Olive mill leaves are usually of poorer quality compared to those freshly cut and dried, due to inadequate handling, tissue damage, delays in sampling, transport, and drying. Even so, within the frame of circular economy the interest in their exploitation in the field of feeds is growing as they are still expected to contain bioactive phenols. Thus, it is desirable to be able to screen them after drying, with regards to the content in total or individual (oleuropein) phenols and decide on further use. To do so various techniques are required, which makes evaluation costly and time-consuming. An alternative would be the use of infrared (IR) spectroscopy combined with predictive models, and desirable to measure on site of drying. Even though portable IR spectrometers are available in the NIR region, there is no available information for such purpose. A single publication regards the use of a benchtop spectrometer, and plant material carefully collected and handled [1]. Considering this, dried and ground leaves from 5 different olive mills located in the region of Lakonia, (n=20) were examined with a portable nano FT-NIR instrument (1350-2500 nm) using an optical fiber in the reflection mode. In parallel wet chemistry was applied to measure their total phenol (14-57 g GAE/kg), flavonoid (1.7-5.5 g QUE/kg) and oleuropein content (0.4-56.8 g/kg). Three statistically significant models were obtained applying PLS to preprocessed spectra in the range 1600-2500 nm after trials, with R2 0.43, 0,52 and 0,66 respectively.
References: Can et al. 2018, J. Food Meas. Characterization, 12:2747–2757
Funding: This research has been co-financed by the European Regional Development Fund of the European Union and Greek National Funds through the operational program Competitiveness Entrepreneurship and Innovation under the call RESEARCH-CREATE-INNOVATE (project code: T2EDK-03891)