Jacobo Iglesias

Solid-phase microextraction method for the determination of volatile compounds associated to oxidation of fish muscle

A procedure for the determination of volatile compounds derived from lipid oxidation of fish muscle samples is presented. Analytes are concentrated on a solid-phase microextraction fiber employed in the headspace mode (HS-SPME), and selectively determined using gas chromatography in combination with mass spectrometry (GC-MS). The influence of several parameters on the efficiency of microextraction such as type of fiber, volume of sample, time, temperature, salting-out effect and stirring was systematically investigated. A saline extraction of fish muscle followed by incubation on a Carboxen-polydimethylsiloxane fiber during 30min at 60 degrees C gave the most effective and accurate extraction of the analytes. Quantification of them was performed by MS in the selected ion monitoring mode and by the internal standard method. Satisfactory linearity, repeatability and quantification limits were achieved under these conditions. The method was applied to the determination of the volatile compounds associated to oxidation of Atlantic horse mackerel (Trachurus trachurus) minced muscle and excellent correlations were obtained with chemical indexes for monitoring lipid oxidation as peroxide value and thiobarbituric acid reactive substances. This combined technique is fast, simple, sensitive, inexpensive and useful to monitor target compounds associated to fish rancidity as 1-penten-3-ol, 2,3-pentanedione or 1-octen-3-ol.

Caffeic Acid as Antioxidant in Fish Muscle: Mechanism of Synergism with Endogenous Ascorbic Acid and α-Tocopherol

In an emulsion of corn oil in water with the addition of caffeic acid (Caf-OH) and alpha-tocopherol (alpha-TOH), Caf-OH was found to be very active in delaying lipid oxidation without affecting significantly the kinetics for alpha-TOH degradation. In contrast, Caf-OH addition to fish muscle retarded both the degradation of endogenous alpha-TOH and the propagation of lipid oxidation, measured by peroxide value (PV) and thiobarbituric acid reactive substances (TBARS), with increasing effect with increasing Caf-OH addition (55.5-555.1 micromol/kg). Electron spin resonance (ESR) spectroscopy confirmed a higher capacity of Caf-OH to regenerate alpha-TOH via reduction of the alpha-tocopheroxyl radical compared to other cinnamic acid derivatives (o-coumaric, ferulic, and chlorogenic acids). Degradation of endogenous ascorbate (AscH(-)) was accelerated at higher concentration of Caf-OH in fish tissue, suggesting a role of AscH(-) in the regeneration of Caf-OH. These results indicate that the antioxidant mechanism of Caf-OH implies the protection of endogenous alpha-TOH localized in tissue membranes where lipid oxidation is initiated and, at the same time, Caf-OH regeneration by the endogenous AscH(-). These combined effects result in a stronger antioxidant protection against lipid oxidation by favoring, as a final point, the protection of alpha-TOH, which is suggested as the last defense of fish muscle against lipid oxidation.

Antioxidant mechanism of grape procyanidins in muscle tissues: Redox interactions with endogenous ascorbic acid and α-tocopherol

The present study investigates the antioxidant mechanism of grape procyanidins and, in particular, their aptitude to establish redox interactions with two important components of the endogenous antioxidant system of muscle tissues, α-tocopherol (α-TOH) and ascorbic acid (AA). To this end, the progress of lipid oxidation was monitored in fish muscle supplemented with grape procyanidins at the concentrations usually employed in antioxidant food applications, and then related to the redox stability of the endogenous α-TOH and AA. In addition to the lipid oxidation protective effect, the incorporation of procyanidins also provided an improvement of the redox stability of the endogenous components in a straight procyanidinic concentration-dependent manner. Results showed the capacity of procyanidins to repair oxidised α-TOH at medium-long term, and to delay the AA depletion. Therefore, such cooperative redox interaction of exogenous procyanidins adequately complements the natural α-TOH regenerative system supplied by AA that is efficient at the early post mortem stages.

Contribution of galloylation and polymerization to the antioxidant activity of polyphenols in fish lipid systems.

Polyphenolic fractions extracted from pine (Pinus pinaster) bark, grape (Vitis vinifera) pomace, and witch hazel (Hamamelis virginiana) bark were selected for investigating the influence of the number of phenolic units, polymerization, and the content of esterified galloyl residues (galloylation) on their efficacy for inhibiting lipid oxidation in fish lipid enriched foodstuffs. Experiments carried out with nongalloylated pine bark fractions with different polymerization degrees demonstrated that the number of catechin residues per molecule modulates their reducing and chelating properties in solution. In real food systems such as bulk fish oil and fish oil-in-water emulsions, the efficacy against lipid oxidation was highly dependent on the physical location of the antioxidant at the oxidative sensitive sites. The lowest polymerized fractions were the most efficient in bulk fish oil samples, whereas proanthocyanidins with an intermediate polymerization degree showed the highest activity in fish oil-in-water emulsions. Galloylation did not influence the antioxidant effectiveness of proanthocyanidins in bulk fish oils. The presence of galloyl groups favored the antioxidant activity of the polyphenols in emulsions, although results indicated that a high degree of galloylation did not improve significantly the activity found with medium galloylated proanthocyanidins. The results obtained in this research provide useful information about the relationship between structure and antioxidant activity in order to design antioxidant additives with application in fish oil-enriched functional foods.

Structure-activity relationships of polyphenols to prevent lipid oxidation in pelagic fish muscle.

The influence of polymerization (number of monomers) and galloylation (content of esterified gallates) of oligomeric catechins (proanthocyanidins) on their effectiveness to prevent lipid oxidation in pelagic fish muscle was evaluated. Non-galloylated oligomers of catechin with diverse mean polymerization (1.9-3.4 monomeric units) were extracted from pine (Pinus pinaster) bark. Homologous fractions with galloylation ranging from 0.25 to <1 gallate group per molecule were obtained from grape (Vitis vinifera) and witch hazel (Hamamelis virginiana). The results showed the convenience of proanthocyanidins with medium size (2-3 monomeric units) and low galloylation degree (0.15-0.25 gallate group/molecule) to inhibit lipid oxidation in pelagic fish muscle. These optimal structural characteristics of proanthocyanidins were similar to those lately reported in fish oil-in-water emulsions using phosphatidylcholine as emulsifier. This finding suggests that the antioxidant behavior of polyphenols in muscle-based foods can be mimicked in emulsions prepared with phospholipids as emulsifier agents. The present data give relevant information to achieve an optimum use of polyphenols in pelagic fish muscle.

Galloylation and Polymerization: Role of Structure to Antioxidant Activity of Polyphenols in Lipid Systems

Many polyphenols are present in foods and nature as individual congeners, but also polymerized in oligomeric and polymeric entities. Flavanols and their condensed polymers, proanthocyanidins, are widespread components in green tea, red wine, cocoa, grape seeds and pine bark, with an extremely variable number of polyphenolic residues (polymerization degree) and galloyl moieties (galloylation). Polymerization and galloylation are key structural elements in the healthy outcome and antioxidant activity of polyphenols. The present chapter resumes how size and composition diversity, particularly polymerization and galloylation, influence the physicochemical properties relevant for the antioxidant activity of polyphenols in foods and biological systems: the radical scavenging ability, chelation on redox active metals, interfacial partitioning, redox capacity to regenerate, or to be regenerated by co-antioxidants and to inactivate/active pro-oxidants. To evaluate these structural-activity relationships, the physicochemical properties of polyphenols, evaluated either in vitro or in situ in biological systems, will be assessed together with their antioxidant efficiency in food and biological lipid systems.