Quantification of Macro-Components in Raw Milk Using Micro Nir Sensors

Abstract

Near Infrared (NIR) spectroscopy is a rapid and proven method for the compositional analysis of raw milk; however, its usage is limited to laboratories due to instrumentation cost and bulkiness. Recently, several portable NIR sensors have been introduced to extend the application of the technique to in-field measurements and consumer applications. The objective of this study was to investigate the potential of Fabry–Pérot Interferometer (FPI)-based micro NIR sensors to quantify macro-components in raw milk such as fat, protein, lactose, and total solids. An experimental prototype was designed to acquire the spectra of 250 raw milk samples in transmission mode using two micro NIR sensors (S-2.0 (1550-1950 nm) and S-2.5 (2000-2450 nm)). Calibration models were developed for macro-components of raw milk using partial least square (PLS) regression, and prediction performance was assessed using statistical metrics. It was observed that the sensor S-2.0 was able to quantify fat (RMSEP = 0.15%), protein (RMSEP = 0.15%) and total solids (RMSEP = 0.30%). However, S-2.5 resulted in relatively lower prediction accuracy for fat (RMSEP = 0.35% ) and protein (RMSEP = 0.33 %), possibly due to the NIR region's lower penetration power where the sensor S-2.5 captures the response. Finally, both sensors did not accurately quantify lactose (R2 < 0.5), potentially due to their lower resolution and sensitivity. The results showed that the micro/handheld NIR sensors can quantify certain macro-components (fat, protein, and total solids) in raw milk, while they may not be suitable for other components (e.g., lactose).

Keywords: Near-infrared, handheld, Raw milk, Fabry-Pérot Interferometer