A novel method of producing a microcrystalline beta-sitosterol suspension in oil

Current advances in phytosterol free forms and esters: Classification, biosynthesis, chemistry, and detection

Phytosterols are plant sterols that are important secondary plant metabolites with significant pharmacological properties. Their presence in the plant kingdom concerns many unrelated botanical families such as oleageneous plants and cereals. The structures of phytosterols evoke those of cholesterol. These molecules are composed of a sterane ring, also known as perhydrocyclopentanophenanthrene, along with a methyl or ethyl group at C-24 in their side chains, a hydroxyl group at C-3 on ring A, and one or two double bonds in the B ring. Phytosterols display different oxidation degrees at the sterane ring and at the side chain as well as varying numbers of carbons with complex stereochemistries. Fats and water solubilities of phytosterols have been achieved by physical, chemical and enzymatic esterifications to favor their bioavailability and to improve the sensory quality of food, and the efficiency of pharmaceutic and cosmetic products. This review aims to provide comprehensive information starting from the definition and structural classification of phytosterols, and exposes an update of their biogenic relationships. Next, the synthesis of phytosterol esters and their applications as well as their effective roles as hormone precursors are discussed. Finally, a concise exploration of the latest advancements in phytosterol / oxyphytosterols analysis techniques is provided, with a particular focus on modern hyphenated techniques.

Phytosterols: Physiological Functions and Potential Application

Dietary intake of natural substances to regulate physiological functions is currently regarded as a potential way of promoting health. As one of the recommended dietary ingredients, phytosterols that are natural bioactive compounds distributed in plants have received increasing attention for their health effects. Phytosterols have attracted great attention from scientists because of many physiological functions, for example, cholesterol-lowering, anticancer, anti-inflammatory, and immunomodulatory effects. In addition, the physiological functions of phytosterols, the purification, structure analysis, synthesis, and food application of phytosterols have been widely studied. Nowadays, many bioactivities of phytosterols have been assessed in vivo and in vitro. However, the mechanisms of their pharmacological activities are not yet fully understood, and in-depth investigation of the relationship between structure and function is crucial. Therefore, a contemporaneous overview of the extraction, beneficial properties, and the mechanisms, as well as the current states of phytosterol application, in the food field of phytosterols is provided in this review.

Solubilization of free β-sitosterol in milk sphingomyelin and polar lipid vesicles as carriers: Structural characterization of the membranes and sphingosome morphology

High consumption of plant sterols reduces the risk of cardiovascular diseases in humans and provides health benefits. Increasing the amount of plant sterols in the diet is therefore necessary to reach the recommended daily dietary intake. However, food supplementation with free plant sterols is challenging because of their low solubility in fats and water. The objectives of this study were to investigate the capacity of milk-sphingomyelin (milk-SM) and milk polar lipids to solubilise β-sitosterol molecules in bilayer membranes organised as vesicles called sphingosomes. The thermal and structural properties of milk-SM containing bilayers composed of various amounts of β-sitosterol were examined by differential scanning calorimetry (DSC) and temperature-controlled X-ray diffraction (XRD), the molecular interactions were studied using the Langmuir film technique, the morphologies of sphingosomes and β-sitosterol crystals were observed by microscopy. We showed that the milk-SM bilayers devoid of β-sitosterol exhibited a gel to fluid L_α phase transition for T_m = 34.5 °C and formed facetted spherical sphingosomes below T_m. The solubilisation of β-sitosterol within milk-SM bilayers induced a liquid-ordered L_o phaseabove 25 %mol (1.7 %wt) β-sitosterol and a softening of the membranes leading to the formation of elongated sphingosomes. Attractive molecular interactions revealed a condensing effect of β-sitosterol on milk-SM Langmuir monolayers. Above 40 %mol (25.7 %wt) β-sitosterol, partitioning occured with the formation of β-sitosterol microcrystals in the aqueous phase. Similar results were obtained with the solubilization of β-sitosterol within milk polar lipid vesicles. For the first time, this study highlighted the efficient solubilization of free β-sitosterol within milk-SM based vesicles, which opens new market opportunities for the formulation of functional foods enriched in non-crystalline free plant sterols.

