Gloria Márquez-Ruiz

Interactions between fat and food during deep-frying

In deep-fat frying the food is completely surrounded by the frying fat or oil and different events occur within a few minutes: dehydration of food surface, absorption of fat, formation of flavour compounds, development of surface colour, etc. Due to the drastic conditions applied during deep-frying, the frying fat also undergoes degradation. Although much work has been done on modifications of used frying fats and oils under different conditions, changes in the fried substrate have been much less studied. Particularly, there is minimal information on some physical and chemical aspects of the interactions between frying fats and fried foods. In this paper the main changes in the frying fat due to the nature of the food fried in it as well as modifications in the food as a consequence of the fat or oil used as heat transfer medium are reviewed. Fat absorption and lipid exchanges are the main physical changes involved. Chemical reactions include interaction between food constituents and oxidised lipids as well as hydrolysis of frying fats due to food moisture.

Rapid, quantitative determination of polar compounds in fats and oils by solid-phase extraction and size-exclusion chromatography using monostearin as internal standard

Abstract A rapid and simple method was developed for quantitation of polar compounds in fats and oils using monostearin as internal standard. Starting from 50 mg of oil sample, polar compounds were obtained by solid-phase extraction (silica cartridges) and subsequently separated by high-performance size-exclusion chromatography into triglyceride polymers, triglyceride dimers, oxidized triglyceride monomers, diglycerides, internal standard and fatty acids. Quantitation of total polar compounds was achieved through the internal standard method and then amounts of each group of compounds could be calculated. A pool of polar compounds was used to check linearity, precision and accuracy of the method, as well as teh solid-phase extraction recovery. The procedure was applied to samples with different content of polar compounds and good quantitative results were obtained, especially for samples of low alteration level.

Oxidized fats in foods

Purpose of reviewLipid oxidation is the cause of important deteriorative changes in chemical, sensory and nutritional food properties. In particular, the question of whether oxidized fats in the diet may be detrimental to health is nowadays of the upmost concern, but finding an answer is not easy and requires careful consideration of different aspects of lipid oxidation. Recent findingsIn this review, the most recent works on the formation, nature and evaluation of oxidized dietary lipids are addressed; important issues such as the difficulties encountered in estimating their intake and the relationships between oxidants and antioxidants in the diet are discussed, and the latest studies on health implications of oxidized lipids are summarized. SummaryThe current literature reflects various important points. At present, there is no information on the intake of oxidized fats, which is essential to know if the amount of oxidized lipids in normal diets is sufficient to cause the physiological effects claimed. Recently, relevant advances in analytical methodologies for quantitation of specific oxidation compounds have been reported, although their application to improve the analytical definition of the oxidized substrate used in nutritional studies is still a goal to be reached. Alternatively, one of the most promising current tendencies in this field is the study of the molecular targets by which dietary oxidized lipids can influence health. Overall, more selected research based on coordinated multidisciplinary studies is needed to define the role of dietary oxidized fats in health.

Bioavailability of n-3 polyunsaturated fatty acids (PUFA) in foods enriched with microencapsulated fish oil.

Objective: Incorporation of fish oil into food products provides a means of increasing n–3 fatty acid intake, particularly in populations where fish consumption remains low. The aim of the present study was to evaluate the bioavailability of n–3 PUFA in microencapsulated fish-oil-enriched foods compared with an equal amount of n–3 PUFAs contained in fish oil capsules. Methods: Twenty-five healthy female volunteers were randomly assigned to one of two groups for the 4-week intervention: one group received 0.9 g of n–3 PUFA/day as fish oil capsule (capsule group), while the second group (food group) received an equal amount of n–3 PUFA/day from enriched foods. Baseline and post-intervention samples were analysed for platelet fatty acid composition. Results: There was no significant difference in the change in platelet arachidonic acid (AA), eicosapentaenoic acid (EPA), or docosahexaenoic acid (DHA) between the two groups following the intervention. Conclusions: The results indicate that n–3 PUFA from microencapsulated fish-oil-enriched foods are as bioavailable as n–3 PUFA in a capsule. Fortification of foods with microencapsulated fish oil, therefore, offers an effective way of increasing n–3 PUFA intakes and status in line with current dietary recommendations.

Quantitation and distribution of altered fatty acids in frying fats

The distribution and quantity of polar compounds and altered fatty acids in used frying oils, collected by Food Inspection Services of the Junta de Andalucía in Spain, was measured. Additional samples evaluated were sunflower oil, high-oleic sunflower oil, and palm olein that were subjected to thermoxidation and frying in laboratory experiments. A combination of adsorption and high-performance size-exclusion chromatography was applied to the oil samples both before and after transesterification. Through analysis of fatty acid methyl ester derivatives, differentiation of four groups of altered fatty acids (oxidized monomers, nonpolar dimers, oxidized dimers, and polymers) could be attained. Evaluation of real frying samples with polar compound levels around the limit for fat rejection (21.1–27.6% polar compounds) gave values of total altered fatty acids ranging from 8.1 to 11.3%, and levels higher than 20% were found in the most degradated samples. The results obtained clearly support the need for control and improvement of the quality of used fats in fried-food outlets.

