Other Cultured Dairy Products

The emphasis of this chapter has been on those products produced and consumed in the United States. However, there are hundreds of other products produced around the world that, although manufactured via similar processes, have unique and interesting features (Table 4-4).Villi, for example, is widely consumed in Finland is known for its high viscosity and musty flavor and aroma.The ropy texture is due to capsular EPS production by L. lactis subsp. lactis and L. lactis subsp. cremoris, and the musty flavor is caused by growth of the fungal organism Geot-richum candidum. Another popular product is Koumiss, which was traditionally produced from

142 Microbiology and Technology of Fermented Foods Box 4-6. The Microbial Diversity of Kefir Grains

To microbial ecologists, kefir grains represent an amazingly diverse ecosystem.A single grain can harbor more than a million cells, with perhaps dozens of different species present (Table 1). The grains are essentially a natural immobilized cell bioreactor, with the kefir grain serving as an inert support material for the cells.

Table 1. Bacteria, yeast, and mold isolated from kefir grains1.

Bacteria Yeasts and Mold

Lactobacillus brevis Candida kefir1

Lactobacillus fermentum Candida maris

Lactobacillus kefiranofaciens3 Candida inconspicua

Lactobacillus kefiri Candida lambica

Lactobacillusparakefir Candida krusei

Lactobacillusplantarum Saccharomyces cerevisiae

Lactococcus lactis subsp. cremoris Kluyveromyces marxianus

Lactococcus lactis subsp. lactis Geotrichum candidum

Leuconostoc mesenteroides subsp. cremoris Zygosaccharomyces sp. Leuconostoc sp. Streptococcus thermophilus Acetobacter aceti

'Adapted from various sources (in references)

2syn Candida kefyr

3Recently reclassified as Lactobacillus kefiranofaciens subsp. kefirgranum or subsp. kefiranofaciens (Vancanneyt et al.,2004)

Attachment to the grains is mediated via one of several different types of polysaccharide-like material (kefiran being the prototype) that are produced by the resident organisms.The kefir organisms do not appear to be randomly distributed; rather, some are contained mainly within the core of the grains, whereas others are located primarily in the exterior. Symbiotic and synergis-tic relationships likely exist between different organisms, but these relationships are difficult to establish in such a complex system (Leroi and Pidoux, 1993a and 1993b).

Although the precise chemical composition of kefir grains varies depending on the source, they generally contain about 80% to 90% water, 2% to 5% protein, and 8% to 10% carbohydrate (Abraham and De Antoni, 1999;Garrote et al.,2001).Most of the protein faction is in the form of casein, whereas most of the carbohydrate portion is polysaccharide. The irregular, cauliflower-shaped grains range in size from 0.2 cm to more than 2 cm in diameter. In their dry form, they are stable for many months. Although kefir grains are available commercially, many modern manufacturers now use pure lyophylized cultures containing many of the strains ordinarily found in the grains.

The predominant organisms in kefir grains are lactic acid bacteria, with Lactobacillus species accounting for up to 80% of the total (Garrote et al., 2001; Simova et al., 2002;Vancanneyt et al., 2004). Other studies have shown that homofermentative species, including Lactobacillus kefirgranum and Lactobacillus kefiranofaciens, were the most frequently isolated species in kefir grains, whereas heterofermentative Lactobacillus kefir and Lactobacillus parakefir were less common (Takizawa et al., 1998; Simova et al., 2002). Other lactic acid bacteria that have been identified include species of Lactococcus, Streptococcus, and Leuconostoc.Yeasts are also well-represented, and include lactose-fermenting (Saccharomyces kefir) and non-fermenting strains.

It was reported recently that kefir grains likely contain organisms that cannot easily be cultured and that are instead only viable within the confines of the grain environment (Witthuhn et al., 2005). Collectively, the kefir microflora has considerable metabolic diversity, which ex-

Box 4-6. The Microbial Diversity of Kefir Grains (Continued)

plains, in part, the incredible stability and viability of the grains, as well as the wide spectrum of products produced during the fermentation.

References

Abraham,A.G., and G.L. De Antoni. 1999. Characterization of kefir grains grown in cow's milk and in soya milk. J. Dairy Res. 66:327-333.

Leroi, F., and M. Pidoux. 1993a. Detection of interactions between yeasts and lactic acid bacteria isolated from sugary kefir grains. J.Applied Bacteriol. 74:48-53.

Leroi, F., and M. Pidoux. 1993b. Characterization of interactions between Lactobacillus hilgardii and Sac-charomyces florentinus isolated from sugary kefir grains.J.Applied Bacteriol. 74:54-60.

Garrote, G.L.,A.G.Abraham,and G.L. De Antoni. 2001.Chemical and microbiological characterization of kefir grains. J. Dairy Res. 68:639-652.

Simova, E., D. Beshkova,A.Angelov,T. Hristozova, G. Frengova, and Z. Spasov. 2002. Lactic acid bacteria and yeasts in kefir grains and kefir made from them. J. Ind. Microbiol. Biotechnol. 28:1-6.

Takizawa, S., S. Kojima, S.Tamura, S, Fujinaga,Y. Benno, and T. Nakase. 1998.The composition of the Lactobacillus flora in kefir grains. System.Appl. Microbiol. 21:121-127.

Vancanneyt, M., J. Mengaud, I. Cleenwerck, K.Vanhonacker, B. Hoste, P. Dawynndt, M.C. Degivry, D. Ringuet, D.Janssens, and J. Swings. 2004. Reclassification of Lactobacillus kefirgranum Takizawa et al. 1994 as Lactobacillus kefiranofaciens subsp. kefirgranum subsp. nov. and emended description of L. kefira-nofaciens Fujisawa et al. 1988. Int.J. Syst. Evol.Microbiol. 54:551-556.

Witthuhn, R.C.,T. Schoeman, and T.J. Britz. 2005. Characterisation of the microbial population at different stages of Kefir production and Kefir grain mass cultivation. Int. Dairy J. 15:383-389.

Table 4.4. Cultured dairy products from around the world.

Product

Origin

Culture Organisms

Unique Features

Villi

Finland

Lactococcus spp. Leuconostoc spp. Geotrichum candidum

Ropy texture Musty flavor

Skyr

Iceland

Lactobacillus delbreckii subsp. bulgaricus Streptococcus thermophilus

Concentrated, high protein content

Dahi

India

Lactobacillus delbreckii subsp. bulgaricus Streptococcus thermophilus Lactobacillus spp.

Yogurt-like

Koumiss

Russia

Lactobacillus delbreckii subsp. bulgaricus Lactobacillus acidophilus Kluyveromyces spp.

Mare's milk > 1% ethanol

Bulgarian Milk

Bulgaria

Lactobacillus delbreckii subsp. bulgaricus

High acid (>2% lactic acid)

mare's milk. Similar to kefir in that lactic acid and ethanol are both present, this product owes much of its popularity to its putative therapeutic properties.The yogurt-like products dahi and laban are among the most widely-consumed cultured dairy products in India and the Middle East, respectively.

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