Soy proteins as vehicles for enhanced bioaccessibility and cholesterol-lowering activity of phytosterols

BACKGROUND

The formulation of phytosterol (PS)-enriched functional foods has attracted increasing interest in the recent years, owing to its potential health effects. However, the poor solubility and bioavailability greatly limit PS application in this regard. This study investigated whether soy protein isolate (SPI) could effectively perform as a nanocarrier for improving the water solubility, bioaccessibility, and cholesterol-lowering activity of PSs.

RESULTS

In this work, we fabricated SPI-PS nanocomplexes, which not only can enhance the stability and bioaccessibility of PS, but also improve the cholesterol-lowering ability of SPI. This improvement was mainly due to the formation of protein-active substance complexes, through hydrophobic interactions. The complexation with PSs resulted in formation of nanosized particles with greater sizes, lower ζ-potential, and higher surface hydrophobicity. The encapsulation efficiency, loading amount, and solubility of PS were closely related to the applied PS concentration in the mixed dispersions, and the maximal PS solubility in the aqueous phase reached about 1.63 mg mL^-1 at the highest PS concentration (2.0 mg mL^-1 ). The PS molecules in the nanocomplexes were mainly present in the amorphous form. The enhanced in vitro cholesterol-lowering activity of PS nanocomplexes relative to free PS seemed to be closely related to its higher bioaccessibility.

CONCLUSION

The findings are of relevance for the development of food-grade PS ingredients suitable for the formulations of PS-enriched functional foods. © 2022 Society of Chemical Industry.

Water-In-Oil Pickering Emulsions Stabilized by Microcrystalline Phytosterols in Oil: Fabrication Mechanism and Application as a Salt Release System

Recently, Pickering emulsions stabilized by edible particles have attracted significant attention from the scientific community and food industry owing to their surfactant-free character. However, those edible particles are mostly used for stabilizing oil-in-water emulsions, whereas those for water-in-oil emulsions are very limited. In this article, stable water-in-oil Pickering emulsions were prepared through dispersing phytosterol particles in oil phase, and the effects of antisolvent treatment, the type of oil, particle concentration, and water fraction on the stability, type, and morphology of these emulsions were investigated. In addition, the release profile of salt as a model aqueous compound from these emulsions has also been studied. Results showed that due to its higher water content, the antisolvent pretreatment of phytosterol in the ethanol/water system facilitated the dispersion of dried phytosterol particles into oil phase as microcrystals. Water-in-oil Pickering emulsions with droplet sizes of 80-100 μm were fabricated at phytosterol concentrations of 1.5-3% w/v and water fractions of 0.2-0.6. The dissolved phytosterol molecules in oil phase could help in emulsion stabilization through interfacial crystallization during emulsification, evidenced by polar microscopic observations. Moreover, the salt release from phytosterol-stabilized Pickering emulsions showed a temperature-dependent profile which could have potential application in a controlled-release system. The current study provided important information for fabrication of stable water-in-oil emulsion using natural particles.

Production and characterization of biocompatible nanofibrous scaffolds made ofβ-sitosterolloaded polyvinyl alcohol/tragacanth gum composites

Electrospun polyvinyl alcohol (PVA) and tragacanth gum (TG) were used to develop nanofibrous scaffolds containing poorly water-solubleβ-Sitosterol (β-S). Different concentrations and ratios of the polymeric composite includingβ-S (10% w v^-1) in PVA (8% w v^-1) combined with TG (0.5 and 1% w v^-1) were prepared and electrospun. The synthesis method includes four electrospinning parameters of solution concentration, feeding rate, voltage, and distance of the collector to the tip of the needle, which are independently optimized to achieve uniform nanofibers with a desirable mean diameter for cell culture. The collected nanofibers were characterized by SEM, FTIR, and XRD measurements. A contact angle measurement described the hydrophilicity of the scaffold. MTT test was carried out on the obtained nanofibers containing L929 normal fibroblast cells. The mechanical strength, porosity, and deterioration of the scaffolds were well discussed. The mean nanofiber diameters ranged from 63 ± 20 nm to 97 ± 46 nm. The nanofibers loaded withβ-S were freely soluble in water and displayed a remarkable biocompatible nature. The cultured cells illustrated sheet-like stretched growth morphology and penetrated the nanofibrous pores of the PVA/β-S/TG scaffolds. The dissolution was related to submicron-level recrystallization ofβ-S with sufficient conditions for culturing L929 cells. It was concluded that electrospinning is a promising technique for poorly water-solubleβ-S formulations that could be used in biomedical applications.

