Fluorescence spectroscopy is an electromagnetic technique that examines fluorescence in a sample. It works using light to excite electrons in certain molecules, prompting them to emit light, typically in the visible spectrum.
The technique has been widely used to monitor the light absorption of chemical products for a wide range of applications across industry and research alike. Recently, a team of researchers from Singapore and Malaysia pioneered and validated a new approach for real-time, non-invasive monitoring of palm oil quality during the milling process, using light-induced chlorophyll fluorescence (LICF) spectroscopy.
Addressing quality control in palm oil production with fluorescence spectroscopy
In palm oil production, one of the greatest challenges surrounds the maturity of the fruit that is selected to extract oil. A less mature fruit will have higher levels of chlorophyll which can decrease both the quality and quantity of oil from that fruit, as well as generating other effects on the oil’s marketability and even source sustainability.
Jeremiah Hashley, a technical writer with Wavelength Electronics explains: “It is typical for production floors to have human graders looking at fruit to determine the maturity and quality level. Inconsistencies and inaccuracies in human judgement can be problematic when monitoring ripeness and fruit maturity.”
Real-time monitoring for enhanced process optimisation
The research project looked to help overcome these challenges using chlorophyll fluorescence spectroscopy to provide a reliable and efficient method for real-time, non-invasive monitoring of palm oil chlorophyll content, allowing operators to make changes to the fruit used for higher quality oil. Says Hashley: “A real-time and non-invasive design was critical to make quick changes to palm oil refining and make them without disrupting the production process.”
The solution was an in-line LICF probe which uses a high-intensity LED, photodiode, and custom bifurcated fibre-optic probe to measure chlorophyll during the milling process. A 7-1 fibre ratio delivers excitation light and collects fluorescence, with seven fibres transmitting light to the oil sample and one centre fibre collecting the emitted chlorophyll fluorescence. This fluorescence is then analysed by a spectrometer, enabling continuous chlorophyll monitoring for process optimisation.
While laser diodes are typically used in fluorescent spectroscopy, in this case the research team selected an LED. Hashley explains: “The LED was chosen for its long lifespan and low cost. LEDs also do not generate as much heat as laser diodes and do not require as intensive cooling systems for wavelength stability. The smaller size of LEDs could also have contributed to the decision.”
Selecting the right components: LEDs and WLD33ND driver
These advantages make LEDs an attractive option for systems that require long-term stability and reliability without the added complexity of managing heat dissipation. However, the choice of an LED also necessitated the use of a stable driver, and Wavelength Electronics’ WLD33ND driver proved invaluable. The WLD33ND is a versatile laser diode driver that is designed to ensure precise laser current in constant current mode or stable photodiode current in constant power mode. It features electronics compatible with any laser diode type and provides delayed, gradual current ramping for optimal protection.
Despite being primarily a laser driver, it was well-suited for the project. “The WLD33ND is a low-current driver with an output current of up to 2.2A to the LED, but its compact size, current stability, and potential zero leakage current are also crucial for maintaining stable and consistent light emission," says Hashley. This precision in current control was essential for ensuring that the LED provided reliable and repeatable results in the fluorescence system.
One of the biggest challenges for the research team was in validating that their chlorophyll fluorescence technique was viable, so that the design could be incorporated into the palm oil production line. This involved sending samples off-site for confirmation, and, as Hashley reveals: “It was found that there was a very strong correlation coefficient of 0.90 between the chlorophyll fluorescence measurements and the American Oil Chemists’ Society (AOCS) data. Once the chlorophyll and fruit maturity correlation was confirmed, the fluorescent prototype in the oil mill was assembled on the oil lines for monitoring.”
Numerous tests throughout various stages of the milling process yielded consistent results, confirming the system's suitability for continuous quality monitoring. Changes in average chlorophyll concentration were clearly observed alongside varying quality indicators, showcasing the system's ability to adjust to different process conditions.
Says Hashley: “With the LICF design, researchers were able to leverage the natural response of chlorophyll to assess the quality of the palm oil. The average chlorophyll concentration changes were observable with varying quality indicators, demonstrating the system’s capability to adapt to different process conditions. The correlation between the chlorophyll sensor measurements and AOCS results was still very strong, with a correlation coefficient of 0.88. This high accuracy confirms the effectiveness of the in-line sensing system for real-time monitoring of palm oil quality.”
The broader potential of this technology
Beyond the immediate application in palm oil production, Hashley also sees potential for similar chlorophyll monitoring techniques to be applied in other industries. The system’s ability to measure chlorophyll concentrations could be leveraged in any process where biomarkers like chlorophyll need to be detected and measured with high accuracy. “The accuracy and repeatability of chlorophyll measurements and the system’s integration into the milling process offer significant improvements in quality control and process optimisation,” he says.
Industries such as food production, environmental monitoring, and pharmaceuticals could also benefit from the technologies developed for this project. Researchers and engineers working in these fields could utilise Wavelength Electronics' drivers and controllers to ensure the stability and precision necessary for high-quality optical sensing. Hashley also highlights Wavelength’s commitment to supporting customisation for researchers and companies with specific needs, adding: “Wavelength does offer product variations for customers that need customisation, usually to reduce the cost of goods. For many researchers, Wavelength’s instruments or modules offer exactly the customisation and easy setup they need to speed up their experimental design without sacrificing versatility or performance.”
Engineers and other innovators in fluorescence, spectroscopy, optical sensing and academia can find out more details about the research project, and Wavelength Electronics’s role within it by reading the company’s latest White Paper. It details how the researchers developed their method; the optical components behind it, including the Wavelength Electronics WLD33ND driver; the challenges they faced; the results and potential broader application potential.
