Further Optimization by Response Surface Experimentation
On the basis of single-factor experimentation previously carried out,
Box-Behnken’s central combination experiments were designed to
investigate into multiple factor cross-effects on OR and carry out
further optimization of conditions of operation. Four factors with three
levels were selected in the response surface. The results showed that
the OR of pecan kernels oil was significantly affected by four factors,
i.e. the quantity of added water, sieve mesh number, time of agitation
and temperature of baking. Table 2 indicates the results of
experimentation. Table 3 shows the test result of significance of
regression equation for predicting OR. Fig. 4-6 show the response
surface analysis results obtained by employing Design Expert 8.0.6
software. Significant cross-effect of baking temperature and amount of
added water as well as that of sieve mesh number and amount of added
water on OR were found. These three factors significantly affected OR,
respectively.
The final regression model in terms of coded factors established by
employing SAS 8.0 in performing regression fitting on the various
factors and response values is as follows:
OR = 97.33 + 1.82 * A —0.76* B + 2.74 * C + 0.36 * D —1.15 * AB
—0.4 * AC + 0.07 * AD + 1.08 * BC —0.43 * BD —0.028 * CD —2.61 *
A2 —2.15 * B2 —3.72 *
C2 —1.09 * D2
In above formula, A means baking temperature, B means quantity of added
water, C means sieve mesh number, D represents agitation time.
The optimal combination of conditions of operation (experimentation)
previously developed by single factor experimentation still had the
highest OR (Table 2). Other condition combinations of operation
(experimentation) including A-95 ℃, B-1.4 mL, C-100, D-30 min; A-95 ℃,
B-1.4 mL, C-100 meshes, D-35 min; A-95 ℃, B-1.35 mL, C-100 meshes, D-30
min; and A-95 ℃, B-1.4 mL, C-100 meshes, D-30 min had a slightly lower
OR, but no statistical significance of difference was found.
OR was not improved by the response surface experimentation. Therefore,
the single factor experiments established condition combination of
operation which was optimum and gave the highest OR.