Application of impedance spectroscopy for the characterization of hams during post-salting / Aplicación de la espectroscopia de impedancia para la caracterización de jamones durante el post-salado

Background: The smart control for food and feed technologies consist in the development of new methods that facilitate the control of productive processes guaranteeing the quality and safety of agrofood products. The importance given to this research line is a clear indicator of the interest of all of the agents implicated in promoting the introduction of innovative technologies. The goal is to implement new, fast, economical, analytical techniques, which constitute a real alternative to traditional control procedures. Objective: The aim of this study was to evaluate the use of an electronic sensor based on the impedance spectroscopy technique for the characterization of hams during the post-salting step (8, 10, 12 and 14 weeks). Materials and methods: 60 hams from three different categories (fat, semi-fat and lean), were tray salted under the conditions of a company (xNaCl = 0.11 g/g dry matter). For each time, samples were first evaluated with the electronic method (non-destructive analysis) and then analytical determinations of: mass variation, moisture content, fat content, salt content and water activity were performed on each ham in different zones. The electric data were evaluated using Principal Component Analysis (PCA) and regression with Partial Least Squares (PLS) through the analytical data. Results: The PCA analysis discriminated between the different evaluated zones. At eighth week 79.06% of the variance was explained and at tenth week, the 82.53%. No relation was observed for the different ham categories. The correlation between the impedance signal and the analytical determinations showed the best cross validation coefficient (R2CV) values for moisture content (0.75) and water activity (0.73). Conclusions: The impedance spectroscopy technique generated different signals between the zones of analysis during the first two post-salting times, eight and ten weeks, in which physicochemical differences were also observed as a consequence of the variation in the salt concentration between zones.

Antecedentes: El control inteligente de los alimentos y las tecnologías alimentarias, consiste en el desarrollo de nuevos métodos que facilitan el control de los procesos productivos y garantizan la calidad y seguridad de los productos agroalimentarios. La relevancia concedida a esta línea de investigación es un claro indicador del interés de todos los agentes implicados en impulsar la introducción de tecnologías innovadoras. La meta es implementar nuevas técnicas analíticas rápidas y económicas, que constituyan una alternativa real a los procedimientos tradicionales de control. Objetivo: Evaluar el uso de un sensor electrónico basado en la técnica de la espectroscopia de impedancia para la caracterización de jamones durante el post-salado (8, 10, 12 y 14 semanas). Materiales y métodos: 60 jamones de tres categorías diferentes (grasa, semigrasa y magra) fueron salados en bandeja bajo las condiciones de una empresa (xNaCl = 0.11 g/g base seca). A cada tiempo establecido, las muestras seleccionadas se evaluaron utilizando el método electrónico (análisis no destructivo) y se realizaron determinaciones analíticas de: variación de masa, contenido de humedad, contenido de grasa, contenido de sal y actividad de agua, en diferentes zonas de la muestra. La información electrónica se analizó mediante análisis de componentes principales (PCA) y correlaciones (PLS) entre la señal de impedancia y las determinaciones analíticas. Resultados: El análisis de PCA discriminó entre las diferentes zonas de análisis evaluadas. A la octava semana se explicó un 79.06% de la varianza de las muestras y a la décima, un 82.53%. No hubo relación entre las diferentes categorías de jamones. La correlación estadística de la señal de impedancia con las determinaciones analíticas mostró los mejores valores de coeficiente de validación cruzada (R2CV) para el contenido de humedad (0.75) y la actividad de agua (0.73). Conclusiones: La técnica de espectroscopia de impedancia generó señales diferentes entre las zonas de análisis durante los dos primeros tiempos de post-salado, ocho y diez semanas, en los que también se observaron diferencias fisicoquímicas como consecuencia de la variación en la concentración salina entre zonas.

UDP-galactose 4-epimerase from Kluyveromyces fragilis: equilibrium unfolding studies.

UDP-galactose 4-epimerase from yeast (Kluyveromyces fragilis) is a homodimer of total molecular mass 150 kDa having possibly one mole of NAD/dimer acting as a cofactor. The molecule could be dissociated and denatured by 8 M urea at pH 7.0 and could be functionally reconstituted after dilution with buffer having extraneous NAD. The unfolded and refolded equilibrium intermediates of the enzyme between 0-8 M urea have been characterized in terms of catalytic activity, NADH like characteristic coenzyme fluorescence, interaction with extrinsic fluorescence probe 1-anilino 8-naphthelene sulphonic acid (ANS), far UV circular dichroism spectra, fluorescence emission spectra of aromatic residues and subunit dissociation. While denaturation monitored by parameters associated with active site region e.g. inactivation and coenzyme fluorescence, were found to be cooperative having delta G between -8.8 to -4.4 kcals/mole, the overall denaturation process in terms of secondary and tertiary structure was however continuous without having a transition point. At 3 M urea a stable dimeric apoenzyme was formed having 65% of native secondary structure which was dissociated to monomer at 6 M urea with 12% of the said structure. The unfolding and refolding pathways involved identical structures except near the final stage of refolding where catalytic activity reappeared.