The first step of the statistical approach to the analysis
optimization was to establish the criteria that will define
the experimental factors that have a significant effect on
the response variables. Therefore, to optimize the ethanol
production it was first performed as a 24 factorial design.
Four relevant factors for the fermentative process were
selected in a factorial design 24. The variables, studied
simultaneously were: TRS concentration in sugar cane
molasses (150 and 250 g L1), temperature (25 and
35 C), agitation (180 oscillations per minute and static culture)
and culture time (12 and 24 h), as shown in Table 1.
The main effects of the three factors concentration in
sugar cane molasses (2.72), temperature (3.27), and (8.47)
are all positives, and agitation rate is negative (6.66).
The growth time (X4) main effect is the most significant factorial
design effect value for the production of ethanol. The
inclusion of agitation rate reduces the average ethanol production.
Therefore, the subsequent runs were performed in
a static format. Higher ethanol productions, 22.69 g L1
and 30.08 g L1 were obtained in static culture (run 11
and 12 in Table 1). According to Lee and Huang (2000)
Z. mobilis is able to obtain an ethanol production close
to the theoretical one from glucose through Entner–Doudoroff
pathway under aerobic conditions.
Based upon the results obtained in the 24 factorial
design a 23 factorial design was developed using new variation
levels in order to move sequentially in the direction of
maximizing the ethanol production. To define the best culture
conditions it was necessary to test new sugar concentrations,
temperature and culture time in a 23 factorial