Francesc Guardiola

Determination of hydroperoxides in foods and biological samples by the ferrous oxidation-xylenol orange method: a review of the factors that influence the method's performance.

The oxidation of lipids yields both primary and secondary oxidation compounds that produce undesirable biological effects [1– 3] and includes loss of nutritional value and sensory problems in foods [4,5]. Primary oxidation products include lipid hydroperoxides (HP) which can further decompose into secondary oxidation products and/or react with other compounds present in the food or biological material [6–8]. The measurement of HP, in connection with free radicals and other reactive oxygen species, has been used as indication of oxidative stress in biological samples [7,9–13] and associated with the pathogenesis of several diseases such as atherosclerosis [14,15], cancer [16,17], and neurodegenerative diseases [18–20]. Unfortunately, the majority of analyses to assess lipid oxidation in biological and food samples determine only secondary oxidation products, whereas the determination of HP could give an early and more accurate indication of the oxidative status. Hence, a proper assessment of the degree of oxidation in any kind of sample should be accomplished by the appropriate selection of the methods that include the determination of both primary oxidation products and their decomposition products [8,21,22]. However, the determination of lipid HP is quite challenging because many different kinds of HP are produced from lipid oxidation and HP are reactive compounds that rapidly react and decompose

Cholesterol oxidation in frozen dark chicken meat: influence of dietary fat source, and α-tocopherol and ascorbic acid supplementation.

A factorial design assessed the effect of dietary fat source (beef tallow, fresh and oxidized sunflower oils, and linseed oil), and α-tocopheryl acetate (α-TA) and ascorbic acid (AA) supplementation (225 and 110 mg/kg feed, respectively) on the cholesterol oxidation product (COP) content and 2-thiobarbituric acid (TBA) values in raw and cooked dark chicken meat vacuum packaged and stored at -20°C for 7 months. COP determination showed good linearity, recovery and precision. Dietary α-TA was highly effective in protecting raw or cooked meat from cholesterol and fatty acid oxidation, regardless of its degree of unsaturation. In contrast, AA supplementation was ineffective and even promoted oxidation in raw meat from broilers fed unsaturated fat diets that had not been supplemented with α-TA. Oxidation values (raw or cooked meat) from α-TA or α-TA+AA supplemented diets were not statistically different (P>0.05). TBA and COP values were significantly correlated in raw samples (r=0.6466, P=0.0001).

Dietary Strategies to Improve Nutritional Value, Oxidative Stability, and Sensory Properties of Poultry Products

Consumers demand both safer and more nutritious food products exempt of non-natural origin preservatives or other food additives. In this frame, products with lower fat content and/or a higher ratio in unsaturated fatty acids, especially n-3 fatty acids, are desired because these lipids can help prevent the development of cardiovascular and inflammatory pathologies. The intake of meat products is of interest because they are an excellent source of vitamins and minerals. In addition, the shelf-life of meat products can be extended by the presence of natural antioxidants coming from different sources such as plant extracts. Therefore, different strategies have been studied to improve the nutritional value, oxidative stability, and sensory characteristics of meat products and eggs through different mineral and natural dietary supplements. In comparison to other strategies, dietary supplements present the advantage that first the living animals may efficiently distribute the compounds throughout the tissues and second, the dietary supplementation is safer because the resulting enriched meat products and eggs ensure tolerable amounts in humans. Poultry meats and eggs are widely consumed and their fatty acid profile and tocopherol content can be easily modified through different dietary strategies thus being excellent models to improve their nutritional value and oxidative stability.

Comparison of three methods for the determination of oxysterols in spray-dried egg

Three methods for the GC determination of oxysterols (OSs) in spray-dried egg, which combine different steps of purification, are compared. In addition, the efficiency of silica cartridges in the purification of OSs using four different systems of elution with increasing polarities is studied. The absence of cholesterol oxidation during the application of the analytical procedures is checked, and the linearity of the response and the chromatographic limits of detection and quantification are established. The methods are characterized by the calculation of precision and recovery for the different OSs. The method based on saponification alone is rejected, since it shows much lower precision. The method that includes saponification and silica cartridge purification offers higher reliability than the method based on cartridge purification alone, because it shows a higher precision and larger samples can be processed, which improves the limits of detection and quantification.

