Applied_Spectroscopy_Practica_01_01 - 35

Nakashima et al.
233
Figure 1. Handy Vis-NIR spectrometer. (a) Schematic configuration of two monochromators, (b) measuring optics, and (c) photographic
images of the spectrometer and the dark and white cover plates. (d) Reflection spectra of the white reference (MgO) and a mini tomato at 0
and 43 days. (e) Absorption spectra of the white reference (MgO) and the mini tomato at 0 and 43 days.
Color values of L*, a*, and b* were calculated from the R
spectra based on the L*a*b* color space recommended by the
CIE (second CIELAB 1976 color space).14,15 Their daily changes
are plotted in Figs. 2e-2g. L* (black/white) values decreased from
about 50 to 20 during the mini tomato ripening (Fig. 2e).
The a* (minus green, plus red) values started from −6.7,
stayed in minus values (green) until about 35 days, and then
increased rapidly to about+13 at 43 days and after staying
at red a*, which decreased and fluctuated at the late stage
due to degradation of the mini tomato (Fig. 2f).
The b* (minus blue, plus yellow) values first decreased from
about 20 to 10 and then increased to about 23; after about 50
days the b* values fluctuated due to degradation (Fig. 2g).
Reflectance and Absorption Spectra During Mini
Tomato Ripening
Representative R spectra obtained by using the spectrometer
are shown in Figs. 1d and 3a. They show changes with time in
several wavenumber regions. In order to examine quantitative
changes in absorption bands, R spectra are converted
to Abs spectra by the following equation:
Absorbance(Abs) =−log R
(2)
Although diffuse R can be used as quantitative spectra for
granular or powdery materials, mini tomato samples are not
considered to be composed of granular structures with diffuse
reflection. Moreover, the minus logarithm of R (Abs)
is often taken as quantitative spectra in R spectroscopy of
plants and food products.16-19
Representative Abs spectra of mini tomato converted
from the reflection spectra are shown in Figs. 1e and 3b.
Their 400 to 800 nm wavelength region is expanded in
Fig. 3c.
A small band around 970 nm can be recognized in Figs. 1e
and 3b. This band is considered to be mainly due to a combination
of overtones of symmetric and antisymmetric
stretching vibrations of water molecules.19-21 This band
may include a small component around 980-960 nm due to
OH vibrations of sugars.20,22
Although several bands due to sugar components have been
reported around 730, 830, 910, and 930 nm together with the
960 nm band due to combinations and overtones of CH and
OH vibrations in the direct spectroscopic measurement of
foods,19,20,22 they are not recognizable in the present spectra.
In the wavelength region from 400 to 800 nm, several
absorption bands are observed (Figs. 1e and 3c). A small
band around 490 nm can be recognized during the early
stage of mini tomato ripening. This 490 nm band can be
mainly due to carotenoids such as β-carotene, since they
have generally absorption bands in the 440-500 nm region.1,8
A band around 565 nm became apparent at the later stage
of ripening (Figs. 1e and 3c). This band is considered to be

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