Physicochemical characteristics of peel of galgal cultivars
Table 1 depicted the physicochemical properties of galgal cultivars (PBG, HRG, and HPG). The results showed that there were significant differences (p < 0.05) between the three parameters in terms of peel thickness, color (L*, a*, and b*), total soluble solids (TSS), and pH. In terms of peel thickness, it was noticed highest in HPG (03.92), followed by PBG (03.57), and lowest in HRG (02.83). This indicated that HRG has a thinner peel compared to PBG and HPG. Regarding color, the L* value was observed highest in HPG (64.83), followed by PBG (61.97), and lowest in HRG (55.52). The a* was not significantly differ (p < 0.05) in case of PBG and HRG, but HPG (-13.12). The b* value was noticed highest in HPG (61.33), followed by PBG (49.85), and lowest in HRG (49.90). The highest L* value indicated, the colour towards lightness and -a* values indicated that the peel colour towards the green colour and b* showed the colour towards the yellow. In terms of TSS and pH, there were no significant differences (p < 0.05) between galgal cultivars. The TSS and pH values were relatively similar, ranging from 06.52 to 06.84 and 04.01 to 04.16, respectively. Citron TSS was found to be 6.20 ᵒB and pH was noted as 2.36 and titrable acidity was calculated as 3.81 [14]. The Titrable acidity (%) values were not significantly different (p < 0.05) between the three samples (PBG: 7.23%, HRG: 7.42%, HPG: 7.54%) respectively.
Table 1
Physicochemical characteristics of Galgal cultivars (PBG, HRG and HPG)
Parameter | PBG | HRG | HPG |
Peel thickness | 03.57 ± 0.23a | 02.83 ± 0.16b | 03.92 ± 0.37a |
Colour L* a* b* | 61.97 ± 0.54b | 55.52 ± 0.33c | 64.83 ± 0.55a |
-14.51 ± 0.35a | -14.49 ± 0.84a | -13.12 ± 0.47b |
49.85 ± 0.51b | 49.90 ± 0.61b | 61.33 ± 0.50a |
TSS | 06.84 ± 0.21a | 06.52 ± 0.15a | 06.74 ± 0.11a |
pH | 04.14 ± 0.11a | 04.01 ± 0.01a | 04.16 ± 0.02a |
Titrable acidity (%) | 07.23 ± 0.17a | 07.42 ± 0.12a | 07.54 ± 0.11a |
Moisture content (%) | 81.64 ± 0.12c | 82.44 ± 0.13b | 83.42 ± 0.15a |
Total sugars (%) | 07.40 ± 0.01a | 06.89 ± 0.12b | 06.79 ± 0.11b |
Reducing Sugar (%) | 03.82 ± 0.02a | 03.31 ± 0.05c | 03.65 ± 0.03b |
Crude fiber (%) | 01.70 ± 0.02a | 01.55 ± 0.01c | 01.67 ± 0.01b |
Pectin (%) | 03.52 ± 0.13a | 03.31 ± 0.11a | 03.44 ± 0.13a |
Protein (%) | 00.13 ± 0.01a | 00.11 ± 0.01a | 00.12 ± 0.01a |
Crude fat (%) | 04.22 ± 0.02a | 02.25 ± 0.04c | 02.87 ± 0.05b |
Ash (%) | 02.89 ± 0.15a | 02.64 ± 0.12ab | 02.52 ± 0.13b |
Total phenols (mg GAE/g) | 08.25 ± 0.17a | 07.26 ± 0.15c | 07.87 ± 0.14b |
Total flavonoids (mg/100g) | 06.18 ± 0.11c | 07.23 ± 0.12b | 07.55 ± 0.14a |
Ascorbic acid (mg/100g) | 39.58 ± 0.01a | 38.33 ± 0.13c | 38.65 ± 0.12b |
Total carotenoid (mg/g) | 81.54 ± 0.10a | 80.24 ± 0.12b | 79.54 ± 0.17c |
Total chlorophyll | 15.69 ± 0.12a | 15.20 ± 0.14b | 13.45 ± 0.12c |
Values are means of triplicate ± standard deviation. |
Within a row with the same lowercase letter are not significantly different at p < 0.05 |
Moisture contents were significantly different (p < 0.05) among the samples (PBG: 81.64%, HRG: 82.44%, HPG: 83.42%) respectively. HPG was having the highest moisture content and PBG was having the lowest. Study conducted by other worker [15] showed the moisture content of lemon peel at the range of 81.23%. Total sugars content was also significantly different (p < 0.05) between the three cultivars (PBG: 7.40%, HRG: 6.89%, HPG: 6.79%) respectively. PBG was having the highest total sugar content and HRG and HPG was having similar lower values. Reducing sugar content of galgal cultivars were significantly different (p < 0.05). PBG (3.82%) was having the highest reducing sugar content and HRG (3.31%) was having the lowest. Crude fiber percentage was low in peel which was ~ 1% in all galgal cultivars. Pectin and protein of PBG, HRG and HPG were not significantly differ (p < 0.05). Crude fat content was found to be highest in PBG (4.22%) followed by HPG (2.87%) and HRG (2.25%) respectively. Study conducted previously [16] revealed the fat content of lemon peel at the range of 4.2%. The ash content was highest in PBG (2.89%), followed by HRG (2.64%) and HPG (2.52%) respectively.
