Carotenoide

El carotenoide licopeno confiere su color rojo al tomate.

Los carotenoides son pigmentos orgánicos que se encuentran de forma natural en plantas y otros organismos fotosintéticos como algas, algunas clases de hongos y bacterias. Se conoce la existencia de más de 700 compuestos pertenecientes a este grupo.

Los de carbono, aunque no todos los carotenoides se ajustan estrictamente a esta regla. Estos átomos de carbono se encuentran ordenados formando cadenas poliénicas conjugadas en ocasiones terminadas en anillos de carbono. A los carotenoides que contienen átomos de oxígeno se les conoce más específicamente como xantofilas. Los restantes constituyen el grupo de los llamados carotenos.

Su color, que varía desde amarillo pálido, pasando por anaranjado, hasta rojo oscuro, se encuentra directamente relacionado con su estructura: los enlaces dobles carbono-carbono interactúan entre sí en un proceso llamado conjugación. Mientras el número de enlaces dobles conjugados aumenta, la longitud de onda de la luz absorbida también lo hace, dando al compuesto una apariencia más rojiza. Por ejemplo, el fitoeno que posee únicamente tres enlaces dobles conjugados absorbe luz en el rango ultravioleta y apareciendo por tanto incoloro a la vista, el licopeno, compuesto que confiere su color rojo al tomate contiene 11 enlaces dobles conjugados. Existen también carotenoides de color verde (ζ-Caroteno), amarillo (β-caroteno), y anaranjado (neurosporaxantina).

En organismos fotosintéticos los carotenoides desempeñan un papel vital en los centros de reacción, ya sea participando en el proceso de transferencia de energía, o protegiendo el centro de reacción contra la autooxidación. En los organismos no fotosintéticos, los carotenoides han sido vinculados a los mecanismos de prevención de la oxidación.

Los animales son incapaces de sintetizar carotenoides y deben obtenerlos a través de su dieta, siendo estos compuestos importantes por su función biológica como pro-vitamina A.

Como ejemplo de estos compuestos en la naturaleza, podemos citar al carotenoide mejor conocido, el que da al grupo su nombre, el caroteno, encontrado en zanahorias y responsable de su color anaranjado brillante. El color rosado del flamenco y el del salmón, y la coloración roja de las langostas, también son producidos por carotenoides.

Entre las aplicaciones más importantes de los carotenoides podemos mencionar su uso como pigmentos naturales, así como su papel como complemento alimenticio.

editorial:shenny

Obtenido de "http://es.wikipedia.org/wiki/Carotenoide"Categorías: Carotenoides | Bioindicadores | Colorantes alimentarioslast change: 07/31/2003 08:50:00

Phenolic Compounds

Like all the groups reviewed until now, this one does also consist of a large number of molecules of heterogeneous structure. Their common feature is the presence of at least one hydroxyl-substituted aromatic ring system.

Most phenolic compounds belong to the flavonoids. Lignin, the primary substance of wood, is the most common member of this group. The following table outlines the most important groups of plant phenolic compounds.

Flavonoids: In 1975, the number of identified flavonoids was estimated to be larger than 2000. Some important representatives and their biological significance are listed in

the table below.

The basic structure of flavonoids is derived from the C15 body of flavone. They differ from other phenolic substances in the degree of oxidation of their central pyran ring. And, very fundamentally, also in their biological properties. While some classes (the flavonones, for example) are colourless, the members of other classes (the anthocyanes, for example) are always coloured and known as pigments of flowers or other plant parts. Anthocyanes are normally red or yellow, their colour is pH-dependent. Blue

pigments are achieved by chelate formation with certain metal ions (FeIII or AlIII, for example).

The variability of the flavonoids is largely based on the hydroxylation and/ or methylation pattern of the three ring systems. A correlation between two flavonoids points often to a relationship between the producing plant species. They have therefore proven to be suitable traits for the study of the phylogenetic relations between higher

plants. The quinones are another group of phenolic compounds. We have already met some of its members that function as co-factors. Accordingly, they do not actually belong to the secondary plant products but have to be counted among those of the basic metabolism. As has been mentioned before, phenolic compounds occur usually not unbound within plant tissues. They are mostly coupled to other molecules, often to glucosyl residues, but to sulphate- or acetyl-residues, too. One of the reasons may be that they are toxic when in a free state and are detoxified, at least partially, if coupled. Many low molecular weight compounds, for example thymol, are used in medicine as antiseptics due to their toxicity. Different types of bonds between flavonoids (for example anthocyanes) and a glycosyl residue lead to different derivatives that increase the range of flower colours (and colour shades). The glycosylation of flavonoids has an additional, ecologically not less important function. It has been brought into connection with pest protection and protection against other animals. Based on their biological functions, phenolic compounds can be classified as follows:

The Ecological Meaning of Some Phenolic Compounds for Plants

function group

example(s) and plant species

where the effect was studied

flower pigments

anthocyanes

chalcons

aurones

yellow flavonoids

flavones

cyanidin-3,5-diglucosid in Rosa

coreopsin in Coreopsis tinstoria

aureusin in Anthirrhinum majus

gossypetine-7-glucoside in Gossypium

apigenin-7-glucoside in Bellis perennis

fruit pigments

anthocyanines

isoflavones

chalcons

petunidin glucoside in Atropa belladonna

osajin in Maclura pomifera

ocanin in Kyllingi brevifolia

allelopathic substances

quinones

phenols

phenolcarboxylic acids

hydrocinnamic acid

juglon in Juglans regia

hydroquinone in Arctostaphylos

sialic acid in Quercus falcata

ferulic acid in Adenostoma

protection against pests

quinones

tannines

flavonols

juglon in Carya ovata

gallotannine in Quercus robur

quercitine-glycosids in Gossypium

fungicide

isoflavones

phenolcarboxylic acids

dihydrochalones

luteon in Lupinus

protocatechunic acid in Allium

phloridcine in Malus pumila

phytoalexines

stilbens

phenylanthrenes

isoflavanes

pterocarpanes

phenylpropanoids

fucocoumarins

reservatrol in Arachis hypogaea

orchinol in Orchis militaris

vestitiol in Lotus corniculatus

pisatin in Pisum sativum

coniferyl alcohol in Linum usitiltissimum

psoralen in Petroselinum crispum

according to J. B. HARBORNE, 1980