Cholesterol oxidation during storage of UHT-treated bovine and caprine milk

Cholesterol and Its Oxidation Derivatives Content in Market Dairy Products

Cholesterol oxidation products (COPs) are contaminants of food of animal origin. Increased levels of these compounds in the human body are associated with an increased risk of many non-communicable diseases. Dairy products are mentioned among the main sources of these compounds in the diet. The objective of this study was to evaluate the contents of cholesterol and its oxidized derivatives in eleven groups of dairy products, willingly consumed in European countries. The levels of COPs were determined by applying the GC-TOF/MS method. In the tested products, cholesterol and its oxidation derivatives, such as 7-ketocholesterol, 7α-hydroxycholesterol, 7β-hydroxycholesterol, 5,6β-epoxycholesterol and 5,6α-epoxycholesterol, were determined. The studied dairy products differed in their contents and profiles of oxysterols. The highest contents of COPs were found in cheese with internal mold (13.8 ± 2.5 mg kg-1) and Cheddar (11.7 ± 3.5 mg kg-1), while the lowest levels were detected in yoghurt (0.94 ± 0.30 mg kg-1) and kefir (0.57 ± 0.11 mg kg-1). 7-ketocholesterol and 5,6β-epoxycholesterol were the dominant oxysterols. The ratio of oxidized derivatives to total cholesterol was on average 1.7%. Our results confirmed that dairy products are an important dietary source of COPs. Their levels should be monitored in dairy products to provide the best health quality.

Oxidative Status of Ultra-Processed Foods in the Western Diet

Ultra-processed foods (UPFs) have gained substantial attention in the scientific community due to their surging consumption and potential health repercussions. In addition to their well-established poor nutritional profile, UPFs have been implicated in containing various dietary oxidized sterols (DOxSs). These DOxSs are associated with a spectrum of chronic diseases, including cardiometabolic conditions, cancer, diabetes, Parkinson's, and Alzheimer's disease. In this study, we present a comprehensive database documenting the presence of DOxSs and other dietary metabolites in >60 UPFs commonly consumed as part of the Western diet. Significant differences were found in DOxS and phytosterol content between ready-to-eat (RTE) and fast foods (FFs). Biomarker analysis revealed that DOxS accumulation, particularly 25-OH and triol, can potentially discriminate between RTEs and FFs. This work underscores the potential utility of dietary biomarkers in early disease detection and prevention. However, an essential next step is conducting exposure assessments to better comprehend the levels of DOxS exposure and their association with chronic diseases.

Metabolomics reveals changes in metabolite composition of duck eggs under the impact of long-term storage

BACKGROUND

Eggs are essential food sources as they provide low cost and high nutritional content of animal protein. The preservation period is one of the apparent factors affecting egg quality. Previous studies based on traditional detection techniques demonstrated that storage period would significantly influence egg weight, eggshell weight, albumen height, haugh unit (HU) and albumen viscosity. Herein, we employed non-targeted metabolome technology to reveal the comprehensive changes in metabolite composition in duck eggs under the impacts of storage period.

RESULTS

The results showed that the primary metabolites in the yolk of duck eggs are amino acids, carbohydrates and lipids. In contrast, the primary metabolites in the albumen are amino acids, benzene and indoles. We screened 43 and 16 different metabolites, respectively, in the albumen and yolk of duck eggs with different preservation periods. In addition, kyoto encyclopedia of genes and genomes (KEGG) enrichment was performed, and the results showed that various nutrients were degraded in the egg after preservation, thus affecting the quality of duck eggs. These nutrients included amino acids, fatty acids, nucleotides, sugars and vitamins; meanwhile, ammonia, biogenic amines and some flavor substances were produced, affecting the quality of the eggs.

CONCLUSION

Ourfindings can contribute to a holistic understanding of metabolite composition changes in duck eggs during deterioration in storage. © 2022 Society of Chemical Industry.

Metabolism and the Effect of Animal-Derived Oxysterols in the Diet on the Development of Alzheimer's Disease

BACKGROUND

The rapid worldwide increase in the incidence of Alzheimer's disease is associated with changing nutrition patterns. Recently, some articles have highlighted the link between Alzheimer's disease and dietary cholesterol. It was found that elevated levels of some of its fractions in the brain and circulation affect metabolism.

SUMMARY

Previous studies have considered the relationship between Alzheimer's disease and oxidized cholesterol molecules in the brain. To date, there are limited data available on the relationship between oxidized cholesterol in the brain and Alzheimer's disease. There is a link between a diet high in cholesterol and its oxidized forms, leading to hypercholesterolemia, which is one of significant risk factors of dementia, and Alzheimer's disease. Oxidized cholesterol can be absorbed in the small intestine and cross the blood-brain barrier, leading to increased inflammation and endogenous oxidative process. Animal-origin foods are sources of oxidized cholesterol, with cholesterol oxidation beginning already after slaughter and occurring during storage and processing.