In terms of phytochemical content, PBG had the highest total phenols (8.25mg GAE/g), followed by HPG (7.87mg GAE/g) and HRG (7.26mg GAE/g). HRG had the highest total flavonoids (7.23mg/100g), followed by HPG (7.55mg/100g) and PBG (6.18mg/100g). PBG had the highest ascorbic acid content (39.58mg/100g), followed by HPG (38.65mg/100g) and HRG (38.33mg/100g) respectively. The total phenol content of lemon was observed by [17] in the range of 5.07 to 25.24 mg gallic acid/g. In terms of pigment content, PBG had the highest total carotenoids (81.54mg/g), followed by HRG (80.24mg/g) and HPG (79.54mg/g) respectively. PBG also had the highest total chlorophyll content (15.69mg/g), followed by HRG (15.20mg/g) and HPG (13.45mg/g) respectively. These results suggest that PBG extract has the highest content of crude fat, ash, total phenols, ascorbic acid, total carotenoids, and total chlorophyll, while HRG extract has the highest total flavonoid content. These findings could be useful for the development of plant-based food products or dietary supplements with specific phytochemical profiles.
Extraction & Yield of Essential oils
Table 2 shows the results of different techniques used for the extraction of essential oils from PBG, HRG, and HPG, respectively. The highest % yield of essential oil was obtained using supercritical CO2 extraction with 09.40% (PBG), 07.56% (HRG), and 06.25% (HPG), respectively. This indicates that the supercritical CO2 extraction technique was the most efficient for the extraction of essential oil, but on the other side, this technique is quite expensive because the running and maintenance costs of the equipment are high. The Clevenger extraction technique yielded 3.50% (PBG), 2.50% (HRG) and 01.92% (HPG) of essential oil, respectively, which is relatively lower than supercritical CO2 extraction but higher than all other extraction techniques. Steam distillation, on the other hand, yielded only 00.90% (PBG), 00.81% (HRG), and 00.79% (HPG) respectively, indicating that it was not a very efficient technique for the extraction of essential oil from peel. Moreover, among the different MAE and UAE techniques used, the MAE for 20 min technique yielded the highest amount of essential oil 02.49% (PBG), 01.42% (HRG) and 01.21% (HPG) respectively. The UAE techniques yielded relatively lower amounts of essential oil compared to the MAE techniques. Steam distillation was found to be the least efficient technique for essential oil extraction. The Clevenger extraction method was found to be the most economical method of extraction because only water and heat are utilized in processing.
