Extraction of crude polysaccharides from Duchesnea indica (Andrews) Focke: optimization by response surface methodology

Figures & data

Table 1. Plackett–Burman factorial design for screening significant parameters.

Extraction temperature (ºC)	Extraction time (h)	Extraction cycle (No)	pH	Sedimentation time (h)	De-proteintimes (No)	Dialysis time (h)	Ratio of water to raw material (mL/g)	Dummy 1	Dummy 2	Dummy 3	Yield (%)	EC50 (μg/mL)
Factor 1	Factor 2	Factor 3	Factor4	Factor 5	Factor 6	Factor 7	Factor 8	Factor 9	Factor 10	Factor 11	Response 1	Response 2
60	2	3	5	24	3	12	60	1	1	−1	4.95	300
60	2	1	9	6	3	48	10	1	1	1	4.51	294
60	8	3	9	24	1	12	10	−1	1	1	5.59	287
60	8	3	5	6	3	48	60	−1	−1	1	5.28	297
60	8	1	9	24	1	48	60	1	−1	−1	5.87	292
100	2	3	9	6	1	12	60	1	−1	1	5.33	286
100	2	3	9	24	3	48	10	−1	−1	−1	5.36	296
100	8	1	9	6	3	12	60	−1	1	−1	5.54	281
100	2	1	5	24	1	48	60	−1	1	1	6.23	295
100	8	1	5	24	3	12	10	1	−1	1	5.96	293
100	8	3	5	6	1	48	10	1	1	−1	5.39	288
60	2	1	5	6	1	12	10	−1	−1	−1	4.37	309

Fig. 1. Pareto chart for yield analysis: The size of the effects of each parameter is proportional to the height of the bar.

Notes: (1) Ratio of water to raw material; (2) Extraction temperature; (3) Extraction time; (4) Sedimentation time; (5) Dummy 3; (6) Deprotein times; (7) Dialysis time; (8) Extraction cycle; (9) Dummy 1; (10) Dummy 2; and (11) pH.

Table 2. ANOVA for DIPs yield.

Source	Sum of squares	df	Mean square	F value	p-Value prob > F
Model	2.61	3	0.87	9.53	0.0051
Extraction temperature	0.87	1	0.87	9.58	0.0148
Extraction time	0.69	1	0.69	7.57	0.025
Ratio of water to raw material	1.04	1	1.04	11.43	0.0096

Fig. 2. Effect of extraction parameters on yield of DIPs (extraction time, h; extraction temperature, ºC; ratio of water to raw material, mL/g).

Table 3. Independent variables and their levels used in the response surface design.

Independent variables	Levels
	−1	0	1
Extraction time (X1) (h)	5	6	7
Extraction temperature (X2) (ºC)	90	95	100
Ratio of water to raw material (X3) (mL/g)	25	30	35

Table 4. Box–Behnken design (coded) and results for extraction yield of DIP.

No.	X1/Extraction time (h)	X2/Extraction temperature (ºC)	X3/Ratio of water to raw material (mL/g)	Y/DIPs yield (%)
1	−1	−1	0	4.28
2	−1	1	0	5.36
3	−1	0	−1	4.68
4	−1	0	1	5.89
5	1	−1	0	4.82
6	1	1	0	6.47
7	1	0	−1	5.93
8	1	0	1	6.26
9	0	−1	−1	4.46
10	0	−1	1	5.26
11	0	1	−1	5.71
12	0	1	1	6.48
13	0	0	0	6.20
14	0	0	0	6.24
15	0	0	0	6.22

Table 5. Estimated regression model of relationship between response variable (yield of DIP) and independent variables (X₁, X_2, and X₃).

Variables	DF	SS	MS	F-value	p-Value
X1	1	1.34	1.34	705.34	<0.0001
X2	1	3.38	3.38	1783.64	<0.0001
X3	1	1.21	1.21	638.00	<0.0001
	1	0.55	0.55	292.57	<0.0001
	1	1.33	1.33	701.44	<0.0001
	1	0.075	0.075	39.57	0.0015
	1	0.081	0.081	42.86	0.0012
	1	0.19	0.19	102.16	0.0002
	1	2.25 × 10^−4	2.25 × 10^−4	0.12	0.7444

Notes:

SS—Sums of squares; DF—Degree freedom; MS—Mean squares.

Table 6. Analysis of variance for the fitted quadratic polynomial model of DIPs extraction.

Source	SS	DF	MS	F-value	Prob > F
Model	7.98	9	0.89	468.02	<0.0001
Residual	9.475 × 10^−3	5	1.895 × 10^−3
Lack of fit	8.675 × 10^−3	5	2.892 × 10^−3	7.23	0.1239^NS
Pure error	8.000 × 10^−4	2	4.000 × 10^−4
Cor total	7.99	14
R^2= 0.9988	= 0.9967		=0.9824		CV = 0.77

Notes:

SS—Sums of squares; DF—Degree of freedom; MS—Mean squares; NS—Non-significant.

Fig. 3. 3-D response surface plot and contour plot for DIPs yield as a function of extraction time and extraction temperature (X₁: extraction time; X₂: extraction temperature).

Fig. 4. 3-D response surface plot and contour plot for DIPs yield as a function of extraction time and ratio of water to raw material (X₁: extraction time; X₃: ratio of water to raw material).

Fig. 5. 3-D response surface plot and contour plot for DIPs yield as a function of extraction temperature and ratio of water to raw material (X₂: extraction temperature; X₃: ratio of water to raw material).

Fig. 6. Normal probability plot of the residuals.

Fig. 7. Residuals vs. predicted values. The residuals scatter randomly at around ±1.5.

Table 7. Predicted and experimental values of the responses at optimum and modified conditions.

	Extraction time (h)	Extraction temperature (ºC)	Ratio of raw material to water (mL/g)	Yield of DIP(%)	EC50 (μg/mL)
Optimum conditions (predicted)	6.16	98.51	30.94	6.51	–
Modified conditions (actual)	6.2	98	31.00	6.430 ± 0.078	287