TABLE 3.

Activity of UDP-N-acetylglucosamine 4-epimerase in cell extracts of S. thermophilus LY03 and S. thermophilus Sfi20^a grown either on glucose or combinations of glucose and fructose, galactose, or lactose or on lactose or combinations of lactose and fructose, galactose, or glucose^a

Carbohydrate source (concn [M])	Time point	Mean activity of UDP- N-acetylglucosamine 4-epimerase (nmol mg of cell protein−1 min−1) ± SD in S. thermophilus:
		LY03	Sfi20
Glucose (0.42)	1	165 ± 23	215 ± 65
	2	209 ± 22	230 ± 55
	3	145 ± 34	201 ± 30
Glucose (0.28) + fructose (0.14)	1	175 ± 37	210 ± 29
	2	210 ± 11	240 ± 16
	3	136 ± 19	209 ± 40
Glucose (0.28) + galactose (0.14)	1	169 ± 10	178 ± 9
	2	189 ± 11	219 ± 21
	3	123 ± 42	188 ± 10
Glucose (0.28) + lactose (0.07)	1	201 ± 43	187 ± 23
	2	209 ± 13	211 ± 13
	3	132 ± 12	187 ± 4
Lactose (0.22)	1	180 ± 33	144 ± 12
	2	203 ± 34	174 ± 14
	3	155 ± 12	163 ± 12
Lactose (0.15) + fructose (0.14)	1	199 ± 45	189 ± 18
	2	210 ± 27	197 ± 43
	3	145 ± 23	182 ± 24
Lactose (0.15) + galactose (0.14)	1	179 ± 23	175 ± 15
	2	189 ± 12	201 ± 5
	3	166 ± 14	200 ± 10
Lactose (0.15) + glucose (0.14)	1	187 ± 11	189 ± 12
	2	174 ± 12	212 ± 38
	3	168 ± 11	190 ± 14

^aS. thermophilus LY03 and S. thermophilus Sfi20 were grown in batch cultures in MRS broth on lactose or glucose or combinations of lactose or glucose with other carbohydrates at 42°C and at a constant pH of 6.2. Samples were taken at three time points of the fermentation course, representing the exponential growth phase (point 1), the end of the exponential growth phase (point 2), and the stationary phase (point 3). Each value is always the average of two measurements; the standard deviation is approximately 12%.