Sesame seeds are produced by the sesame plant (Sesamum indicum), an annual with yellow, white or pink flowers which grows to around one meter in height. Sesame is grown mainly in India, China and Mexico due to the presence of cheap labour. This relates to the fact that the seeds are picked by hand due to their delicate oils. Sesame seeds are encased in a pod and this pod protects these delicate oils from attack by oxygen, a process that would lead to rancidity. Sesame seeds are prized for their high oil content and sesame was historically one of the most important oils crops for humans. Evidence suggests that sesame seeds may have been grown domestically over 3000 years ago in the middle East region. The fat content of sesame seed is around 50 %, with 40 % of this being monounsaturated fatty acids and 45 % polyunsaturated fatty acids. The oil within sesame seeds is therefore highly unsaturated and this explains the oils tendency to easily become rancid. As well as being a good source of nutrients, sesame oil is also used for other purposes such as in massage oils (because it is a good emollient) and in cosmetics.
Sesame seeds also contain high amounts of certain minerals. In particular they are rich in calcium, although they also contain high concentrations of oxalic acid which may reduce the bioavailability of the calcium (and other minerals) somewhat. Other minerals found in sesame seeds include copper, magnesium, iron and zinc, although the exact mineral content of the seed will depend on the quality of the soil and its mineral composition. Sesame seeds also contain the vitamins thiamine (vitamin B1) and riboflavin (vitamin B2). The protein content of sesame seeds is comparable to other vegetable sources of protein with particularly high concentrations of methionine and tryptophan. Sesame seeds contain high concentrations of lignans, polyphenolic substances that are often associated with the fibre component of the seeds. Lignans are bioavailable in humans and are thought to have beneficial antioxidant effects. The main lignan in sesame seeds is called sesamin, and some evidence suggests that it is the sesamin that is responsible for the ability of sesame seeds to lower cholesterol levels. Sesamin may do this by inhibiting the production of cholesterol in the liver.
Sesamin has also been shown to increase tissue levels of vitamin E and vitamin K. This may relate to the ability of sesamin to inhibit the α-hydroxylation of these vitamins in cytochromes and thus inhibit their metabolism, increasing tissue levels. Therefore part of the beneficial antioxidant effects of sesamin may come from sparing other vitamins through its action on vitamin E. Evidence also suggests that sesamin may be able to inhibit the delta 5-desaturase enzyme in the essential fatty acid pathway. Delta 5-desaturase is responsible for the addition of a double bond to dihomo-gamma linolenic acid (DHGL, C20:3 (n-6)) and eicosatetraenoic acid (ETA, C20:4 (n-3)) to form arachidonic acid (AA, C20:4 (n-6)) and eicosapentaenoic acid (EPA, C20:5 (n-3)), respectively. Delta 5-desaturase is normally under the hormonal control of insulin, and it is unclear as to the clinical significance of this effects. Certainly in cell culture experiments sesamin can interfere with essential fatty acid metabolism and cause accumulation of the products in tissues. However, the beneficial effects of sesame seeds on skin health (which would require flux through the essential fatty acid pathway) might suggest that this effect is not apparent in human cells in vivo.
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