Carotenoids: What They Are and Why They Are Challenging to Formulate with?
Carotenoids belong to a group of compounds called phytochemicals. These compounds are responsible for disease protection in plants. They are essential for photosynthetic organisms as they provide protection from too much light and have antioxidant properties. Aside from photosynthetic organisms like plants, algae, and cyanobacteria, some members of fungi and non-photosynthetic bacteria can also produce carotenoids.
Beta carotene is the most popular carotenoid, commonly used as a colorant for the yellow-orange color in various foods (Francis, 1996; Ngamwonglumlert and Devahastin, 2019). Other common types of carotenoids, such as lutein, zeaxanthin, and astaxanthin, can be found in algae, bacteria, and plants. Carotenoids added to food, feed, and dietary supplements can be challenging in these complex systems as well as storage conditions, which can affect the solubility and stability of these compounds.
Sources and Types of Carotenoids
Carotenoids are of great interest in the food, animal feed, and dietary supplement industries for a variety of reasons, but they are most often used for their pigmentation properties for products seeking to use naturally derived pigment sources. Their distinct and vibrant colors seen in nature have attracted many ingredient manufacturers to source and produce extracts for further formulations in finished products.
Some foods containing carotenoids include carrots, yams, sweet potatoes, papaya, and mangoes. Animals and humans cannot manufacture carotenoids themselves. Certain animals live off carotenoid-rich plants resulting in strongly orange pigmented bodies. Salmon, for example, is a rich orange color due to their diet consisting of krill and shrimp. These krill and shrimp consume carotenoid-rich algae and phytoplankton.
When producing dietary supplements containing carotenoids, the industry faces challenges related to the bioavailability and absorption of carotenoid active compounds once consumed due to their stability during digestion. However, research and development of new forms, including novel encapsulation techniques, may prove helpful to combat this challenge.
Beta-carotene
Beta-carotene used in food production is obtained from the algae Dunaliella salina or fungi Blakeslea trispora. It is a vitamin A precursor and the most important of all the provitamins A (Clark, 2007).
However, processing might have positive and negative effects on beta-carotene. Due to isomerization and degradation, processing might decrease the stability of beta-carotene. Still, the same processing will also increase the bioaccessibility, or the amount of beta-carotene that can be released from the carrot matrix during digestion (Knockaert et al., 2015).
While beta-carotene is most often used for coloring, other carotenoids are most often used for dietary supplements.
Lutein
Lutein can be found in several organisms, from yeasts to algae to plants. Due to its antioxidant potential and role in preventing age-related macular degeneration, it is a compound of interest in pharmacology, dietary supplements, food, and animal and fish feed industries.
In the feed industry, their main applications are to brighten the poultry feathers and deepen the color of egg yolk. However, due to the instability and chemical changes that can happen to lutein during food processing, its use in the food industry is limited. The different conditions in food processing, such as light, extreme pH, oxygen levels, and high temperatures, can affect the integrity of lutein (Ochoa Becerra et al., 2020).
To compensate for the decrease in the total concentration of lutein during the food process, researchers aim to increase the bioavailability of lutein instead. Several studies aimed to compare different preparations of lutein and their effects on bioavailability once inside the body. For instance, lutein encapsulated polymeric chitosan twice increased lutein concentration in the plasma, liver, and eye (Arunkumar et al., 2013). More stable preparation of lutein through hydrophilic nanoemulsions can also increase plasma lutein concentration by 1.3x compared to those delivered in pill form (Ochoa Becerra et al., 2020).
Zeaxanthin
Zeaxanthin primarily acts as a bacterial metabolite, a cofactor in bioprocesses, and an antioxidant. It is derived from a hydride of beta-carotene. Zeaxanthin, together with lutein, primarily make up the xanthophyll carotenoids found in the retina of the eye. They are also the predominant component of the central macula.
Lutein and zeaxanthin (L/Z) are therefore responsible for the fine-feature vision of the eyes. These carotenoids can be obtained through dietary sources, but other factors like absorption and bioavailability once inside the body complicate their supposed functions.
