(composition: glycerol: 5.0 g, sodium propionate: 4.0 g, sodium caseinate: 2.0 g, K2HPO4: 0.5 g, asparagine: 0.1 g, MgSO4•7H2O: 0.1 g, FeSO4•7H2O: 1.0 mg, water: 1000 ml and pH: 8.0±0.1) and incubated in orbital shaker at 28 °C and 190 rpm for 7 days.