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Table 4 Levels of independent variables established according to central composite design for enzymatic esterification of hexyl dihydrocaffeate condition level (coded and, un coded)

From: Optimization of enzymatic esterification of dihydrocaffeic acid with hexanol in ionic liquid using response surface methodology

Independent variable

Independent variable level

Low (−1)

Medium (0)

High (+1)

Axial (−1.66)

Axial (+1.66)

Reaction timea

24

48

72

8.0

88.0

Reaction Tempb

40

50

60

33.3

66.7

Conc. of hexanolc

2.2

5.5

8.8

0.0

11.0

Enzyme amountd

15

25

35

8.3

41.6

  1. aReaction time (h)
  2. bReaction temperature (°C)
  3. cConcentration of hexanol (substrate molar ratio was selected correspondingly to 0.5 − 2((2.2–8.8) × 10−4 mM) of hexanol to dihydrocaffeic acid (4.4 × 10−4 mM)
  4. d15–35% relative to the total weight of substrates