Applied_Spectroscopy_Practica_01_01 - 38

6
26
Applied Spectroscopy Practica
Figure 4. Changes with time in band areas of (a) Chl a (640-710 nm), (b) lycopene (545-600 nm), (c) carotenoids (460-520 nm), and
(f) water+ sugar (920-1050 nm). (d) Curve fitting of the band area changes with time of Chl a (640-710 nm) (a) by the first-order kinetic
decrease for 100 days, (e) curve fitting of the band area changes with time of lycopene (545-600 nm) (b) by the first-order kinetic increase
from 36 to 44 days.
exponential curve (Fig. 4d) with a correlation factor R = 0.988.
The first-order reaction rate constant k was obtained to be k=
3.52×10-2 d-1=4.07×10-7 s-1. Although the temperature varied
greatly from 41.8 °C to 10.2 °C with an average of 25.9 °C,
this simple trend is surprising. It is fortunate to be able to apply
the first-order kinetics because only the inverse time is in the
unit of the rate constants without the concentration term.
Therefore, without knowing the absolute concentrations of
chlorophylls, relative band area changes with time could be
used to determine the first-order rate constants.
The decrease kinetics of chlorophylls have been evaluated
at higher temperatures in food processing and cooking sciences.30-32
Chlorophyll synthesis and degradation rates have
been evaluated for cyanobacteria (Synechocystis sp. PCC
68003) with and without photosystems I and II during its incubation
at 30 °C.33 However, the chlorophyll decrease rates in
natural systems have never been quantitatively reported to the
authors' knowledge. Interestingly, the obtained chlorophyll
decrease rate constant at around 26 °C of k= 4.07×10-7 s-1
is in the same order as that reported for the cyanobacteria
with its photosystems I and II (k= 8.61×10-7 s-1
Although further studies are required on the natural chlorophyll
degradation rates in other plants including vegetables
and fruits, the present study provides the first natural data.
Lycopene Increase Rate During Mini Tomato Ripening
The increase of the 640-710 nm band area due to lycopene
appeared to be quasi-exponential with time for the ripening
period (36-44 days; Fig. 4b). This trend was fitted by the following
equation assuming the first-order reaction:
C = C0(1-exp(−kt)) + C1
(4)
The lycopene increase was well fitted by this exponential
curve (Fig. 4e) with a correlation factor R= 0.974. The firstorder
reaction rate constant k was obtained to be k= 2.80 ×
10-1 d-1 = 3.24 ×10-6 s-1, at an average temperature of
about 23 °C, again without knowing the absolute concentrations
of lycopene by relative band area changes with time.
This lycopene increase rates are about one order magnitude
larger than the Chl a decrease rate determined above.
Quantitative Monitoring of the Daily Ripening Process
of Mini Tomato
at 30 °C).
The ripening processes of fruits/vegetables such as tomatoes
have been studied by dividing them into several stages and analyzing
representative chemical components.1-4 Nondestructive
Vis-NIR spectroscopy with color measurements has been conducted
to evaluate the lycopene contents and soluble solid contents
(Brix).5,8,9,11 However, quantitative changes of chemical
components with small time intervals were lacking. Therefore,
the present study provides the detailed daily changes of chlorophyll,
lycopene, and carotenoids and their relations to color values.
These quantitative data will be useful to decide the timing of
the harvest of mini tomatoes. In fact, in the present study, the
lycopene content appeared to be maximum at 44 days
(Fig. 4b), two days after the maximum reddishness (a* value;
Applied_Spectroscopy_Practica_01_01

Table of Contents for the Digital Edition of Applied_Spectroscopy_Practica_01_01