Preparation and characterization of phytosterol-loaded nanoparticles with sodium caseinate/dextran conjugates

Sodium caseinate (SC)/dextran conjugates were prepared via Maillard reaction under controlled dry-heating conditions. Moreover, the nanoparticles of phytosterols (PS) encapsulated by SC or SC/dextran were produced using the emulsion evaporation method. The encapsulation efficiency (78.81 ± 5.22%) of PS in SC/dextran nanoparticles was higher than that (73.5 ± 2.78%) in SC nanoparticles. Compared with the compact and dense structure of SC nanoparticles, SC/dextran nanoparticles existed as relatively loose aggregates. The result of differential scanning calorimetry demonstrated that the encapsulation of PS greatly decreased its crystallinity. The released rates of PS from SC and SC/dextran nanoparticles under acidic gastric conditions were 8.59% and 4.73%, respectively. After 7 h of intestinal digestion, the released rate (52.19%) of PS from SC/dextran nanoparticles was significantly higher than that from SC (32.67%) nanoparticles. Therefore, SC/dextran conjugates prepared by the Maillard reaction are more suitable to be used as wall material for the nano-encapsulation of PS.

Preparation and characterization of soybean protein isolate/pectin-based phytosterol nanodispersions and their stability in simulated digestion

In this study, stigmasterol was nanoencapsulated in soy protein isolate -pectin-based nanodispersions. Based on the particle size and zeta-potential, the optimal pectin/SPI ratio of stigmasterol nanodispersion was determined to be 1:10. At this ratio, nanodispersions was manufactured with an average particle size of 477 ± 33 nm, an encapsulation efficiency of 89.37%, and a loading amount of 17.87%. The physical properties and morphology of the nanodispersion were investigated. Fourier transform infrared spectroscopy and differential scanning calorimetry analysis revealed that stigmasterol was loaded in nanodispersions successfully. The pectin, which was used to stable nanodispersion, could restrict the release of stigmasterol in the simulated gastric fluid. This experiment indicated that the presence of pectin can improve the stability of the nanodispersion and can be used to achieve controlled release of bioactive compounds.

Fabrication and characterization of stable oleofoam based on medium-long chain diacylglycerol and β-sitosterol

Oleofoams have emerged as attractive low-calorie aeration systems, but saturated lipids or large amount of surfactants are commonly required. Herein, an innovative strategy was proposed to create oleofoams using medium-long chain diacylglycerol (MLCD) and β-sitosterol (St). The oleofoams prepared using MLCD and St in ratios of 15:5 and 12:8 exhibited smaller bubble size and much higher stability. MLCD crystals formed rigid Pickering shell, whereby air bubbles acted as "active fillers" leading to enhanced rigidity. Both Pickering and network stabilization for the MLCD-St oleofoam provided a steric hindrance against coalescence. The gelators interacted via hydrogen bonding, causing a condensing effect in improving the gel elasticity. The oleofoams and foam-based emulsions exhibited a favorable capacity in controlling volatile release where the maximum headspace concentrations and partition coefficients showed a significantly decrease. Overall, the oleofoams have shown great potential for development of low-calorie foods and delivery systems with enhanced textural and nutritional features.

Phase Behavior and Polymorphism of Saturated and Unsaturated Phytosterol Esters

This study investigated how the physicochemical characteristics of phytosterol esters are influenced by the chain length and degree of unsaturation of the fatty acid ester moiety. Saturated and unsaturated phytosterol esters (PEs) were synthesized by the esterification of different types of fatty acids (stearic, palmitic, lauric, oleic, and linoleic acid) to β-sitosterol. The non-isothermal crystallization and melting behavior of the pure PEs were analyzed. It was proven by X-ray diffraction that saturated β-sitosteryl esters and β-sitosteryl oleate formed a bilayer crystal structure. The lamellar spacings of the bilayer structure decreased with decreasing fatty acid chain length and with an increasing degree in unsaturation. The degree of unsaturation of the fatty acid chain of the β-sitosteryl esters also influenced the type of subcell packing of the fatty acid moieties in the bilayer structure, whether or not a metastable or stable liquid crystalline phase was formed during cooling. Furthermore, it was found that the melting temperature and enthalpy of the β-sitosteryl esters increased with an increasing fatty acid chain length while they decreased with an increasing degree of unsaturation. The microscopic analyses demonstrated that β-sitosteryl oleate formed much smaller spherulites than their saturated β-sitosteryl analogues.

