Portable Near-Infrared Spectrometers in the Agro-Food Industry

Introduction

The agro-food industry plays a vital role in the global economy, evolving to meet consumer demands for quality, convenience, variety, and health. Compliance with regulations on health, safety, environmental laws, and sustainable production is also crucial. Spectroscopic techniques, particularly near-infrared (NIR) spectroscopy, have been extensively studied in the agro-food industry. NIR spectroscopy, pioneered by Norris and Hart, with contributions from Williams, McClure et al., and Norris et al., has been used to rapidly analyze moisture, protein, fat content, and other properties in agricultural and food products. This technique has proven useful in assessing microstructural properties and even sensory attributes.

Recent attention has focused on miniaturizing and making spectroscopic devices portable. Portable instruments offer advantages such as cost reduction, improved safety, and increased accuracy by avoiding sample transport. These devices can be incorporated into field-ready, handheld or machinery-mounted devices, and even deployed from drones or planes for remote monitoring in larger areas.

Figure 1. Quantity of research papers that have explored the application of portable NIR spectrometers in the agro-food industry from 2003 to 2012.

Proposed method and system

Several studies have been conducted using a system consisting of USB4000 VIS-Nir or USB2000+ VIS-Nir spectrometer provided by Ocean Insight. The bands commonly observed in NIR spectra are associated with bonds that involve the presence of hydrogen atoms, such as C–H, N–H, O–H, and S–H. These types of bonds are often found in a wide range of organic compounds and some inorganic compounds. In the initial stages, this method was used for determining the dry matter content, measuring the soluble solids content (SSC), and assessing the water content. Additionally, this technique was employed to conduct microstructural measurements, including stiffness, internal damage, and even sensory attributes. The findings presented in this study utilize the root mean square error of prediction (RMSEP) or the root mean square error of cross-validation (RMSECV) as metrics to evaluate the accuracy of models based on near-infrared (NIR) data.

The USB4000-VIS-NIR spectrometer offered by Ocean Insight is a reliable and sturdy device. It is equipped with a 3648-element linear CCD array detector, ensuring excellent signal-to-noise performance. The spectrometer also features enhanced electronics for efficient control of both the spectrometer itself and its accessories. With a wavelength range of 350 to 1100 nm, a spectral resolution of 1.5 to 2.3 nm, and an impressive dynamic range of 1300:1 for a single acquisition, the USB4000-VIS-NIR spectrometer delivers exceptional performance. It boasts a signal-to-noise ratio of 300:1 at full signal, further enhancing its capabilities. USB4000-VIS-NIR spectrometers are renowned for their popularity and are widely used in various applications. They are particularly well-suited for basic absorbance, reflectance, and emission measurements.

Figure 2. USB4000 VIS-Nir Spectrometer.

The USB2000+VIS-NIR spectrometer is equipped with a 2048-element detector, a multibandpass order-sorting filter, and a 25 µm slit, allowing for optical resolution of approximately 1.5 nm (FWHM). It covers a wavelength range of 350-1100 nm and has a remarkably compact design. The spectrometer offers plug-and-play capabilities and a simplified interface, operating without the need for external power. Simply connect the VIS-NIR spectrometer to an available USB port on computer, eliminating the requirement for analog converters. It provides a dynamic range of 1300:1 for a single acquisition and a signal-to-noise ratio of 250:1 at full signal. The USB2000+VIS-NIR spectrometer is an excellent choice for researchers and individuals who perform various basic spectroscopy measurements in their work.

Figure 3. USB2000+ VIS-Nir Spectrometer.

Application

The following sections provide a comprehensive overview of the applications of portable NIR spectrometers in the agro-food industry. These sections include detailed information about the samples being analyzed, their specific characteristics, and, when applicable, the spectrometer used, its acquisition mode, and its spectral range.

For example, in the case of measuring the soluble solids content (SSC) of pears, the USB4000 VIS-Nir spectrometer was used along with the diffuse reflectance method within the wavelength range of 800 nm to 950 nm. This analysis also incorporated major qualitative and quantitative multivariate analysis techniques. The achieved root mean square error of prediction (RMSEP) for this analysis ranged from 0.48 to 0.67.

Similarly, when analyzing mandarin, the USB4000 VIS-Nir spectrometer was used to measure the soluble solids content (SSC), titratable acidity (TA) in terms of malic acid per liter (L), ascorbic acid, and surface color. The transmittance method was employed within the wavelength range of 400 nm to 1040 nm. The obtained root mean square error of prediction (RMSEP) for SSC, TA, ascorbic acid (mg/100 g), and surface color (E) fell within the respective ranges of 0.64 < RMSEP < 0.65, RMSEP = 0.09, 2.7 < RMSEP < 2.8, and 0.81 < RMSEP < 0.82.

Figure 4. Typical spectra of mandarin fruits.

Beside, There have been numerous studies on the application of portable NIR devices in the field of grape cultivation. One study utilized the USB2000+ VIS-Nir spectrometer to measure the soluble solids content (SSC), pH, and anthocyanin concentration (mg/g) of grapes. The measurements were conducted within the wavelength range of 630 nm to 1100 nm. The achieved root mean square error of prediction (RMSEP) for SSC, pH, and anthocyanin concentration fell within the respective ranges of 1.010 < RMSEP < 1.267, 0.088 < RMSEP < 0.159, and 0.183 < RMSEP < 0.315.

Conclusion

Portable NIR spectroscopy has numerous applications in the agro-food industry, as highlighted by the studies examined. Key advantages include cost-effectiveness, in situ analysis, and nondestructive measurements. Portable devices offer affordability, making them accessible to a wider range of users. On-site analysis enables real-time decision-making, saving time and resources. Nondestructive measurements allow for further testing or repeated analysis. Overall, portable NIR spectroscopy provides cost-effective, rapid, and nondestructive analysis, making it an invaluable tool in optimizing agricultural processes, ensuring food quality, and promoting sustainability in the agro-food sector.