Naturally Occurring Carotenoids In Plant And Animal Foods

In plant foods, carotenoids exist in various physical and morphological states depending on the carotenoid and the commodity. In leafy vegetables, carotenoids are associated primarily with chloroplasts as integral components of the photosynthetic apparatus. In fruits, roots, and tubers, carotenoids associate with chromoplasts or other intracellular structures, although the precise nature of their molecular orientation is largely uncharacterized (27). Most plant-associated carotenoids appear to exist in complexa-tion with proteins or polysaccharides, rather than as true solutions in oil droplets. Although most common vegetable oils contain low concentrations of soluble carotenoids that impart yellow hues, a notable exception is the highly pigmented red palm oil, which is used sparingly in foods in some tropical countries.

Sources of Variation in Carotenoid Content of Plant Foods

Published data on the carotenoid content of fruits and vegetables reflect considerable variation for most species. For example, the ^-carotene content (mg per 100 g fresh weight) has been reported to vary from 4 to 10 for carrot, 0.3 to 8.0 for tomato, and 0.1 to 5.2 for sweet potato (28). Variety, maturation, source, and analytical accuracy all contribute, in usually unknown proportions, to the reported variation. Recently, a carotenoid composition database was compiled by the USDA Food Composition Laboratory that contains updated analytical data for many fruits, vegetables, and processed foods available in the United States (29). The data were obtained predominantly by HPLC, in some cases with structural verification by mass spectrometry. A compilation of existing data on carotenoid content of foods available in other countries is also available (30), although much of these data were obtained by methods that do not clearly distinguish between different carotenoids or carotenoid isomers. Older analytical techniques often overestimate the provitamin A carotenoid content of foods, particularly fruits (31). Actual varietal differences in /i-carotene content can be as high as 100-fold in carrots and tomato, and breeding techniques have increased the /^-carotene content of sweet potatoes by threefold in the past 50 years (28). Several tomato varieties are now marketed with widely varying concentrations of ly-copene and yS-carotene.

Data concerning seasonal variation in carotenoid content have been reported for many plant foods, including carrot, kale, lettuce, snap beans, and turnip greens. In general, carrots harvested in summer contain higher levels of carotenoids than those harvested in winter months, whereas leafy and green vegetables exhibit the opposite effect of season (28). The effect of maturation on the carotenoid content of plant foods also varies by commodity. In general, carotenoid concentration of fruits and nonleafy vegetables increases with maturity, whereas that of leafy vegetables increases to a lesser extent or decreases (28). Postharvest losses of carotenoids in fruits and vegetables tends to be low. For example, the loss of ^-carotene in fresh broccoli and green beans is very slight up to 9 days after harvest under typical refrigeration conditions (32). However, physical damage to fresh plant foods that disrupts normal compartmentalization can release lipoxygenases and increase exposure to oxygen or light, resulting in carotenoid oxidation and changes in product hue (5,33).

Carotenoids in Animal Foods

Dietary intake of carotenoids from animal foods is low compared to that from plant foods because of the relatively low rates of deposition of feed-associated carotenoids in most animal tissues. Tissue concentrations are entirely dependent on the carotenoid content of the feed. In animal foods, the carotenoids are localized predominantly in adipocytes, and thus generally accumulate in fatty tissues to a greater extent than in lean tissues. Animal food sources of carotenoids include egg yolks, chicken, certain fish such as salmon, and crustaceans. Xanthophylls tend to be the predominant carotenoids in animal foods, because their efficiency of tissue deposition is usually higher than that of the carotenes. Examples of the deliberate pigmentation of animal tissues using carotenoids include the use of yellow corn or marigold extracts in chicken feed and crab (or shrimp) shell waste or synthetic astaxanthin in shrimp and salmon feeds (34).

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