Phytosterol esters are usually composed of phytosterols and fatty acids and also include other types of carboxylic acids such as ferulic acid and acetic acid. They are active substances with many physiological functions, synthesised by chemical, physical and biological methods. Esterification increases the solubility of phytosterols in oils and fats by about 20 times, while retaining the chemical structure and physiological functions of phytosterols and fatty acids. However, phytosterol esters still have disadvantages such as poor stability, poor water solubility and low bioavailability. Therefore, the research and development of a stable delivery system for phytosterol esters is of great importance to broaden their range of applications. The delivery system can not only effectively reduce the effects of environmental factors on phytosterol esters, but also solve the problems of poor stability, poor water solubility and low bioavailability, thus greatly expanding its application range. Currently, research is being carried out on the delivery of phytosterol esters using delivery systems in the food, medical and cosmetic fields. These delivery systems include nanoparticles, liposomes, microcapsules and emulsions. However, these delivery systems all have defects to varying degrees. Therefore, how to optimise the existing delivery systems so that phytosterol esters can exert ideal physiological functions in practical applications has become the focus of current research in the field of phytosterol esters.
Figure 1. Applications of phytosterol and phytosterol ester.(Cong Jiang, et al.; 2024)
Phytosterol Esters Biological Activity
As a synthetic active ingredient, phytosterol ester has the dual physiological functions of phytosterols and fatty acids. It has excellent physiological activity in promoting human nutrition and health, and mainly plays a role in lowering cholesterol, antioxidant and anti-cardiovascular disease effect.
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Cholesterol-Lowering Effect
Phytosterol esters retain the excellent cholesterol-lowering activity of phytosterols and can effectively reduce the body's intake of cholesterol. Different types of phytosterol esters have obvious hypolipidemic effects and can regulate cholesterol levels in the body.
Phytosterol esters have excellent antioxidant activity and have significant scavenging effects on hydroxyl radicals (-OH), superoxide anion radicals and DPPH free radicals.
Phytosterol esters also have anti-tumour, promote apoptosis of cancer cells, anti-cardiovascular, antibacterial, anti-inflammatory, improve cellular fibrosis, inhibit cellular ferroptosis, improve cellular steatosis and improve patients with non-alcoholic fatty liver disease (NAFLD) metabolic disorders, uric acid lowering and other effects.
Phytosterol Ester Delivery System
Phytosterol esters have a wide range of biological activities and can be used as active ingredients in food and medicine. However, they are susceptible to adverse changes caused by environmental factors such as temperature, pressure and light during processing and storage. Therefore, phytosterol esters are administered using various delivery systems such as nanoparticles, liposomes, microcapsules and emulsions. Using a delivery system to deliver phytosterol esters can protect them from environmental factors while improving their stability, water solubility and bioavailability.
The nanoparticle delivery system is one of the nanoparticle delivery systems. The main feature is that the particle size of nanoparticles is 1 ~ 100 nm. Therefore, by embedding the bioactive ingredients through the nanoparticles, the delivery and controlled release of bioactive ingredients can be well achieved. Using nanoparticles to carry plant sterol esters can improve their water solubility and bioavailability, but there are still some drawbacks in current research. Firstly, the preparation of nanoparticle delivery systems requires the involvement of emulsifiers, but commonly used emulsifiers have certain drawbacks. Secondly, the nanoparticle delivery system is easily affected by factors such as pH and temperature; and thirdly, the preparation process of the nanoparticle delivery system is complex and costly, making it unsuitable for large-scale industrial production. Therefore, in the future, it is necessary to develop natural, non-toxic emulsifiers to improve the safety of nanoparticles, to investigate new macromolecular substances as carriers for the preparation of nanoparticles to improve their stability, and to optimise the preparation process to achieve industrial production.
Liposomes are monolayer or multilayer lipid vesicles composed of phospholipids, which are similar to cell membrane structures. Since phospholipids are amphiphilic molecules with hydrophilic heads and hydrophobic tails, when forming a bilayer, the hydrophilic heads will automatically form on the outer surface, while the hydrophobic tails will face each other to form a bilayer structure. This vesicle will have a hydrophilic internal space and a hydrophobic phospholipid molecule sandwich. The internal cavity formed can embed hydrophilic substances, while the hydrophobic sandwich can embed lipophilic substances. Due to the special structure of liposomes, liposomes have good drug-carrying properties and targeting properties as transport carriers, and can significantly improve the stability, water solubility and bioavailability of the embedded materials. Because phytosterol esters and phytosterols have similar molecular structures to cholesterol and can interact with liposome membranes in a similar manner to cholesterol, incorporating phytosterol esters into liposomes through homogenization can significantly improve vesicle stability and encapsulation efficiency.
In summary, in the liposome delivery system, plant sterol esters can not only exert their unique biological activity as the embedded core material, but also replace cholesterol to stabilise the liposome membrane structure. Liposome delivery systems have many advantages, such as high encapsulation rate and good targeting, but they also have certain disadvantages. For example, they are easily affected by external environmental factors during storage, causing aggregation and precipitation, which limits their application in food, medicine and other fields. Therefore, it is necessary to modify liposomes to improve the stability of the liposome membrane structure, to develop new steroids as membrane structure stabilisers, and to optimise and develop new processes to achieve industrial production.
Microcapsules have the functions of protecting active ingredients, reducing nutrient loss and controlling release, and are widely used in the food industry. Related studies have shown that microcapsules can not only improve the dispersibility, water solubility and emulsification dispersibility of the core material, but also enhance the protection of the easily oxidised components in the core material, increase the stability of the core material, extend the shelf life of the product, improve the nutritional value of the product and facilitate transportation.
An emulsion is a uniform system consisting of a dispersed phase dispersed in a continuous phase in the form of droplets. Emulsifiers are usually added to the emulsion system to improve the stability of the emulsion system. Encapsulation using an emulsion carrier system can effectively prevent degradation of the encapsulated substance, thereby improving its stability.
References
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Shrestha SC, et al.; Formulation and Characterization of Phytostanol Ester Solid Lipid Nanoparticles for the Management of Hypercholesterolemia: An ex vivo Study. Int J Nanomedicine. 2021, 16:1977-1992.
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Panpipat W, et al.; Thermal properties and nanodispersion behavior of synthesized β-sitosteryl acyl esters: a structure-activity relationship study. J Colloid Interface Sci. 2013, 407:177-86.
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McPherson TB, et al.; Phytostanol tablets reduce human LDL-cholesterol. J Pharm Pharmacol. 2005, 57(7):889-96.
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Cong Jiang, et al.; Artificial preparation, biosynthetic, health effects, and applications of phytosterol and phytosterol ester: A review. Food Bioscience. 2024, Volume 59, 104023
