Beef meat electrical impedance spectroscopy and anisotropy sensing for non-invasive early assessment of meat ageing Jean-Louis Damez * , Sylvie Clerjon, Saı ¨d Abouelkaram, Jacques Lepetit UR370 Qualite ´ des Produits Animaux, INRA, F-63122 Saint-Gene `s-Champanelle, France Received 26 January 2007; received in revised form 9 July 2007; accepted 15 July 2007 Available online 8 August 2007 Abstract The objective of this work was to study the electrical anisotropy behaviour of beef meat during maturation for the purpose of early assessment of meat ageing. Early assessment of beef meat fibre strength allows customised ageing of raw materials and optimisation of refrigerated storage times. During the maturation phase connection proteins break down, causing structural changes, fragmentation of myofibrils and degradation of the cytoskeleton. These modifications produce effects on the strongly anisotropic character of the muscle structure that can be observed using a sensor based on the emission of a polarised wave. For example, by tracking variations in imped- ance according to the angle between the electrical field direction and the main direction of fibres, a measurement of structural state, and thus of maturation state, can be obtained. In this study, two specific directions were used: along and across meat fibres. A simple method using a sensor with aligned electrodes was used to measure lineic impedances and study contact impedances as parameters of interest. A lineic impedance index was defined as the difference between lineic impedance across and along meat fibres. The lineic impedance index and the contact impedance were shown to be closely correlated to meat fibres strength. These two parameters can therefore be used to predict meat maturation state. Ó 2007 Elsevier Ltd. All rights reserved. Keywords: Meat ageing; Tenderness; Electrical impedance spectroscopy; Anisotropy; Impedance; Sensor 1. Introduction The use of electrical measurements to study meat goes back to the 1930s with the pioneering work of Callow (1936, 1939), who was the first to describe the basic electri- cal properties of meat. In the decade 1960–1970 much work was carried out in the medical field on the electric proper- ties of biological tissues (skeletal muscles, cardiac muscle, skin, bone, etc.) (Ducrot et al., 1970; Fourcade et al., 1970; Thomasset, 1963). These studies were designed to evaluate the structural and (or) physiological integrity of these tissues. They prompted mathematical developments and the construction of models of the electrical properties of various biological tissues. 1.1. Evaluation of meat quality by electrical impedance 1.1.1. Evaluation of pH After the first works of Callow (1936), most of the work on electrical impedance of meat published since the 1970s concerns the use of this variable to monitor fall in pH or to evaluate ultimate pH mainly in pork (Swatland, 1985) but also in beef (Byrne, Troy, & Buckley, 2000). A major quality problem in pork is preventing the production of pale soft exudative (PSE) meats, which have low pH and are strongly exudative, and so are unsuitable for process- ing. In beef, one quality problem is dark firm dry (DFD) meats with high pH and high susceptibility to spoiling. These two quality defects are associated with membrane modifications and changes in the extracellular medium. They are therefore bound to affect electrical properties. Most of the studies in this field have been focused on the early detection of quality defects, i.e. 45 min to 1 h after 0260-8774/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.jfoodeng.2007.07.026 * Corresponding author. Tel.: +33 4 73 62 41 87; fax: +33 4 73 62 40 89. E-mail address: damez@clermont.inra.fr (J.-L. Damez). www.elsevier.com/locate/jfoodeng Journal of Food Engineering 85 (2008) 116–122