The impact of singlet oxygen on lipid oxidation in foods - Oxidation in Foods and Beverages and Antioxidant Applications - page 69

added and 4 ppm of the photosensitizer chlorophyll. The emulsion was stored in
light and the oxidation was measured using a variety of end points. The
chlorophyll-photosensitized oxidation of the oil in the food model was also
significantly reduced by the addition of PC and was assigned to possible
quenching of singlet oxygen.
3.4.5 Natural antioxidants
Carotenoids
The influence of carotenoids on oxidation has been studied widely in diverse
food systems (Dondeena and Kilara, 1992). -carotene is considered to be the
most powerful physical singlet oxygen quenching agent in foods and is a
particularly effective quencher of singlet oxygen. One molecule of -carotene
can quench 250 to 1000 molecules of singlet oxygen (Foote, 1976). The rate of
singlet oxygen quenching by carotenes is highly dependent on the number of
conjugate double bonds in the carotenoid. Also the type and number of
functional groups on the ring portion of the molecule play an important role. The
importance of the functional groups is strongly linked to the solubility of the
carotenoids (Kobayashi and Sakamoto, 1999). Besides the solubility, the
effectiveness of carotenoids also depends on the number of double bonds in the
skeleton. A total of five carotenoids have been evaluated for their singlet oxygen
quenching efficacy in a chlorophyll-sensitized photooxidation of soybean oil
(Lee and Min, 1990). The results showed that the effectiveness of the
carotenoids increased with the number of double bonds. Those carotenoids with
seven or fewer double bonds are ineffective as quenchers, being unable to accept
the energy from singlet oxygen. A comparison of quenching rates of several
polyenes and carotenoids has been reported (Beutner et al., 2000).
Polyphenols
Polyphenols have been generally known as quenchers of triplet oxygen.
However, several studies shown that some polyphenols can also inhibit singlet
oxidation. Tea catechins have been found to quench singlet oxygen in an ethanol
solution (Mukai et al., 2005) and other plant extracts such as from Piper Betel
have been shown to delay light induced photooxidation (Bhattacharya et al.,
2007).
3.5 Vitamin loss in foods due to singlet oxygen
3.5.1 Vitamin D
Vitamin D plays a key role in the normal mineralization and growth of bones. Its
mode of action is linked to the stimulation of calcium absorption in the intestine.
Milk is frequently fortified with vitamin D because it is an important source of
calcium. Unfortunately, this vitamin is rapidly destroyed under light storage
(United States Public Health Services/Food and Drug Administration, 1993).