Table 2
Extraction of Essential Oil from peel
Sample | Technique used | Time (minutes) | % Yield of EO (PBG) | % Yield of EO (HRG) | % Yield of EO (HPG) |
EO | Clevenger | 60 | 03.50 ± 0.01b | 02.50 ± 0.01b | 01.92 ± 0.01b |
EO | Steam Distillation | 80 | 00.90 ± 0.05f | 00.81 ± 0.02h | 00.79 ± 0.01g |
EO | MAE for 10 min | 50 | 02.42 ± 0.04d | 01.31 ± 0.05e | 01.00 ± 0.05f |
EO | MAE for 15 min | 50 | 02.45 ± 0.02cd | 01.38 ± 0.01cd | 01.10 ± 0.04e |
EO | MAE for 20 min | 47 | 02.49 ± 0.05c | 01.42 ± 0.03c | 01.21 ± 0.02cd |
EO | UAE for 10 min | 49 | 01.52 ± 0.03e | 01.10 ± 0.02g | 01.10 ± 0.01e |
EO | UAE for 15 min | 46 | 01.55 ± 0.04e | 01.21 ± 0.01f | 01.18 ± 0.03d |
EO | UAE for 20 min | 41 | 01.58 ± 0.06e | 01.35 ± 0.03de | 01.24 ± 0.02c |
EO | Supercritical CO2 | 70 | 09.40 ± 0.02a | 07.56 ± 0.01a | 06.25 ± 0.01a |
Values are means of triplicate ± standard deviation |
Within a coloumn with the same lowercase letter are not significantly different at p < 0.05 |
Characterization of Essential oils
Table 3 illustrated the characterization of compounds present in the essential oils of three different cultivars of galgal, namely PBG, HRG, and HPG, using GCMS. While some compounds were common among all cultivars, others were unique to specific cultivars. For example, à-Pinene was found in all cultivars with concentrations of 0.70% (PBG), 2.65% (HRG), and 0.68% (HPG), respectively. D-Limonene was found to be the predominant compound in all samples, with concentrations of 42.94%, 56.59%, and 88.69% in PBG, HRG, and HPG, respectively. HPG had the highest content of D-Limonene, while PBG had the lowest. Linalool and Germacrene D were two other components that were common in all samples. The concentration of linalool was found to be 0.22% (PBG), 1.11% (HRG), and 2.05% (HPG), while Germacrene D was found to be in the range of 1.13%, 0.15%, and 0.09% in PBG, HRG, and HPG, respectively. Linalool was highest in HPG, while Germacrene D was highest in PBG. Additionally, some compounds were common in any two cultivars, such as à-Phellandrene, which was found in HRG (0.09%) and HPG (0.13%) only. Similarly, á-Myrcene was common in HRG and HPG, with HRG containing a good amount of á-Myrcene (27.09%) and HPG having a low amount of á-Myrcene (3.05%). á-Ocimene was found to be common in PBG (3.48%) and HPG (0.95%). ç-Terpinene was common in PBG and HRG cultivars, with a range of 0.17% and 0.25%, respectively. Terpinen-4-ol was also found to be common in PBG (0.66%) and HRG (0.87%), respectively. In HRG, à-Terpineol was prevalent at a concentration of 0.80%, while in HPG, it was present at a concentration of 0.09%. Additionally, Geraniol and cis-à Bergamotene were detected only in HRG and HPG, with concentrations of 0.18%, 0.05% and 0.43%, 0.33%, respectively. Geranyl acetate was found in both PBG and HRG, with concentrations of 0.15% and 0.36%, respectively.
