Table 2.

Final population densities of L. lactis MG 1363 in CDM containing different pools of milk peptidesa

Amino acid source in CDMFinal population size (CFU/ml)b with peptides having a molecular size of:
30 kDa10 kDa1 kDa
Peptides aloneNGc NGNG
Peptides + Q, H, L, M(1.9 ± 0.9) × 108 (2.4 ± 0.5) × 108 (3.7 ± 1.4) × 107
Acidic peptides + Q, H, L, MNDd NGNG
Neutral peptides + Q, H, L, MND(6.3 ± 3.2) × 107 (3.0 ± 2.2) × 107
Basic peptides + Q, H, L, MND(1.4 ± 0.3) × 107 (5.9 ± 2.0) × 106
  • a Peptides were isolated from milk by isoelectric precipitation, ultrafiltration, and C18solid-phase extraction and added to CDM at final concentrations five times those of the peptides in milk, i.e., 500 μg/ml for the 30-kDa pool, 225 μg/ml for the 10-kDa pool, and 20 μg/ml for the 1-kDa pool. Gln (Q), His (H), Leu (L), and Met (M) were added at concentrations of 2.7, 0.7, 3.6, and 0.8 mM, respectively. Acidic, neutral, and basic peptides were obtained from the whole peptide pool by ion-exchange solid-phase extraction and used at final concentrations five times those of the peptides in milk. Respective ratios of the three peptides fractions were 1:1.5:1.5 in the 10-kDa pool and 0:24:1 in the 1-kDa fraction, respectively.

  • b The values shown are means of six experiments ± the confidence limits (P = 0.95).

  • c NG, no growth (inoculation level of CDM was about 5 × 105 CFU/ml).

  • d ND, not determined.