Table 2.

⊿_OD values of substrates 2, 4, 7, 11, 14, 17, 18, 21 and 22.

Substrates	⊿ OD values
2 (used in Holt’s method)	0.198±0.004
4	0.052±0.002
7	0.216±0.003
11	0.425±0.003
14	0.273±0.004
17	0.033±0.003
18	0.284±0.002
21	0.278±0.005
22	0.306±0.003