Physical properties and cookie-making performance of oleogels prepared with crude and refined soybean oil: a comparative study

The objective of this research was to fabricate crude soybean oil oleogels (CSO) using β-sitosterol (BS) and/or monoacylglycerol (MAG) and compare their role with that of refined soybean oil oleogels (RSO) in cookie making. Both crude and refined soybean oil oleogels were formed with BS or MAG, or the combination of both (1 : 1) at a fixed concentration of 10 wt%. The thermal behavior of the oleogels was measured using differential scanning calorimetry (DSC). The crystal structure and morphology of the oleogels were characterized using X-ray diffraction (XRD) and polarized light microscopy (PLM). The hardness of the oleogel and commercial vegetable shortening was compared using a texture analyzer. The characteristics of cookies made with the oleogels were compared with those of cookies made with commercial vegetable shortening. Overall, the incorporation of BS and/or MAG into crude and refined soybean oil can produce oleogels with solid-like properties. Refined soybean oil formed stronger and firmer oleogels as compared to crude soybean oil. RSO structured by BS presented branched fiber-like, elongated plate-like, and needle-like crystals while the same oil gelled by MAG contained spherulite crystals. RSO made with the combination of BS and MAG displayed crystal morphologies from both BS and MAG. The same crystal morphologies were observed in CSO with lower quantities. Comparing the quality of cookies made with the oleogels and commercial vegetable shortening, equal or better performance of both RSO and CSO in terms of weight, thickness, width, spread ratio, and hardness of cookies than that of commercial vegetable shortening was observed. By combining the results of the physical characterization and cookie making performance, it can be concluded that both crude and refined soybean oleogels could resemble commercial shortening, which offers the possibility of using oleogels to replace shortening in the baking industry.

Phytosterol-based oleogels self-assembled with monoglyceride for controlled volatile release

BACKGROUND

Oleogels have recently emerged as a subject of growing interest among industrial and academic researchers as an alternative to saturated/trans-fat and delivery of functional ingredients. Phytosterols, comprising plant-derived natural steroid compounds, are preferred for oleogel production because they are both natural and healthy. In the present study, phytosterol-based oleogels self-assembled with monoglyceride were studied with respect to tuning volatile release.

RESULTS

Microscopy images of the bicomponent oleogels of β-sitosterol and monoglyceride showed the formation of a new three-dimensional network of entangled crystals and a controllable microstructure. Our analysis from differential scanning calorimetry and small angle X-ray scattering results suggests the self-assembly of β-sitosterol and monoglyceride via intermolecular hydrogen bonds into spherulitic microstructures. The results showed that the release rate (v₀ ), maximum headspace concentrations (C_max ) and partition coefficients (k_a/o ) for oleogels showed a significantly controlled release and were tunable via the microstructure of phytosterol-based oleogels under both dynamic and static conditions. In addition, the solid-like oleogels had interesting thixotropic and thermoresponsive behaviors, probably as a result of intermolecular hydrogen bonding.

CONCLUSION

The self-assembly of phytosterol-based oleogels with monoglyceride was attributed to intermolecular hydrogen and is demonstrated to be a promising tunable and functional strategy for delivering flavor compounds. © 2017 Society of Chemical Industry.

Phytosterols-induced viscoelasticity of oleogels prepared by using monoglycerides

Monoglycerides (MGs) and phytosterols (PS) are known to form firm oleogels with liquid oil. However, the oleogels are prone to undergo polymorphic transition over time that lead to crystals' aggregation thus, compromises physical properties. Thus, we combined MGs with PS to control the crystallization and modify the morphology of the combination oleogels, as both components are reported to interact together. The oleogels were prepared at different ratio combinations and characterized in their rheological, thermal, morphology, and diffraction properties. The results showed that the 8:2 MGP:PS exhibited higher storage modulus (G') than the MGP mono-component. The combination oleogels exhibited effects on the crystallization and polymorphic transition. Consequently, the effects led to change in the morphology of the combination oleogels which was visualized using optical and electron microscope. The resultant effect on the morphology is associated with crystal defect. Due to observable crystals of MGP and PS, it is speculated that the combination oleogels formed a mixed crystal system. This was confirmed with diffraction analysis in which the corresponding peaks from MGP and PS were observed in the combination oleogels. However, the 8:2 oleogel exhibited additional peak at 35.41Å. Ultimately, the 8:2 was the optimum combination observed in our study. Interestingly, this combination is inspired by nature as sterols (phytosterols) are natural component of lipid membrane whilst MGP has properties similar to phospholipids. Hence, the results of our study not only beneficial for oil structuring, but also for the fields of biophysical and pharmaceutical.

