Tanumihardjo - Carotenoids and Human Health

Department of Nutritional Sciences, University of Wisconsin-Madison, 1415 Linden Dr, Madison, WI 53706, USA

Sara A. Arscott

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Key Points

A large number of epidemiological studies have linked diets rich in fruits and vegetables with reduced risk of cancer and other chronic diseases []. Information on individual- and population-level carotenoid intake relies on accurate knowledge about amounts in foods. For these reasons, the sources and content of carotenoids in food are of major interest to researchers, nutritionists, food processors, manufacturers, and consumers.

Over 700 carotenoids have been characterized in nature []. They are secondary plant compounds synthesized and localized in cellular plastids. Their major roles in plants are as accessory light harvesting pigments in chloroplasts of photosynthetic tissues, absorbing light mostly in the blue-green wavelength range, and in chromoplasts of non-photosynthetic tissues such as fruits, flowers, and roots. They also serve to mediate photoprotection through quenching the excess energy of chlorophyll or singlet oxygen and as an attractant to pollinators as in flowers.

Structurally, carotenoids are a related family of C40 isoprenoid polyene compounds, the majority of which are composed of eight isoprenoid units, like -carotene (Figure ). Hydrocarbons, such as - and -carotene, found in carrots, are referred to as carotenes and oxygenated derivatives, such as lutein and -cryptoxanthin, found predominantly in corn and tangerines, respectively, are referred to as xanthophylls. The most characteristic feature of carotenoids is their conjugated double-bond chain that forms a chromophore responsible for the characteristic colors ranging from colorless (phytoene), to yellow (lutein), orange (-carotene), and red (lycopene). This structure allows carotenoids to act in the energy transfer reactions of photosynthesis and as antioxidants.

Several tables and databases of the carotenoid content of foods have been compiled to aid in classifying certain carotenoids of interest and quantification of intake []. Analytical methods of carotenoid analysis have improved greatly in the last couple of decades and the use of high-performance liquid chromatography (HPLC) has facilitated more accurate separation and quantification of the wide array of different carotenoid pigments often present in a single food. However, inherent difficulties exist in accurately quantifying food carotenoids.

The carotenoid content of foods is highly variable and is affected by a number of factors including genotype (variety or cultivar), season, geography, cultivation variation, stage of maturity at harvest, and postharvest storage conditions. Thus, identifying absolute carotenoid content of a type of fruit, vegetable, or other food is not possible and should more reasonably be considered as a range of values. Additionally, processing of foods can lead to quantitative as well as qualitative changes because carotenoids are susceptible to isomerization and oxidation. Also, food processing and cooking can disrupt the matrix of a food which can have an impact on bioavailability and should be considered when evaluating intake. Lastly, while the analytical method itself is subject to several sources of error [] and the analytical effort behind the databases has helped to elucidate not only the levels but also the nature, distribution, and variability of food carotenoids.

This chapter serves as an overview of food sources of carotenoids, sources of variation in food carotenoids, and the effects of food processing and preparation on carotenoid stability.

Fruits and vegetables provide nearly 90 % of the carotenoid intake in the USA []. Three of these carotenoids, -carotene, -carotene, and -cryptoxanthin, can be converted to retinol (vitamin A) in the body and are referred to as provitamin A carotenoids. Quantification of these carotenoids in foods facilitates an understanding of fruit and vegetable sources of vitamin A. In the past, carotenoid quantification was focused on total vitamin A activity. With the recognition of beneficial effects of carotenoids on human health, independent of their vitamin A activity, accurate quantification of individual carotenoids has become paramount.

While this chapter is focused on the six predominant carotenoids, improvements in analytical techniques have led to more specific and detailed information on carotenoids such as phytoene in tomatoes []. The health implications of these carotenoids are not yet known.

In 1998, the United States Department of Agriculture (USDA) collaborated with the Nutrition Coordinating Center (NCC) at the University of Minnesota to release the USDANCC Carotenoid Database for the US Foods as an update to the original 1993 USDA-National Cancer Institute (NCI) Carotenoid Database [. It was originally developed from a review of published articles reporting food carotenoid values. Better analytical methods based on HPLC and more references in the literature allowed the 1998 release to improve upon the original database by including a greater variety of fruits and vegetables and a number of other sources of carotenoids in the US diet including eggs, butter, margarine, corn meal, and mixed dishes. Additionally, different forms of a particular food such as raw, cooked, canned, and frozen were separated unlike the earlier version which aggregated them.

The USDANCC database is the most comprehensive documentation of carotenoid content of a wide range of US foods to date, and was incorporated into the USDA National Nutrient Database for Standard Reference [ presents selected foods from that database. The database lists the food content of -carotene, -carotene, -cryptoxanthin, lycopene, and lutein plus zeaxanthin as g per 100 g fresh weight. Lutein and zeaxanthin, both oxygenated xanthophylls, are not always separated by some analytical techniques and often grouped together. Confidence codes associated with each carotenoid value were established as a summary of five quality indices (analytic method, quality control, number of samples, sample handling, and sampling plan). A confidence code of A means that the user can have considerable confidence in the value; B indicates some problems existed regarding the data that the values were based on, and C represents the lowest confidence based on limited quantity or quality of data. While a C rating is analytically acceptable, the value lacks the carotenoid variability inherent in food and may not be representative of available foods. Only 2 % of individual carotenoid values were assigned an A, 14 % B, and 84 % C. This suggests that as of 1999, there existed a considerable dearth of robust data on food carotenoids in the USA. As analytical techniques continue to improve and a wider variety of foods analyzed, it will be important to update databases such as the USDANCC database to reflect the range of carotenoid levels in foods.