Headspace solid-phase microextraction of oil matrices heated at high temperature and phthalate esters determination by gas chromatography multistage mass spectrometry

A solvent-free analytical approach based on headspace solid-phase microextraction (SPME) of oil matrices heated at high temperatures coupled to gas chromatography with mass spectrometry detector (GC-ion trap) has been developed for the determination of phthalic acid esters (PAEs) in oil matrices without sample manipulation. For this study, three fibers, i.e., 85 microm-polyacrylate (PA), 50/30 microm-divinylbenzene-carboxen-polydimethylsiloxane (DVB/CAR/PDMS) and 100 microm-polydimethylsiloxane (PDMS) were tested. Variables affecting the SPME headspace composition such as incubation sample temperature, sample incubation time and fiber exposition time were optimized. The optimal values found were 250 degrees C for sample incubation temperature and 30 min for incubation and extraction time. PA fiber was not suitable for the lightest polar phthalates which showed poor extraction and repeatability values. PDMS fiber had very poor response for some of the heavier and non-polar phthalates, whereas DVB/CAR/PDMS fiber showed the best response and repeatability values for the majority of the phthalates studied. The main benefit of the analytical method proposed is the absence of sample manipulation and hence avoidance of possible contamination coming from glassware, environment, solvents and samples.

Sensitive and accurate quantitation of monoepoxy fatty acids in thermoxidized oils by gas–liquid chromatography

A sensitive and accurate methodology for quantitation of monoepoxy fatty acid methyl esters (FAME) by gas-liquid chromatography is proposed. Analytical problems of interfering compounds, ie, methyl monoester of azelaic acid and methyl docosanoate, were solved by a second methylation step with diazomethane and by elimination of nonpolar FAME by adsorption chromatography, respectively. Six monoepoxy FAME were identified and quantitated in olive and sunflower oils heated at 180 degrees C for 15 h: trans-9,10- and cis-9,10-epoxystearate coming from oleate and trans-12,13-, trans-9,10-, cis-12,13- and cis-9,10-epoxyoleate coming from linoleate. Results demonstrated total recovery of monoepoxy compounds after nonpolar FAME elimination with the additional advantage of sample concentration, which allowed quantitation of monoepoxy FAME in the initial oils. Also, repeatability was excellent as relative standard deviations ranged from 2.2 to 5.1% for on-column injection and from 0.1 to 2.0% for automatic split injection.

Combination of adsorption and size-exclusion chromatography for the determination of fatty acid monomers, dimers and polymers

Abstract A procedure based on adsorption and size-exclusion chromatography is proposed for evaluating fatty acid monomers, dimers and polymers in fats subjected to thermal oxidation. Starting from fatty acid methyl esters, two fractions of different polarity are obtained by silica column chromatography and submitted to a second separation by high-performance size-exclusion chromatography. The procedure allows the determination of unaltered fatty acids in addition to four groups of degradation compounds: non-polar fatty acid dimers, oxidized fatty acid monomers, polar fatty acid dimers and fatty acid polymers.

Relationships between quality of crude and refined edible oils based on quantitation of minor glyceridic compounds

The relationships between crude and refined oils are examined by quantitation of minor glyceridic compounds, namely, oxidized triglyceride monomers, dimers and diglycerides, associated with oil quality. Particularly, two groups of compounds, i.e. oxidized triglyceride monomers and diglycerides, are of especial interest as they are indicative of oxidative and hydrolytic alterations, respectively. Olive, sunflower and soybean oils differing in initial quality, as evaluated by classical indices and levels of undesirable minor compounds, were subjected to physical and alkali refining in a laboratory system. In all assays, results indicated that amounts of oxidized triglyceride monomers and diglycerides in refined oils remained close to those found in the starting crude oils. Triglyceride dimers were the only group of compounds showing a significant increase, which was dependent on fatty acid composition and initial quality of crude oils. The main conclusion is that quantitation of minor glyceridic compounds in refined oils not only offers a new possibility for quality evalution but also allows the crude oils to be characterised by the presence of markers of oxidative and hydrolytic alterations.

Characterisation of aldehydic acids in used and unused frying oils

Abstract Aldehydic acids, expected to be present in auto-oxidised lipids as a result of decomposition of hydroperoxides by β-scission reactions, were analysed in unused and in frying oils used for two days. The oils studied were partially hydrogenated rapeseed/palm oil mixture, conventional sunflower oil and high oleic acid sunflower oil. The method involved saponification of lipids, elimination of the unsaponifiable matter, transmethylation and further fractionation of the methyl esters into polar and non-polar fractions by silica column chromatography. Both fractions were analysed by high-performance size-exclusion chromatography to determine the levels of non-polar dimers, polar dimers and oxidised monomers. The polar fraction was also analysed by gas chromatography and gas chromatography–mass spectrometry. Using this approach, the aldehydic acid methyl esters: methyl 8-oxooctanoate, methyl 9-oxononoate, methyl 10-oxo-8-decenoate, methyl 11-oxo-9-undecenoate and methyl 12-oxo-9-dodecenoate were characterised in used as well as unused frying oils.