Critical Analysis on Characterization, Systemic Effect, and Therapeutic Potential of Beta-Sitosterol: A Plant-Derived Orphan Phytosterol

Beta-sitosterol (BS) is a phytosterol, widely distributed throughout the plant kingdom and known to be involved in the stabilization of cell membranes. To compile the sources, physical and chemical properties, spectral and chromatographic analytical methods, synthesis, systemic effects, pharmacokinetics, therapeutic potentials, toxicity, drug delivery and finally, to suggest future research with BS, classical as well as on-line literature were studied. Classical literature includes classical books on ethnomedicine and phytochemistry, and the electronic search included Pubmed, SciFinder, Scopus, the Web of Science, Google Scholar, and others. BS could be obtained from different plants, but the total biosynthetic pathway, as well as its exact physiological and structural function in plants, have not been fully understood. Different pharmacological effects have been studied, but most of the mechanisms of action have not been studied in detail. Clinical trials with BS have shown beneficial effects in different diseases, but long-term study results are not available. These have contributed to its current status as an "orphan phytosterol". Therefore, extensive research regarding its effect at cellular and molecular level in humans as well as addressing the claims made by commercial manufacturers such as the cholesterol lowering ability, immunological activity etc. are highly recommended.

Effect of Phytosterols on the Crystallization Behavior of Oil-in-Water Milk Fat Emulsions

Milk has been used commercially as a carrier for phytosterols, but there is limited knowledge on the effect of added plant sterols on the properties of the system. In this study, phytosterols dispersed in milk fat at a level of 0.3 or 0.6% were homogenized with an aqueous dispersion of whey protein isolate (WPI). The particle size, morphology, ζ-potential, and stability of the emulsions were investigated. Emulsion crystallization properties were examined through the use of differential scanning calorimetry (DSC) and Synchrotron X-ray scattering at both small and wide angles. Phytosterol enrichment influenced the particle size and physical appearance of the emulsion droplets, but did not affect the stability or charge of the dispersed particles. DSC data demonstrated that, at the higher level of phytosterol addition, crystallization of milk fat was delayed, whereas, at the lower level, phytosterol enrichment induced nucleation and emulsion crystallization. These differences were attributed to the formation of separate phytosterol crystals within the emulsions at the high phytosterol concentration, as characterized by Synchrotron X-ray measurements. X-ray scattering patterns demonstrated the ability of the phytosterol to integrate within the milk fat triacylglycerol matrix, with a concomitant increase in longitudinal packing and system disorder. Understanding the consequences of adding phytosterols, on the physical and crystalline behavior of emulsions may enable the functional food industry to design more physically and chemically stable products.

Super-cooled and amorphous lipid-based colloidal dispersions for the delivery of phytosterols

Super-cooled and amorphous lipid-based colloids are highly desirable delivery systems because of their ability to encapsulate compounds in a soluble or in a non-crystalline state. In this study, we demonstrate the preparation and characterization of super-cooled and amorphous lipid-based nanoscale colloidal dispersions containing high concentrations of phytosterols (PSs). PSs are highly hydrophobic natural bioactive compounds that are known to significantly reduce blood cholesterol levels in humans, but are insoluble in water and are poorly soluble in common lipids such as triacylglycerols (TAGs). Using the ultrahigh pressure homogenization of pre-heated dispersions, followed by temperature quenching, colloidal dispersions with varying concentrations of PSs in the lipid phase are prepared. Long and medium chain TAGs in combination with a non-ionic surfactant are used. The particle size, morphology and stability are analysed by dynamic and static light scattering, electron microscopy, and X-ray diffraction. Rapid temperature quenching enables the formation of stable colloidal dispersions of 10 wt% PSs, more than five times the equilibrium solubility at room temperature. Super-cooled emulsions are formed using liquid TAG, whereas amorphous particles are formed in the case of solid TAG. In both cases, the complete suppression of the crystallization of both PSs and lipids is observed due to the nanoscale confinement. The colloidal dispersions are stable for at least four months. The insights of this work will help understand the colloid formation and particle morphology control in the development of delivery systems for hydrophobic bio-actives such as drugs, cosmeceuticals, nutraceuticals, nutritional and agricultural nanoscale formulations.

