TABLE 3.

Free amino acid changes during growth of S. thermophilus ST18 in milk

Amino acidMean (SD) amino acid concn (μM)a
InitialEnd of the 1st exponential phaseMiddle of the nonexponential phaseBeginning of the 2nd exponential phaseEnd of the 2nd exponential phase
Asn2.4bNDdNDNDND
Asp16.7 (1.8)14.1 (0.9)e14.7 (0.2)21.0 (7.3)3.6 (0.7)e
Gln5.9 (0.9)NDfNDND4.2 (1.1)e
Glu216.1 (7.0)207.7 (15.1)188.2 (4.6)168.2 (8.1)e50.4 (4.3)f
Thr9.3 (2.6)6.6 (0.6)4.1 (1.2)eNDe2.7 (0.3)f
Ser10.6 (0.8)6.6 (1.4)4.4 (1.0)2.0b4.5 (1.2)e
Pro21.1 (4.0)24.3 (1.1)29.6 (2.5)53.8 (2.6)f96.8 (9.2)e
Gly70.0 (6.9)60.3 (0.8)48.2 (5.0)17.0 (2.8)eNDf
Ala28.4 (3.5)26.6 (0.6)21.3 (2.6)e7.3 (0.9)f5.9 (1.1)e
CysNDNDNDNDND
MetNDNDND5.7 (0.2)fNDf
Leu4.8 (0.4)NDfND4.0bND
Ile3.9 (0.5)NDfND1.9bND
Val12.7 (0.9)7.7 (1.8)7.5 (0.8)5.9bND
Tyr2.5bNDND9.9 (0.9)f23.0 (1.3)f
PheNDNDND11.4 (4.0)e15.4 (4.1)
TrpNDNDNDNDND
His3.1 (1.4)ND4.0b8.6 (0.3)e12.7 (1.1)e
Lys13.4 (3.2)11.4 (3.3)19.1 (5.2)e47.9 (3.3)f45.6 (17.8)
Arg13.4 (4.1)10.1 (8.8)c11.5 (9.9)c16.2 (1.7)NDf
  • a From three independent determinations.

  • b Not detected in two of three cultures.

  • c Not detected in one of three cultures.

  • d ND, not detected.

  • e Significant change in concentration at a P value of 0.95.

  • f Significant change in concentration at a P value of 0.99.