J.A. Ortuño

El ácido fítico en la alimentación humana/Phytic acid in human nutrition:

nutrientes’ capaces de disminuir la disponibilidad de los nutrientes esenciales (Mitjavila, 1990). Estos compuestos se clasifican en funci6n del tipo de nutrientes con los que interfieren según afecten a la digestion o al metabolismo de las proteinas, a la asimilaci6n de los minerales, o inactiven o aumenten el requerimiento en vitaminas. Hay que tener en cuenta que un mismo antinutriente puede formar parte de uno o varios de estos grupos. Este es el caso del Scido fitico, cuya acci6n se basa en la formacion de complejos insolubles con proteinas y minerales, convirti6ndolos en no asimilables por el organismo bajo condiciones fisiol6gicas (Reddy y Salunkhe, 1981; Harland, 1989). No obstante, en los ultimos anos se han desarrollado numerosos estudios sobre los efectos

Proximate and mineral composition of dried salted roes of hake (Merluccius merluccius, L.) and ling (Molva molva, L.)

Proximate analyses and mineral composition of dried salted roes of hake (Merluccius merluccius) and ling (Molva molva) were determined. Both roes contained a significant amount of protein (39.1 and 43.6%, respectively) and lipid (14.13 and 14.80, respectively) because of their physiological role as reserves. Because this product is a typical food of one particular area, no specific data have been found in the literature about proximate and mineral compositions. Only trace elements (Fe, Cu and Zn) and macronutrients (crude protein and carbohydrates) varied with the type of roe. The most important minerals were Fe, Zn, K and Na. However, Na content was very high, and for this reason dried salted roe cannot be recommended for people who require dietetic control of blood pressure.

In vitro protein digestibility and mineral availability of green beans (Phaseolus vulgarisL) as influenced by variety and pod size

Three varieties of green beans (Cleo, Strike and Sentry) were harvested and sorted into four fractions according to pod size (diameter 10 mm). Ash content and dietary fibre increased significantly as pod size increased mainly in Cleo and Strike beans. Strike showed the highest fibre content (378.0 g kg -1 ) but the lowest carbohydrate (364.6 g kg -1 ) and ash (68.4 g kg -1 ) values. Mean values for Fe and Mg content were higher in Cleo beans (70.9 and 27.1 mg kg - 1 , respectively), Zn, Cu and Mg were higher in Strike beans (48.7 mg kg -1 , 22.4 mg kg -1 and 3.15 g kg -1 , respectively) while Na and Ca values were maximum in Sentry (459.1 mg kg -1 and 7.11 g kg -1 , respectively). Trypsin inhibitor was negatively related to in vitro protein digestibility but no relationship was found between this last parameter and phytic acid content. This antinutrient, together with dietary fibre, and a negative influence on in vitro mineral dialysability of green beans.

Determination of zinc (II) in pharmaceuticals based on a flow-through bulk optode.

A method based on flow injection (FI), was applied for the determination of Zn (II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphthol in a plasticized poly (vinyl chloride) membrane entrapped in a cellulose support. The calibration graph plotting the reflectance at 562 nm versus [Zn (II)] was linear in the range 0.16-3.27 mgl(-1) (2.5 x 10(-6)-5 x 10(-5) M) with a detection limit of 0.10 mgl(-1). The variation coefficients of the sensor response for 0.33 mgl(-1) of Zn (II) were +/-0.11% for consecutive measurements (n=10), +/-0.19% between days (n=5) and +/-0.22% between different membranes (n=6). The sensor can be readily regenerated with the same acetic/acetate carrier of pH 3.9. The FI method proposed was applied to the determination of zinc (II) in pharmaceuticals.

Assay of acetylcholinesterase activity by potentiometric monitoring of acetylcholine

An acetylcholine-selective electrode based on a plasticized polymeric membrane has been developed. The electrode exhibited good selectivity for acetylcholine (ACh) over choline and some common ions, low drift, and a fast response to ACh. The response was linear over an ACh concentration range of 1×10(-6) to 1×10(-3) M with a slope of 59.1±0.1 and a detection limit of 1.5×10(-7)±1.2×10(-8) M. The electrode was used to monitor enzymatic ACh hydrolysis catalyzed by acetylcholinesterase (AChE) at different substrate and enzyme concentrations. A kinetic data analysis permitted the determination of the Michaelis-Menten constant of the enzymatic hydrolysis and AChE activity in the range of 2×10(-5) to 3.8×10(-1)U ml(-1).