KEY MESSAGES

High-heat food preparation and storage of cooked products in the refrigerator followed by subsequent heating may significantly increase the amount of oxidized cholesterol products. Therefore, a diet low in cholesterol oxidation products and high in plants with antioxidative properties seems to be most preventable and should be implemented as early as possible.

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.

Oxysterols as Reliable Markers of Quality and Safety in Cholesterol Containing Food Ingredients and Products

Cholesterol is a lipid of high nutritional value that easily undergoes oxidation through enzymatic and non-enzymatic pathways, leading to a wide variety of cholesterol oxidation products (COPs), more commonly named oxysterols. The major oxysterols found in animal products are 7α-hydroxycholesterol, 7β-hydroxycholesterol, 7-ketocholesterol, 5α,6α-epoxycholesterol, 5β,6β-epoxycholesterol, cholestan-3β,5α,6β-triol, and 25-hydroxycholesterol. They are all produced by cholesterol autoxidation, thus belonging to the non-enzymatic oxysterol subfamily, even if 7α-hydroxycholesterol and 25-hydroxycholesterol are, in part, generated enzymatically as well. A further oxysterol of the full enzymatic origin has recently been detected for the first time in milk of both human and bovine origin, namely 27-hydroxycholesterol. Nowadays, gas or liquid chromatography combined to mass spectrometry allows to measure all these oxysterols accurately in raw and in industrially processed food. While non-enzymatic oxysterols often exhibited in vitro relevant cytotoxicity, above all 7β-hydroxycholesterol and 7-ketocholesterol, 27-hydroxycholesterol, as well as 25-hydroxycholesterol, shows a broad spectrum in vitro antiviral activity, inhibition of SARS-CoV-2 included, and might contribute to innate immunity. Quantification of oxysterols was afforded over the years, almost always focused on a few family's compounds. More comprehensive COPs measurements, also including oxysterols of enzymatic origin, are, nowadays, available, which better display the many advantages of systematically adopting this family of compounds as markers of quality, safety, and nutritional value in the selection of ingredients in processing and storage. Regarding foodstuff shelf life, COPs monitoring already provided useful hints for more suitable packaging. The identification of a subset of non-enzymatic and enzymatic oxysterols to be routinely assessed in food production and storage is proposed.

Oxysterols: From redox bench to industry

More and more attention is nowadays given to the possible translational application of a great number of biochemical and biological findings with the involved molecules. This is also the case of cholesterol oxidation products, redox molecules over the last years deeply investigated for their implication in human pathophysiology. Oxysterols of non-enzymatic origin, the excessive increase of which in biological fluids and tissues is of toxicological relevance for their marked pro-oxidant and pro-inflammatory properties, are increasingly applied in clinical biochemistry as molecular markers in the diagnosis and monitoring of several human and veterinary diseases. Conversely, oxysterols of enzymatic origin, the production of which is commonly under physiological regulation, could be considered and tested as promising pharmaceutical agents because of their antiviral, pro-osteogenic and antiadipogenic properties of some of them. Very recently, the quantification of oxysterols of non-enzymatic origin has been adopted in a systematic way to evaluate, monitor and improve the quality of cholesterol-based food ingredients, that are prone to auto-oxidation, as well as their industrial processing and the packaging and the shelf life of the finished food products. The growing translational value of oxysterols is here reviewed in its present and upcoming applications in various industrial fields.

Dietary cholesterol oxidation products: Perspectives linking food processing and storage with health implications

Dietary cholesterol oxidation products (COPs) are heterogeneous compounds formed during the processing and storage of cholesterol-rich foods, such as seafood, meat, eggs, and dairy products. With the increased intake of COPs-rich foods, the concern about health implications of dietary COPs is rising. Dietary COPs may exert deleterious effects on human health to induce several inflammatory diseases including atherosclerosis, neurodegenerative diseases, and inflammatory bowel diseases. Thus, knowledge regarding the effects of processing and storage conditions leading to formation of COPs is needed to reduce the levels of COPs in foods. Efficient methodologies to determine COPs in foods are also essential. More importantly, the biological roles of dietary COPs in human health and effects of phytochemicals on dietary COPs-induced diseases need to be established. This review summarizes the recent information on dietary COPs including their formation in foods during their processing and storage, analytical methods of determination of COPs, metabolic fate, implications for human health, and beneficial interventions by phytochemicals. The formation of COPs is largely dependent on the heating temperature, storage time, and food matrices. Alteration of food processing and storage conditions is one of the potent strategies to restrict hazardous dietary COPs from forming, including maintaining relatively low temperatures, shorter processing or storage time, and the appropriate addition of antioxidants. Once absorbed into the circulation, dietary COPs can contribute to the progression of several inflammatory diseases, where the absorbed dietary COPs may induce inflammation, apoptosis, and autophagy in cells in the target organs or tissues. Improved intake of phytochemicals may be an effective strategy to reduce the hazardous effects of dietary COPs.