Food protein-based phytosterol nanoparticles: fabrication and characterization

Phytosterols are a group of plant sterols with well-recognized LDL-cholesterol lowering effects. The water solubility and bioaccessibility of these compounds can be greatly improved by encapsulation within food protein-based nanoparticles.

Structure and dynamics of water molecules confined in triglyceride oils

Water molecules confined in triglyceride oil form specific hydrogen-bonded structures involving the oil carbonyl groups.

Effects of microcrystalline plant sterol suspension and a powdered plant sterol supplement on hypercholesterolemia in genetically obese Zucker rats

Because dietary fat appears to be an effective vehicle for dispensing plant sterols into the diet, a special plant-sterol-containing ingredient has recently been developed. This ingredient is a plant sterol suspension in oil in which the sterols are in microcrystalline form. The objective of the present study was to analyse the cholesterol-lowering effects and safety of two different plant sterol preparations, an orally administered microcrystalline plant sterol suspension (MPS) in rapeseed oil and a powdered plant sterol supplement, in obese Zucker rats. Dietary plant sterol supplements (0.5%, w/w) were given concurrently with a high cholesterol diet (HCD, 1% cholesterol and 18% fat, w/w). No significant changes in serum triglyceride, blood glucose, serum glutamate oxaloacetic transaminase and glutamic pyruvic transaminase values or body and liver weights were observed. The powdered plant sterol supplement lowered the serum cholesterol by 25% (P< 0.05) and the MPS diet by 35% (P< 0.001) compared with HCD by the end of the 12-week experiment. Interestingly, the plant sterol supplements also produced a marked reduction in serum ubiquinone levels, suggesting a possible effect on isoprene synthesis. Unlike the powdered plant sterol, both MPS and plain rape-seed oil decreased the serum baseline diene conjugation values, suggesting that they protect against oxidative stress-induced lipid peroxidation in rats. This lipid peroxidation diminishing effect is probably due to some antioxidative components in rapeseed oil. These findings indicate that an unesterified plant sterol, such as the microcrystalline suspension in oil, effectively prevents cholesterol absorption in obese Zucker rats.

Use of Near-Infrared for Quantitative Measurement of Viscosity and Concentration of Active Ingredient in Pharmaceutical Gel

Near infrared (NIR) spectroscopy is gaining worldwide interest as an analytical tool for quality control of raw materials, intermediate products, and final dosage forms. This technique can be used without sample preparation, therefore, avoiding the need for reagents and solvents. Quantitative NIR analyses involve calibration by sophisticated mathematical techniques that have been used extensively since the advent of microcomputing and chemometrics. The main objective of this investigation was to use transmission near-Infrared spectroscopy to measure the potency of an active ingredient in a topical gel preparation. A second objective was to evaluate the effect of gel viscosity on the NIR reflectance spectra. Four gel formulations with different ibuprofen concentrations were used for quantitative determination of the active ingredient, and five gel formulations with different viscosity values were used for the evaluation of the effect of viscosity change on the near-infrared reflectance spectra. The laboratory ibuprofen quantitative determination was compared to near-infrared transmission data using linear, quadratic, cubic and partial least square techniques to determine the relationship between ultraviolet (UV) determination and near-infrared spectra. For viscosity, the laboratory data were compared to near-infrared diffuse reflectance data using the same techniques used to determine the relationship between Brookfield viscometer determination and near-infrared spectra. The results demonstrated that an increase in ibuprofen concentration and viscosity produced an increase in near-infrared absorbance. Series of model equations were developed from the calibration of laboratory vs. the near-infrared data for each formulation. The near-infrared spectroscopy method is an alternative method that does not require sample pretreatment for quantitative measurement of active ingredient and viscosity of pharmaceutical gel.

Phytosterols: applications and recovery methods

Phytosterols, or plant sterols, are compounds that occur naturally and bear close structural resemblance to cholesterol, but have different side-chain configurations. Phytosterols are relevant in pharmaceuticals (production of therapeutic steroids), nutrition (anti-cholesterol additives in functional foods, anti-cancer properties), and cosmetics (creams, lipstick). Phytosterols can be obtained from vegetable oils or from industrial wastes, which gives an added value to the latter. Considerable efforts have been recently dedicated to the development of efficient processes for phytosterol isolation from natural sources. The present work aims to summarize information on the applications of phytosterols and to review recent approaches, mainly from the industry, for the large-scale recovery of phytosterols.

