Non-destructive Phenotyping of Chili Pepper Ripening Using Spectroscopic Probes: A Potential Approach for Shelf-Life Measurement

Abstract

This study explores the application of spectroscopic techniques (laser induced fluorescence, Raman and attenuated total reflectance Fourier transform infrared) coupled with principal component analysis for the nondestructive, extraction free and rapid evaluation of biochemical changes associated with ripening of chili peppers at four stages (mature, pre-ripe, ripe and post-ripe). The analysis of the fluorescence spectra of the exocarp of chili pepper shows a decrease in the intensity of chlorophyll bands at 685 and 735 nm and an increase in the intensity of carotenoid fluorescence bands at 490–500 nm and 565–580 nm with progress in the ripening stages. These changes are regarded to be significant phenotypic markers for the ripening of chili peppers. The observed changes in the position of carotenoid bands in Raman spectra at 1004, 1156, 1188, and 1524 cm−1 with increase in their intensity indicating the accumulation of carotenoids and change in the carotenoid composition from β-carotene in the mature chilis to capsanthin in the ripe chilis. In addition, the infrared spectra show changes in the carbohydrates, amide II, amide I and cutin at various stages of ripening. Also, the variation in the position of pectin bands indicates change in its molecular mass with decreasing content. The determined spectral signatures can be used as biomolecular index for effective monitoring of the ripening of chili peppers. The commercial application of noninvasive spectroscopic probes will be advantageous for the phenotyping of economically important plant parts, screening, grading, shelf life estimation and quality standardization.