Table 2 Variables and test levels for Plackett-Burman experiment ( ^a indicates model terms are significant)

X₁

NH₄Cl (g/L)

2

4

-0.475

0.637

X₂

KH₂PO₄ (g/L)

1.4

2.8

1.433

0.157

X₃

Mineral solution (ml/L)

1

2

-3.215

0.002^a

X₄

Lithium L-lactate (g/L)

5

10

2.987

0.004^a

X₅

MgSO₄ (g/L)

0.03

0.06

-0.151

0.88

X₆

L-Methionine (g/L)

0.02

0.04

0.89

0.378

X₇

Inosine (g/L)

1

2

-0.899

0.374

X₈

Initial pH

7.5

9

2.617

0.013^a

X₉

Incubation time (h)

48

96

3.48

0.001^a

X₁₀

Incubation temperature (°C)

30

37

-1.097

0.277

X₁₁

Inculum size (%)

2

4

1.116

0.269