7α and 7β-Hydroxycholesterols Formed in a Dry Egg Nog Mix Exposed to Fluorescent Light

Excipient-related impurities in liposome drug products

Liposomes are widely used in the pharmaceutical industry as drug delivery systems to increase the efficacy and reduce the off-target toxicity of active pharmaceutical ingredients (APIs). The liposomes are more complex drug delivery systems than the traditional dosage forms, and phospholipids and cholesterol are the major structural excipients. These two excipients undergo hydrolysis and/or oxidation during liposome preparation and storage, resulting in lipids hydrolyzed products (LHPs) and cholesterol oxidation products (COPs) in the final liposomal formulations. These excipient-related impurities at elevated concentrations may affect liposome stability and exert biological functions. This review focuses on LHPs and COPs, two major categories of excipient-related impurities in the liposomal formulations, and discusses factors affecting their formation, and analytical methods to determine these excipient-related impurities.

Chromatographic separation of cholesterol in foods

Based on the current literature and on experience gained in the laboratory, a simplified procedure using direct saponification (0.4 M potassium hydroxide in ethanol and heating at 60 degrees C for 1 h) is the most appropriate method for the determination of total cholesterol in foods. Extraction of the unsaponifiable matter with hexane is efficient and no extra clean-up is required before quantification. An internal standard, 5 alpha-cholestane or epicoprostanol, should be added to the sample prior to saponification and, together with reference standards, carried through the entire procedure to ensure accurate results. A significant improvement in cholesterol methodology has been achieved by decreasing the sample size and performing all the sample preparation steps in a single tube. The method has the advantages of elimination of an initial solvent extraction for total lipids and errors resulting from multiple extractions, transfers, filtration and wash steps after saponification. The resulting hexane extract, which contains a variety of sterols and fat soluble vitamins, requires an efficient capillary column for complete resolution of cholesterol from the other compounds present. The development of fused-silica capillary columns using cross-linked and bonded liquid phases has provided high thermal stability, inertness and separation efficiency and, together with automated cold on-column gas chromatographic injection systems, has resulted in reproducible cholesterol determinations in either underivatized or derivatized form. If free cholesterol and its esters need to be determined separately, they are initially extracted with other lipids with chloroform-methanol followed by their separation by column or thin-layer chromatography and subsequently analysed by gas or liquid chromatography. Although capillary gas chromatography offers superior efficiency in separation, the inherent benefits of liquid chromatography makes it a potential alternative. Isotope dilution mass spectrometry has been widely accepted as a reliable analytical method for highly accurate determination of cholesterol in serum and several definitive methods have been reported. The combination of capillary gas chromatography with mass spectrometry has become an excellent approach for the determination of cholesterol in complex mixtures of sterols and tocopherols, providing high resolution with positive identification. When used to determine cholesterol in multi-component foods, spectrophotometric methods have been documented to overestimate significantly the amount of cholesterol owing to the presence of other interfering substances. A re-evaluation of food products should be undertaken using the more specific chromatographic methods to accumulate data that will more accurately reflect the true cholesterol content.

Food analysis on silica-bound HPLC phases

HPLC analysis of food on various silica bonded phases has been described. Technical and theoretical aspects of the materials such as normal-, reverse-, ion-exchange-, affinity-, chiral-, size-exclusion-, and ion-phases have been discussed. Special problems such as mobile phase or solvent-selection, selectivity and mechanisms of resolution on these bonded phases have been mentioned. Application of various bonded materials such as amino, cyano, diol, amino-cyano, C-18, C-8, anion-exchangers, strong and weak-cation exchangers, chiral and enzyme bound affinity phases to analyze and determine food components such as carbohydrates, food colors and pigments, flavors, proteins, vitamins and toxins has been described.

Cholesterol autoxidation 1981-1986

Literature published between 1980 and 1986 dealing broadly with the topic of cholesterol autoxidation is reviewed. The review builds on the detailed 1981 monographic treatment of the topic by the author and covers new items of chemistry, analysis, and metabolism.

Occurrence of lipid oxidation products in foods

Lipid oxidation products are ubiquitous in foods, although much variation exists in the levels present. Although these levels are generally low, the problem of lipid oxidation severely compromises the quality of some foods and limits the shelf-life of others. Lipid oxidation represents a key barrier in the development of new food products and processes, especially convenience items and processes required to manufacture them. Deleterious changes in foods caused by lipid oxidation include loss of flavour, development of off-flavours, loss of colour, nutrient value and functionally, and the accumulation of compounds which may be detrimental to the health of consumers. All foods that contain lipids are susceptible to oxidation but especially affected are foods which are dehydrated, subjected to high temperatures or cooked and subsequently stored, e.g. dehydrated eggs, cheeses and meats, foods fried in frying oils, and cooked (uncured) meats. Specific examples of compounds which are of health concern include lipid peroxides and the free radicals involved in their formation and propagation, malonaldehyde, and several cholesterol oxidation products. Coronary artery disease (CAD) may be in part caused by the consumption of lipid oxidation products.