Citrus fruits are known for their fragrance and juicy, bitter flavour, and are widely accepted as part of a nutritional diet. Grapefruit (citrus paradisi) is a subtropical citrus fruit that was discovered in Barbados in the 18th century. Varieties of grapefruit include: Ruby Red, Pink, Thompson, Sweetie, Marsh and Duncan.

Grapefruit is a good source of vitamin C. It contains pink and red colours due to the carotenoid lycopene, which has anti-cancer properties. Grapefruit also contains the fibre pectin, which can play a role in reducing plasma cholesterol as indicated in a study.

“Citrus fruits are known for their fragrance and juicy, bitter flavour, and are widely accepted as part of a nutritional diet.”

It can also have weight-loss benefits. This effect of grapefruit and grapefruit products was researched in a study involving body weight and metabolic syndrome in 91 obese patients. After 12 weeks, the fresh grapefruit group had lost 1.6kg, the grapefruit juice group had lost 1.5kg, the grapefruit capsule group had lost1.1 kg, and the placebo group had lost 0.3kg. Thus a weight loss was well established on groups dieting on grapefruit and grapefruit products.

Grapefruit is rich in phenolic acids as shown in Table 1 (right).

Grapefruit compounds

Grapefruit juice has been shown to increase the oral bioavailability of several clinically important drugs by inhibiting first pass metabolism. Several compounds in grapefruit juice have shown different biological activities. Unique among them are furocoumarins with potent inhibitory activity against cytochrome P450 enzymes.

The important compounds of grapefruit juice considered to be involved in the pharmacokinetic interaction are flavonoids (naringin, naringenin, narirutin, quercetin, kaempferol, hesperidin, neohesperidin, didymin, and poncirin), furanocoumarins (6′,7′-dihydroxy-bergamottin, bergamottin, bergamottin-6′,7′-epoxide, bergapten, epoxy-bergamottin) and sesquiterpens (nootkatone). Nootkatone is also an expensive flavour and fragrance ingredient, used in the beverage industry.

Bergaptol, the most abundant furanocoumarin from grapefruit, has potent radical scavenging activity.

Anti-cancer properties

Additional research has also shown that the grapefruit flavanone naringenin inhibited the proliferation of breast cancer cells via impaired glucose uptake, indicating that naringenin may possess therapeutic potential as an anti-proliferative agent and thereby reducing growth of malignant cells.

“Grapefruit is a good source of vitamin C.”

Studies show that red grapefruit contains higher quantities of bioactive compounds and has higher antioxidant potential than white grapefruit. As a diet supplement, it positively influences serum lipid levels, especially serum triglycerides and also exerts serum antioxidant activity.

Grapefruit seeds play an important role too. Grapefruit seed extract (GSE) is well recognised for its antimicrobial activity. In various meat and fish applications, GSE has demonstrated bacterial inhibition and therefore a potential for a natural preservative for industrial food application. Red Mexican grapefruit seeds act as a source of bioactive limonoids namely obacunone, nomilin, limonin, deacetylnomilin (DAN) and limonin-17-beta-D-glucopyranoside (LG), and in addition to the antibacterial effects, they also possess strong antioxidant properties. Citrus limonoids have shown that they could inhibit the growth of cancer in the colon, lungs, mouth, stomach and breasts in animal and cell culture studies.

Thus, grapefruit acts as a treasure of various nutrients and bioactives that could be explored further.

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