It is already mentioned that various lactic acid bacterial strains differ in amino acid converting abilities and that these activities are in fact linked to the ability to synthesize amino acids (18,19) focused on the flavor-forming and the amino acid forming abilities of Lactococcus strains isolated from various natural sources, the so-called wild lactococci (Fig. 8). These strains originated from dairy and nondairy environments, and they were found to have unique properties when compared to commercially available starter strains. For instance, many of these strains do not degrade caseins, produce antimicrobial compounds, and/or have low acidifying activity. When the amino acids-forming capacities of these strains were determined using the single omission technique (125), it was found that these strains had a much larger potential to synthesize amino acids as compared to industrial strains. Lactococci used in dairy fermentations are known for their limited capacity for biosynthesis of amino acids, which explains their complex nutritional requirements; they require several amino acids for growth (18,126-128). For instance, most dairy Lactococcus strains need glutamate, valine, methionine, histidine, serine, leucine and isoleucine. Industrial L. lactis subsp. cremoris strains require even more different amino acids for growth (18). Wild L. lactis subsp. cremoris strains generally require two to three amino acids while some L. lactis subsp. lactis strains only need one amino acid. The absence of some amino acid biosynthetic pathways in dairy lactococci might be a consequence of their adaptation to dairy products because in milk, the amino acids are readily available from the proteolytic degradation of caseins. Wild strains are not naturally associated with a rich environment such as milk, which makes them more dependent on their own biosynthesis of amino acids compared to industrial strains. The large natural biodiversity that is found within lactic acid bacteria species offers good possibilities for flavor diversification. It can obviously also be applied in various other fermented food products.
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