Non-invasive monitoring of drying processes: case of laser light backscattering and moisture content
- Publication Type
- Lecture
- Authors
- Argyropoulos, D; Nagle, M; Romano, G; Udomkun, P; Müller, J
- Year of publication
- 2015
- Conference name
- 29th EFFoST International Conference
- Conference location
- Athens, Greece
- Conference date
- 10 - 12 November 2015
- Keywords
- drying, moisture
Drying is a widely used technique for the conservation of a great variety of agricultural products. A critical issue in the food industry is to continuously monitor moisture changes during drying in order to prevent over-drying and to minimize quality losses. Nowadays, interest in using innovative, non-invasive, sensor-based technologies for monitoring food properties is increasing. Therefore, the feasibility of a laser light backscattering at wavelengths of 532, 635, 650 and 780 nm in combination with a CCD camera for predicting moisture content in some fruits (banana, apple, papaya, mango, bell pepper) was investigated. The experiments were carried in a high-precision laboratory dryer in which a load cell has been incorporated to measure the weight loss of the sample. Drying was conducted at different air temperatures (50-80 °C), specific humidity of 10 g/kg and constant air velocity of 0.9 m/s. For the standard laboratory analysis, Karl Fischer Titration was used to determine the moisture content. From laser images, backscattering parameters such as the illuminated area and light intensity, representing photon migration in the fruit tissue were analysed to assess changes in moisture. The results showed that backscattering parameters were able to predict moisture content of all investigated fruit examples during drying. However, while moisture prediction for some species was independent of laser colour, the method only worked at certain wavelengths for others. Excellent correlations were generally obtained for yellow coloured samples and white samples which brown during drying. Meanwhile, the moisture content of red and green peppers could only be measured with red and green lasers, respectively. This creates some product-specific limitations with respect to the application of lasers for moisture content prediction. The presented optical technique shows the potential to be applied in the future as a fast method for in-line monitoring of moisture content in established industrial drying processes.