Foucaud C, Juillard V
Institut National de la Recherche Agronomique, Unité de Recherches Laitières et Génétique Appliquée, Jouy-en-Josas, France.
J Dairy Res. 2000 May;67(2):233-40. doi: 10.1017/s0022029900004192.
To explain the limited nutritional value of milk cultured with proteinase-positive (Prt+) strains of Lactococcus lactis for the subsequent growth of dairy lactococci, we investigated further the time courses of modifications in the free amino acid and peptide contents of cultured milk. When growing in milk for up to 24 h, Prt+ strains of Lc. lactis progressively accumulated amino acids and casein-derived peptides. The growth of proteinase-negative (Prt-) wild-type strains and peptide transport mutants of Lc. lactis in cultured milk showed that casein-derived peptides could sustain growth up to 5 x 10(8) cfu/ml, depending on the extent of casein degradation during the preliminary growth of Prt+ strains and the Prt- strains. Of the casein-derived oligopeptides, < 25% were transported into the cell and used for Lc. lactis growth. However, they played a prominent role, contributing 90% to growth. In contrast, di- and tripeptides did not contribute to growth, suggesting that either few were released from caseins or they did not supply essential amino acids.
为了解释用乳酸乳球菌蛋白酶阳性（Prt+）菌株培养的牛奶对后续乳球菌生长的营养价值有限的原因，我们进一步研究了培养牛奶中游离氨基酸和肽含量变化的时间进程。当在牛奶中生长长达24小时时，乳酸乳球菌的Prt+菌株会逐渐积累氨基酸和酪蛋白衍生肽。乳酸乳球菌蛋白酶阴性（Prt-）野生型菌株和肽转运突变体在培养牛奶中的生长表明，酪蛋白衍生肽能够维持生长至5×10⁸ cfu/ml，这取决于Prt+菌株和Prt-菌株在初步生长过程中酪蛋白的降解程度。在酪蛋白衍生的寡肽中，不到25%被转运到细胞中并用于乳酸乳球菌的生长。然而，它们发挥了重要作用，对生长的贡献达90%。相比之下，二肽和三肽对生长没有贡献，这表明要么从酪蛋白中释放出来的很少，要么它们不能提供必需氨基酸。