Phase transitions, solubility, and crystallization kinetics of phytosterols and phytosterol-oil blends

The thermal properties, solubility characteristics, and crystallization kinetics of four commercial phytosterol preparations (soy and wood sterols and stanols) and their blends with corn oil were examined. Differential scanning calorimetry (DSC) revealed narrow melting peaks between 138 and 145 degrees C for all phytosterol samples, reversible on rescan. Broader and less symmetrical melting transitions at lower temperatures with increasing oil content were observed for two samples of phytosterol-oil admixtures. The estimated, from the solubility law, deltaH values (34.7 and 70.7 mJ/mg for wood sterols and stanols, respectively), were similar to the DSC experimental data. Fatty acid esters of soy stanols differing in the chain length of the acyl groups (C2-C12) exhibited suppression of the melting point and increase of the fusion enthalpy with increasing chain length of the acyl group; the propionate ester exhibited the highest melting point (Tm: 151 degrees C) among all stanol-fatty acid esters. Solubility of phytosterols in corn oil was low (2-3% w/w at 25 degrees C) and increased slightly with a temperature rise. Plant sterols appeared more soluble than stanols with higher critical concentrations at saturation. The induction time for recrystallization of sterol-oil liquid blends, as determined by spectrophotometry, depended on the supersaturation ratio. The calculated interfacial free energies between crystalline sediments and oil were smaller for sterol samples (3.80 and 3.85 mJ/m2) than stanol mixtures (5.95 and 6.07 mJ/m2), in accord with the higher solubility of the sterol crystals in corn oil. The XRD patterns and light microscopy revealed some differences in the characteristics among the native and recrystallized in oil phytosterol preparations.

Physical changes of beta-sitosterol crystals in oily suspensions during heating

The aim of this research was to describe the thermal behavior of beta-sitosterol crystals in oil-suspensions with a focus on the role of water during heating. The suspensions were prepared by recrystallization in order to achieve a microcrystalline particle size. The structural changes together with the mechanical properties of the suspensions during heating were studied by using variable temperature X-ray powder diffractometry (VT-XRPD), differential scanning calorimetry (DSC), and dynamic mechanical analysis (DMA). Hydrated beta-sitosterol crystals in an oil-suspension dehydrated, despite the composition of the suspensions, at low temperatures. At high beta-sitosterol concentration, the monohydrate crystal form changed partially to a hemihydrated form, and when only a small amount of water was initially incorporated, the hemihydrate crystal form dehydrated to a mostly anhydrate crystal form. The released water, which was immiscible in the surrounding oil, caused the recrystallization of hydrated beta-sitosterol during cooling. This procedure indicated a reversible dehydration process. Structural and thermal analysis of beta-sitosterol crystals in suspensions, together with mechanical analysis made it possible to understand various physical changes during heating.

A comparison of the effect of medium- vs. long-chain triglycerides on the in vitro solubilization of cholesterol and/or phytosterol into mixed micelles

Despite clinical evidence of the cholesterol-lowering effects of phytosterols, the exact mechanisms involved are still unclear. Displacement of cholesterol by phytosterols from mixed micelles, which is due to their greater hydrophobicity, is one of the hypotheses for the lumenal effects contributing to the reduction of intestinal cholesterol absorption. In this study a dynamic in vitro lipolysis method was used to examine the solubilization behavior of cholesterol and/or phytosterols during lipolysis to probe the efficacy of cholesterol displacement from mixed micelles by phytosterols. The effects of lipid chain length on sterol solubilization were studied by using microcrystalline suspensions containing 17% phytosterol or cholesterol, formulated in long-chain TG (LCT) and medium-chain TG (MCT). When digesting cholesterol-suspended in LCT, the entire cholesterol dose was incorporated into the micellar phase. For the cholesterol formulation suspended in MCT, 50.3% of the initial dose was recovered in the micelles. Under the respective conditions, we observed lower solubilization of phytosterols than of cholesterol (roughly fourfold). Only 25% of the initial phytosterol dose was solubilized from suspensions formulated with LCT, and 13% was solubilized from MCT formulations. Co-administration of phytosterol and cholesterol suspensions showed a significant reduction of cholesterol solubilization, particularly when dosed in MCT, with approximately 25% of the cholesterol dose solubilized. Insignificant amounts of cholesterol were displaced by phytosterols when cholesterol was presolubilized in the mixed micelles. The results show that, compared with LCT, mixed micelles containing MCT lipolysis products have a reduced solubilizing capacity for cholesterol, which adds to the effectiveness of the phytosterols in displacing cholesterol. This suggests potential benefits of using medium chain length lipids in cholesterol-lowering phytosterol products.

