Mónica Armenteros

Analysis of protein carbonyls in meat products by using the DNPH-method, fluorescence spectroscopy and liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS).

Liquid chromatography-electrospray ionisation-mass spectrometry (LC-ESI-MS) was applied as an advanced methodology to study the suitability of using α-aminoadipic semialdehyde (AAS) and γ-glutamic semialdehyde (GGS) as protein oxidation markers in meat products. The results obtained were compared to those obtained by using the DNPH-method and fluorescence spectroscopy for the analysis of protein carbonyls. Lipid oxidation was also investigated in order to elucidate the relationship between lipid and protein oxidation measurements. Both semialdehydes were originally detected in a food system which proves that lysine, arginine and proline are degraded as a result of oxidative reactions to yield AAS and GGS in meat products. A lack of consistency was observed between the MS results for AAS and GGS and the values obtained by the DNPH-method and the fluorescence spectroscopy. Unlike the last two methods, AAS and GGS measurements have proved to be unaffected by the composition or the structure of the food matrix providing precise information about the fate of particular amino acids during processing of muscle foods. These semialdehydes, and particularly GGS, could be used as indicators of protein oxidation in meat products like TBARS numbers are commonly used as lipid oxidation markers. In fact, a significant correlation was found between GGS values and TBARS highlighting the timely interaction between lipid and protein oxidation.

Biochemical and sensory changes in dry-cured ham salted with partial replacements of NaCl by other chloride salts.

The reduction of the content of sodium chloride in dry-cured ham was studied in to prevent the problems related to high sodium intake (i.e. the hypertension). One of the possibilities to reduce the sodium content is the partial replacement of sodium chloride by mixtures of potassium, magnesium and calcium chloride salts. The effect of two salting formulations (formulation II: 50% NaCl-50% KCl and formulation III: 55% NaCl, 25% KCl, 15 CaCl(2) and 5 MgCl(2)) on the protease activity through the dry-curing process and on the sensory characteristics of the final product was evaluated and compared to those of control hams (formulation I, 100% NaCl). Sensory attributes were all affected in the hams containing CaCl(2) and MgCl(2) while hams containing 50% KCl and NaCl (formulation II) were better valued, except for the attribute taste probably due to the potassium contribution to bitter taste.

Effect of different temperature-time combinations on lipid and protein oxidation of sous-vide cooked lamb loins.

Forty-five lamb loins were subjected to sous-vide cooking at different combinations of temperature (60, 70 and 80 °C) and time (6, 12 and 24 h) to assess the effect on the oxidative stability of lipids and proteins. Heating induced both lipid and protein oxidation in lamb loins. Higher cooking temperature-time combinations increased conjugated dienes and decreased thiobarbituric reactive substances (TBARS) values and hexanal. Total protein carbonyls increased throughout time at all cooking temperatures considered, while α-aminoadipic (AAS) and γ-glutamic semialdehydes (GGS) increased when cooking at 60 °C but not at 80 °C. Links between the decrease in secondary compounds from lipid oxidation due to cooking at higher temperatures and for longer times with the increased levels of 3-methylbutanal and greater differences between total protein carbonyls and AAS plus GGS were hypothesised.

Biochemical and sensory properties of dry-cured loins as affected by partial replacement of sodium by potassium, calcium, and magnesium.

An attempt to decrease the NaCl content in dry-cured products through the use of three different salting treatments (II: 55% NaCl, 25% KCl, 15% CaCl(2), 5% MgCl(2); III: 45% NaCl, 25% KCl, 20% CaCl(2), 10% MgCl(2); and IV: 30% NaCl, 50% KCl, 15% CaCl(2), 5% MgCl(2)) in comparison to a control (I: 100% NaCl) was assayed to evaluate the biochemical and sensory characteristics in the final product. Most proteolytic enzyme activities from the loins submitted to the experimental salting treatments, especially treatments II and IV, remained higher than those salted traditionally (control). The higher aminopeptidase activity was also reflected in a larger release of free amino acids. Finally, a sensory paired comparison test revealed that those loins salted with the treatment II were not significantly different from the loins salted traditionally (100% NaCl), so that this treatment could be successfully used for sodium reduction.

Influence of partial replacement of NaCl with KCl, CaCl2 and MgCl2 on lipolysis and lipid oxidation in dry-cured ham.