Effect of industrial processing and storage procedures on oxysterols in milk and milk products

Oxysterols are products of enzymatic and/or chemical cholesterol oxidation. While some of the former possess broad antiviral activities, the latter mostly originate from the deterioration of the nutritional value of foodstuff after exposure to heat, light, radiation and oxygen, raising questions about their potential health risks. We evaluated the presence of selected oxysterols in bovine colostrum and monitored the evolution of their cholesterol ratio throughout an entire industrial-scale milk production chain and after industrially employed storage procedures of milk powders. We report here for the first time the presence of high levels of the enzymatic oxysterol 27-hydroxycholesterol (27OHC) in concentrations of antiviral interest in bovine colostrum (87.04 ng mL^-1) that decreased during the first postpartum days (56.35 ng mL^-1). Of note, this oxysterol is also observed in milk and milk products and is not negatively affected by industrial processing or storage. We further highlight an exponential increase of the non-enzymatic oxysterols 7β-hydroxycholesterol (7βOHC) and 7-ketocholesterol (7KC) in both whole (WMPs) and skimmed milk powders (SMPs) during prolonged storage, confirming their role as reliable biomarkers of cholesterol oxidation over time: after 12 months, 7βOHC reached in both SMPs and WMPs amounts that have been found to be potentially toxic in vitro (265.46 ng g^-1 and 569.83 ng g^-1, respectively). Interestingly, industrial processes appeared to affect the generation of 7βOHC and 7KC differently, depending on the presence of fat in the product: while their ratios increased significantly after skimming and processing of skimmed milk and milk products, this was not observed after processing whole milk and milk cream.

Thermal oxidation of cholesterol: Preliminary evaluation of 2-methyl-6-heptanone and 3-methylbutanal as volatile oxidation markers

Cholesterol oxidation in food and model systems is usually monitored by evaluating cholesterol oxidation products, but the analysis is time-consuming and expensive. Therefore, the determination of volatile compounds deriving from cholesterol thermoxidation could be valuable to identify other possible oxidation markers. Cholesterol alone and in the presence of a triacylglycerol mixture (tripalmitin, tristearin, and triolein) were thermoxidized at 170°C for 15min. In both model systems, the total volatile compounds increased three times when oxidation time rose from 5 to 15min. The main classes of volatile compounds were aldehydes, ketones, alcohols and hydrocarbons, displaying a similar behavior in both systems. After 5min of oxidation, 2-methyl-6-heptanone was the main volatile compound, followed by 3-methylpentane, 2,3-dimethyl-1-pentene and 3-methylbutanal. To verify if 2-methyl-6-heptanone could be used as volatile marker of cholesterol oxidation, data were compared with the total cholesterol oxidation products content of each system. A significant correlation between total cholesterol oxidation products content and 2-methyl-6-heptanone amount was found when cholesterol was oxidized alone (r(2)=0.994) and in presence of triacylglycerols (r(2)=0.998). When egg yolk was thermoxidized at 80°C for 6h, 3-methylbutanal was the volatile compound that better explained the oxidative trend in this food system, showing a significant correlation with cholesterol oxidation rate (r=0.91). In conclusion, 2-methyl-6-heptanone and 3-methylbutanal could represent an easy and cheaper strategy for monitoring cholesterol oxidation in model systems and food samples, respectively; however, a deeper investigation on the amount and type of volatile compounds generated from cholesterol oxidation according to the food matrix, should be carried out.

Light-induced lipid oxidation in sheep milk: effects of dietary grape seed and linseed, alone or in combination, on milk oxidative stability

The present work aimed to investigate the milk oxidative stability when the sheep diet includes a source of polyphenols (grape seed, (GS)) and a source of polyunsaturated fatty acids (linseed, (LIN)), alone or in combination (MIX) compared to a control group (CON). For this purpose light-induced oxidation in milk was studied. After 24 h of light exposure the lipid hydroperoxides increased in milk in the LIN and MIX groups. The calculated ratio between the level of lipid hydroperoxides and unsaturated fatty acids (UFAs) in milk was lower in the GS and MIX than in the LIN group. At the same time the level of the ratio between hexanal/linoleic acid in milk was lower in the GS and MIX than in the CON group. Although the dietary inclusion of grape seed did not reduce the level of lipid oxidation products in sheep milk, it effectively reduced the extent of oxidation of UFA.