2Amity Institute for Herbal Research & Studies, Amity University UP, Sector-125, Noida-201313, India
3Dept. of Microbiology, CCS University campus, Meerut-250004 (India)
Thus the above study depicts that antimicrobial activity of lemon oil is much better than its lemon peel extract and has potential to be used as food bio preservative.
Keywords: Lemon peel; Lemon oil; Antimicrobial; Food spoilage bacteria; Waste-management
The antimicrobial properties of plant extracts, volatile oils and their constituents from a wide variety of plants have been assessed and reviewed [15,14,10,11,17,1,12,13]
Gould has emphasized the possible use of spices and derivatives like alternatives for inclusion in a new perspective of food conservation called “natural anti-microbial system”, which could use the synergistic effect of antimicrobial compounds from animal, plant and/ or microbial origin, more physical procedures in order to create an inhospitable environment for microbial survival in foods [9].Citrus is genus of flowering plants in the family Rutaceae, native to tropical and subtropical areas in Southeast Asia. Citrus fruits have peculiar fragrance partly due to flavonoids and limonoids present in the peel and these fruits are good sources of vitamin C and flavonoids [24]. The antioxidant/ radical scavenging capacity and reducing power ability of different extracts of orange peel were investigated and results showed that ethanolic extract showed the highest values for yield i.e. total phenolic content, total flavonoid content, chelating and antioxidant activities (% DPPH scavenging activity). It was also observed that solvent played a vital role in the extraction of the plant constituents, specifically, methanol and ethanol were highly polar among the solvents used [16]. It is also found to have antifungal activity [27].
Lemon (Citrus sinensis) peel is an agri-horticultural waste produced in large quantities from various fruit processing industries. It is normally discarded and dumped in the environment that can create environmental concerns [23].
Citrus by-products, if utilized fully, could be major sources of phenolic compounds. The peels, in particular, are an abundant source of natural flavonoids, and contain higher amount of phenolics compared to the edible portions. It has been reported that the contents of total phenolics in peels of lemons, oranges, and grapefruit were 15% higher than those in the peeled fruits [24].
Flavonoids in citrus are a major class of secondary metabolites. The peel contains the highest amount of flavonoids than other parts and those flavonoids present in citrus fruits belong to six peculiar classes according to their structure. They are: flavones; flavanones; flavonols; is of lavones; anthocyanidins and flavanols [24].
Flavonoids from citrus that have been extensively studied for anti-oxidative, anti-cancer, anti-viral, and anti-inflammatory activities, effects on capillary fragility, and an observed inhibition of human platelet aggregation. Recent research suggests that citrus fruits possess another health benefit phytochemicals called limonoids, highly oxygenated triterpenoid. Citrus limonoids appear in large amounts in citrus juice and citrus tissues as water soluble limonoid glucosides or in seeds as water insoluble limonoid aglycones. The limonoid aglycones are responsible for the development of delayed bitterness in citrus and are converted to the non bitter limonoid glucosides during fruit maturation [23].
In this context, studies on the antimicrobial effect of lemon peel extract and lemon oil were carried out against ten bacterial strains (7 Gram-positive and 3 Gram-negative) and seven fungi known to cause food spoilage.
The flasks were closed with cotton plug and aluminium foil. The lemon peel was soaked in 50% aqueous-ethanol for 48h at room temperature with intermittent shaking. The mixture was centrifuged at 3500 X g for 20 min and finally filtered through Whatmann filter paper No.1 [2]. The pellet was discarded and the supernatant was collected and concentrated under reduced pressure in a rotary vacuum evaporator (Buchi Type) until semisolid residue was obtained. This was dried inside the crucible under a controlled temperature (45°C) to obtain solid powder [18]. The process of extraction was repeated until the weight of 500mg was obtained.
The powder was weighed and reconstituted in Dimethyl Sulfoxide (DMSO) and were sieved through a fine mesh cloth and sterilized using a membrane filter (0.45-micron sterile filter). This extract was considered as the 100% concentration. These were stored in the refrigerator at 4°C for testing antimicrobial sensitivity.
The results were expressed in terms of the diameter of the inhibition zone: < 9mm, inactive; 9-12mm, partially active; 13- 18mm, active; >18mm, very active (Junior and Zanil, 2000).
