METHOD FOR DETERMINING THE QUALITY OF FRUIT AND BERRIES AND APPARATUS FOR SORTING FRUIT AND BERRIES

Abstract: The invention relates to a method for determining the maturity and quality of fruit and berries by measuring the quantity of chlorophyll fluorescence and to an apparatus for sorting fruit and berries. The method is based on determining the quantity of fluorescence by chlorophyll of fruit and berry. The invention comprises causing the chlorophyll molecule to fluoresce by irradiating the fruit and berries with electromagnetic radiation of a suitable wavelength and measuring the degree of fluorescence. Advantages of the method are the very high sensitivity, its being completely non-destructive and the very high speed. These advantages of the invention make it possible to construct a sorter apparatus in which fruit and berries are selected on the basis of the quantity of chlorophyll. Because the intensity of the chlorophyll fluorescence is directly related to the quantity of chlorophyll, it will now be possible to sort fruit and berries as to the stage of ripening and quality.

Description: 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 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 reflections 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 contents 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 (1 987), 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 during the measurement, because the chlorophyll is photosynthetically 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 ( 1 986) 9:261 -272. The photosynthesis activity does not directly depend on the quantity of chlorophyll in plant material. The chlorophyll fluorescence 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 Fluorescence in Photosynthesis, H. K. Lichtenthaler (ed .) 1 988, 1 21 -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- 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. Ml (USA) 1 8-21 May 1 987, 1 201 -1 206, 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 fluorescence 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 invention is to provide an apparatus with which fruit and berries can quickly and accurately be sorted as to quality. The method according to the invention is characterized in that the electromagnetic radiation has such a wavelength that the chlorophyll present in the fruit and berries shows prompt fluorescence, which fluorescence is measured. The method according to the invention can very well be performed in an apparatus as mentioned in the preamble, which is characterized in that the electromagnetic radiation has such a wavelength that the chlorophyll present in the fruit and berries shows prompt fluorescence, which fluores- cence is measured in the measuring 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 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 chlorophyll 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 principle, 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 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 by. a light source in the described spectral range and the CCD camera can be provided with an optical filter so that predominantly the chlorophyll fluorescence is measured.

Claims: Claims 1 . A method for determining the quality and stage of maturity of fruit and berries by irradiation with electromagnetic radiation, characterized in that the electromagnetic radiation is of such a wavelength that the chlorophyll present in the fruit and the berries shows prompt fluorescence, which fluorescence is measured. 2. A method according to claim 1 , characterized in that the irradiated electromagnetic radiation has a wavelength between 400 and 700 nm and in that the fluorescence is measured between 600 and 800 nm. 3. A method according to claim 1 or 2, characterized in that the fruit or the berries are frozen. 4. A method according to claim 1 , 2 or 3, characterized in that the berries are blue berries. 5. 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, a part for measuring the signal returning from the fruit and berries, and a separation part which operates on the basis of the signal returning from the fruit and berries, characterized in that the electromagnetic radiation has such a wavelength that the chlorophyll present in the fruit and berries shows prompt fluorescence, which fluorescence is measured in the measuring part. 6. An apparatus according to claim 5, characterized in that the signal returning from the fruit and berries is measured with a photodiode, photomultiplier or electronic camera. 7. An apparatus according to claim 5 or 6, characterized in that the irradiated electromagnetic radiation is generated by a lamp, laser or LED. -

Inventors: BINO RAOUL JOHN, JALINK HENDRIK, VAN DER SCHOOR ROB, BINO, RAOUL, JOHN, JALINK, HENDRIK, VAN DER SCHOOR, ROB
Applicants: BINO RAOUL JOHN, CPRO DLO, JALINK HENDRIK, SCHOOR ROB V D, BINO, RAOUL, JOHN, CENTRUM VOOR PLANTENVEREDELINGS- EN REPRODUKTIEONDERZOEK (CPRO-DLO), JALINK, HENDRIK, VAN DER SCHOOR, ROB
Application year: 1999
Main classification: G01N21
IPC codes: B07B13, B07C5, G01N21, G01N33