The contents of total phenols and some flavonoids, vitamin C and antioxidant
activity in freeze dried tissues of onion, cabbage, artichoke and sweet pepper in
relation to the effect of two thermal processing treatments i.e. blanching and
microwaving were studied. Vegetables were freeze dried after processing (more
than the fresh ones) before hydrolyzed and extraction. Total phenols content in
edible parts, was higher in sweet pepper but lower in onion. Thermal processing
induced lowering effect on total phenols (mg I 100g) in onion, however, the effect
by blanching exceeded those resulted from microwaving thermal treatment. Effects
on these compounds but towards decrease were observed with microwave treatment
in pepper and artichoke but in cabbage was increased. Meanwhile, blanching caused
an increase in total phenols of sweet pepper as well as cabbage while in artichoke
were slightly affected. The level of myricetin in cabbage exceeded those in onion and
not detected in artichoke and pepper. Conceming the level of quercetin, it was
obviously shown that sweet pepper the superior followed by artichoke and onion was
contained the leowest quantities, however, it was not detected in cabbage leaves.
Myriceten was sharply but negatively affected in cabbage leaves to be undetected by
blanching and slightly by microwave treatment. On yellow onion tissues, this active
material was quietly reduced by blanching and reversely responded by microwave
treatment. The quercetin in artichoke as well as sweet pepper increased
pronouncedly by blanching and also by microwave treatment but with a lower degree. Sweet pepper fruits characterized by the highest percentages of vitamin C
followed by that in the leaves of cabbage and the lowest content was in bulbs of
onion. The highest effect of heat treatment was in onion followed by pepper and no
response with cabbage tissues. Blanching tissues at boiling water for 5 min.
decreased pronouncedly the level of vitamin C by 33.91, 53.85 and 2.70 % for
pepper, onion and cabbage, respectively, while exposure to microwave thermal
treatment decreased Vitamin C by 53.04 , and 69.23 % in sweet pepper and onion,
respectively, while. cabbage tissues did not show any response with this treatment.
The antioxidants activity were higher in pepper than the other tested veget.-:bles. This
activity raised in all vegetables except pepper by blanching and microwave.