Grapefruit seed extract
Grapefruit seed extract (GSE), also known as citrus seed extract, is a liquid derived from the seeds, pulp, and white membranes of grapefruit. While there has been no scientific demonstration of efficacy, this extract has been claimed by some practitioners of alternative medicine to possess antibacterial, antiviral, and anti-fungal properties. Indeed, it has been recommended by some nutritionists for the treatment of candidiasis, earache, throat infections, and diarrhea. Some natural food retailers claim this extract to be a safe, natural, and an effective preservative. Recent studies have identified synthetic preservatives in commercial grapefruit seed extracts. When preservatives were not present in some of the extracts, laboratory tests found the natural extracts to have little or no natural antimicrobial attributes of their own. An early proponent was Dr. Jacob Harich (19191996). Some of the manufacturers of GSE have claimed that their extract has compounds nearly identical to benzethonium chloride but the 2001 study overiewed by chemist G. Takeoka and ran by fellow researchers have documented that commercial GSE preparations contain the synthetic compound benzethonium chloride that couldn't have been made from GSE. Yet, promoters from book authors to cosmetic companies still affirm this extract has strong natural healing properties even though the validity of the studies portray the opposite.

# History
The grapefruit is a sub-tropical citrus tree grown for its fruit which was originally named the "forbidden fruit" of Barbados. The fruit was first documented in 1750 by Rev. Griffith Hughes describing specimens from Barbados. All parts of the fruit have uses. The fruit is mainly consumed for a tangy juice. The peel is expressed into an aromatherapy oil and is also a source of dietary fiber. The seed and pulp as a by-product of the juice industry is sold as cattle feed and is manufactured for use to make an extract. GSE was originally developed by Dr. Jacob Harich, a nuclear physicist. In 1963, he journeyed to Florida, the heart of grapefruit country, and began research and later marketing of GSE. Today, GSE is mostly promoted at health food shops and on the internet.

# Scientific research
Anecdotal claims for an antimicrobial effect are loosely supported by small abstract scientific experiments which apparently show some antimicrobial activity in in vitro assays such as the agar diffusion test. However, there is considerable scientific evidence that the anti-microbial activity associated with grapefruit seed extract is attributable to the contamination or adulteration of commercial GSE preparations with synthetic antimicrobials or preservatives. After careful evaluation of the anecdotal claims for an antimicrobial effect, the preliminary studies state that the Citricidal brand of GSE was used for testing. That said, despite the anecdotal antimicrobial claims, according to the 2001 GSE study, the Citricidal brand as well as the Nutribiotic brand were both contaminated with synthetic benzethonium chloride that was implausible to be made from grapefruit seeds. Another in vitro study claimed GSE has antimicrobial activity against bacteria. As the same with the branded in vitro test that was contaminated with preservatives, the ethanolic extract tested had been adulterated with a preservative known as ethanol used in the extraction process. Ethanol, also known as ethyl alcohol, is effective in inhibiting bacteria. Nevertheless, as a result of marketing by manufacturers in the health food arena and a few misinterpreted studies conducted in vitro that tested contaminated extracts which were not pure GSE processed without solvents or brands which are known to contain preservatives, the controversy over the effectiveness of GSE continues even when studies conclude  self-made pure GSE has no natural antimicrobial properties and commercial GSE has been identified with contamination from synthetic preservatives.
Independent studies have shown that commercial preparations contain the compound benzalkonium chloride, which is a synthetic antimicrobial commonly used in disinfectants and cleaning products, the related compound benzethonium chloride, the antibiotic triclosan, or the preservative methylparaben. Some samples were shown to contain up to 22% benzalkonium chloride by weight, despite the known allergenicity and toxicity of the compound at higher doses. These chemicals were not present in grapefruit seed extracts prepared in the laboratory, and GSE preparations without the contaminants were found to possess no significant antimicrobial effect. Self-made citrus seed extracts had no broad-spectrum capabilities as a preservative. Although GSE is sold in health food markets, there is no good evidence for any natural antimicrobial activity.
A study that examined the antiviral properties of GSE found that GSE had no efficacy as a disinfectant for feline calicivirus and feline parvovirus.
Grapefruit seed extract has been advocated to be a powerful antimicrobial with proven activity against bacteria and fungi. However, independent studies have shown the efficacy of grapefruit seed extract as an antimicrobial is not demonstrated. Although citrus seed extract is claimed to be a highly effective plant-based preservative by some natural personal care manufacturers, studies asserted that the universal antimicrobial benefits associated with GSE are merely from the presence of synthetic preservatives. Natural GSE has no antimicrobial properties.

# Properties
There is good evidence that the extract of citrus grapefruit seed has low levels of antioxidant properties.
Analysis research revealed the constituents of the seed extract and pulp are made up of flavonoids, ascorbic acid (commonly known as vitamin C), tocopherols, citric acid, limonoids, sterols, and minerals. A study suggests the consumption of the bioactive compounds found in grapefruit seed and pulp may help suppress the development colon cancer. Another study showed the flavonoid naringin is an excellent plasma lipid lowering and plasma antioxidant active elevating flavonone.

# Preparations
Self-made pure GSE processed without solvents is prepared by grinding the grapefruit seed and juiceless pulp, then mixing with glycerin.
Commercially available GSE sold to consumers are made from the seed, pulp, glycerin, and synthetic preservatives all blended together.

# Precautions
Consequential to the identification of preservatives in commercial GSE which are sold at some natural food markets,
people who are sensitive to eating synthetic preservatives may exercise caution in administering
GSE at any dilution to prevent an allergic reaction.
Grapefruit can have a number of interactions with certain drugs, increasing the potency of many compounds. Grapefruit has components that inhibit the production of a particular enzyme in the intestine. Thus, it is this effect that increases the rate of absorption of several drugs.

# GSE controversy
GSE usage has been popularized by many companies within the scope of the health food industry. There are books exclusively dedicated to GSE. This extract is promoted by marketers on the internet. Some health food stores continue to recommend it. Some consumers believe this extract is an effective natural preservative despite the findings of multiple scientific studies have concluded the universal antimicrobial activity is merely from contamination with synthetic antimicrobials.