Lactobacillus vermiforme Lactobacillus fructivorans Lactobacillus lindneri Lactobacillus sanfranciscensis Lactobacillus versmoldensis Lactobacillus farciminis Lactobacillus mindensis Lactobacillus alimentarius Lactobacillus kimchii Lactobacillus paralimentarius Lactobacillus arizonensis Lactobacillus plantarum Lactobacillus reuteri Lactobacillus pontis Lactobacillus frumenti Lactobacillus mucosae Lactobacillus fermentum Lactobacillus thermotolerans Lactobacillus amylophilus Lactobacillus acetotolerans Lactobacillus amylolyticus Lactobacillus gallinarum Lactobacillus helveticus Lactobacillus acidophilus Lactobacillus amylovorus Lactobacillus crispatus j— Lactobacillus delbrueckii subsp. lactis '— Lactobacillus delbrueckii subsp. bulgaricus Lactobacillus psittaci Lactobacillus jensenii Lactobacillus gasseri Lactobacillus johnsonii

Figure 2-6. Phylogeny of Lactobacillus based on 16S rRNA sequence analysis. Not all of the species are listed.

Accordingly, Group I lactobacilli consist of obligate homofermenting species, Group II contains facultative heterofermenting species, and Group III contains obligate heteroferment-ing species (Table 2-5). These groups can be further divided on the basis of other biochemical properties.

Despite their metabolic diversity, lactobacilli generally are quite fastidious, and many species require nutrient-rich environments. They are not especially proteolytic or lipolytic, and amino acids, peptides, and fatty acids are usually required for rapid growth. Some strains are particularly demanding, requiring an array of vitamins, nucelotides, and other nutrients. Lacto-bacilli, of course also need fermentable carbohydrates, and, depending on their source or habitat, they ferment a wide array of sugars. Thus, not only are most common sugars (e.g., glucose, fructose, lactose) fermented, but many plant-derived carbohydrates, such as cellobiose, amygdalin, and trehalose, are also used. Several species even ferment starch (Table 2-5).

Numerous species of Lactobacillus are relevant in fermented foods. Some are added directly in the form of starter cultures (Chapter 3), but there are even more endogenous lacto-bacilli present in the raw material or equipment surfaces that indirectly contribute to the manufacture or to the finished properties of fermented foods.

Starter culture lactobacilli are used primarily in dairy and sausage applications.There are two main species used as dairy starter cultures (mainly for cheese and yogurt), Lactobacillus helveticus and Lactobacillus delbrueckii subsp. bulgaricus. Other common dairy-related species include Lactobacillus casei and Lactobacillus acidophilus (both used frequently as probi-otics). Starter cultures for sausage fermentations contain Lactobacillusplantarum or Lactobacillus sakei subsp. sakei.

Sourdough breads are also made using het-erofermentative Lactobacillus sanfranciscen-sis, Lactobacillus brevis, and other lactobacilli. Pure starter cultures for sourdough breads are available, but wild cultures, propagated "in house," are still commonly used (Chapter 8).

For the production of sauerkraut, kimchi, and other fermented vegetables, the natural microflora is all that is necessary to initiate and perform the fermentation, although pure starter cultures containing L. plantarum and L. brevis and related species have become more common for so-called "controlled pickle" fermentations.

Finally, it is very important to emphasize, despite the general association of a particular species with a particular fermented food, that a given species will often be used in or appear in quite dissimilar situations. In many cases, the species name may even add to the confusion. Thus, L. sakei was originally isolated from sake, Japanese rice wine,yet this same organism can be isolated from fermented sausage and is even used in sausage starter cultures. Likewise, L. plantarum is not just found in plant material or in pickle brines, as its name might indicate, but also appears to be a normal inhabitant of the human intestinal tract.

As one would expect, the lactobacilli are genetically very diverse. Although the lactic acid bacteria, as a group, generally have a low %G+C (35 to 40), some lactobacilli have %G+C as low as 32 and others are as high as 55. The lacto-bacilli also are positioned phylogenetically in one of two distinct branches. For example, L. plantarum and L. brevis belong to the "Lacto-bacillus-Pediococcus" branch, whereas L. del-brueckii, L. helveticus and L. acidophilus are located in a separate "Lactobacillus delbrueckii" branch (Figures 2-2 and 2-6). Plasmids are common in the lactobacilli, although for many of these plasmids, the functions of the encoded genes are not established. Lactose metabolism is encoded on at least one plasmid, and several bacteriocin production and antibiotic-resistant systems are also plasmid-encoded.

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