Page 88 - Natural Antioxidants, Applications in Foods of Animal Origin

Natural Antioxidants: Occurrence and Their Role in Food Preservation 67
VetBooks.ir that pigment may have. The characteristic pattern of alternating single and

double bonds in the polyene backbone of carotenoids allows them to absorb
excess energy from other molecules, while the nature of the specific end
groups on carotenoids may influence their polarity. The former may account
for the antioxidant properties of biological carotenoids, while the latter may
explain the differences in the ways that individual carotenoids interact with
biological membranes (Britton, 1995).
The most important carotenoids are α-carotene, β-carotene,
β-cryptoxanthin, lutein, violaxanthin, neoxanthin, and lycopene. β-carotene,
α-carotene, and β-cryptoxanthin are carotenes that are converted into vitamin
A or retinol in the body. β-carotene is the most widely studied carotenoid.
Lutein and zeaxanthin are both stored in the retina of the eye; however,
neither converts to vitamin A. Both are powerful antioxidants and may be
very important for healthy eyes. Carotenoids are singlet oxygen quenchers
and protect the oil from photo-oxidation (Psomiadou & Tsimidou, 1998). The
structure of some carotenoids of plant origin is provided in Figure 2.7. Among
the vegetable oils, palm oil is the richest source of carotenoids, especially β-
and α- carotenes. In comparison, other vegetable oils contain little amounts of
carotenoids, especially coconut, palmkernel, sesame, and groundnut oils have
very low content of carotenoids. The dark red-orange color of oil palm fruit is
due to the high concentration of carotenoids and anthocynanins. Crude palm
oil, extracted commercially by pressing, contains 400–1000 ppm of carot-
enoids, the variation being due to process conditions, species of oil palm,
and level of oxidation. Carotenoids in palm oil are α-carotene, β-carotene,
phytoene, phytofluene, cis β-carotene, cis α-carotene, δ-carotene, γ-carotene,
ζ-carotene, neurosporene, β-zeacarotene, α-zeacarotene, and lycopene (Table
2.8) (Yap et al., 1991; Jalani et al., 1997). Carotenoids are fat-soluble nutri-
ents and categorized as either xanthophylls or carotenes according to their
chemical composition. Carotenoids are singlet oxygen quenchers and protect
the oil from photo-oxidation (Psomiadou & Tsimidou, 1998).

TABLE 2.8 Composition of Carotenoids in Palm Oil, Given as % of Total Carotenoids (Yap
et al., 1991; Jalani et al., 1997).
Carotenoids Elaeis guineesis variety Elaeis oleifera variety crude
crude palm oil palm oil
Total (ppm) 500–700 4300–4600
Phytoene 1.27 1.12
Cis β-carotene 0.68 0.48
Phytofluene 0.06 Trace