Presence of phytosterol oxides in crude vegetable oils and their fate during refining

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.

Chemical conversions of free phytosterols during the bleaching of corn oil

Phytosterols have health benefits; however, they are partially removed during the bleaching of corn oil. We evaluated the chemical conversion of free phytosterols (FPs) during bleaching. FP degradation accelerated with increased time and temperature, following a first-order kinetic model. In the n-heptane system, air and activated clay promoted the chemical conversion of the FPs. Sterenes formation was analysed under different conditions using a zero-order kinetic model. The apparent activation energies revealed sterene formation decreasing in the following order: campesta-3,5-diene ≈ stigmasta-3,5,22-triene > stigmasta-3,5-diene. Isomers of the above were not detected, indicating that these sterenes were the only primary products of FPs. The desorption test indicated that the FP loss from corn oil was not only due to FPs being adsorbed the activated clay, but also FPs adsorbed at acidic activated sites being degraded. This study presents a vital scientific foundation for retaining FPs to develop healthier and more nutritious oils.

Identification and Safety Evaluation of Ochratoxin A Transformation Product in Rapeseed Oil Refining Process

Ochratoxin A (OTA) is an important mycotoxin detected in edible oil, and it can be effectively removed by classical edible oil refining processes. However, the fate of OTA in the refining process has not been reported. In this study, we systematically tracked the OTA changes during the oil refining process by fortifying 100 μg/kg OTA in crude rapeseed oil. Results showed that about 10.57%, 88.85%, and 0.58% of OTA were removed during the degumming, deacidification, and decolorization processes. Among them, 16.25% OTA was transferred to the byproducts, including 9.85% in degumming wastewater, 5.68% in soap stock, 0.14% in deacidification wastewater, and 0.58% in the decolorizer; 83.75% OTA was found to transform into the lactone ring opened OTA (OP-OTA) during the deacidification stage, which is attributed to the hydrolysis of the lactone ring of OTA in the alkali refining. The OP-OTA was verified to distribute in the soap stock, and small amounts of OP-OTA could be transferred to deacidified wastewater when the OTA pollution level reached 500 μg/kg in crude rapeseed oil. The OP-OTA exhibited strong toxicity, especially nephrotoxicity, as reflected by the cell viability assay and in silico toxicity. Therefore, the safety of the soap stock processing products from OTA-contaminated rapeseed deserves attention.

Presence of cholesterol oxides in milk chocolates and their correlation with milk powder freshness

Cholesterol oxidation products (COPs) of non-enzymatic origin are mainly found in meat, fish, eggs and milk, mostly originating from the type of feeding, processing and storage. To verify the significance of COPs as biomarkers of cholesterol autoxidation and milk freshness, we quantified them in chocolates containing whole milk powders (WMPs) of increasing shelf-lives (i.e. 20, 120, and 180 days). Non-enzymatic total COPs (both free and esterified) ranged from 256.57 ± 11.97 to 445.82 ± 11.88 ng/g, increasing proportionally to the shelf-life of the WMPs, thus reflecting the ingredients’ freshness. Based on the expected theoretical COPs, the effect of processing was quantitatively less significant in the generation of oxysterols (41–44%) than the contribution of the autoxidation of the WMPs over time (56–59%), pointing to the shelf-life as the primary determinant of COPs. Lastly, we quantified COPs of major commercial milk chocolates on the Italian market, which followed a similar distribution (from 240.79 ± 11.74 to 475.12 ± 12.58 ng/g). Although further replications of this work are needed, this study reports preliminary results and a practical example of a first application of non-enzymatic COPs as markers to further quantify and characterize the nutritional quality and freshness, not only of ingredients but also of composite products.

