431
20.5.9 Pro-vitamin A Activity
About 50 of the 700 carotenoids that exist in nature have activity of provitamin A
(Rodriguez-Amaya 1997; Okada et al. 2008). In humans, only three among them
are the most potent precursors of vitamin A. these are β-cryptoxanthin, α-carotene
and β-carotene (Thane and Reddy 1997; Park et al. 2009; Carrillo-Lopez et al.
2010). In the body, they are normally converted into retinol or vitamin A (Zeb and
Mehmood 2004). Among the carotenoids containing foods, vegetables and fruits,
β-carotene is the main provitamin A component (Imamura et al. 2006). Serious eye
disorders like night blindness are prevented by β-carotene, the precursor of vitamin
A (Takahashi et al. 2006). Additionally, carotenoids found in food are usually well
digested to release these carotenoids from the matrix of food in order to act physiologically as a vitamin A (Carrillo-Lopez et al. 2010). Most of the carotenoids that
serve as provitamin A must have the structure of β-ionone. In animals, they act as
regulators of process related to photo-energy by trapping energy from light (Stahl
and Sies 2005). Carotenoids like α-carotene, lycopene, β-carotene, lutein and
β-cryptoxanthin are seen in plasma of human (Romanchik et al. 1995). From these
carotenoids, β-carotene, β-cryptoxanthin and α-carotene are regarded as provitamin
A carotenoids while others like lutein and lycopene are regarded as non-provitamin
A carotenoids. In addition to the presence of β-ionone ring as a credential for provitamin A activity, proper position and number of methyl groups in the polyene chain
is also required (Wirtz et al. 2001). The bioconversion of carotenoids involve the
action of a cleavage enzyme called mono or dioxygenase. This enzyme breaks the
double bonds in a polyene link into two retinal molecules. These molecules are then
metabolized to other derivatives such as retinoic acids which are involved in the
promotion of visual action, embryonic development for pregnant mothers, differentiation of epithelial cells, and body growth (Handelman 2001). But the requirement
for vitamin A derived from carotenoids is minutes which is about 200 μg/day for a
healthy adult a higher dose is toxic in human. It was reported that in low income
nations, about 80% of vitamin A are derived from provitamin A carotenoids (Stahl
and Sies 2003).
20.5.10 Cardio-Protective Activity
Oxidative stress and consistent severe low state of inflammation in the cardiovascular system, mainly leads to the formation of cardiovascular disorders. Low density
lipoproteins cholesterol (LDLc) that were modified via oxidative stress are involved
in the initial formation and progression of atherosclerosis, which finally leads to
coronary heart disorders. Normally, atherosclerosis may be as a result of the production of foam cells serving as a source of reactive free radicals that result to
LDLc oxidation. Hence, LDLc oxidation protection by antioxidants may prevents
coronary heart diseases in humans. Putting into consideration that lycopene and
20 Carotenoids as Functional Bioactive Compounds
20.5.9 Pro-vitamin A Activity
About 50 of the 700 carotenoids that exist in nature have activity of provitamin A
(Rodriguez-Amaya 1997; Okada et al. 2008). In humans, only three among them
are the most potent precursors of vitamin A. these are β-cryptoxanthin, α-carotene
and β-carotene (Thane and Reddy 1997; Park et al. 2009; Carrillo-Lopez et al.
2010). In the body, they are normally converted into retinol or vitamin A (Zeb and
Mehmood 2004). Among the carotenoids containing foods, vegetables and fruits,
β-carotene is the main provitamin A component (Imamura et al. 2006). Serious eye
disorders like night blindness are prevented by β-carotene, the precursor of vitamin
A (Takahashi et al. 2006). Additionally, carotenoids found in food are usually well
digested to release these carotenoids from the matrix of food in order to act physiologically as a vitamin A (Carrillo-Lopez et al. 2010). Most of the carotenoids that
serve as provitamin A must have the structure of β-ionone. In animals, they act as
regulators of process related to photo-energy by trapping energy from light (Stahl
and Sies 2005). Carotenoids like α-carotene, lycopene, β-carotene, lutein and
β-cryptoxanthin are seen in plasma of human (Romanchik et al. 1995). From these
carotenoids, β-carotene, β-cryptoxanthin and α-carotene are regarded as provitamin
A carotenoids while others like lutein and lycopene are regarded as non-provitamin
A carotenoids. In addition to the presence of β-ionone ring as a credential for provitamin A activity, proper position and number of methyl groups in the polyene chain
is also required (Wirtz et al. 2001). The bioconversion of carotenoids involve the
action of a cleavage enzyme called mono or dioxygenase. This enzyme breaks the
double bonds in a polyene link into two retinal molecules. These molecules are then
metabolized to other derivatives such as retinoic acids which are involved in the
promotion of visual action, embryonic development for pregnant mothers, differentiation of epithelial cells, and body growth (Handelman 2001). But the requirement
for vitamin A derived from carotenoids is minutes which is about 200 μg/day for a
healthy adult a higher dose is toxic in human. It was reported that in low income
nations, about 80% of vitamin A are derived from provitamin A carotenoids (Stahl
and Sies 2003).
20.5.10 Cardio-Protective Activity
Oxidative stress and consistent severe low state of inflammation in the cardiovascular system, mainly leads to the formation of cardiovascular disorders. Low density
lipoproteins cholesterol (LDLc) that were modified via oxidative stress are involved
in the initial formation and progression of atherosclerosis, which finally leads to
coronary heart disorders. Normally, atherosclerosis may be as a result of the production of foam cells serving as a source of reactive free radicals that result to
LDLc oxidation. Hence, LDLc oxidation protection by antioxidants may prevents
coronary heart diseases in humans. Putting into consideration that lycopene and
20 Carotenoids as Functional Bioactive Compounds