Abstrac


One of the priority areas of the European Commission’s Seventh Framework Programme is 
Smart Control for Improved Food and Feed Technologies. Its objective is 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.

At present, the majority of methods used for the determination of physicochemical properties of 
food in industry are destructive, leaving the piece under consideration useless. The design of 
non-destructive measurement systems is a challenge, but in addition to preserving the integrity 
of the analysed samples, new analytical techniques must be cheap, easy to use, and not require 
highly trained personnel.

In the present thesis a low cost, flexible, light, punctual, user-friendly, non-destructive 
measurement system was developed. It determines the physicochemical properties of food 
products based on the measurement of electrical impedance.

The measurement system applies an electric signal to the food and measures its response in a 
frequency sweep between 1Hz and 1MHz, using impedance spectroscopy. A correlation 
between the impedance values and the physicochemical parameters is established by means of 
multivariate analysis tools, obtaining statistical prediction models which can be used to 
determine the properties of the samples.

The developed measurement system has of three parts:

Electronic measurement equipment. The use of impedance spectroscopy requires the 
generation and sampling of variable amplitude sine waves of up to 1MHz. Therefore in 
the development of the measurement equipment multiprocessing digital techniques were 
used, based on complex programmable logic devices (CPLD).

PC Application. Software designed so the user can quickly and simply modify the 
parameters (amplitude, range of frequencies, current range, etc.) of the signals that are 
applied to the samples. It deals with the voltage and current data, calculating, storing and 
graphically representing the values of the impedance spectra.

Electrodes. Two types of electrodes were designed with different geometries and reduced 
dimensions compared to the samples, so the readings carried out are of a punctual and 
non-destructive character. They have been named “Double electrode” and “Arrowhead 
electrode”. The first consists of two very fine parallel stainless steel needles. The second, 
designed with serigraphic techniques using thick-film technology, consists of two 
conductive paste electrodes fixed on an arrow shaped alumina base. In some applications 
a third electrode named “Needle electrode” was used which consists of a coaxial needle of 
the type used in electromyography formed by two concentric stainless steel conductors 
separated by resin.

The developed measurement system was applied to the following assays:

Determination of the percentage of salt in brine and minced beef.
Study of the level of curing in pork loin samples.
Study of the level of curing in cheese.
Study of fish freshness.

The reliability of the measurement system was demonstrated by its validation. The suggested 
technique possesses adequate analytical properties in terms of exactness as well as precision and 
sensitivity. Excellent predictions were obtained in some cases and a high level of classification 
in others. The developed system possesses a high capacity for differentiation even in high 
concentrations of sodium chloride, making an important contribution to this field.