Nature knows how to manage itself. For millions of years, critters – including humans – have thrived around bacteria. Yet with the innumerable species of cazillions of bacteria – some potentially lethal – we are still around.
Western medicine suggests that without the ‘miracle’ of pharmaceutical antibiotics, millions of people would be dead by now. Certainly, we can agree that antibiotics have saved lives. But there is a critical caveat – besides the fact that antibiotics were discovered from nature: As we have illustrated with our research published on this website, the massive use of prescriptive antibiotics is also responsible for lethal antibiotic-resistant strains of bacteria. These have become significantly more powerful than the ones antibiotics were supposed to treat.
Furthermore, it turns out that nature provides numerous antibiotic agents that can fight bacteria without creating lethal mutants. In fact, some of nature’s antibiotics have been found to fight antibiotic-resistant strains of bacteria.
Citrus peel extracts tested as antibiotics
Over the centuries, citrus peel has been used by traditional healers to fight infections and other conditions. We have described the research supporting these traditions. Traditional healers have used peels fresh, dried or steeped in tea.
Now we find that the citrus peels are antibiotic. And they challenge and even beat pharmaceutical antibiotics in combating some species of bacteria.
Researchers from Taiwan’s prestigious Hungkuang University recently conducted a series of studies that tested two species’ citrus peels against a range of bacteria species.
The researchers also tested the popular antibiotic streptomycin as a control medicine. This enabled the study to compare the ability of citrus peel extracts to inhibit different bacteria as measured against the prescription antibiotic.
Producing pomelo and grapefruit peel extracts
The researchers produced the citrus peel extracts from Star Ruby grapefruit (Citrus paradisi) and Pomelo (Citrus grandis). The peels were taken from the fresh fruits. The researchers purchased the fresh grapefruits and the pomelos from a local fruit distributor.
For the fresh-pressed extracts, they hand-peeled the fruits and then pressed the peels using a juice presser.
For the distilled extracts, the researchers boiled the peels in water for three hours and collected the extract using a type of distillation method called the Clevenger apparatus. This collects the steam at the top of a column while heating with a Bunsen burner below. The upper column is cooler, allowing the steam to be cooled and collected into another flask.
Several bacteria tested
The researchers then tested each of these citrus peel extracts against a number of different bacteria. These included both gram-negative and gram-positive bacteria, including some very infective bacteria:
Escherichia coli, Salmonella enterica and Pseudomonas aeruginosa (gram-negative). Plus gram-positive bacteria Staphylococcus aureus and Streptococcus faecalis. These are some heavy-hitting bacteria, known to cause a number of different infectious diseases – sometimes fatal.
Citrus peels inhibit bacteria
The researchers used a standard of measurement accepted around the world by the scientific community in bacteria testing – called zone of inhibition. This measures the amount of space around the antibiotic that will inhibit the growth of the bacteria. The greater this inhibition zone, the more effective the antibiotic.
An inhibition zone of between 6 and 9 millimeters is considered to be a moderate inhibition, while a zone of 10-14 millimeters is considered strong and over 15 mm is considered very strong.
The researchers found that both the cold-pressed peel extracts and the distilled peel extracts inhibited all the bacteria. The cold-pressed grapefruit peel extract inhibited the bacteria from a low of 6.9 mm (in the case of P. aeruginosa) to a high of 21.6 mm (in the case of Salmonella enterica) – with the rest mostly over the “strong” zone of 10 mm.
When the same bacteria were compared against the antibiotic streptomycin, the cold-pressed grapefruit peel extract inhibited two of the five bacteria greater than the antibiotic: Salmonella enterica (20.6 mm verses 17.3 mm) and Streptococcus faecalis (17.3 versus 10.9) were inhibited by the cold-pressed grapefruit peels more than the antibiotic.
Meanwhile the distilled extracts also inhibited all the bacteria except for P. aeruginosa – which both extracts had zones of a mere 6.3 mm. However, the distilled pomelo peels also inhibited Salmonella enterica and Streptococcus faecalis greater than the antibiotic streptomycin.
While slightly less than the antibiotic, both the distilled and cold-pressed citrus peels significantly inhibited the sometimes dangerous bacteria E. coli and S. aureus. These were both in the ‘strong’ inhibition zone of between 10 and 14 mm.
Again, both the cold-pressed grapefruit peels and the distilled pomelo peels inhibited Salmonella enterica and Streptococcus faecalis bacteria significantly more than did the antibiotic streptomycin.
What makes citrus peels so antibiotic?
The researchers asked themselves this very same question. So they analyzed the two extracts using gas chromatography – a way to reveal chemical composition.
The researchers found that the extracts contained antibacterial ingredients such as limonene (at 32% to 96%), myrcene (up to 3%) and pinene (from .85% to 14%). Other types of citrus peels have shown these ranges but also contain terpinenes ranging from 0.1% to 23%.
Though with smaller percentages, other antibacterial compounds were also found in both the cold-pressed and distilled extracts. These include thujene and citral – found in the distilled pomelo peel extract. They also include germacrene and caryophyllene found among the cold-pressed grapefruit peels.
The peels also contained oils such as oleic acid, decenoic acid, palmitic acid and stearic acid.
The researchers also found that the cold-pressed pomelo peel extract contains oleylamide – which binds to the GABA and cannabinoid receptors, making the peels likely to encourage sleep and reduce pain. This is also consistent with traditional use of citrus peels.
Other citrus peels also antibiotic
This research and others illustrates that for certain types of bacteria – practically any type of citrus peel will be effective. As mentioned above, many contain the same mix of bacteria-resisting chemicals.
For example, another 2015 study tested cold and hot water and ethanol extracts from the peels of oranges.
The research found the orange peel water extracts inhibited the bacteria Aggregatibacter actinomycetemcomitans. Orange peels extracted with alcohol also inhibited Porphyromonas gingivalis and Prevotella intermedia bacteria. These are the bacteria that produce gingivitis and periodontal disease.
Citrus peel extracts can be made quite easily. A cold-pressed extract can be made simply by crushing the peels. A hot water extract can be made simply by steeping the crushed peels in hot boiling water for awhile. An alcohol extract is made by steeping the peels in alcohol. Steeping overnight should leave a syrup that can be used as a liniment.
Ming-Chiu Ou, Yi-Hsin Liu, Yung-Wei Sun, and Chin-Feng Chan, “The Composition, Antioxidant and Antibacterial Activities of Cold-Pressed and Distilled Essential Oils of Citrus paradisi and Citrus grandis (L.) Osbeck,” Evidence-Based Complementary and Alternative Medicine, vol. 2015, Article ID 804091, 9 pages, 2015. doi:10.1155/2015/804091
Hussain KA, Tarakji B, Kandy BP, John J, Mathews J, Ramphul V, Divakar DD. Antimicrobial effects of citrus sinensis peel extracts against periodontopathic bacteria: an in vitro study. Rocz Panstw Zakl Hig. 2015;66(2):173-8.
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