Amino acids and in vitro protein digestibility changes in green asparagus (Asparagus officinalis, L.) during growth and processing

Abstract This paper reports on the amino acid, in vitro protein digestibility and dietary fiber changes in green asparagus during development and processing. Green asparagus spears were classified into fine (F, ≤8 mm), middle (M, 9–11 mm), thick (T, 12–14 mm), very thick (VT, 15–19 mm) and extra thick (ET, ≥20 mm). This plant food was found to be a good source of protein (> 30% DW), containing most of the essential and nonessential amino acids. However, the arginine, cystine, γ-amino-butyric acid, glutamine, lysine, ornithine, phenylethanolamine, serine and taurine contents decreased significantly ( P ≤ 0.05) with blanching and canning. Green asparagus protein showed an adequate amino acid score according to FAO/WHO recommendations, and seemed to contribute most of the essential amino acids, except histidine and lysine, which were limiting amino acids. In-vitro protein digestibility (IVPD) tended to decrease during development (77.30% at F to 71.43% at ET), improving during processing, mainly after blanching. The increase in soluble dietary fiber and decrease in insoluble dietary fiber during processing might relate to the improvement of IVPD noted.

Kinetic methods for the determination of cadmium(II) based on a flow-through bulk optode.

Three kinetic methods based on flow injection, flow, and stopped-flow injection were applied for the determination of Cd(II) using a flow-through bulk optode membrane that incorporates 1-(2-pyridylazo)-2-naphtol (PAN) in a plasticized poly(vinyl) chloride membrane entrapped in a cellulose support. The calibration graphs plotting the reflectance at 560 nm versus [Cd(II)](1/2) for the first two methods and versus [Cd(II)] for the third were linear up to 56.2 mg l(-1). The detection limits of the methods were 0.01, 0.06 and 0.8 mg l(-1), respectively. The FI method was selected for application purposes. The variation coefficient of the sensor response for 11.2 mg l(-1) of Cd(II) was +/-0.31 and +/-0.65% between different membranes. The sensor can be readily regenerated with a carrier (acetic-acetate) buffer of pH 4. The FI method was applied to the determination of cadmium in an alloy and in water.

Voltammetric behaviour and square-wave voltammetric determination of the potent antioxidant and anticarcinogenic agent ellagic acid in foodstuffs

The voltammetric behaviour of ellagic acid (EA) is investigated by cyclic, differential pulse and square-wave voltammetry (CV, DPV and SWV, respectively). Based on the anodic oxidation peak at approximately 0.42V in acetic/acetate buffer (pH 5.5) a robust and a highly reliable square-wave voltammetric method is presented for the determination of EA. The oxidation peak current was linearly dependent on the concentration of EA in the range of 1.0×10(-7)-1.5×10(-6)mol/L (r=0.9997), with a detection limit of 1.0×10(-8)mol/L (S/N=3) and a quantification limit of 3.4×10(-8)mol/L (S/N=10), good reproducibility and a satisfactory level of selectivity towards others polyphenols. The proposed method was applied to the determination of free and total EA in fruits, nuts and juices with good analytical results being obtained.

Biodisponibilidad del selenio y métodos de evaluación/Selenium bioavailability and methods of evaluation

hasta 1979, cuando un grupo de investigadores chinos puso de manifiesto la relaci6n entre la baja concentraci6n del selenio y la enfermedad de Keshan, una miocardiopatia que afecta sobre todo a ninos pequenos y mujeres en edad f6rtil (Keshan Disease Research Group, 1979). Ademas de esta enfermedad, las principales patologias asociadas con la deficiencia del selenio en el hombre son problemas musculares, alteraciones sanguineas, enfermedades neurologicas degenerativas, trastornos digestivos, enfermedades cardiovasculares y afecciones reumaticas (N~ve et al., 1987). En los animales, la prevenc16n de varias enfermedades cr6nicas tales como la necrosis hepatica, la fibrosis pancreatica o la degeneraci6n de los m6sculos esquel6tico y cardiaco, se han corregido con un adecuado suplemento de este.elemento traza (Neve et al., 1984). De todas las funciones biol6gicas del selenio, la mas conocida e importante es la de formar parte,

Facilitated ion transfer of protonated primary organic amines studied by square wave voltammetry and chronoamperometry

The transfer of the protonated forms of heptylamine, octylamine, decylamine, procaine and procainamide facilitated by dibenzo-18-crown-6 from water to a solvent polymeric membrane has been investigated by using cyclic square wave voltammetry. The experimental voltammograms obtained are in good agreement with theoretical predictions. The values of the standard ion transfer potential, complexation constant and diffusion coefficient in water have been obtained from these experiments, and have been used to draw some conclusions about the lipophilicity of these species and the relative stability of the organic ammonium complexes with dibenzo-18-crown-6. The results have been compared with those provided by linear sweep voltammetry. Calibration graphs were obtained with both techniques. An interesting chronoamperometric method for the determination of the diffusion coefficient of the target ion in the membrane has been developed and applied to all these protonated amines.