Increased susceptibility to exacerbated liver injury in hypercholesterolemic ApoE-deficient mice: potential involvement of oxysterols

The contribution of metabolic factors to the severity of liver disease is not completely understood. In this study, apolipoprotein E-deficient (ApoE-/-) mice were evaluated to define potential effects of hypercholesterolemia on the severity of carbon tetrachloride (CCl4)-induced liver injury. Under baseline conditions, hypercholesterolemic ApoE-/- mice showed increased hepatic oxidative stress (SOD activity/4-hydroxy-2-nonenal immunostaining) and higher hepatic TGF-beta1, MCP-1, and TIMP-1 expression than wild-type control mice. After CCl4 challenge, ApoE-/- mice exhibited exacerbated steatosis (Oil Red O staining), necroinflammation (hematoxylin-eosin staining), macrophage infiltration (F4/80 immunohistochemistry), and fibrosis (Sirius red staining and alpha-smooth muscle actin immunohistochemistry) and more severe liver injury [alanine aminotransferase (ALT) and aspartate aminotransferase] than wild-type controls. Direct correlations were identified between serum cholesterol and hepatic steatosis, fibrosis, and ALT levels. These changes did not reflect the usual progression of the disease in ApoE-/- mice, since exacerbated liver injury was not present in untreated age-paired ApoE-/- mice. Moreover, hepatic cytochrome P-450 expression was unchanged in ApoE-/- mice. To explore potential mechanisms, cell types relevant to liver pathophysiology were exposed to selected cholesterol-oxidized products. Incubation of hepatocytes with a mixture of oxysterols representative of those detected by GC-MS in livers from ApoE-/- mice resulted in a concentration-dependent increase in total lipoperoxides and SOD activity. In hepatic stellate cells, oxysterols increased IL-8 secretion through a NF-kappaB-independent mechanism and upregulated TIMP-1 expression. In macrophages, oxysterols increased TGF-beta1 secretion and MCP-1 expression in a concentration-dependent manner. Oxysterols did not compromise cell viability. Taken together, these findings demonstrate that hypercholesterolemic mice are sensitized to liver injury and that cholesterol-derived products (i.e., oxysterols) are able to induce proinflammatory and profibrogenic mechanisms in liver cells.

Antioxidative effect of lipophilized caffeic acid in fish oil enriched mayonnaise and milk

The antioxidative effect of lipophilized caffeic acid was assessed in two different fish oil enriched food products: mayonnaise and milk. In both emulsion systems, caffeic acid esterified with fatty alcohols of different chain lengths (C1-C20) were better antioxidants than the original phenolic compound. The optimal chain length with respect to protection against oxidation was, however, different for the two food systems. Fish oil enriched mayonnaise with caffeates of medium alkyl chain length (butyl, octyl and dodecyl) added resulted in a better oxidative stability than caffeates with shorter (methyl) or longer (octadecyl) alkyl chains. Whereas in fish oil enriched milk emulsions the most effective caffeates were those with shorter alkyl chains (methyl and butyl) rather than the ones with medium and long chains (octyl, dodecyl, hexadecyl and eicosyl). These results demonstrate that there might be an optimum alkyl chain length for each phenolipid in each type of emulsion systems.

Polycyclic aromatic hydrocarbons in frying oils and snacks.

The high incidence of lung cancer observed among Chinese women has been associated with exposure to fumes from cooking oil. Polycyclic aromatic hydrocarbons (PAHs) are a class of potentially mutagenic substances emitted from cooking oils heated at high temperatures. The objective of this study was to investigate whether deep frying with different oils under different conditions leads to the development of PAHs either in the oil or in the fried product (snacks). PAH analysis was carried out with solid-phase extraction followed by reverse-phase high-performance liquid chromatography and spectrofluorometric detection. Different oils were used to fry chips and extruded snacks in different industrial plants (continuous frying) at temperatures between 170 and 205 degrees C, and peanut oil was used to fry French fries and fish (discontinuous frying) at temperatures between 160 and 185 degrees C. No appreciable differences in PAH load was observed in the same oil before and after frying. Both before and after frying, the benzo[a]pyrene concentration in oils ranged from trace to 0.7 ppb. All the analyzed samples, including oils from fried snacks, had benzo[a]pyrene concentrations well below the 2 ppb limit recently proposed by the European Community.

