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Objective quantification of free fatty acids in edible oils using RGB sensor-based multi-wavelength colourimetric
Fazliyana 'Izzati Za'abar1, Pei Fern Ooi1, Nur Hidayah Azeman2
1Department of Electrical, Electronic and Systems Engineering, Faculty of Engineering and Built Environment, Universiti Kebangsaan Malaysia, Bangi, Malaysia.
Introduction:
The presence of free fatty acids (FFAs) in edible oil varies and presents challenges in visual quantification due to inconsistent colour transitions during titration. In conventional colourimetric titration, the endpoint is often subjectively identified. As per the Malaysian Palm Oil Board (MPOB) standard, neutralisation occurs when a faint pink hue persists for 30 s. However, this definition lacks an objective reference, which impacts its reproducibility. To address this limitation, this study developed an objective RGB (red, green, and blue) sensor-based multi-wavelength colourimetric titration method for quantifying FFAs in edible oils.
Materials And Methods:
Two pH indicators were evaluated: red cabbage extract and phenolphthalein. In the first experiment, red cabbage extract was used with acetic acid (CH3COOH) and sodium hypochlorite (NaClO), and colour changes were monitored using an RGB colour sensor. Data were processed through minimum-maximum normalisation and equal interval classification. In the second experiment, phenolphthalein was employed to detect FFAs in cooking and olive oils, with illumination provided by multi-wavelength lasers and RGB light-emitting diodes (LEDs). RGB changes were recorded to determine the neutralisation point and compute FFA content using MATLAB.
Results:
Results showed that laser-based illumination produced sharper spectral transitions and reduced signal noise. Linear regression analysis revealed a positive linear correlation between RGB values and FFA concentration in cooking oil, while olive oil displayed weaker yet similar trends. Measured FFA contents were 0.33% for cooking oil and 0.45% for olive oil.
Conclusion:
The findings confirm that RGB sensor systems, combined with tailored illumination and data analysis, can enhance endpoint accuracy in titration and support the development of low-cost, portable diagnostic tools for oil quality monitoring. This approach shows strong potential for further development into real-time, in situ monitoring platforms for industrial and consumer applications. © 2026 Society of Chemical Industry.
