Note: Descriptions are shown in the official language in which they were submitted.
CA 02337903 2001-O1-03
WO 00/02036 PCT/NL99/00411
Method for determining the quality of fruit and berries and apparatus for
sorting fruit and berries.
The invention relates to a method for determining the quality of fruit and
berries by irradiating fruit and berries with electromagnetic radiation. The
chlorophyll present in the fruit or berries shows prompt fluorescence as a
result of this irradiation. The present invention also relates to an apparatus
for sorting fruit and berries, at least consisting of a feeder part for the
fruit
and berries, a part for irradiating the fruit and berries with electromagnetic
radiation and a part for measuring the chlorophyll fluorescence signal
returning from the fruit and berries, and a separation part which operates
on the basis of the chlorophyll fluorescence signal returning from the fruit
and berries. By chlorophyll all appearances of the chlorophyll molecule are
meant, such as the chlorophyll known as leaf green, protochlorophyll, etc.
The method of the invention is particularly suitable for determining the
quality of blue berries and can especially be used with frozen berries.
Below the invention will be described on the basis of blue berries.
Measuring the amount of chlorophyll of berries is a good method for
measuring the maturity and thus the quality of berries. It appears that
during the ripening of berries the chlorophyll content of the berry
decreases. The apparatus known up until now, sorts blue berries as to
colour. Green berries can be separated from red and blue berries, because
the difference in colour is sufficiently evident. However, red berries cannot
be separated from blue berries by means of the used method of colour
measurement. These red berries are of inferior quality compared to the blue
berries, because they have not fully ripened. A second problem in colour
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measurement is that with frozen berries a white frost is created. As a
result it is very difficult to sort berries as to colour, because of the
reflec-
tions of the irradiated light on the white coloured white frost and because
the green, red or blue colour of the berry can no longer be measured due to
the white frost. By only measuring the chlorophyll fluorescence signal of
the berries, it is possible to determine the different degrees of maturity of
blue berries. It has been found that green berries have a very high
chlorophyll fluorescence signal, red berries have a lower chlorophyll
fluorescence signal and blue berries have a very low chlorophyll fluores-
cence signal. It has further been found that despite the white frost on
frozen berries it is possible to sort berries as to maturity and quality on
the
basis of the chlorophyll fluorescence signal. Chlorophyll fluorescence is
hardly hindered by the white frost and is much more sensitive than a
colour measurement. There are commercially available apparatus which
determine the maturity of blue berries by measuring the chlorophyll con-
tents with fluorescence.
In the art it is known that by using chlorophyll fluorescence chlorophyll can
be measured. In "Application of chlorophyll fluorescence to postharvest
physiology and storage of mango and banana fruit and the chilling
tolerance of mango cultivars", Asian Food Journal (1987), 3(2), 55-59,
R.M. Smillie, S.E. Hetherinton, R.N. Grantley, R. Chaplin and N.L. Wade
used the chlorophyll fluorescence technique to measure the photosynthesis
activity of fruit. They examined the changes in the photosynthesis activity
during ripening and under the influence of low temperatures by measuring
the chlorophyll fluorescence signal of the skin. The speed with which the
chlorophyll fluorescence signal decreased during exposure to low
temperatures was used to select varieties that are insensitive to cold. They
do not mention the possibility to sort blue berries as to maturity by
measuring prompt fluorescence. Neither do they mention the possibility to
sort frozen berries as to maturity by measuring prompt fluorescence. In
case pf fresh fruit and leafs the chlorophyll fluorescence signal changes
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during the measurement, because the chlorophyll is photosyntheticafly
active. This as opposed to the chlorophyll in a frozen berry, There is no
photosynthesis in a frozen berry. The chlorophyll fluorescence signal is
constant over a short period of time of some minutes. In the method
according to the invention the prompt quantity of chlorophyll fluorescence
is measured, so instantaneous to the irradiation of the berry with
electromagnetic radiation. The amplitude of the chlorophyll fluorescence
signal is now a measure for the quantity of chlorophyll. The measuring
method of Smillie in total requires one hour because of adjustment to the
dark for one hour and some seconds for monitoring the changes in the
chlorophyll fluorescence signal. The measuring method according to the
invention can be carried out in a fraction of a second. The usual method
for measuring photosynthesis activity in plant material comprises the use of
the pulse amplitude modulation (PAM) fluorometer of U. Schreiber,
described in "Detection of rapid induction kinetics with a new type of high
frequency modulated chlorophyll fluorometer", Photosynthesis Research
(1986) 9:261-272. The photosynthesis activity does not directly depend
on the quantity of chlorophyll in plant material. The chlorophyll fluores-
cence signal however does directly depend on the quantity of chlorophyll.