Thermal degradation of stigmasterol under the deodorisation temperature exposure alone and in edible corn oil

Phytosterols are commonly found in vegetable oils and possess health benefits for humans. While investigating the chemical conversion of stigmasterol at deodorisation temperatures, gas chromatography-mass spectrometry (GC-MS) and ultra-high performance liquid chromatography coupled to high-resolution mass spectrometry (UHPLC-HRMS) experiments led to the identification of 5-ethyl-6-methyl-3-heptene-2-one, 3-hydoxy-steroid, 3-ketostigmasterol, and 3,7-diketostigmasterol as by-products. The identification of these compounds assisted in the interpretation of the stigmasterol oligomers characterised by high-pressure size exclusion chromatography (HPSEC). A similar analysis was conducted in stripped corn oil at the deodorisation temperatures. As such, 5-ethyl-6-methyl-3-heptene-2-one, 3-hydoxy-steroid, 3-ketostigmasterol and 3,7-diketostigmasterol were also detected in stripped corn oil, while the contents of 3-hydoxy-steroid and 5-ethyl-6-methyl-3-heptene-2-one were higher than those of 3-ketostigmasterol, as revealed by quantum chemical simulations. In addition, stripped corn oil exhibited the characteristic of preventing stigmasterol degradation below 200 °C, whereas it enhanced the chemical conversion (such as esterification and degradation) of stigmasterol at higher temperatures.

Effect of DL-Methionine Supplementation on Tissue and Plasma Antioxidant Status and Concentrations of Oxidation Products of Cholesterol and Phytosterols in Heat-Processed Thigh Muscle of Broilers

In this study, the hypothesis that supplementation with methionine (Met) as DL-Met (DLM) in excess of the National Research Council (NRC) recommendations improves the antioxidant system in broilers was investigated. Day-old male Cobb-500 broilers (n = 72) were divided into three groups which were fed a control diet or diets supplemented with two levels of DLM in which the concentrations of Met + Cys exceeded the recommendations of NRC by 15-20% (group DLM 1) or 30-40% (group DLM 2), respectively. The three groups of broilers did not show differences in body weight gains, feed intake, and feed conversion ratio. However, broilers of groups DLM 1 and DLM 2 had higher concentrations of glutathione (GSH) in liver and thigh muscle and lower concentrations of cholesterol oxidation products (COPs) in heat-processed thigh muscle than broilers of the control group. Concentrations of several oxidation products of phytosterols in heat-processed thigh muscle were also reduced in groups DLM 1 and DLM 2; however, the concentration of total oxidation products of phytosterols was not different between the three groups. The study shows that DLM supplementation improved the antioxidant status due to an increased formation of GSH and reduced the formation of COPs during heat-processing in thigh muscle.

Formation of 5α-Sitostan-3-one, 5α-Campestan-3-one, and Steroidal Hydrocarbons in Edible Oils during Catalytic Hydrogenation

Targeted analysis confirmed the presence of new phytosterol degradation products in fully hydrogenated commercial samples. EI-MS, APCI-MS, and 1D-NMR experiments led to the identification of 10 novel markers of catalytic hydrogenation, among which 5α-sitostan-3-one and 5α-campestan-3-one, isomers of saturated and monounsaturated steroidal hydrocarbons, were reported in edible oils for the first time. Examination of the phytosterol degradation mechanism was done by the catalytic transfer deuteration technique. The mitigation strategy of potentially detrimental compounds included optimization of processing parameters. The effect of catalyst dosage (≤0.1% based on Ni basis) and temperature region (>180 °C) were the most crucial factors in phytosterol degradation control.

Controlled release and macrophage polarizing activity of cold-pressed rice bran oil in a niosome system

Phytosterols, α-tocopherol and γ-oryzanol are scientifically recognized as major health promoting compounds found in cold-pressed rice bran oil (CRBO).

Oxysterols formation: A review of a multifactorial process

Dietary sterols are nutritionally interesting compounds which can suffer oxidation reactions. In the case of plant sterols, they are being widely used for food enrichment due to their hypocholesterolemic properties. Besides, cholesterol and plant sterols oxidation products are associated with the development of cardiovascular and neurodegenerative diseases, among others. Therefore, the evaluation of the particular factors affecting sterol degradation and oxysterols formation in foods is of major importance. The present work summarizes the main results obtained in experiments which aimed to study four aspects in this context: the effect of the heating treatment, the unsaturation degree of the surrounding lipids, the presence of antioxidants on sterols degradation, and at last, oxides formation. The use of model systems allowed the isolation of some of these effects resulting in more accurate data. Thus, these results could be applied in real conditions.

