J. Phys. IV France 125 (2005) 857-860  EDP Sciences, Les Ulis DOI: 10.1051/jp4:2005125198 Photoacoustic spectroscopy and thermal relaxation method to evaluate corn moisture content F. Pedrochi 1 , A.N. Medina 1 , A.C. Bento 1 , M.L. Baesso 1 , M.L.S. Luz 2 and V.A. Dalpasquale 2 1 Departamento de Física, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900, Maringá, PR, Brazil 2 Departamento de Agronomia, Universidade Estadual de Maringá, Av. Colombo, 5790, 87020-900, Maringá, PR, Brazil Abstract. In this study, samples of popcorn with different degrees of moisture were analyzed. The optical absorption bands at the mid infrared were measured using photoacoustic spectroscopy and were correlated to the sample moisture. The results were in agreement with moisture data determined by the well known reference method, the Karl Fischer. In addition, the thermal relaxation method was used to determine the sample specific heat as a function of the moisture content. The results were also in agreement with the two mentioned methods. 1. INTRODUCTION The determination of moisture content is very important for the conservation of grains as well as for definition of the commercial value of the products [1]. Corn is the third most cultivated cereal in the world, and one of the difficulties for farmers is to determine the amount of moisture for microorganisms control and also for price reasons. The moisture reduces the quality and time of validly of the grains. The presence of microorganisms is dependent on both the moisture surface and the amount of free OH inside the grain [2]. There are several methods for moisture measurements; that can be divided in direct and indirect methods. The indirect methods use physical properties that depend on the amount moisture in the sample, such as electrical conductivity and capacitance. The direct methods are based on the water lost by the sample as a consequence of both the temperature and the time used in the drying process. These procedures, direct and indirect, demand the use of reference methods, like the Karl Fischer, which is based on chemical reaction to evaluate the water content. The latter is time consuming and a destructive method, indicating the need for more accurate techniques. Photothermal methods have shown to be an alternative way to measure moisture content [3]. The use of optical absorption bands of OH molecules in the mid infrared is certainly a fingerprint for moisture detection. Therefore Photoacoustic Spectroscopy (PAS) appears to be an adequate method to obtain grain moisture. The aim of this work is use the Photoacoustic Spectroscopy to determine the amount moisture of corn. The results are compared to those obtained with conventional methods, and also to the specific heat of the sample measured by using the thermal relaxation method [4]. Article published by EDP Sciences and available at http://www.edpsciences.org/jp4 or http://dx.doi.org/10.1051/jp4:2005125198