Optimizing the crystal size and habit of beta-sitosterol in suspension

The aim of this work was to survey how processing parameters affect the crystal growth of beta-sitosterol in suspension. The process variables studied were the cooling temperature, stirring time and stirring rate during recrystallization. In addition, we investigated the effect a commonly used surfactant, polysorbate 80, has on crystal size distribution and the polymorphic form. This study describes the optimization of the crystallization process, with the object of preparing crystals as small as possible. Particle size distribution and habit were analyzed using optical microscopy, and the crystal structure was analyzed using X-ray diffractometry. The cooling temperature had a remarkable influence on the crystal size. Crystals with a median crystal length of approximately 23 microm were achieved with a low cooling temperature (<10 degrees C); however, a fairly large number of crystals over 50 microm appeared. Higher cooling temperatures (>30 degrees C) caused notable crystal growth both in length and width. Rapid (250 rpm), continuous stirring until the suspensions had cooled to room temperature created small, less than 50 micro m long (median <20 microm), needle-shaped crystals. The addition of surfactant slightly reduced the size of the initially large crystals. Both hemihydrate and monohydrate crystal forms occurred throughout, regardless of the processing parameters. By using an optimized process, it was possible to obtain a microcrystalline suspension, with a smooth texture.

Physical stability of a microcrystalline beta-sitosterol suspension in oil

Sterols have been shown to reduce plasma cholesterol by blocking the absorption of cholesterol from the gut. The physical properties of crystalline plant sterols limit their use in foods. A coarse-grained structure can be avoided by recrystallisation, a method that affords a reduction in the particle size. A previous work described how to produce a microcrystalline beta-sitosterol suspension. The present study deals with the stability of that suspension. Recrystallisation was carried out by two different methods; one based on rapid the other based on slow cooling, whereby six different compositions were made containing 5-30% of beta-sitosterol and secondly either 5 or 20% water was added. The particle size and habit were evaluated during a 16 weeks storage period (+4 or -19 degrees C) by way of optical microscopy. The crystal structure and degree of crystallinity was analysed by X-ray diffraction. Suspensions can, in most cases, be stored for 16 weeks without any changes to the size and habit. The only evidence of crystal growth came from a suspension with a low sterol concentration at a temperature of +4 degrees C. This is due to the dissolution-diffusion process which is affected by temperature and viscosity. Suspensions containing higher amounts of sterol remained stable, if stored at +4 or -19 degrees C, for 16 weeks. The suspensions included both hemihydrous and monohydrous beta-sitosterol crystals. Suspensions containing less sterol showed greater amounts of monohydrated crystals. This illustrates more water penetration into the crystals. A higher sterol concentration led to a larger number of smaller crystals creating reflections similar to hemihydrated crystals.

Effect of beta-sitosterol on precipitation of cholesterol from non-aqueous and aqueous solutions

The aim of the present work was to study the solubility and phase behaviour of the beta-sitosterol-cholesterol mixed crystals in the presence and absence of water. Cholesterol, beta-sitosterol and 3:1, 1:1 and 1:3 mixtures of these were co-precipitated from acetone and acetone-water solutions. Precipitated crystals were analysed using powder X-ray diffraction (PXRD), differential scanning calorimetry (DSC), optical microscopy and Karl-Fischer titrimetry. The quantification of the sterols in solutions was preformed using GC-MS. The solubility of the sterols was mutually limiting. In the aqueous system, the solubility of both the sterols were significantly lower than in the absence of water, but the decrease in the solubility was considerably greater with the more hydrophobic beta-sitosterol. In the aqueous system, the total sterol solubility decreased with the increasing proportion of beta-sitosterol. The formation of new crystal structures, solid solutions of cholesterol and beta-sitosterol, was observed in non-aqueous as well as in aqueous environments except with the lowest cholesterol proportion in the system, in which case mixed crystals with eutectic behaviour were formed.