For determining the photosynthesis activity therefore a correction for the
quantity of chlorophyll has to be made. This is done by calculating a
quotient, so that said quotient is independent from the quantity of
chlorophyll. The method described according to the invention, however,
uses the measured quantity of chlorophyll fluorescence as measure for the
quantity of chlorophyll.
According to H.K. Lichtenthaler in "In vivo chlorophyll fluorescence as a
tool for stress detection in plants ", Application of Chlorophyll Fluores-
cence in Photosynthesis, H.K. Lichtenthaler (ed.) 1988, 121-142, Kluwer
Academic Press, Dordrecht, the quantity of chlorophyll cannot be
measured by means of photosynthesis measurements. The parameters
measured for calculating the photosynthesis by using chlorophyll fluores-
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cence can even increase in signal strength when the quantity of chlorophyll
decreases. This is the result of re-absorbtion of the emitted chlorophyll
fluorescence decreasing because of the lower concentration of chlorophyll.
This is contrary ~to the statement according to the invention that the
chlorophyll fluorescence can be used for determining the quantity of
chlorophyll. In "Reflectance and chlorophyll fluorescence signatures of
leaves" in Proceedings IGARSS'87 Symp. Ann. Arbor. MI (USA) 18-21
May 1987, 1201-1206, H.K. Lichtenthaler and C. Buschmann show that
around 690 and 730 nm the chlorophyll fluorescence signal of leaves is not
linear to the quantity of chlorophyll. It was also demonstrated that a lower
quantity of chlorophyll could emit a larger chlorophyll fluorescence signal.
From these two articles it appears that the literature indicated that it was
not to be expected that there was a relation between the quantity of
chlorophyll and the strength of the chlorophyll fluorescence signal.
Therefore it was not likely to an expert in the field of chlorophyll fluores-
cence that by means of chlorophyll fluorescence the quantity of chlorophyll
could be determined. It was not likely either that blue berries with a white
frost could be sorted as to maturity and quality by using chlorophyll
fluorescence.
Thus an object of the present invention is to provide a method which
enables one to sort fruit and berries as to maturity and thus quality on the
basis of the quantity of chlorophyll. Characteristic for the invention are the
very high sensitivity and the high speed with which the chlorophyll fluores-
cence of fruit and berries can be measured. A further object of the inven-
tion is to provide an apparatus with which fruit and berries can quickly and
accurately be sorted as to quality.
electromagnetic radiation has such a ,)that the chlorophyll
present in the fru' rues shows prompt fluorescence, which fluores-
AMENDED SHEET
CA 02337903 2001-O1-03
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In one aspect the invention relates to a non-destructive
method for determining the maturity and quality of fleshy
fruits comprising irradiating a fruit with electromagnetic
radiation comprising wavelengths capable of causing the
chlorophyll of the fruit to fluoresce, passing the signal
returning from the fruit through a filter capable of
filtering out the wavelengths used for exciting the chlo-
rophyll of the fruit to obtain a chlorophyll fluorescence
signal and measuring said signal.