Oxysterols in cosmetics-Determination by planar solid phase extraction and gas chromatography-mass spectrometry

Sterol oxidation products (SOPs) are linked to several toxicological effects. Therefore, investigation of potential dietary uptake sources particularly food of animal origin has been a key issue for these compounds. For the simultaneous determination of oxysterols from cholesterol, phytosterols, dihydrolanosterol and lanosterol in complex cosmetic matrices, planar solid phase extraction (pSPE) was applied as clean-up tool. SOPs were first separated from more non-polar and polar matrix constituents by normal phase thin-layer chromatography and then focussed into one target zone. Zone extraction was performed with the TLC-MS interface, followed by gas chromatography-mass spectrometry analysis. pSPE showed to be effective for cleaning up cosmetic samples as sample extracts were free of interferences, and gas chromatographic columns did not show any signs of overloading. Recoveries were between 86 and 113% with relative standard deviations of below 10% (n=6). Results of our market survey in 2016 showed that some cosmetics with ingredients of plant origin contained phytosterol oxidation products (POPs) in the low ppm range and therefore in line with levels reported for food. In lanolin containing products, total SOPs levels (cholesterol oxidation products (COPs), lanosterol oxidation products (LOPs), dihydrolanosterol oxidation products (DOPs)) being in the low percent range exceeded reported levels for food by several orders of magnitudes.

Oxidation of β-sitosterol and campesterol in sunflower oil upon deep- and pan-frying of French fries

Fried foods, both deep-fried and pan-fried, are enjoyed by people worldwide. Frying is one of the main factors leading to formation of phytosterols (PS) oxidation products (POP) in vegetable oils. The aim of this study was to measure the oxidation of β-sitosterol (24α-ethyl-5-cholesten-3β-ol) and campesterol (24α-methyl-5-cholesten-3β-ol) in commercial sunflower oil (SFO) during deep- and pan-frying of French fries for different periods (30, 60, 120 and 240 min). The total amount of PS in SFO was 4732 μg/g, wherein the major PS were β-sitosterol and campesterol. The results of POP were confirmed by the GC-MS analysis that monitored the formation of oxides during frying. Upon frying, total PS content decreased whereas the highest decrease was measured after 240 min of frying. The oxidative stability (OS) of different sitosterol and campesterol during both frying methods was evaluated. In general, pan frying resulted in more PS oxidation than deep frying. β-Sitosterol oxides predominated while campesterol oxides were formed to a lesser extent. 7-Ketositosterol, followed by 7β-hydroxysitosterol, 5,6-epoxy derivatives and 7α-hydroxysitosterol were the main POP induced during frying. The proportion of 7-keto derivatives decreased during frying while the proportion of 7β-hydroxy derivatives increased. The formation of POP might be a limiting factor for frying in SFO for long periods.

Plant sterols from foods in inflammation and risk of cardiovascular disease: a real threat?

High dietary intakes of cholesterol together with sedentary habits have been identified as major contributors to atherosclerosis. The latter has long been considered a cholesterol storage disease; however, today atherosclerosis is considered a more complex disease in which both innate and adaptive immune-inflammatory mechanisms as well as bacteria play a major role, in addition to interactions between the arterial wall and blood components. This scenario has promoted nutritional recommendations to enrich different type of foods with plant sterols (PS) because of their cholesterol-lowering effects. In addition to cholesterol, PS can also be oxidized during food processing or storage, and the oxidized derivatives, known as phytosterol oxidation products (POPs), can make an important contribution to the negative effects of both cholesterol and cholesterol oxidation oxides (COPs) in relation to inflammatory disease onset and the development of atherosclerosis. Most current research efforts have focused on COPs, and evaluations of the particular role and physiopathological implications of specific POPs have been only inferential. Appreciation of the inflammatory role described for both COPs and POPs derived from foods also provides additional reasons for safety studies after long-term consumption of PS. The balance and relevance for health of all these effects deserves further studies in humans. This review summarizes current knowledge about the presence of sterol oxidation products (SOPs) in foods and their potential role in inflammatory process and cardiovascular disease.

