Background
Methods
Fruit source
Drying procedure
Oven drying
Freeze drying
Drying method | Drying time (h) | Residual moisture (kg water/kg dry matter) |
---|---|---|
Freeze dried | 16 | 0.087 ± 0.002b
|
40 °C | 22 | 0.093 ± 0.002a
|
50 °C | 17 | 0.094 ± 0.002a
|
60 °C | 12 | 0.096 ± 0.004a
|
Colour
Peel preparation
Determination of individual phenolic acids and flavonoids concentration
Determination of total phenolic concentration
Determination of total tannin concentration
Determination of total flavonoid concentration
Radical scavenging activity (RSA)
Ferric reducing antioxidant power
Determination of ascorbic acid concentration
Antibacterial assay
Microdilution assay
Mushroom tyrosinase inhibition assay
Statistical analysis
Results and discussion
Drying time and residual moisture content
Peel colour
Drying method | Colour attributes | ||||
---|---|---|---|---|---|
L*
| a* | C*
|
h° | ΔE
| |
Fresh peel | 51.01 ± 1.67b
| 28.85 ± 1.70a
| 35.14 ± 1.60a
| 34.61 ± 2.05b
| – |
Freeze dried | 61.46 ± 1.59a
| 23.33 ± 1.28b
| 29.99 ± 0.86b
| 38.85 ± 2.18ab
| 17.77 ± 1.07b
|
40 °C | 41.51 ± 1.09c
| 24.33 ± 1.01b
| 33.13 ± 0.77a
| 42.32 ± 1.70a
| 18.72 ± 1.14ab
|
50 °C | 39.29 ± 1.37c
| 25.24 ± 0.88b
| 33.25 ± 0.78a
| 39.82 ± 1.76ab
| 23.10 ± 2.42a
|
60 °C | 42.04 ± 0.92c
| 25.24 ± 1.16b
| 35.08 ± 0.66a
| 43.78 ± 1.90a
| 16.82 ± 2.00b
|
Individual phenolic acid and flavonoid compound
Drying method | ||||||
---|---|---|---|---|---|---|
Punicalin (mg CE/kg DM) | Rutin | p-Coumaric | +Catechin (mg/kg DM) | -Epicatechin | Hesperidin | |
Freeze dried | 708.38 ± 48.86b
| 4666.03 ± 311.70a
| nd | 674.51 ± 21.30a
| 70.56 ± 0.22a
| 16.45 ± 1.65a
|
40 °C | 768.11 ± 1.67b
| 2135.00 ± 0.00c
| nd | 377.26 ± 22.05c
| 28.93 ± 1.55c
| 5.07 ± 0.02b
|
50 °C | 672.98 ± 26.93b
| nd | 0.45 ± 0.02 | 340.64 ± 21.06c
| 31.95 ± 3.37bc
| 4.59 ± 0.54b
|
60 °C | 888.04 ± 57.57a
| 3401.36 ± 0.00b
| 0.57 ± 0.52 | 443.41 ± 0.30b
| 34.74 ± 0.11b
| 1.77 ± 0.54c
|
Total phenolic (TPC), total tannins (TTC) and flavonoid concentration (TFC)
Radical scavenging activity (RSA) and ferric reducing antioxidant power (FRAP) and vitamin C concentration
Antibacterial activity
Treatment | Gram negative | Gram positive | ||
---|---|---|---|---|
Escherichia coli
|
Klebsiella pneumonia
|
Staphylococcus aureus
|
Bacillus subtilis
| |
Freeze dried | 0.39 | 0.39 | 0.20 | 0.20 |
40 °C | 0.20 | 0.20 | 0.20 | 0.20 |
50 °C | 0.20 | 0.20 | 0.10 | 0.10 |
60 °C | 0.39 | 0.39 | 0.39 | 0.39 |
Streptomycin (mg/ml) | 0.02 | 0.02 | 0.02 | 0.02 |
Tyrosinase inhibitory activity
Treatment | Monophenolase | Diphenolase |
---|---|---|
(IC50 mg/ml) | ||
Freeze dried | 107.73 ± 10.08a
| 86.93 ± 15.23ab
|
40 °C | 45.07 ± 6.05b
| 119.79 ± 20.23a
|
50 °C | 22.95 ± 1.53c
| 74.05 ± 10.27ab
|
60 °C | 64.27 ± 10.35b
| 62.09 ± 2.98b
|
Arbutin (mg/ml) | 44.00 ± 5.56b
| 14.99 ± 2.52c
|
Multivariate analysis
Principal component analysis
Loadings | F1 | F2 |
---|---|---|
Catechin | 0.864 | 0.487 |
Epicatechin | 0.930 | 0.363 |
Punicalin | −0.543 | 0.653 |
Hesperedin | 0.999 | 0.033 |
RSA | −0.649 | 0.760 |
Vit C | −0.300 | −0.511 |
TF | 0.983 | 0.182 |
TP | 0.964 | 0.264 |
TT | 1.000 | 0.014 |
FRAP | 0.875 | 0.165 |
Rutin | 0.564 | 0.652 |
p-coumaric | −0.715 | 0.457 |
Lightness (L*) | 0.945 | 0.315 |
Chroma (C*) | −0.984 | 0.174 |
Hue angle (h°) | −0.791 | 0.303 |
Redness (a*) | −0.930 | 0.053 |
TCD | −0.551 | 0.821 |
MCwb
| −0.969 | 0.236 |
RMC | −0.994 | −0.114 |
Scores | ||
Freeze dried | 6.147 | 0.816 |
40 °C | −1.067 | −2.055 |
50 °C | −1.511 | −1.356 |
60 °C | −3.569 | 2.595 |