Examples of some food sources of major carotenoids in the North American Diet.
1. Introduction
Global dietary guidelines recommend increased consumption of plant-based foods as a good source of essential nutrients, such as vitamins and minerals. However, recent research has shown that plants also contain a wide variety of biologically active compounds other than the essential nutrients that may play an important role in human nutrition and health. Over the past few decades, extensive research has been directed at identifying these biologically active compounds, their chemical properties, and biological activities and mechanisms of action. It is now recognized that consumption of these compounds is an important complimentary approach in the prevention, treatment, and management of several of human diseases. Although, technically they are not recognized as nutrients but are referred to as “phytonutrients,” “nutraceuticals,” “functional ingredients,” and “beneficial bioactive compounds” [1]. The scope of these compounds has now expanded beyond foods to include therapeutics, pharmaceuticals, and cosmeceuticals. Unlike essential nutrients, there are no recommended levels of daily intake for these compounds as of now. Several thousand phytonutrients have been identified as being present in plants. Although not all of them have been studied in detail, two classes of the phytonutrients that have been studied extensively include the water-soluble and the fat-soluble carotenoids [2]. The focus of this book is in the area of carotenoids and their role in human nutrition and health.
Carotenoids are organic pigments produced mainly by plants. However, some algae, bacteria, and fish have also been known to contain carotenoids. They are responsible for a full spectrum of colors all the way from yellow to red. The recent recommendation by health professionals to consume multicolored foods reflects the importance of carotenoids as an important part of a healthy diet [3]. Over 1000 carotenoids have so far been identified and classified into xanthophylls containing oxygen in their molecule and carotenes contain no oxygen. Carotenoids, amongst which β-carotene is an important and well-known carotene. Other important carotenes include α-carotene, lycopene, β-cryptoxanthin, and lutein. They contain eight isoprene molecules and 40 carbon atoms. One of the characteristic features of carotenes is the presence of multiple, ranging from 9 to 11, conjugated double bonds [2, 4].
The typical chemical structure of β-carotene is shown in Figure 1.
Humans cannot synthesize carotenoids in their bodies and must get them from their diet. Many studies have shown that low intake of carotenoids, low concentration of serum carotenoids, and low accumulation of carotenoids in various organs, such as skin and eyes, are risk factors for developing the abovementioned disorders. Taking carotenoid-rich foods and supplements has been shown to reduce these risks [5].
The antioxidant property of carotenoids is associated with the presence of these conjugated double bonds. Oxidative damage is closely associated with inflammatory damage of tissues, and in turn, with initiation and progression of several human chronic diseases [6, 7, 8, 9]. To understand the role of carotenoids in human health, several
Common carotenoids, their food sources, and amounts are shown in Table 1. The amounts shown in the table an approximation and vary depending on several factors.
Carotenoid | Food source | Amount (μgrams/100 grams) |
---|---|---|
Β-Carotene | Carrots, cooked | 9771 |
Spinach, cooked | 5300 | |
Green collard | 5400 | |
Cantaloupe | 3000 | |
Β-Carotene | Beet greens | 2500 |
Apricot, dried | 2192 | |
Broccoli, cooked | 1300 | |
Tomato, raw | 520 | |
Α-Carotene | Carrots, cooked | 3723 |
Lycopene | Tomatoes, raw | 3100 |
Tomato juice | 10,000 | |
Tomato pasta | 36,500 | |
Tomato ketchup | 12,390 | |
Tomato sauce | 13,060 | |
Β-Cryptoxanthin | Tangerine | 1060 |
Papaya | 470 | |
Lutein | Spinach, cooked | 12,475 |
Green collard | 16,300 | |
Beet green | 7700 | |
Broccoli, cooked | 1839 | |
Green peas, cooked | 1690 |
2. Challenges and future research
Since the discovery of β-carotene in carrot juice almost two centuries ago, several thousand more carotenoids have now been identified. Over the past couple of decades, a great deal of advancement has been made in terms of our understanding the role of carotenoids in human health. Studies have produced information in terms of the chemical and biological properties of carotenoids, their dietary sources, and mechanisms of action. Martini et al. [10] in 2022 provided insight into the future directions in research related to carotenoids. Similarly, Melendez-Martinez et al. [11] and Rocha et al. [12] also pointed out to the need for future research on carotenoids and human health.
In recent years, a few of the carotenoids have been subjected to basic, preclinical, and clinical investigations to understand their role in human nutrition and health. More new knowledge about carotenoids is now being generated relating to their chemistry, dietary and supplemental sources, biological properties, mechanisms of action, and their role in human health. However, there is still a need for clear understanding about the results, particularly from limited number of interventional clinical studies.
Recognizing the need for more recent information, this book is being published to present the readers up to date knowledge on carotenoids, including techniques of isolation; characterization of their chemical, physical, and biochemical properties; sources; mechanisms of action; and basic
Some of the biological mechanisms and disease prevention of carotenoids are shown in Table 2.
Biological actions of carotenoids | Examples of disease prevention |
---|---|
Antioxidant function | Cancer |
Anti-inflammatory function | Diabetes |
Provitamin A activity | Cardiovascular diseases |
Immune response | Cataract and other ophthalmic disorders |
Gap junction communication | Human immunodeficiency viruses (HIV) |
Drug metabolism | Age-related macular degeneration (AMD) |
UV Protection | Neurogenerative diseases |
Antimicrobial | Respiratory disorders |
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