In a further aspect the invention relates to a method for
sorting fleshy fruits comprising feeding each fruit indivi-
dually to a~irradiation area, irradiating the fruit in the
irradiating area with electromagnetic radiation comprising
wavelength capable of causing the chlorophyll in the fleshy
fruit t.o fluoresce, passing the signal returning from the
fruit through a filter capable of filtering out the wave-
lengths used for exciting the chlorophyll of the fruit to
obtain a chlorophyll fluorescence signal and measuring said
signal, and separating the fruits into classes based on
their individual fluorescence signal, wherein the values
that define the classes are chosen on the basis of the
distribution of the chlorophyll fluorescence signals of a
sample of the fruits having known properties.
AMENDED SHEET
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apparatus as mentioned in the preamble, which is c enzed in that the
electromagnetic radiation has s wavelength that the chlorophyll
present in the ~ berries shows prompt fluorescence, which fluores-
part.
The present invention is based on a fluorescence measurement which is
very specific to the chlorophyll present. Other substances which influence
the colour of the blue berries but do not fluoresce, will not contribute to
the fluorescence signal. Also according to the invention small differences in
the quantity of chlorophyll in the blue berries can be shown, because of
the principle that a fluorescence measurement is very sensitive.
According to the invention it now appears that a difference in chlorophyll
contents of individual blue berries can be shown directly, even when the
envelopes cannot be discerned by means of a colour measurement. In
literature no data are known on measuring the quantity of chlorophyll
fluorescence in blue berries in relation to the degree of maturity and
quality. A suitable method for measuring the chlorophyll contents
comprises irradiating at least a part of the chlorophyll molecules with
electromagnetic radiation, preferably with a wavelength between 400 and
700 nm, as a result of which at least a part of the chlorophyll molecules
are electronically excited. The excited molecules mainly loose their energy
by heat dissipation and for about 3% by emission of fluorescence which
preferably is measured between 600 and 800 nm.
When according to the invention the intensity of the chlorophyll
fluorescence of each blue berry is separately measured, the blue berries
can be sorted as to the stage of maturity and quality.
The invention is very sensitive, entirely non-destructive and very quick.
These are the characteristics of the invention which make it possible to
AMENDED SHEET
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manufacture a sorting apparatus with which blue berries can be selected
on the basis of the quantity of chlorophyll fluorescence. Because the
quantity of fluorescence by chlorophyll has a direct relation to the maturity
of the blue berries sorting as to quality is possible.
The present invention can also be used for many kinds of fruit, such as
many other kinds of berries (for instance red berries), blackberries, cherries
and strawberries. The invention also works for fruit in which the quantity
of chlorophyll changes during ripening.
It is preferred to carry out a chlorophyll measurement in an apparatus as
shown in figure 1. This is a simple embodiment of the apparatus. The light
source has a spectral distribution of the light between 400 and 660 nm.
This light is directed to the blue berries. At least a part of the chlorophyll
molecules is electronically excited. At least a part of the excited
chlorophyll
molecules falls to the ground state while emitting fluorescence. At least a
part of the chlorophyll fluorescence is captured with a lens. The filter
ensures that predominantly fluorescence is detected by the CCD camera.
After measuring the chlorophyl! fluorescence for instance a valve can
subsequently be operated with an electronic circuit such as a micro
processor, which valve takes out the blue berries from the main stream
that have a higher or lower signal than a pre-determined value. The sorting
from the main stream with a valve can take place with any known prin=
ciple, such as an air stream, liquid pulse or mechanical valve. It is pointed
out that sorting can be performed on berries which are in the air, but also
for berries that are contained in a liquid. Sorting in a liquid can for
instance
take place in order to minimize the possibility of damage of very delicate
fruit.
The person skilled in the art will see that in the above-mentioned preferred
embodiments of the sorting apparatus, the light source could be a lamp
with optical filters, a LED or a laser. Furthermore it is also possible to use
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one or several photodiodes or photo multipliers for the CCD camera.
The invention can also be used in any fruit sorter apparatus. It can be built
in in all kinds of sorter apparatus. The invention can particularly be used in
the known colour sorter apparatus. The light source can be replaced b~ a
light source in the described spectral range and the CCD camera can be
provided with an optical filter so that predominantly the chlorophyll fluores-
cence is measured.
