Le kéfir. Caractères physico-chimiques, microbiologiques et nutritionnels. Technologie de production. Une revue

Abstract

RésuméLe kéfir est un lait fermenté préparé à l'aide d'un levain constitué par les grains de kéfir. Il est produit principalement en URSS et en second lieu dans plusieurs pays, notamment d'Europe, où une législation existe concernant sa qualité et sa fabrication.Ce produit est caractérisé par la présence d'acide lactique et d'alcool, produits respectivement par des bactéries lactiques et des levures en association avec des bactéries acétiques.Les grains, composés essentiellement d'un polysaccharide microbien, présentent une structure complexe. Le rôle joué par les micro-organismes dans leur formation et la localisation de ces derniers dans le grain sont discutés.La production du kéfir à l'échelle industrielle comprend plusieurs étapes. Le traitement du lait et des grains ainsi que les conditions d'incubation, de maturation et de conservation sont d'une grande importance et influencent la qualité du produit. L'optimisation de la production industrielle a amené à remplacer les grains par des levains prêts à l'emploi. D'autres études visent à prolonger le temps de conservation du produit et à appliquer des traitements qui répondront à des demandes diverses.Le kefir possède les qualités nutritionnelles des autres laits fermentés (digestibilité du lait améliorée par la fermentation, consommation sans problème par les individus intolé-rant au lactose ... ), d'où sa popularité et la nécessité d'une étude plus approfondie de ses qualités spécifiques.Mots clés: Kéfir -Laits fermentés -Association -Bactéries lactiques -Levures. Summary Ke'ir. Physico-chemical, microbiological and nutritional characters. Production technology. A review.Kefir is a fermented milk prepared with the kefir grains. It is mainly produced in the USSR and secondly in numerous other countries, mostly in Europe where legislation exists concerning to its quality as weil as its production. This beverage is characterized by the presence of lactic acid and alcohol produced respectively by lactic acid bacteria and yeasts. These two microbial groups predominate associated with acetic acid bacteria.The grains, which are principally composed of a microbial polysaccharide have a complex structure. They are produced only from grains already existing. The microorganisms involved and their localization in the grain are briefly discussed.Industrial production of kefir includes several steps. The milk and grains treatment as weil as the incubation, ripening and storage conditions play a central role on the quality of the beverage. The attempts to lower the cost of kefir production led to the substitution of grains by ready-to-use starter cultures. Other studies concentrate on the prolongation of the product's shelf-life and the use of new treatments stimulating its consumption.Kefir possesses the nutritional properties of other fermented milks (improved digestibility compared with milk, consumption without problems by lactose-intolerant individuals ... ) what justifies both its popularity and the need for a further study of its specifie qualities.

Preservation of Kefir Grains, a Comparative Study

“…The microflora of kefir grains is variable, depending on the source of the grain. Among the yeasts isolated include: Candida kefir, the imperfect form of Kluyveromyces lactis (2,3,17,18); Kluyveromyces lactis (3,18); Saccharomyces cerevisiae (3,17,19,20); Saccharomyces delbrueckii (18,19); Torulopsis holmii (21), Candida holmii and Saccharomyces unisporus (3, 18); Torulaspora delbrueckii and Candida friedricchii (3); Pichia lwt/vol. 30 (1997) fermentum and Kluyveromyces marxianus (20).…”

“…30 (1997) fermentum and Kluyveromyces marxianus (20). Geotrichum candidum is said to be on the surface of many grains but it does not alter the quality of the product (2,7). Two yeasts and a mould were isolated from kefir grains in this work.…”

“…Marshall et al (6) showed that some regions of grains are composed of lactobacilli and others of yeast. Kefir quality depends on properties such as chemical composition, microflora, rheology and organoleptic features (2). Storage at 4 °C, wet or dried, has been proposed as an alternative method for preserving kefir grains (7,8).…”

“…They are composed mostly of proteins and polysaccharides in which the complex microflora is enclosed. The chemical composition of kefir grains is 890-900 g/kg water, 2 g/kg lipid, 30 g/kg protein, 60 g/kg sugars and 7 g/kg ash (2). The activity of the grain depends on the viability of the microflora.…”

Microbiological and chemical changes during the manufacture of Kefir made from cows’ milk, using a commercial starter culture

“…The industrial manufacture of Kefir using grains as the starter culture is very difficult due to the complexity of their microbiological composition, which varies widely depending on the origin of the grains and conditions of storage and handling (Kandler & Kunath, 1983;La Rivie`re, Kooiman, & Schmidt, 1967;Ottogalli, Galli, Resmini, & Volonterio, 1973;Zourari & Anifantakis, 1988). At the same time, it is difficult to maintain the stability of the microbiological composition of the Kefir grains over time, i.e., during the production of successive batches (Marshall & Cole, 1985).…”