Page 96 - Natural Antioxidants, Applications in Foods of Animal Origin

Natural Antioxidants: Occurrence and Their Role in Food Preservation 75
VetBooks.ir 2.14.1 ANTIOXIDATIVE EFFECT OF SESAME LIGNANS

Sesaminol has sesamol as a moiety and has far stronger antioxidative activity
than sesamol because sesamol is easily dimerized and its products have lower
activity (Fukuda et al., 1986a). The markedly strong and stable antioxidative
property may be provided by the presence of a bulky samin group at the
ortho position of the phenol group in sesamol similar to the BHT molecule
(Namiki, 2007). Sesamin is the main characteristic lignan of sesame seed
with a content of about 0.4% in seed oil, but it has no free phenol group and
showed very weak or no antioxidative effect in conventional in vitro tests.
However, sesamin exhibits significant physiological activities assumed to
be due to antioxidative activity in vivo. Another important issue concerning
the stereochemical structure of sesame lignans is the fact that the artifact
episesamin, which is produced during food processing, has stronger physi-
ological activities than native sesamin (Namiki, 2007). Sesame lignans have
been found to exhibit various unique functions, such as a synergistic effect
with tocopherols on vitamin E activity and the specific inhibition of fatty
acid metabolism. These are quite different from the activities of other poly-
phenolic antioxidants, including sesamol, and they do not always appear to
be based upon their antioxidative activity. These facts suggest the existence
of some unique biochemical activity in sesame lignans due to their charac-
teristic structures in addition to their antioxidative activities (Namiki, 2007).

2.14.2 SESAME LIGNANS IN FOOD PRESERVATION

Sesame oil is highly resistant to oxidative deterioration. In ancient Egypt
it was used for making mummies, and in Japan it has been evaluated as
the best oil for deep frying tempura because of its superior stability against
deterioration by heating. There are two different kinds of sesame oil, roasted
and unroasted. The antioxidative activities of these oils were demonstrated
in experiments with other common vegetable oils that were stored at 60 °C.
Soybean oil, rapeseed oil, and others showed rapid increase after about 10
days, whereas both roasted and unroasted sesame oils were very stable.
The unroasted oil remained unchanged for 30 days, while no oxidation was
observed even after 50 days in the roasted oil (Fukuda & Namiki, 1988).
Roasted sesame seed oil has a characteristic flavor and red-brown color
probably caused by the Maillard-type reaction during roasting. The anti-
oxidative activity increases mainly in proportion to the roasting tempera-
ture along with the brown color, indicating that some products of the roast