Cholesterol oxides are similar to cholesterol but have additional functional groups, like hydroxyl, ketone, or epoxide groups, in the sterol nucleus or side chain. They are naturally produced in human tissues during the conversion of cholesterol and can also be found in high-cholesterol foods. The levels of cholesterol oxides vary depending on storage, cooking, and processing. Egg yolks, frozen meat, butter, cheese, cream, heated tallow, and egg-based products may contain cholesterol oxides. Heating, spray-drying, and deep-frying increase their content. For example, clarified butter (ghee) contains 12% cholesterol oxides due to the high heat used in its production. Comparing cholesterol oxide levels in foods is challenging due to different analytical methods and lack of proper validation. Procedures for extracting, purifying, and quantifying cholesterol oxides have been summarized in previous studies.
Cholesterol oxides, which can be harmful to health, are present in certain food products.
Dairy Foods:
- Fresh milk, condensed milk, and skimmed milk do not contain cholesterol oxides.
- Full cream milk may have small amounts of cholesterol oxides.
- Commercial milk powders and infant formulas have low levels of cholesterol oxides.
- Freshly opened full cream powders have traces of cholesterol oxides.
- Cholesterol oxide levels in fresh milk powders produced by low or medium heat spray-drying are very low.
Egg and Egg Products:
- Fresh egg yolks have negligible amounts of cholesterol oxides.
- Cooking and dehydration increase the cholesterol oxide content in eggs.
- Egg products used in commercially prepared foods may have significant cholesterol oxide contents.
Meat and Meat Products:
- Fresh meat has minimal cholesterol oxide levels, but meat products can contain higher amounts.
- Cholesterol oxidation in meat can increase due to various factors, such as storage conditions, processing methods, and exposure to light.
- Beef hamburgers and fried products tend to have higher cholesterol oxide levels.
- Additives like nitrites and ascorbic acid can help reduce cholesterol oxide formation in processed meats.
Seafood:
- Fresh, frozen, and smoked herring contain low levels of cholesterol oxides.
- Salt-dried fish species can have varying cholesterol oxide levels.
- Grilling certain fish may cause slight increases in cholesterol oxides.
- The presence of cholesterol oxides in processed marine products raises concerns about their safety.
Fried Foods:
- Foods cooked in butter or tallow can absorb cholesterol oxides.
- French-fried potatoes and deep-fried foods cooked in animal/vegetable fat can have significant cholesterol oxide levels.
- Cholesterol oxide content in fried foods depends on frying fat composition, time, and temperature.
Storage and Cooking Methods:
- Cholesterol oxide levels can be influenced by storage conditions, such as exposure to oxygen, heat, and light.
- Heating during processing, drying, and non-ideal storage conditions can lead to higher cholesterol oxide levels.
- Different packaging and limited shelf time in supermarkets can affect cholesterol oxide production in dairy spreads.
It's important to be aware of the potential risks of consuming cholesterol oxides, especially in precooked products, and consider storage and cooking methods that minimize their formation.
Why are Cholesterol Oxides Important in Human Nutrition?
Cholesterol oxides are significant in human nutrition because of their effects on the body. These oxides are easily absorbed into the bloodstream from food and transported in low-density lipoprotein (LDL) to the liver. Recent studies have shown that unesterified cholesterol oxides also bind with serum albumin.
Unlike regular cholesterol, which is eliminated through bile secretions, it's unclear if cholesterol oxides follow the same pathway. Research has identified a specific group of enzymes called p-450 7α-hydroxylases that catalyze cholesterol oxides.
Many cholesterol oxides have atherosclerotic properties and can influence cholesterol metabolism. Animal studies have shown that when consumed at high levels, cholesterol oxides are more damaging to the aorta's endothelium and can induce arteriosclerosis compared to pure cholesterol. LDL hydroperoxides derived from cholesterol oxides have also been linked to aorta fiber proteolysis.
Studies have found that high concentrations of 7β-hydroxycholesterol in the serum predict rapid progression of carotid arteriosclerosis. It's important to note that when healthy young men consumed salami and Parmesan cheese, most of the cholesterol oxides in their blood were in the form of acyl esters rather than non-esterified cholesterol oxides. Proper hydrolysis of acyl esters is crucial when analyzing cholesterol oxides in food samples. The amount of cholesterol oxides in salami and Parmesan cheese can vary depending on manufacturing and analysis methods.
The elevated presence of cholesterol oxides in Indian ghee, accounting for 12.3% of the total cholesterol content, could potentially elucidate the increased susceptibility to arteriosclerosis observed within Indian immigrant communities in the USA and UK. This correlation arises from the widespread consumption of ghee among this particular group.
Limited understanding of the physiological importance of cholesterol oxides is due to a lack of accurate analytical procedures. Reliable methods for analyzing cholesterol oxides in foods are crucial. However, it is widely accepted that cholesterol oxides have negative impacts on human metabolism beyond tissue levels. Various approaches can be used to prevent cholesterol oxidation in foods, such as reducing total cholesterol content, incorporating antioxidants into the diet, processing food at lower temperatures, using oxygen-excluding packaging, and storing food in low-light conditions. Manufacturers of high-cholesterol processed foods should consider these preventive measures to avoid the formation of harmful compounds.
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