Magdi M. Mossoba

Bio: Magdi M. Mossoba is an academic researcher from Center for Food Safety and Applied Nutrition. The author has contributed to research in topics: Conjugated linoleic acid & Trans fat. The author has an hindex of 38, co-authored 148 publications receiving 6255 citations. Previous affiliations of Magdi M. Mossoba include Food and Drug Administration.

Evaluating acid and base catalysts in the methylation of milk and rumen fatty acids with special emphasis on conjugated dienes and total trans fatty acids

Abstract: Milk analysis is receiving increased attention. Milk contains conjugated octadecadienoic acids (18∶2) purported to be anticarcinogenic, low levels of essential fatty acids, and trans fatty acids that increase when essential fatty acids are increased in dairy rations. Milk and rumen fatty acid methyl esters (FAME) were prepared using several acid-(HCl, BF3, acetyl chloride, H2SO4) or base-catalysts (NaOCH3, tetramethylguanidine, diazomethane), or combinations thereof. All acid-catalyzed procedures resulted in decreased cis/trans (Δ9c, 11t-18∶2) and increased trans/trans (Δ9t, 11t-18∶2) conjugated dienes and the production of allylic methoxy artifacts. The methoxy artifacts were identified by gas-liquid chromatography (GLC)-mass spectroscopy. The base-catalyzed procedures gave no isomerization of conjugated dienes and no methoxy artifacts, but they did not transesterify N-acyl lipids such as sphingomyelin, and NaOCH3 did not methylate free fatty acids. In addition, reaction with tetramethylguanidine coextracted material with hexane that interfered with the determination of the short-chain FAME by GLC. Acid-catalyzed methylation resulted in the loss of about 12% total conjugated dienes, 42% recovery of the Δ9c,11t-18∶2 isomer, a fourfold increase in Δ9t,11t-18∶2, and the formation of methoxy artifacts, compared with the base-catalyzed reactions. Total milk FAME showed significant infrared (IR) absorption due to conjugated dienes at 985 and 948 cm−1. The IR determination of total trans content of milk FAME was not fully satisfactory because the 966 cm−1trans band overlapped with the conjugated diene bands. IR accuracy was limited by the fact that the absorptivity of methyl elaidate, used as calibration standard, was different from those of the other minor trans fatty acids (e.g., dienes) found in milk. In addition, acid-catalyzed reactions produced interfering material that absorbed extensively in the trans IR region. No single method or combination of methods could adequately prepare FAME from all lipid classes in milk or rumen lipids, and not affect the conjugated dienes. The best compromise for milk fatty acids was obtained with NaOCH3 followed by HCl or BF3, or diazomethane followed by NaOCH3, being aware that sphingomyelins are ignored. For rumen samples, the best method was diazomethane followed by NaOCH3.

Chemical effects of ultrasound on aqueous solutions. Evidence for hydroxyl and hydrogen free radicals (.cntdot.OH and .cntdot.H) by spin trapping

Abstract: Results of spin-trapping and electron spin resonance studies are reported that provide conclusive evidence for the formation of hydroxyl radicals (.OH) and hydrogen atoms (.H) during the sonolysis of aqueous solutions. Nonvolatile nitrone spin traps, 5,5-dimethyl-1-pyrroline-N-oxide (DMPO), ..cap alpha..-tert-butyl-..cap alpha..-(1-methyl-4-pyridinio)nitrone (PyBN), and ..cap alpha..-4-pyridyl-N-tert-butylnitrone 1-oxide(POBN), were used. Experiments were carried out in which scavengers competed with these spin traps for the radicals formed. The formate radical and ethanol were used as scavengers since the reactions of HCOO/sup -/ and C/sub 2/H/sub 5/OH with .OH, .H, and e/sub aq//sup -/ are well known. As a final test, aqueous POBN solutions containing CdSO/sub 4/, a well-known e/sub aq//sup -/ scavenger, were sonicated with no decrease in the signal intensity of H-POBN adduct being noted. This was interpreted as indication that no e/sub aq//sup -/ was being formed. (BLM)

Methods for analysis of conjugated linoleic acids and trans-18:1 isomers in dairy fats by using a combination of gas chromatography, silver-ion thin-layer chromatography/gas chromatography, and silver-ion liquid chromatography.

Abstract: Conjugated linoleic acids (CLA) are octadecadienoic acids (18:2) that have a conjugated double-bond system. Interest in these compounds has expanded since CLA were found to be associated with a number of physiological and pathological responses such as cancer, metastases, atherosclerosis, diabetes, immunity, and body fat/protein composition. The main sources of these conjugated fatty acids are dairy fats. Rumen bacteria convert polyunsaturated fatty acids, especially linoleic and linolenic acids, to CLA and numerous trans- containing mono- and diunsaturated fatty acids. It has been established that an additional route of CLA synthesis in ruminants and monogastric animals, including humans, occurs via delta9 desaturation of the trans-18:1 isomers. To date, a total of 6 positional CLA isomers have been found in dairy fats, each occurring in 4 geometric forms (cis,trans; trans,cis; cis,cis; and trans,trans) for a total of 24. All of these CLA isomers can be resolved only by a combination of gas chromatography (GC), using 100 m highly polar capillary columns, and silver-ion liquid chromatography, using 3 of these 25 cm columns in series. Complete analysis of all the trans-18:1 isomers requires prior isolation of trans monoenes by silver-ion thin-layer chromatography (TLC), followed by GC analysis using the same 100 m capillary columns operated at low temperatures starting from 120 degrees C. These analytical techniques are required to assess the purity of commercial CLA preparations, because their purity will affect the interpretation of any physiological and/or biochemical response obtained. Prior assessment of CLA preparations by TLC is also recommended to determine the presence of any other impurities. The availability of pure CLA isomers will permit the evaluation and analysis of individual CLA isomers for their nutritional and biological activity in model systems, animals, and humans. These techniques are also essential to evaluate dairy fats for their content of specific CLA isomers and to help design experimental diets to increase the level of the desired CLA isomers in dairy fats. These improved techniques are further required to evaluate the CLA profile in monogastric animals fed commercial CLA preparations for CLA enrichment of animal products. This is particularly important because absorption and metabolism will alter the ingested-CLA profile in the animal fed.

