Figures (5)  Tables (4)

    • Figure 1. 

      Diagram of the microwave-assisted extraction equipment.

    • Figure 2. 

      Response surfaces for TPC graphs (a) and (b) are for solvent : water; graphs (c) and (d) are for solvent : ethanol-water.

    • Figure 3. 

      Response surfaces for TACDPPH, graphs (a) and (b) are for solvent:water; graphs (c) and (d) are for solvent:ethanol-water.

    • Figure 4. 

      Response surfaces for TACCUPRAC graphs (a) and (b) are for solvent : water; graphs (c) and (d) are for solvent : ethanol-water.

    • Figure 5. 

      SEM images of red cabbage extracts. (a) Red cabbage extract from CE (100×), (b) red cabbage extract from CE (2,500×), (c) red cabbage extract from MAE (100×), (d) red cabbage extract from MAE (2,500×)

    • Independent variables Code levels
      −1 0 1
      Extraction time (X1, min) 5 10 15
      Solid : solvent ratio (X2, 1/X) 20 30 40
      Microwave power (X3, W) 200 400 600

      Table 1. 

      Coded and actual values of the independent variables.

    • Source Sum of squares df Mean square F-value p-value
      Model (TPC) 2.34E+06 8 2.92E+05 67.92 0.0001 Significant
      X1 20274.94 1 20274.94 4.72 0.0819
      X2 1.69E+06 1 1.69E+06 392.13 < 0.0001
      X3 22967.4 1 22967.4 5.34 0.0688
      X1X2 22734.61 1 22734.61 5.29 0.0698
      X1X3 12778.04 1 12778.04 2.97 0.1453
      X2X3 3159.87 1 3159.87 0.7352 0.4304
      X12 26836.11 1 26836.11 6.24 0.0546
      X22 2.33E+05 1 2.33E+05 54.26 0.0007
      X32 0 0
      Residual 21488.64 5 4297.73
      Lack of fit 14143.94 1 14143.94 7.7 0.0501 Not significant
      Pure error 7344.7 4 1836.18
      Cor total 2.36E+06 13
      Model (TACDPPH) 9307.92 8 1163.49 4871.42 < 0.0001 Significant
      X1 193.06 1 193.06 808.33 < 0.0001
      X2 6939.72 1 6939.72 29055.95 < 0.0001
      X3 29.43 1 29.43 123.22 0.0001
      X1X2 306.43 1 306.43 1282.97 < 0.0001
      X1X3 262.93 1 262.93 1100.85 < 0.0001
      X2X3 16.56 1 16.56 69.31 0.0004
      X12 14.59 1 14.59 61.1 0.0005
      X22 708.01 1 708.01 2964.36 < 0.0001
      X32 0 0
      Residual 1.19 5 0.2388
      Lack of fit 0.5408 1 0.5408 3.31 0.143 Not significant
      Pure error 0.6534 4 0.1633
      Cor total 9309.12 13
      Model (TACCUPRAC) 184.87 8 23.11 16.62 0.0033 Significant
      X1 5.4 1 5.4 3.88 0.106
      X2 109.62 1 109.62 78.82 0.0003
      X3 1.45 1 1.45 1.04 0.3537
      X1X2 55.2 1 55.2 39.7 0.0015
      X1X3 1.78 1 1.78 1.28 0.309
      X2X3 1.23 1 1.23 0.8834 0.3904
      X12 0.7006 1 0.7006 0.5038 0.5096
      X22 1.42 1 1.42 1.02 0.3587
      X32 0 0
      Residual 6.95 5 1.39
      Lack of fit 3.91 1 3.91 5.13 0.0863 Not significant
      Pure error 3.05 4 0.7619
      Cor total 191.83 13

      Table 2. 

      ANOVA for the quadratic equations of Design Expert 12.0.1 for MAE of TPC, TACDPPH, and TACCUPRAC in red cabbage and statistical indicators for each response (solvent : water).