For instance, the consumption of fats like olive oil, salad dressings, or whole eggs with food rich in zeaxanthin can increase the absorption of the carotenoid. On the other hand, competition of absorption between carotenoids in the same meal, consumption of pectin and sugar, and certain localization of carotenoids within the chloroplasts and chromoplasts may decrease the bioavailability of zeaxanthin and lutein. Finally, cooking can decrease the content but increase the bioavailability of carotenoids in food (Eisenhauer et al., 2017).
Astaxanthin
Astaxanthin is an oxygenated carotenoid known for its potent antioxidant activity, which is ten times higher than that of other carotenoids. In vitro studies showed that astaxanthin is an effective reactive oxygen species (ROS) and nitrogen species quencher.
As such, this carotenoid is extensively applied in foods, dietary supplements, cosmetics, and feed. The United States Food and Drug Administration (US FDA) approved astaxanthin as a feed additive for use in aquaculture in 1987. In 1999, it was approved as a dietary supplement (Hu, 2019).
Despite these functions, astaxanthin has a low oral bioavailability unless incorporated in lipid or lipophilic compounds. In a study by Odeberg et al. (2003), the researchers found that the highest bioavailability of astaxanthin can be obtained by formulating it with high content of hydrophilic synthetic surfactant polysorbate 80.
What Factors Affect Carotenoids?
Several conditions and factors affect the concentration, bioavailability, and absorption of carotenoids. Jintasataporn and Yuangsoi (2012) studied the stability of carotenoids during feed processing and under different storage conditions. They measured the stability of total carotenoid content in feed production. The researchers found that the total carotenoid content was quite stable with or without antioxidants until the processing of dried feed.
Oxidation Reactions
Enzymatic and non-enzymatic oxidation is the primary cause of carotenoid destruction during the processing and storing of dietary carotenoids. Enzymatic oxidation converts oxidized metabolic products into hydrogen peroxide (H2O2) and then to water using iron, zinc, copper, and manganese as cofactors. Non-enzymatic oxidation, on the other hand, terminates the free radical chain reactions and results in the formation of vitamin E, A, C, flavonoids, glutathione, carotenoids, and other phytochemicals.
An increase in enzymatic oxidation results in the loss of provitamin A activity due to oxidation during product processing.
Temperature
Thermal processes break down cell walls and enhance the bioavailability of carotenoids. It also increases the isomerization of b-carotene (Hwang et al., 2012). The pelleting process requires constant heat and air to hasten the process and retain nutrition. Haaland and his colleagues also found that the optimal temperature for drying pellets should be at temperatures not exceeding 190 °F or 87.8 °C.
Light
Studies found that dark storage maintains the stability of carotenoids as intense light intensity (1875-3000 lux) accelerates carotenoid loss. Illuminated environments increase the degradation of carotenoids through oxidative reactions (Atencio et al., 2022).
Heat, light, and oxygen are the primary factors that contributed to the total carotenoid degradation during storage (Jintasataporn and Yuangsoi, 2012). As such, factors during packaging such as minimal oxygen conditions, use of antioxidants, choice of light sources, and storage temperature must be considered to optimize the retention of carotenoids in food products.
Why Is It Difficult to Add Carotenoids to Foods and Supplements?
The main struggles with using carotenoids in food, feed, and supplement products are their low water solubility and stability. As such, newer techniques and formulations of carotenoid ingredients have been developed over the years to overcome these issues. Some novel solutions include interesting formulations using encapsulation or emulsion techniques as well as formulations with hydrophilic substances to increase solubility in water, or lipid-based formulas to improve the stability of the compounds.
Proper temperature, lower oxygen levels, and decreased light exposure can also retain much of the carotenoids found in food products and supplements. During storage, the optimal temperature and absence of antioxidants are essential to retaining the carotenoid concentration.
Carotenoids found in plant sources are in all-trans-form, but if your finished product requires heat, it can produce other isomers of the compound. There is generally a low bioavailability of carotenoids in foods, as the former is associated with proteins in the plant matrix. Food processing techniques like homogenizing, chopping, and pasteurization can disrupt this matrix and increase the bioavailability of carotenoids (Stahl et al., 1992). Wache and colleagues (2003) found that those cleaved to form 9-cis-isomers produced more DHA (antioxidants) than those that produced all-trans-b-carotene.
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