Effect of phytosterols and their oxidation products on lipoprotein profiles and vascular function in hamster fed a high cholesterol diet

Human diets contain phytosterols and their oxidation products. We investigated effect of β-sitosterol (Si), stigmasterol (St), β-sitosterol oxidation products (SiOP) and stigmasterol oxidation products (StOP) on plasma total cholesterol and their interaction with the gene expression of enzymes, proteins and transporters involved in cholesterol absorption and metabolism. Sixty male hamsters were fed the control diet or one of four experimental diets containing 0.1% Si, 0.1% SiOP, 0.1% St and 0.1% StOP, respectively, for six weeks. SiOP and StOP groups had the relative liver weights greater than their corresponding non-oxidized forms, indicating they were possibly toxic. Results showed both Si and St groups reduced while SiOP and StOP hamsters lost the capacity of lowering plasma total cholesterol (TC), low-density lipoprotein cholesterol (LDL) and triacylglycerols (TG) compared with the control group. Si and St but not SiOP and StOP were anti-atherosclerotic. RT-PCR analysis demonstrated Si and St but not SiOP and StOP down-regulated mRNA levels of intestinal acyl CoA: cholesterol acyltransferase (ACAT2) and microsomal triglyceride protein (MTP). Aortas from Si and St hamsters relaxed better than those from the control and their corresponding SiOP and StOP-treated hamsters. It was concluded that Si and St not SiOP and StOP were beneficial in improving lipoprotein profile and aortic function.

Current and new insights on phytosterol oxides in plant sterol-enriched food

Over the past 15 years, plant sterol-enriched foods have faced a great increase in the market, due to the asserted cholesterol-lowering effect of plant sterols. However, owing to their chemical structures, plant sterols can oxidize and produce a wide variety of oxidation products with controversial biological effects. Although oxyphytosterols can derive from dietary sources and endogenous formation, their single contribution should be better defined. The following review provides an overall and critical picture on the current knowledge and future perspectives of plant sterols-enriched food, particularly focused on occurrence of plant sterol oxidation products and their biological effects. The final objective of this overview is to evince the different aspects of plant sterols-enriched food that require further research, for a better understanding of the influence of plant sterols and their oxides on consumers' health.

Stability of plant sterols in ingredients used in functional foods

The content of plant sterol (PS) and their oxidation products (POPs) in eight ingredients used to enrich functional foods was studied. A gas chromatographic (GC) technique with mass-spectrometric detection was used for identification, while GC with a flame ionization detector (GC-FID) was used for quantification. β-Sitosterol was the most abundant phytosterol, and the main POPs found were derived from this compound (7α/β-hydroxysitosterol, 7-ketositosterol, and sitostanetriol). The total amount of POPs found in the ingredients ranged from 29.03 to 110.02 μg/100 g PS. The β-sitosterol oxidation rates ranged from 10 to 50 μg β-sitosterol oxides/100 g of β-sitosterol. In view of this low rate of oxidation in the ingredients tested, it can be concluded that the PS remain stable in these ingredients. Significant correlations (p < 0.01) were found between total oxysitosterols versus β-sitosterol contents (R(2) = 86.5%) and between total POPs and total PS (R(2) = 81.6%).