Sodium intake above nutritional recommendations may involve harmful consequences to health such as the increased risk of cardiovascular diseases. Dry-cured ham constitutes a product with a relatively large amount of sodium. Thus, to obtain a healthier product for consumers with reduced sodium content, two formulations containing KCl alone (formulation II) or mixed with CaCl2 and MgCl2 (formulation III) have been proposed to partially replace NaCl. Lipolysis and lipid oxidation occurring in hams processed with these formulations have been studied since they have direct influence on the final flavor. No significant differences in acid lipase activity or lipid oxidation were found at the end of the process between the alternative formulations and formulation I (control with 100% NaCl). Differences in some free fatty acids, generated along the processing, were detected among treatments and at the end of dry-curing. Data suggests a slight trend towards a major lipolysis during treatment III.

Pre-freezing raw hams affects quality traits in cooked hams: potential influence of protein oxidation.

The influence of protein carbonylation and lipid oxidation on colour and texture changes in cooked hams from fresh and pre-frozen (frozen/thawed) raw material was studied. Samples from three muscles, biceps femoris (BF) quadriceps femoris (QF) and semimembranosus (SM) were analysed for the gain of specific protein carbonyls, α-aminoadipic and γ-glutamic semialdehydes, the gain of TBA-RS and their colour and texture properties by instrumental and sensory techniques. The formation of protein carbonyls occurred concomitantly with an intense loss of redness and increase of hardness. Both phenomena were found to be more intense in QF and SM muscles in cooked hams elaborated from frozen material. Lipid oxidation played a negligible role on the impaired quality traits observed in cooked hams as a result of pre-freezing. Plausible mechanisms by which protein carbonylation may be implicated in the loss of quality in cooked hams produced from pre-frozen material are discussed.

Evolution of nitrate and nitrite during the processing of dry-cured ham with partial replacement of NaCl by other chloride salts

Nitrate and nitrite are commonly added to dry-cured ham to provide protection against pathogen microorganisms, especially Clostridium botulinum. Both nitrate and nitrite were monitored with ion chromatography in dry-cured hams salted with different NaCl formulations (NaCl partially replaced by KCl and/or CaCl(2), and MgCl(2)). Nitrate, that is more stable than nitrite, diffuses into the ham and acts as a reservoir for nitrite generation. A correct nitrate and nitrite penetration was detected from the surface to the inner zones of the hams throughout its processing, independently of the salt formulation. Nitrate and nitrite achieved similar concentrations, around 37 and 2.2 ppm, respectively in the inner zones of the ham for the three assayed salt formulations at the end of the process, which are in compliance with European regulations.

Mediterranean Berries as Inhibitors of Lipid Oxidation in Porcine Burger Patties Subjected to Cooking and Chilled Storage

The efficiency of extracts from Arbutus unedo L. (AU), Crataegus monogyna L. (CM), Rosa canina L. (RC), and Rubus ulmifolius Schott. (RU) to inhibit lipid oxidation in raw, cooked and cooked and chilled (2°C/12 d) porcine burger patties, was investigated. The modification of the fatty acid profile during processing treatments (cooking and chilling), the quantitative measurements of thiobarbituric acid reactive substances (TBA-RS), and lipid-derived volatiles, were used as indicators of lipid oxidation. Polyunsaturated fatty acids (PUFA) gradually decreased during cooking and the subsequent storage of cooked burger patties with this decrease being significantly greater (P<0.05) in control patties than in those with added berry extracts. In accordance, the control patties showed significantly higher TBA-RS numbers and counts of lipid-derived volatiles in all treatments when compared to the berry-added counterparts (P<0.05). Results from the present work show, for the first time, that extracts from A. unedo, C. monogyna, R. canina, and R. ulmifolius are promising antioxidants which could enhance the nutritional, safety and sensory properties of porcine burger patties.

Application of Natural Antioxidants from Strawberry Tree （Arbutus unedo L.） and Dog Rose （Rosa canina L.） to Frankfurters Subjected to Refrigerated Storage

The effect of the addition of natural antioxidants from strawberry tree (Arbutus unedo L.; AU) and dog rose (Rosa canina L.; RC), in frankfurters elaborated with or without the addition of antioxidant additives (sodium ascorbate and nitrite) was studied. Six different types of experimental frankfurters were prepared depending on the addition of phenolic-rich extracts from RC and AU and the presence (P) or absence (C) of antioxidant additives. Thiobarbituric acid reactive substances (TBARS)-numbers significantly increased during chilled storage of C-frankfurters while additives and fruit phenolics inhibited lipid oxidation in P-frankfurters. The amount of protein carbonyls significantly increased in all treatments except in P-AU frankfurters. The discoloration process that occurred during the chilled storage was reduced by the addition of substances with proven antioxidant activity (P-frankfurters). Texture characteristics as hardness, springiness, cohesiveness and gumminess also suffered a significant deterioration in C-frankfurters. The use of phenolic fruit extracts in combination with traditional antioxidant additives is a successful strategy to enhance the oxidative stability of frankfurters without modifying their color and texture properties.