With rapid economic development and improved living standards, the demand for poultry products is increasing. People not only emphasize nutrition and taste but also pay attention to appearance, color, and physiological functions. However, as the growth rate of poultry accelerates and intensive farming becomes more prevalent, the use of natural pigments has decreased. This has resulted in a fading color of poultry products, failing to meet consumer expectations in terms of quality. To address this issue, coloring agents are gradually being applied to feed, with 8'-apo-β-carotenal gaining significant attention as an important feed coloring agent in recent years.
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Physical and Chemical Properties of 8'-Apo-β-Carotenal
8'-apo-β-carotenal with the molecular formula C30H40O and a molecular weight of 416.65, is a deep purple crystal or powder with a metallic luster. Its boiling point is 575.7°C, and its melting point is around 140°C, with a density of 0.949 g/cm3. It is sensitive to light and oxygen and should be stored in light-resistant containers filled with inert gas. 8'-apo-β-carotenal is soluble in chloroform, sparingly soluble in methanol and vegetable oil, and insoluble in water. It is a carotenoid compound with coloring properties and provitamin A activity.
Physiological Functions of 8'-Apo-β-Carotenal
Coloring Function
8'-apo-β-carotenal serves as an excellent natural pigment and coloring agent, widely used in pharmaceuticals, jams, ice cream, edible oils, and animal feed. In the feed industry, 8'-apo-β-carotenal acts as a coloring agent for poultry feed, effectively enhancing the color of egg yolks and improving the economic efficiency of poultry production.
Conversion to Vitamin A
Studies have shown that 8'-apo-β-carotenal possesses provitamin A activity and can be converted into vitamin A in the body. This conversion helps prevent and treat night blindness, prevents macular degeneration, and protects vision.
Induction of Cytochrome P450 1A
Natural 8'-apo-β-carotenal is metabolized from β-carotene in the body. Researchers found that it does not bind to the aromatic hydrocarbon receptor in mice but can induce the production of cytochrome P450 1A (CYP1A) through the aromatic hydrocarbon receptor-dependent pathway. This induction further participates in the metabolism of drugs, exogenous substances, and some endogenous substances.
Coloration Mechanism
In organic chemistry, there are numerous organic compounds containing π-bonded functional groups. These substances contain one or more groups with excess electrons, including C=C, C=O, C=S, C=N, N=N, etc. The unsaturation of these conjugated double bonds is a key structural feature of coloring agents such as carotenoids, lutein, lycopene, β-carotene, xanthophylls, 8'-apo-β-carotenal, and 8'-apo-β-carotenyl acetate. These structures exhibit absorbance of radiation above 200 nm and, with an increase in the number and types of these groups, experience a phenomenon known as redshift, thereby entering the visible light wavelength range. These groups responsible for imparting color to substances are termed chromophores or color-bearing groups.
Absorption and Metabolism
Absorption
Insufficient understanding of the absorption mechanisms of carotenoids has hindered the assessment of their bioavailability and their use as essential elements in animal experiments. Previous research studied the absorption mechanisms of non-provitamin A-active carotenoids, lycopene, and lutein, in experimental mice. The study, conducted in three parts, first involved continuous duodenal administration of lycopene and lutein emulsions to mice, with mesenteric lymph collected and analyzed every 2 hours. It was found that the absorption pattern of lycopene and lutein resembled that of triglycerides, with their concentrations in lymph reaching equilibrium within 6 hours. In the second experiment, mice were administered lycopene and lutein at concentrations of 5, 10, 15, and 20 µmol/L, showing a dose-dependent increase in their lymphatic concentrations. The average absorption rates of lycopene and lutein were 16% and 6%, respectively, and were not linearly related to the administered concentrations. The third experiment confirmed that there was no significant interference in the absorption of lycopene and lutein when both were administered to mice at a concentration of 20 µmol/L, validating that lycopene is absorbed through intestinal mucosal cells.
In addition, researchers have found that both major components of carotenoids, carotenes, and xanthophylls, are passively absorbed by animals and humans through passive diffusion. In the in vitro cell experiment model, emulsified and gelatinous forms of carotenoids were preferentially absorbed by intestinal epithelial cells, a process greatly influenced by dietary components and a critical factor in measuring the bioavailability of carotenoids in feed. However, some studies suggest that the absorption of carotenoids may not be simple passive diffusion but may involve other transport pathways.
Metabolic Transport
In metabolic transport, it is proposed that carotenoids undergo partial oxidation to retinal post-absorption. Through successive enzymatic actions including retinal dehydrogenase, lecithin retinol acyltransferase, and acyl-CoA retinol acyltransferase, retinal is converted to retinol and retinyl esters. These compounds eventually form chylomicrons, entering lymphatic circulation alongside fats before reaching the liver.
Detection Methods of 8'-Apo-β-Carotenal
Due to the significant economic importance of 8'-apo-β-carotenal, attributed to its outstanding physiological functions, its application prospects are vast. Despite no reported toxic incidents associated with 8'-apo-β-carotenal, the potential adverse effects of its extensive use on human health remain undetermined. To regulate the use of this coloring agent, researchers have established corresponding detection methods.
The detection of 8'-apo-β-carotenal can be carried out using spectrophotometry, providing qualitative identification and quantitative analysis methods. Qualitative identification includes three methods: solution identification, heating test, and reaction test, which can determine whether a powder is red, brown crystals, or crystalline fine powder of 8'-apo-β-carotenal. Quantitative analysis involves fully dissolving the sample using ultrasonic water bath method, followed by shaking with ethanol and chloroform, and finally quantifying the content of 8'-apo-β-carotenal through colorimetry at specific wavelengths.
Another method is high-performance liquid chromatography (HPLC). Researchers have utilized acetonitrile acidified with formic acid and dichloromethane for extraction, with a C18 column as the basis, and determination conducted using acetonitrile and formic acid solution, achieving high recovery rates and low standard deviations.
Conclusion
The utilization of 8'-apo-β-carotenal as a coloring agent in poultry feed has emerged as a viable solution to the fading color of poultry products. Its distinct physical and chemical properties, coupled with its physiological functions such as provitamin A activity and induction of cytochrome P450 1A, underscore its significance in enhancing both the appearance and nutritional value of poultry products. Furthermore, insights into its absorption and metabolic transport shed light on its effective utilization within the body. To ensure its safe application, detection methods such as spectrophotometry and high-performance liquid chromatography have been developed, offering reliable means for qualitative identification and quantitative analysis. Overall, the adoption of 8'-apo-β-carotenal represents a promising avenue to meet consumer expectations for quality poultry products in the face of evolving agricultural practices.
Reference
- Clark R. M., et al. A comparison of lycopene and canthaxanthin absorption: using the rat to study the absorption of non-provitamin A carotenoids. Lipids. 1998, 33: 159-163.
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