Table 3
Characterization of Essential oil from Galgal cultivars with GCMS
Retention time | Essential Oil |
PBG | HRG | HPG |
Compound Name | Area (%) | Compound Name | Area (%) | Compound Name | Area (%) |
11.47 | | | à-Phellandrene | 0.09 | à-Phellandrene | 0.13 |
11.69 | à-Pinene | 0.70 | à-Pinene | 2.65 | à-Pinene | 0.68 |
12.19 | | | Camphene | 0.18 | | |
13.08 | Bicyclo[2.2.1]heptane, 7,7-dimethyl-2-methylene | 5.24 | | | | |
13.15 | | | á-Myrcene | 27.09 | á-Myrcene | 3.05 |
13.52 | Trans- á-Ocimene | 22.73 | | | | |
14.79 | D-Limonene | 42.94 | D-Limonene | 56.59 | D-Limonene | 88.69 |
15.15 | á-Ocimene | 3.48 | | | á-Ocimene | 0.95 |
15.49 | ç-Terpinene | 0.17 | ç-Terpinene | 0.25 | | |
16.58 | Linalool | 0.22 | Linalool | 1.11 | Linalool | 2.05 |
17.68 | | | | | Limonene oxide, trans | 0.15 |
18.00 | | | Citronellal | 0.28 | Citronellal | 0.04 |
18.29 | | | cis-Verbenol | 0.16 | | |
18.64 | Indolizine | 0.20 | | | | |
18.76 | Terpinen-4-ol | 0.66 | Terpinen-4-ol | 0.87 | | |
19.07 | | | à-Terpineol | 0.80 | à-Terpineol | 0.09 |
19.76 | | | | | Santalol, trans-á- | 0.27 |
19.88 | Citronellol | 0.50 | | | | |
19.93 | | | Geraniol | 0.18 | Geraniol | 0.05 |
20.26 | | | | | Citral | 0.30 |
20.29 | | | Verbenol | 2.98 | | |
20.99 | | | ç-Atlantone | 4.20 | | |
21.49 | | | | | p-Mentha-1,8-dien-7-ol | 0.04 |
22.66 | Elemene isomer | 0.53 | | | | |
23.06 | Geranyl acetate | 0.15 | Geranyl acetate | 0.36 | | |
23.47 | | | 2,6-Octadien-1-ol, 3,7-dimethyl-,acetate, (Z) | 0.42 | | |
23.91 | Cyclohexane, 1-ethenyl-1-methyl-2,4-bis(1-methylethenyl) | 0.59 | | | | |
24.63 | | | Caryophyllene | 0.12 | | |
24.68 | N-(2,5-Dimethylphenyl)piperazine | 10.42 | | | | |
24.82 | | | cis-à Bergamotene | 0.43 | cis-à-Bergamotene | 0.33 |
25.12 | | | á-Famesene | 0.05 | | |
25.37 | Humulene | 1.18 | | | | |
25.91 | Germacrene D | 1.13 | Germacrene D | 0.15 | Germacrene D | 0.09 |
26.16 | | | | | Naphthalene,1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methylethenyl)-,[1S-(1à,7à,8aà)]- | 1.02 |
26.25 | (1S,2E,6E,10R)-3,7,11,11-Tetram ethylbicyclo[8.1.0]undeca-2,6-die ne | 2.28 | | | | |
26.31 | | | á-Bisabolene | 0.74 | | |
26.71 | | | | | à-Maaliene | 0.06 |
27.52 | ç-Elemene | 3.57 | | | ç-Elemene | 0.09 |
28.05 | Caryophyllene oxide | 0.27 | | | | |
29.51 | Neointermedeol | 0.37 | | | Selin-6-en-4à-ol | 0.23 |
29.80 | | | à-Bisabolol | 0.05 | | |
32.18 | Nootkatone | 0.91 | | | | |
PBG contains several unique components, including Bicyclo[2.2.1]heptane, 7,7-dimethyl-2-methylene (5.4%), Trans-á-Ocimene (22.73%), Indolizine (0.20%), Citronellol (0.50%), Elemene isomer (0.53%), Cyclohexane, 1-ethenyl-1-methyl-2,4-bis(1-methylethenyl) (0.59%), N-(2,5-Dimethylphenyl)piperazine (10.42%), Humulene (1.18%), (1S,2E,6E,10R)-3,7,11,11-Tetramethylbicyclo[8.1.0]undeca-2,6-diene (2.28%), Caryophyllene oxide (0.27%), Neointermedeol (0.37%), and Nootkatone (0.91%). Overall, PBG has three dominant compounds, namely Limonene, Trans-á-Ocimene, and D-,N-(2,5-Dimethylphenyl)piperazine, with concentrations above 10%. On the other hand, HRG has its own specific compounds, such as Camphene (0.18%), cis-Verbenol (0.16%), Verbenol (2.98%), ç-Atlantone (4.20%), 2,6-Octadien-1-ol, 3,7-dimethyl-, acetate, (Z) (0.42%), Caryophyllene (0.12%), á-Famesene (0.05%), á-Bisabolene (0.74%), and à-Bisabolol (0.05%). In HRG, only two components, namely D-limonene (56.59%) and á-Myrcene (27.09%), had concentrations above 10%. In addition, HPG had only one component with a concentration above 10%, which was D-limonene. However, HPG contains some unique compounds, including Limonene oxide, trans (0.15%), Santalol, trans-á- (0.27%), Citral (0.30%), p-Mentha-1,8-dien-7-ol (0.04%), Naphthalene,1,2,3,5,6,7,8,8a-octahydro-1,8a-dimethyl-7-(1-methylethenyl)-,[1S-(1à,7à,8aà)]- (1.02%), à-Maaliene (0.06%), and Selin-6-en-4à-ol (0.23%). Furthermore, several studies have revealed the health benefits associated with these compounds.