Bacterial species |
Lemon peel extract |
Lemon oil |
Sodium propionate (+veC) |
DMSO(-veC) |
Bacillus cereus |
11.0 |
29.0 |
15.0 |
0.0 |
Bacillus subtilis |
12.0 |
13.0 |
14.0 |
0.0 |
Bacillus mycoides |
11.0 |
33.0 |
21.0 |
0.0 |
Staphylococcus aureus |
14.0 |
16.0 |
15.0 |
0.0 |
Staphylococcus epidermidis |
12.0 |
17.0 |
13.0 |
0.0 |
Listeria monocytogenes |
Partly |
13.0 |
15.0 |
0.0 |
Micrococcus luteus |
11.0 |
21.0 |
18.0 |
0.0 |
Escherichia coli |
10.0 |
11.0 |
12.0 |
0.0 |
Enterobacteraerogenes |
10.0 |
10.0 |
11.0 |
0.0 |
Pseudomonas aeruginosa |
10.0 |
Partly |
12.0 |
0.0 |
In contrast, the lemon oil exhibited wide range of antimicrobial activity against both groups of bacteria. The maximum zone of inhibition was observed against Bacillus mycoides and Bacillus cereus producing 33mm and 29mm Inhibition Zone Diameter (IZD) respectively.
Amongst the Gram negative bacteria, the lemon peel extract showed equivalent activity against all the test bacteria Pseudomonas aeruginosa, Escherichia coli and Enterobacter aerogenes with IZD of 10.0mm each whereas lemon oil also exhibited partial activity against the same.
Antifungal effects of the lemon peel extract and lemon oil have also been investigated as shown in (Table 2). All the seven test fungi were isolated from the spoiled food products.
Amongst fungus, the lemon peel extract was most effective against Alternaria sp. and Rhizopus sp. with an inhibition zone diameter of 25mm and 16mm respectively while the other test fungi were almost resistant to it.
Fungal species |
Lemon peel extract |
Lemon oil |
Sodium Propionate (+ve C) |
DMSO (-ve C) |
Aspergillus niger |
0.0 |
20.0 |
18.0 |
0.0 |
Aspergillus fumigates |
0.0 |
25.0 |
22.0 |
0.0 |
Aspergillus sp. |
8.0 |
27.0 |
23.0 |
0.0 |
Alternaria sp. |
25.0 |
0.0 |
24.0 |
0.0 |
Rhizomucor sp. |
0.0 |
22.0 |
20.0 |
0.0 |
Rhizopus sp. |
16.0 |
33.0 |
18.0 |
0.0 |
Penicillium sp. |
0.0 |
0.0 |
11.0 |
0.0 |
The MIC for the fungal species was therefore not determined. In contrast, sodium propionate which is used as a standard food preservative inhibited all the test fungal species.
(Table 3) depicts the Minimum Inhibitory Concentration (MIC) of the lemon oil. It ranged from 6.25 to 50 mg/mL. Staphylococcus aureus and Micrococcus luteus was found to be highly sensitive to the extract exhibiting lowest MIC of 6.25 mg/mL each followed by Bacillus cereus and Bacillus mycoides (MIC= 12.5 mg/mL each).
Bacterial species |
Lemon oil (mg/mL) |
Sodium Propionate (mg/mL) |
Bacillus cereus |
12.5 |
12.5 |
Bacillus subtilis |
50 |
25 |
Bacillus mycoides |
12.5 |
6.25 |
Staphylococcus aureus |
6.25 |
12.5 |
Staphylococcus epidermidis |
25 |
12.5 |
Listeria monocytogenes |
50 |
25 |
Micrococcus luteus |
6.25 |
6.25 |
Escherichia coli |
50 |
25 |
Enterobacteraerogenes |
50 |
25 |
Pseudomonas aeruginosa |
-- |
50 |
From these studies, it was observed that although lemon peel is effective against both groups of bacteria but its activity was high in Gram positive bacteria as compared to Gram-negative bacteria. These observations are in accordance with the earlier observations reported by and they also reported that Gramnegative organisms were less susceptible to the herbal extracts than Gram-positive isolates [3,5]. It may possibly be due to the presence of high lipid content in the cell walls of Gram negative bacteria. Gram-positive bacteria such as Staphylococcus epidermidis, Staphylococcus aureus, and Bacillus subtilis contains teichoic acid in the peptidoglycan layer and is therefore inhibited by both lemon peel extracts and lemon oil [19]. Furthermore, the outer membrane of Gram-negative bacteria is known to present barrier to penetration of numerous antibiotic molecules, and the periplasmic space contains enzymes, which are capable of breaking down foreign molecules introduced from outside thus providing greater resistance to them [4].
This could be also attributed to their higher percent of oxygenated compounds and sesquiterpenes as the results of GC/ MS revealed. The observed cytotoxic activity of peels essential oils may be attributed to the presence of limonene, α-pinene, β-myrecene and caryophyllene which had been previously proved to be the cytotoxic components in other essential oils [25]. Other constituent viz. β-pinene, α- terpineol, γ-terpinene and trans-α- bergamotene may have synergistic effects with limonene [20].
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