Lutein is part of the xanthophyll family of carotenoids, typically found in flowers, grains, fruits, and vegetables like spinach and kale. It is widely used in pharmaceuticals, dietary supplements, food, and animal and fish feed industries. Its primary application is enhancing poultry feather colors and deepening egg yolk yellow. However, lutein's use in the food industry is limited due to its instability and chemical changes during food processing. High temperatures, oxygen, light, and extreme pH levels can degrade lutein, affecting its integrity.
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Lutein: Chemical and Biological Properties
Pure lutein is a yellow-orange crystalline, lipophilic solid with the chemical name β, ε-carotene-3,3'-diol (C40H56O2). Lutein's conjugated carbon-carbon double bonds allow free electron movement, causing light absorbance in the blue region of the visible spectrum, giving it a strong yellow-orange color. Lutein generally coexists with its stereoisomer zeaxanthin, with the all-trans isomer being the most stable in nature.
Fig. 1 Structure of all-trans lutein (Becerra M.O., et al. 2020).
Lutein can be esterified or non-esterified with fatty acids, most commonly palmitic acid. Esterified carotenoids are less susceptible to degradation but are not adequately absorbed by the GIT. In marigold flowers, lutein is mainly found in its esterified form and must be purified to its free form after extraction with solvents.
Due to its intense yellow color, lutein is widely used as a natural food colorant. However, its low stability has slowed its integration into the food industry, prompting methods to increase stability.
Lutein's Health Benefits
Eye Health
Lutein and its isomer zeaxanthin are essential for eye health, particularly in preventing age-related macular degeneration (AMD). These carotenoids accumulate in the macula of the retina, where they filter harmful blue light and quench reactive oxygen species. Studies have shown that higher dietary intake of lutein is associated with a reduced risk of AMD and cataracts. This protective effect is attributed to lutein's antioxidant properties, which help maintain retinal health by preventing oxidative damage.
Cardiovascular Health
Lutein's benefits extend beyond eye health to cardiovascular health. Its antioxidant capacity helps reduce oxidative stress, inflammation, and dyslipidemia, all of which are risk factors for cardiovascular diseases. Research has demonstrated that higher blood concentrations of lutein are linked to a lower risk of coronary heart disease and stroke. This highlights lutein's potential in promoting heart health through its inclusion in functional foods.
Infant Nutrition
Lutein is also crucial for infant nutrition, particularly for visual and cognitive development. Breastfed infants typically have higher blood concentrations of lutein compared to those fed with unfortified formula, underscoring the importance of lutein in early development. Including lutein in infant formulas can help ensure adequate intake for infants who are not breastfed, supporting their overall growth and development.
Challenges in Lutein Integration
Stability Issues
Lutein's integration into food products is hindered by its instability under various conditions, such as high temperatures, light, and oxygen. Food processing methods, including cooking and storage, can significantly degrade lutein, reducing its effectiveness. For instance, high temperatures during boiling, sautéing, or steaming can lead to substantial lutein loss. Light exposure can also cause photodegradation, resulting in the formation of colorless compounds that diminish its nutritional value.
Bioavailability Concerns
Bioavailability refers to the portion of a nutrient that enters systemic circulation and is available for physiological functions. Lutein's bioavailability is influenced by its absorption rate, which is often low due to its lipophilic nature. To be absorbed, lutein must be incorporated into mixed micelles in the gastrointestinal tract (GIT). The food matrix, dietary components, and processing methods can either enhance or inhibit this process, affecting the overall bioavailability of lutein.
Enhancing Lutein Stability and Bioavailability
Emulsion-Based Delivery Systems
Emulsion-based delivery systems, such as oil-in-water emulsions, nano-emulsions, microencapsulation, and liposomes, have been developed to improve lutein's stability and bioavailability. These systems protect lutein from degradation by isolating it from adverse conditions and enhancing its solubility and absorption in the GIT. For example, encapsulating lutein in liposomes can increase its bioavailability by facilitating its incorporation into micelles, thereby improving its absorption rate.
Food Processing Techniques
Innovative food processing techniques can help preserve lutein during production and storage. Freezing, for instance, can minimize lutein loss compared to other methods. Adding antioxidants and using vacuum-sealed containers can further reduce degradation during storage. Additionally, optimizing cooking methods, such as steaming rather than boiling, can help retain more lutein in food products.
Marigold Flowers and Microalgae as Sources
Marigold flowers are a primary source of lutein, known for their high lutein content in the petals. However, harvesting and extracting lutein from marigolds is labor-intensive and requires significant solvent use. Microalgae, such as Chlorella and Dunaliella, are emerging as sustainable alternatives due to their rapid growth and high lutein content. These microalgae can be cultivated on a large scale, providing a more efficient and environmentally friendly source of lutein.
Applications and Future Directions
Fortification of Common Foods
Fortifying common foods with lutein can help address dietary deficiencies and promote public health. For instance, incorporating lutein into staple foods such as bread, cereals, and dairy products can increase its intake among the general population. This approach is particularly beneficial in regions with high prevalence of AMD and other lutein-related deficiencies.
Personalized Nutrition
Advancements in personalized nutrition offer new opportunities for optimizing lutein intake. Genetic factors can influence an individual's ability to absorb and metabolize lutein. By understanding these genetic differences, tailored dietary recommendations can be made to enhance lutein bioavailability and effectiveness. This personalized approach can ensure that individuals receive the maximum health benefits from lutein-rich foods.
Research and Development
Ongoing research is essential to further understand the factors affecting lutein stability and bioavailability. Investigating new food processing techniques and delivery systems can lead to innovative solutions for incorporating lutein into a wide range of food products. Additionally, exploring new sources of lutein, such as genetically engineered crops and novel microalgae strains, can provide more sustainable and efficient production methods.
Conclusion
Lutein is a valuable functional food ingredient with significant health benefits, particularly for eye and cardiovascular health. However, its low stability and bioavailability pose challenges for its incorporation into food products. Advances in food processing techniques and emulsion-based delivery systems can enhance lutein stability and bioavailability, making it more effective as a dietary supplement. Future research should focus on developing novel methods to preserve lutein's integrity and improve its absorption in the human body, ensuring that consumers can fully benefit from this important carotenoid.
Reference
- Becerra M.O., et al. Lutein as a functional food ingredient: Stability and bioavailability. Journal of Functional Foods. 2020, 66: 103771.
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