D-limonene exhibits antimicrobial, antioxidant, anticancer, anti-diabetic, and antiviral effects[6, 18, 19], while α-pinene possesses antibacterial, fungicidal, and antiviral properties [20]. α-phellandrene acts as an immunity booster and has antifungal properties [21], while Myrcene has analgesic, antidiabetic, antioxidant, antifungal, and anti-inflammatory properties [22, 23]. α-elemene has anti-tumor effects, and Camphene has anti-fungal, anti-microbial, cholesterol-lowering, and antioxidant properties [24]. Caryophyllene aids in reducing pain and anxiety [25], and Humulene has anti-inflammatory, analgesic, and antibacterial properties [26]. Linalool exhibits anti-inflammatory, antioxidant, and anti-depressant effects [27]. Therefore, numerous studies suggest that essential oils have various health benefits and can be utilized in food preservation as a replacement for synthetic preservatives.
Antioxidant activity of essential oils
Table 4 provided the data on the antioxidant activity of three cultivars, PBG, HRG, and HPG, as measured by four different assays: DPPH, FRAP, ABTS, and reducing power. The results of the study showed that the PBG sample had the highest antioxidant activity as measured by the DPPH and FRAP assays, with values of 94.85% and 128.14 TE/g, respectively. In contrast, the HRG sample had the lowest antioxidant activity in these assays, with values of 88.56% and 120.64 TE/g, respectively. Interestingly, when the reducing power and ABTS assays were used, the PBG and HRG samples showed similar levels of antioxidant activity. The reducing power assay measured the ability of a compound to donate electrons and thereby reduce another substance, while the ABTS assay measured the ability of a compound to scavenge the ABTS + radical cation. Overall, the results suggested that the PBG sample may be particularly effective at scavenging free radicals, which is an important aspect of its antioxidant activity.
Table 4
Antioxidant activity of EO of different galgal cultivars
Sample | DPPH % DPPH Radical Scaveining Activity | FRAP TE/g | Reducing Power AAE/g | ABTS % ABTS Inhibition |
PBG | 94.85 ± 0.96b | 128.14 ± 0.98a | 47.73 ± 0.66c | 46.28 ± 0.22d |
HRG | 88.56 ± 0.54b | 120.64 ± 0.64a | 41.35 ± 0.37d | 42.34 ± 0.41c |
HPG | 86.35 ± 0.46b | 118.45 ± 0.35a | 40.56 ± 0.36d | 41.55 ± 0.34c |
Values are means of triplicate ± standard deviation |
Within a raw with the same lowercase letter are not significantly different at p < 0.05 |
Antimicrobial activity of essential oils
The essential oil's antimicrobial effectiveness against gram-positive (S. aureus) and gram-negative (E. coli) bacteria was studied. The outcomes are illustrated in Fig. 1, indicated that there was a notably (p < 0.05) greater zone of inhibition against S. aureus in comparison to E. coli. The PBG essential oil produced a zone of inhibition ranged from 28–29 mm for S. aureus and 26–28 mm for E. coli. However, the positive control (Streptomycine) demonstrated a significantly greater zone of inhibition of 27–31 mm. The HPG essential oil exhibited a zone of inhibition ranged from 25–26 mm for S. aureus and 24–25 mm for E. coli, with the positive control showed a significantly higher zone of inhibition of 27–31 mm. On the other hand, the HRG showed a zone of inhibition against S. aureus and E. coli of 27–29 mm and 19–22 mm, respectively. The antimicrobial activity of essential oil could be due to its compounds like limonene, α-pinene, Myrcene, Camphene etc. These compounds will diffuse into the cell membrane leads to the leakage of cell wall material [13]. Our results were in accordance with the work done by [13, 28] who observed the antimicrobial properties of Citrus nobilis and orange peel.