Spectroscopic evaluation of the surface quality of apple

A Review of Optical Nondestructive Visual and Near-Infrared Methods for Food Quality and Safety

This paper is a review of optical methods for online nondestructive food quality monitoring. The key spectral areas are the visual and near-infrared wavelengths. We have collected the information of over 260 papers published mainly during the last 20 years. Many of them use an analysis method called chemometrics which is shortly described in the paper. The main goal of this paper is to provide a general view of work done according to different FAO food classes. Hopefully using optical VIS/NIR spectroscopy gives an idea of how to better meet market and consumer needs for high-quality food stuff.

In situ analysis by microspectroscopy reveals triterpenoid compositional patterns within leaf cuticles of Prunus laurocerasus

The cuticular waxes on the leaves of Prunus laurocerasus are arranged in distinct layers differing in triterpenoid concentrations (Jetter et al., Plant Cell Environ 23:619-628, 2000). In addition to this transversal gradient, the lateral distribution of cuticular triterpenoids must be investigated to fully describe the spatial distribution of wax components on the leaf surfaces. In the present investigation, near infrared (NIR) Raman microspectroscopy, coherent anti-Stokes Raman scattering (CARS) microscopy, and third harmonic generation (THG) spectroscopy were employed to map the triterpenoid distribution in isolated cuticles from adaxial and abaxial sides of P. laurocerasus leaves. The relative concentrations of ursolic acid and oleanolic acid were calculated by treating the cuticle spectra as linear combinations of reference spectra from the major compounds found in the wax. Raman maps of the adaxial cuticle showed that the triterpenoids accumulate to relatively high concentrations over the periclinal regions of the pavement cells, while the very long chain aliphatic wax constituents are distributed fairly evenly across the entire adaxial cuticle. In the analysis of the abaxial cuticles, the triterpenoids were found to accumulate in greater amounts over the guard cells relative to the pavement cells. The very long chain aliphatic compounds accumulated in the cuticle above the anticlinal cell walls of the pavement cells, and were found at low concentrations above the periclinals and the guard cells.

Raman microspectroscopic analysis of triterpenoids found in plant cuticles

The above-ground organs of plants are covered by a cuticle, an extracellular membrane performing important physiological and ecological functions, that consists of the fatty acid-derived polymer cutin and waxes. In the cuticular wax of many species, including the leaves of Prunus laurocerasus, triterpenoids are found at high concentrations. This paper investigates the potential of Raman microspectroscopy for the simultaneous detection of structurally similar triterpenoids in plant cuticles. Relative composition analysis was first performed on artificial triterpenoid mixtures consisting of alpha-amyrin and oleanolic acid, as well as oleanolic acid and ursolic acid, the two triterpenoids abundantly found in the cuticles of P. laurocerasus. The different triterpenoids could be distinguished in the mixture spectra and the resulting calculated triterpenoid ratios were consistent with the expected values. Qualitative analysis of the Raman spectra of P. laurocerasus cuticle demonstrated the in situ detectability of the triterpenoids using this approach. It is shown here that Raman microspectroscopy has the potential to provide useful information concerning the spatial distribution of some key chemical components of plant cuticles. This technique thus offers a valuable complement to the current standard analytical methods used for analyzing the bulk composition of plant cuticles.