Silver-ion high-performance liquid chromatographic separation and identification of conjugated linoleic acid isomers

Abstract: This is the first report of the application of silverion impregnated high-performance liquid chromatography (Ag+-HPLC) to the separation of complex mixtures of conjugated linolenic acid (CLA) isomers present in commercial CLA sources and foods and in biological specimens. This method showed a clear separation of CLA isomers into three groups related to their trans,trans, cis,trans or trans,cis, and cis,cis configuration of the conjugated double-bound system. In addition, this method separated within each geometrical isomeric group. Following Ag+-HPLC isolation, gas chromatography (GC)-electron impact mass spectrometry, and GC-direct deposition-Fourier transformed infrared spectroscopy were used to confirm the identity of two major positional isomers in the cis/trans region, i.e., Δ8,10- and Δ11,13-octadecadienoic acid, which had not been chromatographically resolved previously, Furthermore, the potential of this method was demonstrated by showing different Ag+-HPLC profiles exhibiting patterns of isomeric distributions for biological specimens from animals fed a diet containing a commerical CLA preparation, as well as for a commerical cheese product.

Hydrogen Peroxide Synthesis: An Outlook beyond the Anthraquinone Process

Abstract: Hydrogen peroxide (H2O2) is widely used in almost all industrial areas, particularly in the chemical industry and environmental protection. The only degradation product of its use is water, and thus it has played a large role in environmentally friendly methods in the chemical industry. Hydrogen peroxide is produced on an industrial scale by the anthraquinone oxidation (AO) process. However, this process can hardly be considered a green method. It involves the sequential hydrogenation and oxidation of an alkylanthraquinone precursor dissolved in a mixture of organic solvents followed by liquid–liquid extraction to recover H2O2. The AO process is a multistep method that requires significant energy input and generates waste, which has a negative effect on its sustainability and production costs. The transport, storage, and handling of bulk H2O2 involve hazards and escalating expenses. Thus, novel, cleaner methods for the production of H2O2 are being explored. The direct synthesis of H2O2 from O2 and H2 using a variety of catalysts, and the factors influencing the formation and decomposition of H2O2 are examined in detail in this Review.

Applications of Ultrasound to the Synthesis of Nanostructured Materials

Abstract: Recent advances in nanostructured materials have been led by the development of new synthetic methods that provide control over size, morphology, and nano/microstructure. The utilization of high intensity ultrasound offers a facile, versatile synthetic tool for nanostructured materials that are often unavailable by conventional methods. The primary physical phenomena associated with ultrasound that are relevant to materials synthesis are cavitation and nebulization. Acoustic cavitation (the formation, growth, and implosive collapse of bubbles in a liquid) creates extreme conditions inside the collapsing bubble and serves as the origin of most sonochemical phenomena in liquids or liquid-solid slurries. Nebulization (the creation of mist from ultrasound passing through a liquid and impinging on a liquid-gas interface) is the basis for ultrasonic spray pyrolysis (USP) with subsequent reactions occurring in the heated droplets of the mist. In both cases, we have examples of phase-separated attoliter microreactors: for sonochemistry, it is a hot gas inside bubbles isolated from one another in a liquid, while for USP it is hot droplets isolated from one another in a gas. Cavitation-induced sonochemistry provides a unique interaction between energy and matter, with hot spots inside the bubbles of approximately 5000 K, pressures of approximately 1000 bar, heating and cooling rates of >10(10) K s(-1); these extraordinary conditions permit access to a range of chemical reaction space normally not accessible, which allows for the synthesis of a wide variety of unusual nanostructured materials. Complementary to cavitational chemistry, the microdroplet reactors created by USP facilitate the formation of a wide range of nanocomposites. In this review, we summarize the fundamental principles of both synthetic methods and recent development in the applications of ultrasound in nanostructured materials synthesis.

Fourier Transform Infrared (FTIR) Spectroscopy of Biological Tissues

Abstract: This article reviews some of the recent advances on FTIR spectroscopy in areas related to natural tissues and cell biology. It is the second review publication resulting from a detailed study on the applications of spectroscopic methods in biological studies and summarizes some of the most widely used peak frequencies and their assignments. The aim of these studies is to prepare a database of molecular fingerprints, which will help researchers in defining the chemical structure of the biological tissues introducing most of the important peaks present in the natural tissues. In spite of applying different methods, there seems to be a considerable similarity in defining the peaks of identical areas of the FTIR spectra. As a result, it is believed that preparing a unique collection of the frequencies encountered in FTIR spectroscopic studies can lead to significant improvements both in the quantity and quality of research and their outcomes. This article is the first review of its kind that provides...