VOCs determination by adsorbent-Raman system in food and botanicals

Authors: PARK, JINHYUK - Texas A&M University; THOMASSON, J ALEX - Texas A&M University; LEE, KYUNG-MIN - Texas A&M University; Suh, Charles; Perez, Jose; HERRMAN, TIMOTHY - Texas A&M University

Submitted to: Talanta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/4/2020
Publication Date: 3/10/2020
Citation: Park, J., Thomasson, J., Lee, K., Suh, C.P., Perez, J.L., Herrman, T.J. 2020. VOCs determination by adsorbent-Raman system in food and botanicals. Talanta. 12:1595-1605. https://doi.org/10.1039/d0ay00180e.
DOI: https://doi.org/10.1039/d0ay00180e

Interpretive Summary: Plants emit several defensive chemicals when attacked by insect pests. The ability to detect these chemicals in the field instantaneously may provide an alternative strategy for rapidly detecting the presence of insect pest populations and feeding damage. Typically, these chemicals are analyzed by gas chromatography/mass spectrometry (GC/MS) or detected using an electronic nose, which is similar to the technology used by the military to detect odors associated with explosives. Although GC/MS is highly sensitive it lacks portability, while electronic nose equipment is portable but has a narrow range of analysis. As a proof of concept, the objective of our study was to determine if another technology known as Raman spectroscopy could be used to detect and differentiate several chemicals commonly emitted by plants. This technology utilizes a light beam and measures the vibrational characteristics of the chemical to identify or differentiate compounds, and is more suitable for development into a portable system. Our results indicate Raman spectroscopy can accurately differentiate several chemicals commonly released by plants. These findings lay the groundwork for developing a portable, Raman spectroscopy-based detection system that could be attached to a drone, tractor, or robot, and easily maneuvered through agricultural fields to rapidly detect the presence of insect pests and feeding damage.

Technical Abstract: Volatile organic compounds (VOCs) emitted from foods and plants are typically analyzed by gas chromatography/mass spectrometry (GC/MS) or electronic-nose (E-nose) analysis. GC/MS is highly sensitive but lacks portability, while E-nose equipment is portable but has a narrow range of analysis. In this study, a Raman-based VOC detection system was developed along with multivariate analysis for spectral differentiation of VOCs. A 5 µL droplet each of four representative VOCs (linalool, cis-3-hexenyl acetate, cis-3-hexen-1-ol, methyl salicylate) was pre-concentrated with Hayesep Q adsorbent in a sealed chamber. After a given collection time (20 and 60 mins), Raman spectroscopy was used to measure the VOC eluates from each adsorbent. Two collection times were tested, and single VOCs versus VOC mixtures were compared. Finally, Raman spectral data were processed with baseline correction and normalization and analyzed with unsupervised and supervised learning techniques. After 20 minutes of collection, individual and mixed volatiles showed unique spectral features, and the multivariate techniques produced good discrimination among the VOCs. Raman spectroscopy was also used to measure mixtures containing three VOCs at five different concentrations, and when principle component regression was applied, a concentration-estimation curve with a high R2 of 0.953 was generated. This system developed on VOC standards was tested on two types of tea (black and earl grey) to determine the differentiability of tea aromas, and several unique Raman spectra were observed from the tea samples. Therefore, the proposed Raman technique has proven to be effective at fast screening of multiple VOCs given off from foods and plants and is a good candidate for fast and portable applications.