    • Source Sum of squares df Mean square F-value p-value
      Model (TPC) 2.80E+05 9 31099.63 7.02 0.0088 Significant
      X1 19499.18 1 19499.18 4.4 0.0741
      X2 1.93E+05 1 1.93E+05 43.66 0.0003
      X3 6063.76 1 6063.76 1.37 0.2803
      X1X2 2.36 1 2.36 0.0005 0.9822
      X1X3 7959.32 1 7959.32 1.8 0.222
      X2X3 359.1 1 359.1 0.0811 0.7841
      X12 42236.73 1 42236.73 9.53 0.0176
      X22 9986.68 1 9986.68 2.25 0.1769
      X32 2963.88 1 2963.88 0.669 0.4403
      Residual 31011.78 7 4430.25
      Lack of fit 25791.29 3 8597.1 6.59 0.0501 Not significant
      Pure error 5220.5 4 1305.12
      Cor total 3.11E+05 16
      Model (TACDPPH) 8898.31 9 988.7 21.78 0.0003 Significant
      X1 0.2048 1 0.2048 0.0045 0.9483
      X2 7871.99 1 7871.99 173.4 < 0.0001
      X3 7.09 1 7.09 0.1561 0.7045
      X1X2 19.98 1 19.98 0.4401 0.5283
      X1X3 3.96 1 3.96 0.0872 0.7763
      X2X3 3.55 1 3.55 0.0783 0.7877
      X12 432.95 1 432.95 9.54 0.0176
      X22 533.11 1 533.11 11.74 0.011
      X32 75.26 1 75.26 1.66 0.2388
      Residual 317.79 7 45.4
      Lack of fit 66.7 3 22.23 0.3542 0.7899 Not significant
      Pure error 251.08 4 62.77
      Cor total 9216.09 16
      Model (TACCUPRAC) 167.95 9 18.66 25.72 0.0001 Significant
      X1 0.4512 1 0.4512 0.622 0.4562
      X2 137.7 1 137.7 189.81 < 0.0001
      X3 2.59 1 2.59 3.57 0.1009
      X1X2 1.24 1 1.24 1.71 0.2318
      X1X3 0.0462 1 0.0462 0.0637 0.808
      X2X3 5.62 1 5.62 7.74 0.0272
      X12 3.09 1 3.09 4.26 0.0779
      X22 16.41 1 16.41 22.63 0.0021
      X32 0.1155 1 0.1155 0.1592 0.7018
      Residual 5.08 7 0.7254
      Lack of fit 3.32 3 1.11 2.51 0.1973 Not significant
      Pure error 1.76 4 0.44
      Cor Total 173.03 16

      Table 3. 

      ANOVA for the quadratic equations of Design Expert 12.0.1 for MAE of TPC, TACDPPH, and TACCUPRAC in red cabbage and statistical indicators for each response (solvent : ethanol-water, 50:50, v:v).

    • Temperature (°C) Time (h) Solvent* TPC (mg GAE/L) TACCUPRAC (mmol TE/L) TACDPPH (mg DPPH/L)
      40 4 w 1018.5 ± 1.28D 8.9 ± 0.03B 33.1 ± 0.75B
      6 1165.9 ± 1.29C 11.2 ± 0.02A 54.52 ± 0.32A
      70 4 1324.4 ± 2.22A 11.6 ± 0.16A 48.0 ± 0.08A
      6 1192.6 ± 1.28B 11.6 ± 0.31A 50.2 ± 1.78A
      40 4 e-w 1677.3 ± 1.15a 16.77 ± 0.14a 66.3 ± 0.81a
      6 1515.3 ± 1.15b 14.2 ± 0.04b 58.5 ± 0.49b
      70 4 1268.0 ± 2.00c 10.0 ± 0.03d 36.1 ± 1.48d
      6 1202.7 ± 1.15d 10.7 ± 0.03c 44.5 ± 0.65c
      The results are given as the mean of three replicates with the standard deviations. Different letters represent the significant differences (p ≤ 0.05) between the results for each column. Upper case letters represent the solvent-water and lower case letters represent the solvent-ethanol-water. * w: water, e-w: ethanol-water.

      Table 4. 

      TPC, TACCUPRAC and TACDPPH yields of conventional extraction.