Thickness shear mode resonator sensors for the detection of androstenone in pork fat Corrado Di Natale a,b,* , Giorgio Pennazza a , Antonella Macagnano b , Eugenio Martinelli a , Roberto Paolesse a,c , Arnaldo D’Amico a,b a Department of Electronic Engineering, University of Rome ‘‘Tor Vergata’’, Via del Politecnico 1, 00133 Rome, Italy b CNR-IMM, Via del Fosso del Cavaliere, 00133 Rome, Italy c Department of Chemical Science and Technology, University of Rome ‘‘Tor Vergata’’, Via della Ricerca Scientifica, 00133 Rome, Italy Abstract Androstenone is a major natural contaminant in pork meat. Its presence, normally located in the fat tissues, results from the hormones productions connected to the sexual maturity of male pigs. Its presence produces an unpleasant odour, the boar taint. This odour, and flavour in cooked meat, is a strongly perceived by most of the consumers, and it reduces remarkably the quality of meat. Currently available methods, based on enzymatic tests, require long preparation and measurement time. Here a fast screening method based on the thickness shear mode resonators based chemical sensors technology is proposed to measure the presence of volatile part of androstenone from pork fat. Sensitivity and resolutions are comparable with those of human olfaction as it will be demonstrated in the paper. # 2003 Elsevier Science B.V. All rights reserved. Keywords: Androstenone; Boar taint; TSMR sensors; Metalloporphyrins 1. Introduction It is known that male pigs are not widely used for meat unless they are neutered. Indeed, although intact pigs would produce higher quality meat, their use is limited because the meat from boars sometimes is affected by a pronounced off- odour (boar taint) in particular when the meat is heated. One of the main compounds responsible with this problem is androstenone (5a-androst-16-en-3-one) [1] whose molecu- lar structure is shown in Fig. 1. The presence of androste- none in pork meat results in a poor quality of the meat. Its concentration in pork fat may reach 100 mg/g, while the concentration threshold for perception by human senses is around 0.5 mg/g of androstenone diluted in pure pork fat. The perception of androstenone and the consequent sensi- tivity to boar taint changes with individuals and also with cultural attitudes. Recent surveys, for instance, demon- strated that about 30% of Spanish and 18% of German consumers exhibit a strong sensitivity to boar taint [2]. For this reason there is a strong requirement of a fast evaluation of the presence of androstenone in pork meat in the first steps of treatment. Currently, a relatively rapid analysis for androstenone is based on an ELISA-method commercially available (Riedel- deHaen, Seelze, Germany) [3]. This method requires a long and laborious sample preparation and an incubation time of about 1 h before to optically measure the androstenone com- pound. It allows the measure of androstenone up to 10 mg/g with higher sensitivity shown in the range 0.5–0.6 mg/g. On the other hands, chemical sensor technology nowadays offers many solutions to different problems in food analysis. Sensor approach was also proposed to detect the boar taint [4,5]. In this paper a different approach for the development of chemical sensors for the measure of androstenone in the headspace of pork fat is reported and discussed. Such sensor, based on thickness shear mode resonator (TSMR) technology takes advantage by the sensing properties of solid-state metalloporphyrins [6]. Sensors have been tested measuring the headspace of androstenone contaminated pure pork fat. As a major achievement, a resolution comparable with the olfactive threshold shown by humans has been achieved. 2. Experimental 2.1. Sensors TSMR sensors, also known as Quartz microbalances, are commonly utilised for measures both in atmosphere and in Sensors and Actuators B 91 (2003) 169–174 * Corresponding author. Tel.: þ39-06-7259-7348; fax: þ39-06-2020-519. E-mail address: dinatale@eln.uniroma2.it (C. Di Natale). 0925-4005/03/$ – see front matter # 2003 Elsevier Science B.V. All rights reserved. doi:10.1016/S0925-4005(03)00084-4