Onion (apium graveolens )
At 44 million tones the onion is second in line to tomatoes on the world’s most produced vegetable.With more emphasis on disease prevention than cure, there has been an increased interest by scientists on the high content of polyphenolic flavonoids in onions (Mogren et al., 2007). Onion and leek are high in flavonoids (Tarwadi, 2005). Even though the onion has high nutritional value, it is largely consumed for its unique flavour and its ability to improve the flavor of other foods (Randle, 1997). Soil sulfur (S) content however can influence the flavor of a vegetable – e.g.
onions grown in soil that has high sulfur content will have a stronger flavour/smell (Brecht et al., 2006).
The carbohydrates found in onions are fructose, glucose and sucrose (Mogren et al., 2007). The antioxidant flavonoids that are present in onions may reduce heart disease. The flavonol called quercetin is found in high levels in onions mostly in the outer dry scales (Williamson et al., 1996). According to Griffiths et al. (2002), the onion has anti-carcinogenic, antithrombotic, antiplatelet,antiasthmatic and antibiotic abilities. The theosulfinates in onions have anti-microbial properties.Furthermore, the onion is effective against some bacteria like Bacillus subtilis, Salmonella and E. coli.