Optimization of lipase-catalyzed synthesis of fructose stearate using response surface methodology

Figures & data

Table I. The selected four variables and the coded levels of each variable.

Variables	Symbol	Variable level
		Low	Center	High
		−1	0	+1
Reaction temperature (°C)	X1	45	55	65
Water content (%)	X2	0.5	1.5	2.5
Initial stearic acid/fructose molar ratio	X3	1.0	3.0	5.0
Immobilized lipase loading (mg mL^−1)	X4	10	30	50

Figure 1. Lipase-catalyzed synthesis of fructose monostearate.

Table II. The observed and predicted results of BBD for immobilized C. antarctica lipase catalyzed synthesis of fructose stearate.

Run	Pattern	X1/Reaction temperature (°C)	X2/Water content (%)	X3/Stearic acid/fructose molar ratio	X4/Immobilized lipase loading (mg mL^−1)	Y/Yield (%) (observed)	Y/Yield (%) (predicted)
1	0 + 0+	55	2.5	3.0	50	18.42	17.00
2	+ 0 + 0	65	1.5	5.0	30	29.46	29.22
3	0000	55	1.5	3.0	30	23.09	22.94
4	0 − 0−	55	0.5	3.0	10	31.09	32.67
5	0++ 0	55	2.5	5.0	30	17.35	18.65
6	−− 00	45	0.5	3.0	30	26.88	27.66
7	+− 00	65	0.5	3.0	30	38.50	39.32
8	++ 00	65	2.5	3.0	30	10.71	10.15
9	− 00+	45	1.5	3.0	50	11.18	12.13
10	0+− 0	55	2.5	1.0	30	16.58	17.85
11	0 + 0−	55	2.5	3.0	10	13.38	13.39
12	0−+ 0	55	0.5	5.0	30	58.12	56.48
13	00−−	55	1.5	1.0	10	13.66	14.01
14	0000	55	1.5	3.0	30	22.87	22.94
15	+ 00−	65	1.5	3.0	10	11.62	10.30
16	− 0 + 0	45	1.5	5.0	30	14.45	14.36
17	+ 0 − 0	65	1.5	1.0	30	11.17	11.41
18	00++	55	1.5	5.0	50	37.10	36.97
19	− 00−	45	1.5	3.0	10	5.65	4.22
20	00−+	55	1.5	1.0	50	22.67	22.08
21	0000	55	1.5	3.0	30	22.86	22.94
22	0—0	55	0.5	1.0	30	34.87	33.20
23	+ 00+	65	1.5	3.0	50	23.16	24.22
24	0 − 0+	55	0.5	3.0	50	50.76	50.90
25	− 0 − 0	45	1.5	1.0	30	7.69	8.09
26	−+ 00	45	2.5	3.0	30	4.23	3.63
27	00+−	55	1.5	5.0	10	22.40	23.21

Figure 2. The observed and predicted fructose stearate yields (%).

Table III. ANOVA test for the proposed quadratic model.

Source	Sum of squares	Degree of freedom	Mean square	F value	p value Prob> F
Model	4462.71	14	318.77	169.77	< 0.0001	significant
X1	246.79	1	247.88	132.02	< 0.0001	significant
X2	2052.51	1	2121.35	72.21	< 0.0001	significant
X3	284.90	1	434.88	231.61	< 0.0001	significant
X4	374.87	1	357.41	190.35	< 0.0001	significant
X1X2	6.60	1	6.60	3.52	0.0853
X1X3	33.24	1	33.24	17.70	0.0012	significant
X1X4	9.03	1	9.03	4.81	0.0487	significant
X2X3	126.34	1	126.34	67.29	< 0.0001	significant
X2X4	53.51	1	53.51	28.50	0.0002	significant
X3X4	8.09	1	8.09	4.31	0.0600
X^21	457.49	1	457.49	243.65	< 0.0001	significant
X^22	226.17	1	226.17	120.46	< 0.0001	significant
X^23	23.32	1	23.32	12.42	0.0042	significant
X^24	4.95	1	4.95	2.63	0.1306
Residual	22.53	12	1.88
Lack of fit	22.50	10	2.25	133.12	0.0075	significant
Pure error	0.034	2	0.017

R² = 0.99, AdjR² = 0.98.

Figure 3. The estimated response surface plot of the effect of reaction temperature and water content of reaction medium on the fructose stearate yield at constant stearic acid/fructose molar ratio of 3.0 and and immobilized lipase loading of 30 mg mL⁻¹ after 48 h reaction time.

Figure 4. The estimated response surface plot of the effect of stearic acid/fructose molar ratio and immobilized lipase loading on the fructose stearate yield at 55°C and water content of reaction medium of 1.5% after 48 h reaction time.

Figure 5. The estimated response surface plot of the effect of immobilized lipase loading and reaction temperature on the fructose stearate yield at constant stearic acid/fructose molar ratio of 3.0 and water content of reaction medium of 1.5% after 48 h reaction time.

Figure 6. The effect of ILs on fructose stearate yield at the optimized conditions.

Figure 7. Thermal stability of immobilized lipase at 45, 55 and 65°C up to 48 h.