Quantitation of Water Addition in Octopus Using Time Domain Reflectometry (TDR): Development of a Rapid and Non-Destructive Food Analysis Method

Abstract

A rapid and non-destructive method based in time domain reflectometry analysis (TDR), which detects and quantifies the water content in the muscle, was developed for the control of abusive water addition to octopus. Common octopus samples were immersed in freshwater for different periods (0.5–32 h) to give a wide range of moisture contents, representing different commercial conditions. Control and water-added octopus were analyzed with a TDR sensor, and data correlated with moisture content were used for calibration and method validation. A maximum limit of moisture content of 85.2 g/100 g in octopus is proposed for conformity assessment, unless the label indicates that water (>5%) was added. Calibration results showed that TDR analysis can discriminate control and water-added octopus, especially for octopus immersed for longer periods (32 h). In addition, moisture content can be quantified in octopus using only TDR analysis (between 80 and 90 g/100 g; RMSE = 1.1%). TDR data and correlation with moisture content show that this non-destructive methodology can be used by the industry and quality control inspections for assessment of octopus quality and to verify compliance with legislation, promoting fair trade practices, and further contributing to a sustainable use of resources.

Development of a Rapid and Non-Destructive Method for the Detection of Water Addition in Octopus Species (Octopus vulgaris and Eledone cirrhosa) Using Time Domain Reflectometry (TDR)

“…For O. vulgaris , a data set with more than 300 samples from the Portuguese coast was used to propose a limit of moisture content for conformity assessment of commercial products (85.2 g/100 g), taking into account the highest values of the 95% confidence interval (84.4 g/100 g) and the 5% limit of added water [ 26 ]. In the case of E. cirrhosa , the 95% confidence interval obtained with the results of the current study ( n = 44) was 75.7–82.1 g/100 g, and the limit of moisture content for conformity assessment proposed was 83.0 g/100 g.…”

“…The differences in the TDR profiles between control and water-added octopus indicate that the TDR equipment can be calibrated to allow the detection of octopus processed with water. Calibrations can be carried out specifically for each species, as reported previously for O. vulgaris [ 26 ]. However, it would be advantageous to have a non-destructive method able to detect water addition in octopus, even if the octopus species is not known.…”

“…Analysis of TDR data was carried out following the method described by Teixeira et al [ 26 ]. RFQ-Scan ® (Radio Frequency Quality Scan) equipment produced and patented by Sequid GmbH (Bremen, Germany) was used.…”

“…Mendes et al [ 16 ] proposed a method for the detection of water addition to O. vulgaris based in the measurement of the dielectric properties in the microwave region as a function of frequency. Likewise, and targeting the analysis of water illegally added to octopus, Teixeira et al [ 26 ] further developed a fast and non-destructive method involving time domain reflectometry analysis (TDR), which allows the detection and quantification of the added water specifically in O. vulgaris . According to the authors, the correlation found between the TDR data and the moisture content evidences the potential of this nondestructive methodology as a tool for the public quality control regulators and industry stakeholders to assess the quality of octopus and its conformity with regulations.…”

Assessing the quality of octopus: From sea to table

“…This makes fast and accurate quality control methods necessary to detect fraudulent practices during octopus processing. Recently, Teixeira et al (2022) evaluated the possibility of quantifying water addition in octopus using time domain reflectometry. It is a nondestructive food analysis method based on the principle of dielectric spectroscopy, which quantifies the water content in the muscle in an easy, effective, rapid, and reliable way.…”