Lipid peroxidation induced by DHA enrichment modifies paracellular permeability in Caco-2 cells protective role of taurine

Dietary enrichment with docosahexaenoic acid (DHA) has numerous beneficial effects on health. However, the intake of high doses of polyunsaturated fatty acids can promote lipid peroxidation and the subsequent propagation of oxygen radicals. The purpose of this study was to evaluate the effect of DHA on lipid peroxidation and tight junction structure and permeability in Caco-2 cell cultures. Moreover, the effects of taurine, a functional ingredient with antioxidant properties, were also tested. Differentiated Caco-2 cell monolayers were maintained in DHA-supplemented conditions with or without added taurine. Incubation with 100 μM DHA increased lipid peroxidation and paracellular permeability, in parallel with a redistribution of the tight junction proteins occludin and ZO-1. Taurine partially prevented all of these effects. The participation of reactive oxygen and nitrogen species in increased paracellular permeability was also examined using various agents that modify the formation of superoxide radical, hydrogen peroxide, nitric oxide, and peroxynitrite. We conclude that hydrogen peroxide and peroxynitrite may be involved in the DHA-induced increase in paracellular permeability and that the protective role of taurine may be in part related to its capacity to counteract the effects of hydrogen peroxide.

Influence of Different Dietary Doses of n-3-or n-6-Rich Vegetable Fats and α-Tocopheryl Acetate Supplementation on Raw and Cooked Rabbit Meat Composition and Oxidative Stability

This study evaluates the effects of replacing beef tallow added to rabbit feeds (3% w/w) by different doses (0%, 1.5% and 3% w/w) of n-6- or n-3-rich vegetable fat sources (sunflower and linseed oil, respectively) and alpha-tocopheryl acetate supplementation (0 and 100 mg/kg) on the fatty acid composition, alpha-tocopherol content, and oxidation levels [assessed by analyzing thiobarbituric acid (TBA) and lipid hydroperoxide values] in rabbit meat. We also measured these parameters after cooking and refrigerated storage of cooked rabbit meat. Both dietary alpha-tocopheryl acetate supplementation and the dose and source of fat added to feeds influenced meat fatty acid composition, modifying the n-6/n-3 ratio, which was more nutritionally favorable when linseed oil was used. Furthermore, the addition of linseed oil and the supplementation with alpha-tocopheryl acetate enhanced long-chain PUFA biosynthesis. However, the addition of 3% linseed oil increased meat oxidation, and although it was reduced by dietary supplementation with alpha-tocopheryl acetate in raw meat, this reduction was not as effective after cooking. Therefore, dietary supplementation with 1.5% linseed oil plus 1.5% beef tallow and with alpha-tocopheryl acetate would be recommended to improve the nutritional quality of rabbit meat.

Validation of mineralisation procedures for the determination of selenium, zinc, iron and copper in chicken meat and feed samples by ICP-AES and ICP-MS

Mineralisation procedures for determining Fe, Zn, Cu and Se in chicken meat and feed samples were studied. We employed three different sample preparation procedures to determine these elements by ICP-AES and ICP-MS. An open vessel wet mineralisation procedure was used for chicken meat analysis. Here, in the case of the trace elements Cu and Se, it was necessary to concentrate and reduce the acid matrix effects so samples were heated to dryness. However, this procedure causes Se volatilisation losses leading to low recoveries and high variability. Therefore, a closed vessel microwave mineralisation procedure was developed for chicken meat samples. The results obtained using this procedure presented a much lower variability (2.5, 2.0 and 3.1% of RSD for Zn, Fe and Se, respectively) and were consistent with the certified values for the reference material being assessed. Cu content, despite presenting a relatively high variability (RSD = 11%) also agreed with the certified value for the reference material. Recoveries in spiked chicken meat were 103–105% for Zn, 107–108% for Fe, 97–100% for Se and 89–94% for Cu. However, when this procedure was used with feeds, some mineralised samples presented siliceous particles which led to a lower recovery of Zn compared with that recorded when using another microwave mineralisation procedure in which these particles had been dissolved with hydrofluoric acid. This alternative mineralisation procedure for feeds was validated by assessing the precision, recovery and sensitivity when determining each element.