Cytotoxic and apoptotic effects of the oxidized derivatives of stigmasterol in the U937 human monocytic cell line

Dietary exposure to phytosterols has increased in recent years due to the incorporation of these compounds into cholesterol-lowering products. Previous studies have investigated the cytotoxic effects of the oxidized derivatives of β-sitosterol and determined that phytosterol oxidation products (POP) have a similar but less potent toxicity compared to their cholesterol equivalents. In the present study, the cytotoxicity of the oxidized derivatives of stigmasterol were investigated in the U937 cell line. The stigmasta-5,22-diene-3β,7β-diol (7β-OH), 5,6-epoxystigmasta-22,23-diol (epoxydiol), 5,6,22,23-diepoxystigmastane (diepoxide), and (22R,23R)-stigmast-5-ene-3β,22,23-triol (22R,23R-triol) derivatives were identified as the most cytotoxic, and the mode of cell death was identified as apoptosis in cells incubated with 7β-OH, epoxydiol, and diepoxide stigmasterol. The antioxidants α-tocopherol, γ-tocopherol, and β-carotene did not protect against apoptosis induced by 7β-OH and diepoxide stigmasterol; however, α-tocopherol was found to protect against epoxydiol-induced apoptosis. The cellular antioxidant, glutathione, was depleted and the apoptotic protein, Bcl-2, was down-regulated by the stigmasterol oxides identified as apoptotic.

Oxysterols: A world to explore

Oxysterols (oxidized derivatives of cholesterol and phytosterols) can be generated in the human organism through different oxidation processes, some requiring enzymes. Furthermore, oxysterols are also present in food due to lipid oxidation reactions caused by heating treatments, contact with oxygen, exposure to sunlight, etc., and they could be absorbed from the diet, at different rates depending on their side chain length. In the organism, oxysterols can follow different routes: secreted into the intestinal lumen, esterified and distributed by lipoproteins to different tissues or degraded, mainly in the liver. Cholesterol oxidation products (COPs) have shown cytotoxicity, apoptotic and pro-inflammatory effects and they have also been linked with chronic diseases including atherosclerotic and neurodegenerative processess. In the case of phytosterol oxidation products (POPs), more research is needed on toxic effects. Nevertheless, current knowledge suggests they may also cause cytotoxic and pro-apoptotic effects, although at higher concentrations than COPs. Recently, new beneficial biological activities of oxysterols are being investigated. Whereas COPs are associated with cholesterol homeostasis mediated by different mechanisms, the implication of POPs is not clear yet. Available literature on sources of oxysterols in the organism, metabolism, toxicity and potential beneficial effects of these compounds are reviewed in this paper.

Stability of Cholesterol, 7-Ketocholesterol and β-Sitosterol during Saponification: Ramifications for Artifact Monitoring of Sterol Oxide Products

Cholesterol has been used to monitor artifact generation. Stability differences among cholesterol oxide products (COPs) and cholesterol in thermal and alkaline conditions are theorized. Thus, use of cholesterol may be unsuitable for detection of artifacts generated from COPs. Stability of cholesterol was compared to that of 7-ketocholesterol (7-keto) and β-sitosterol (βS) under various thermal and alkaline saponification conditions: 1 M methanolic KOH for 18 h at 24 °C (1 M18hr24°C, Control), 18 h at 37 °C (1M18hr37°C), 3 h at 45 °C (1M3hr45°C), and 3.6 M methanolic KOH for 3 h at 24 °C (3.6M3hr24°C). Trends indicated that cholesterol in solution was more stable than 7-keto under all conditions. Compared to βS, cholesterol was more stable under all conditions except for 1M18hr37°C for which stabilities were similar. Compounds were more labile in heat than alkalinity. Poor recoveries of 7-keto during cold saponification with high alkalinity were attributed to alkaline instability. 7-Keto, less stable than cholesterol, should be used to monitor artifact generation during screening of various methods that include thermal and alkaline conditions. In a preliminary analysis of turkey meat, more 3,5-7-one was generated from spiking with cholesterol than with 7-keto.

Stability of sterols in phytosterol-enriched milk under different heating conditions

Commercially available phytosterol-enriched milk was subjected to usual and drastic heating conditions to evaluate the stability of the sterols at different treatments. Products showed 422.2 mg of phytosterols/100 g of milk and 132 microg of sterol oxidation products (SOPs)/g of fat (277 microg of SOPs/100 g of milk). Schaal oven conditions (24 h/65 degrees C, equivalent to 1 month of storage at room temperature) reduced the phytosterol content by only 4%. Drastic heating treatments (2 min of microwave heating at 900 W or 15 min of electrical heating at 90 degrees C) led to a 60% decrease of total phytosterol content, with a significant increase of TBARs. The oxysterol amount under those conditions (which was higher in microwave-treated samples) was lower than expected, probably because of the degradation of the oxidation products. Usual heating conditions (1.5 min of microwaves) maintained phytosterol content on physiologically active values (301 mg/100 g of milk) with oxidation percentages around 0.12-0.40% for phytosterols and 1.13% for cholesterol.

