BLBS102-c37 BLBS102-Simpson March 21, 2012 14:15 Trim: 276mm X 219mm Printer Name: Yet to Come
716 Part 6: Health/Functional FoodsBetaninOH
OOON O–
+N+OHOH
HOHOOHOHN H N H N H
O OO NH 2OOOOOO OHO–HOOHOHHONH
HHHHVulgaxanthinIndicaxanthinFigure 37.8.Structures of some common betalains.betalains have anticancer properties by virtue of their antiox-
idant and free radical scavenging behavior. They have been
shown to inhibit redox state alteration induced by cytokines
to protect the endothelium layer that line the internal surfaces of
blood vessels. The content of betalains in samples may be mea-
sured by the HPLC and LC-MS/MS analyses (Stintzing et al.
2006).MELANINS
Properties and FunctionsMelanins are dark brown and black pigments found in plants,
animals, and microorganisms. They are formed via the enzy-
matic oxidation of phenolic compounds, for example, tyrosine,
through several intermediates like DOPA and quinones, followedby polymerization to form the large molecular weight melanins.
The enzymes catalyzing the oxidation of the phenolic com-
pounds are polyphenoloxidases, also known as phenolases or
tyrosinases. In animals and humans, melanins occur in the eyes,
hair, skins, and peritoneal lining where they protect tissues from
the detrimental effects of factors like light or UV radiation from
the sun’s rays. Damage from UV radiation is potentiated in vari-
ous ways such as dimerization of thymine in DNA molecules, or
by the effects of reactive O 2 species (e.g., singlet O 2 and super-
oxide radicals (Jagger 1985, Tyrell 1991). Examples of melanins
are eumelanin and pheomelanin. Pheomelanin is dark red-brown
in color and is thought to be responsible for red hair and freckles
in humans, while eumelanin imparts black and brown coloring
to skin and hair (Meredith and Riesz 2004).
Microorganisms synthesize melanins as part of their normal
metabolism, from where they are passed along the food chain
to higher forms of life. In crustacea, the formation of melanins
is sometimes referred to as melanosis or “blackspot” formation,
and connotes spoilage to consumers—mainly due to their lack
of visual appeal. The “blackspot” phenomenon has been exten-
sively studied to develop strategies to control this undesirable
effect and products such as glucose oxidase, glucose, catalase
mixes, or 4-hexyl resorcinol were found to be effective in con-
trolling blackspot formation in raw shrimp (Ogawa et al. 1984,
Ferrer et al. 1989, Yan et al. 1989, Chen et al. 1993, Benjakul
et al. 2005). Nevertheless, these same compounds are desirable
in other situations, such as protecting against UV radiation from
sunlight to prevent damage to the skin and also to minimize glare
in the eyes. This feature of melanin has been exploited by Pho-
toProtective Technologies (United States) in making a variety
of eye wear that filter out colors to reduce the risks of macular
degeneration and cataracts (Anon 2005). Melanin has also been
incorporated in a hair dye, Melancor-NH, for darkening gray
hair in humans.Melanins and HealthMelanin deficiency in humans has been linked with certain ab-
normalities and diseases. Examples include oculocutaneous al-
binism that is characterized by reduced levels of the pigment in
the eyes, hair, and skin, and ocular albinism that affects both eye
pigmentation and visual acuity (Peracha et al. 2008). Melanin
deficiency has also been linked to deafness (Cable et al. 1994)
and Parkinson’s disease (Nicolaus 2005).Measurement of MelaninsMelanin measurements may be carried out by spectrofluorom-
etry (Rosenthal et al. 1973) by measuring the fluorescence in-
duced by excitation at 410 nm and emission at 500 nm, or by
spectrophotometric measurement of the rate of melanochrome
production from 5,6-dihydroxyindole-2-carboxylic acid and 5,6-
dihydroxyindole systems at 540 and 500 nm (Blarzino et al.
1999). Melanin in tissues may also be measured based on spec-
trophotometry, HPLC, and electron spin resonance spectroscopy
(Ito 2006, Hu et al. 1995).