Use of the product of mean intensity ratio (PMIR) technique for discriminant analysis of lycopene-rich vegetable juice using a portable NIR-excited Raman spectrometer

- Lycopene content discriminant analysis with a portable Raman spectrometer was tested.
- Near-infrared Raman spectrometry accurately yielded the lycopene content of juice.
- An index capable of effectively indicating lycopene-rich substances was developed.
- The same methods can be applied to intact fruits and to analyze other ingredients.

In this study, a lycopene-content-based discriminant analysis was performed using a portable near-infrared-excited Raman spectrometer. In the vegetable-juice Raman spectra, the peak intensity of the lycopene band increased with increasing lycopene concentration, but scattering decreased the repeatability of the peak intensity. Consequently, developing a lycopene-concentration regression model using peak intensity is not straightforward. Therefore, a new method known as the product of mean intensity ratio (PMIR) analysis was developed to rapidly identify lycopene-rich samples on-site. In the PMIR analysis, Raman spectra are measured with short exposure times, confirming only the peaks of carotenoids with high concentrations, and thus the lycopene concentrations of vegetable juice samples could be determined successfully. Exposure times of 20 ms and 100 ms could detect lycopene concentrations of ≥5 mg/100 g and ≥2 mg/100 g with 93.2% and 97.7% accuracy, respectively; thus, lycopene-content-based discriminant analysis using the PMIR and a portable Raman spectrometer is feasible.