 586 could not. The optimum growth temperature and pH range for both strains were 37degreesC and 5.5-8.5, respectively. Both strains could also resist pasteurization treatment.
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Microbial exopolysaccharide (EPS) is a biothickener that can be added to a wide variety of food products, where it serves as a viscosifying, stabilizing, emulsifying, and gelling agent. The objective of this study was to investigate the optimum conditions of pH, incubation temperature, and whey protein concentration (WPC) for EPS production by Lactobacillus rhamnosus ATCC 9595. We found that maximal EPS production was achieved at a pH of 5.5 and temperature of 37°C. At the same fermentation conditions, EPS production was affected by the addition of L. rhamnosus GG (a weak-EPS producer). After growth for 24 hr, total EPS production was 583±15.4 mg/L in the single culture system, and 865±22.6 mg/L in the coculture system with L. rhamnosus GG. Based on the presence of WPC, EPS production dramatically increased from 583±15.4 (under no WPC supplementation) to 1,011±14.7 mg/L (under supplementation with 1.0% WPC). These results suggest that WPC supplementation and the co-culture systems coupled with small portions of weak-EPS producing strain can play an important role in the enhancement of EPS production.