Emulsion-based delivery systems for lipophilic bioactive components

There is a pressing need for edible delivery systems to encapsulate, protect, and release bioactive lipids within the food, medical, and pharmaceutical industries. The fact that these delivery systems must be edible puts constraints on the type of ingredients and processing operations that can be used to create them. Emulsion technology is particularly suited for the design and fabrication of delivery systems for encapsulating bioactive lipids. This review provides a brief overview of the major bioactive lipids that need to be delivered within the food industry (for example, omega-3 fatty acids, carotenoids, and phytosterols), highlighting the main challenges to their current incorporation into foods. We then provide an overview of a number of emulsion-based technologies that could be used as edible delivery systems by the food and other industries, including conventional emulsions, multiple emulsions, multilayer emulsions, solid lipid particles, and filled hydrogel particles. Each of these delivery systems could be produced from food-grade (GRAS) ingredients (for example, lipids, proteins, polysaccharides, surfactants, and minerals) using simple processing operations (for example, mixing, homogenizing, and thermal processing). For each type of delivery system, we describe its structure, preparation, advantages, limitations, and potential applications. This knowledge can be used to facilitate the selection of the most appropriate emulsion-based delivery system for specific applications.

Sterol oxidation in ready-to-eat infant foods during storage

The effect of storage on sterol oxidation of ready-to-eat infant foods was evaluated. Two different liquid infant foods (honey or fruits flavors), prepared with milk and cereals, were stored for 0, 2, 4, 7 and 9 months at 25 degrees C. Sterol oxidation products (SOP) were isolated by cold saponification, purified by silica solid-phase extraction, and analyzed by gas chromatography (GC) and GC-mass spectrometry. beta-Sitosterol was the most representative sterol, followed by cholesterol and campesterol. No significant differences in the total and single SOP content (0.8-1 mg/kg of product) were observed with respect to storage time and type of sample; the main SOP found was 7-ketositosterol (<0.2 mg/kg of product). The extent of stigmasterol oxidation (2.9%) was higher than that of cholesterol (1.9%) and beta-sitosterol (1.4%). The type and quality of raw materials, as well as the processing conditions, seem to greatly influence SOP formation and accumulation in infant foods.

Oxidation products of stigmasterol interfere with the action of the female sex hormone 17β-estradiol in cultured human breast and endometrium cell lines

Phytosterols are constituents of plant membranes and are thus contained in low concentrations in vegetable products as well as at high concentrations in functional food designed to reduce serum cholesterol levels. Similar to ChOL, phytosterols are oxidized chemically in food and by biotransformation in vivo. Although oxyphytosterols have been detected in the serum of healthy human subjects, little is known of their biological activity. Therefore, the estrogenic and antiestrogenic activities of a mixture of six oxidation products of stigmasterol (oxy-StOL) were determined at the following endpoints: (i) the affinity to isolated human estrogen receptors (ER), (ii) the basal and 17beta-estradiol (E2)-induced expression of the alkaline phosphatase (AlP) in human endometrial adenocarcinoma (Ishikawa) cells, and (iii) the basal and E2-induced proliferation of human breast adenocarcinoma (MCF-7) cells. Oxy-StOL was able to replace E2 from human ERalpha and ERbeta and induced a weak estrogenic response in MCF-7 cells. Moreover, the E2-induced activity of the AlP in Ishikawa cells as well as the E2-induced proliferation of MCF-7 cells were decreased at noncytotoxic concentrations (up to 10 microM), indicating that at least one component of oxy-StOL represents an estrogen-active compound which might interfere with endogenous estrogens.