Carotenoids, naturally occurring

Carrot oil—The Hquid or the soHd portion of the mixture, or the mixture itself obtained by the hexane extraction of edible carrots (Daucus carota L.) with subsequent removal of the hexane by vacuum distillation. The resultant mixture of soHd and Hquid extractives consists chiefly of oils, fats, waxes, and carotenoids naturally occurring in carrots. 

Carotenoids Naturally occurring tetraterpenoid compounds found in plants and animals. 

FIGURE 18.2 Names and structures of the fat-soluble vitamins and pro-vitamins A carotenoid naturally occurring in foods, (a) Vitamins A and D (b) vitamins E and K.p... 

Carotenoids (Section 26 16) Naturally occurring tetrater penoid plant pigments... 

One of the few phytochemicals that has been subjected to the rigorous testing procedures required by food safety authorities is P-carotene, a naturally-occurring carotenoid that is also a pre-cursor of vitamin A in humans. It is increasingly used as a food colour since the food product can be claimed to contain all natural ingredients. For this reason, detailed toxicological studies were undertaken that enabled the Joint FAO/WHO Expert Committee for Food Additives (JECFA) to set an ADI of 0-5 mg/kg/bw/day based on a NOAEL of 50 mg/day and the application of an uncertainty factor of 10 (JECFA, 1974). This low factor was used because it was argued that the compound occurred naturally in food, that its use as a food additive would not lead to a substantial increase in the total amount normally consumed, and that there had been no reports of adverse effects in humans. The ADI would correspond to an acceptable intake in humans of up to 350 mg/day. 

Subsequent cyclizations, dehydrogenations, oxidations, etc., lead to the individual naturally occurring carotenoids, but little is known about the biochemistry of the many interesting final structural modifications that give rise to the hundreds of diverse natural carotenoids. The carotenoids are isoprenoid compounds and are biosynthesised by a branch of the great isoprenoid pathway from the basic C5-terpenoid precursor, isopentenyl diphosphate (IPP). The entire biosynthesis takes place in the chloroplasts (in green tissues) or chromoplasts (in yellow to red tissues). 

Seventy naturally occurring carotenoid epoxides have been referenced and 43 of them have been fully characterized. These compounds can be formally considered oxidation products as defined above, but they first have the status of carotenoids. They are indeed found in vivo and are possibly biosynthesized from the corresponding non-oxidized carotenoids. If carotenoids containing epoxide functions have been found in humans, the epoxidation reaction has not yet been proven to occur in humans. 

Some 117 naturally occurring apo-carotenoids, 88 of which have been fully identified and another 6 naturally occurring seco-carotenoids have been referenced as carotenoids, thus representing around 15% of the carotenoids numbered to date (see Figure 3.3.1). This subfamily of carotenoids would be even larger if we consider the retinoids andnorisoprenoids. However, these compounds are excluded by nomenclature rules that dictate that they are not deemed to be carotenoids because of the absence of two central methyl groups (at C20 and C20 ). Retinoic acid, retinal. 

There are few naturally occurring oxidation products that do not belong to the families of epoxides or apo-carotenoids. One of those is the metabolite of lycopene known as 2,6-cyclo-lycopene-1,5 diol found in human plasma and at lower levels in tomato products. ... 

Ruhl, R. et al.. Carotenoids and their metabolites are naturally occurring activators of gene expression via the pregnane X receptor. Fur. J. Nutr, 43, 336, 2004. 

After a short presentation of naturally occurring oxygenated cleavage compounds, we describe different ways by which they can be formed starting from the parent carotenoid, and we give some information on their mechanisms of formation when available in the literature. 

The photostability of the natural occurring 9 -cis carotenoids bixin and norbixin, Ligure 12.5, has received the attention of several research groups (Najar et al. 1988, Pimentel and Stringheta... 

Carotenoids are a group of more than 750 naturally occurring molecules (Britton et al. 2004) of which about 50 occur in the normal human food chain. Of these, only 24 have, so far, been detected in human plasma and tissues (Khachik et al. 1995), with only six molecules being abundant in normal human plasma (for chemical formulas see Figure 13.1). Carotenoids are subdivided into two main classes the carotenes, cyclized (e.g., P-carotene) or uncyclized (e.g., lycopene) hydrocarbons, and the xanthophylls, which have hydroxyl groups (e.g., lutein and zeaxanthin), keto-groups (e.g., canthaxanthin), or both (e.g., astaxanthin) as functional groups. 

It is of interest to determine if it is the keto group of 3 -oxolutein that accounts for this observation. Comparison of the uptake by ARPE-19 cells, and ultimately by RPE in situ, of other keto containing carotenoids, such as astaxanthin and canthaxanthin, to find out whether ARPE-19 cells exhibit similar behavior toward all keto carotenoids may provide insights into transport mechanisms. Canthaxanthin and astaxanthin are naturally occurring carotenoids and are used in the food industry to add color to foods such as sausage and fish and as such are part of the human food chain. 

Naturally occurring compounds such as phytochemicals, which possess anticar-cinogenic and other beneficial properties, are referred to as chemopreventers. One of the predominant mechanisms of their protective action is due to their antioxidant activity and the capacity to scavenge free radicals. Among the most investigated chemopreventers are some vitamins, plant polyphenols, and pigments such as carotenoids, chlorophylls, flavonoids, and betalains. Resolution of the potential protective roles of... 

These assays measure the level of protection provided to the naturally occurring carotenoid derivative crocin from bleaching by the radical generator AAPH. The assay was originally suggested by Bors and others (1984) and modified by Tubaro and others (1998), who used it to show that plasma antioxidant capacity is deeply influenced by the consumption of wine. The addition of a sample containing chain-breaking antioxidants results in the decrease in the rate of crocin decay. The sample is monitored for 10 min at 443 nm. 

There is considerable current research under way to determine if the synthetic carotenoids have the same physiological effects, and consequent health benefits, as the naturally occurring compounds. If this proves to be true, we can expect increased interest in this group of colorants. 

---