Tocol contents of oil differed significantly (P < 0.05)
among treatments (Table 3). ç-Tocotrienol was the
major tocol of grapeseed oil, representing 38-72% of the
total tocopherols. ç-Tocotrienol ranged from 5.3 to 48.8
mg/100 g of oil for oil extracted from tannin-free
grapeseed and from seed heated continuously in the
microwave for 9 min, respectively. R-Tocopherol, R-to-cotrienol, and ç-tocotrienol levels increased significantly,
resulting in higher vitamin E equivalents with increased
severity of heat treatment. The concentration of â-tocopherol
of oil extracted from air-dried seed was not
significantly different from that extracted from continuously
microwave-treated seeds. ä-Tocopherol was susceptible
to degradation and decreased sharply (from 7
to 1 mg/100 g of oil) with continuous microwave treatment.
Air-drying and microwave-drying for 24 min
resulted in 15 and 68% decreases, respectively, in
ä-tocopherol content compared to the untreated seeds.
The commercial grapeseed oil contained no ä-tocopherol.
Decrease in ä-tocopherol and no changes in â-tocopherols
due to microwave treatments have previously
been reported in soybeans (Yoshida and Kajimoto,
1989).