Non-destructive method and apparatus for detection of fruit and vegetable quality

• US 5,822,068 A
• Filed: 03/10/1997
• Issued: 10/13/1998
• Est. Priority Date: 03/10/1997
• Status: Expired due to Fees

• Current Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Original Assignee: The Board of Trustees of Michigan State University (Michigan State University)
• Inventors: Song, Jun, Deng, Weimin, Armstrong, Paul R., Beaudry, Randolph M.
• Primary Examiner(s): Evans, F. L.
• Application Number:
  US08/815,115
• Time in Patent Office: 582 Days
• Field of Search: 356/317, 356/318, 356/417, 250/458.1, 250/459.1, 250/910
• US Class Current: 356/417
• CPC Class Codes: G01N 2021/635 Photosynthetic material analysis, e.g. chrorophyll
• CPC Class Codes: G01N 2021/6419 Excitation at two or more wavelengths
• CPC Class Codes: G01N 2021/6421 Measuring at two or more wavelengths
• CPC Class Codes: G01N 21/64 Fluorescence; Phosphorescence
• CPC Class Codes: G01N 33/025 Fruits or vegetables

Abstract

A non-destructive method of testing of fruits and vegetables for post-harvest quality (firmness, texture, aroma and color) using fluorescence intensity of the skin or leaves is described. A low intensity red light source (10) is used to irradiate the skin or leaves of fruits or vegetables to provide a first level F_o of fluorescence intensity above that of red light in the 710 to 740 nM range. A second high intensity red light source is used to produce a maximal second fluorescence intensity F_m in the skin or leaves in the 710 to 740 nM range. The ratio F_v /F_m =(F_m -F_o)/F_m is then preferably determined to provide a measure of the quality of the fruit or vegetable.

Claims

1. A method for indirectly estimating quality of a harvested, edible fruit or vegetable having a skin which comprises:

(a) exposing the skin of the fruit or vegetable to a source of red light which induces a fluorescence intensity at a frequency above the red light from chlorophyll in the skin of the fruit or vegetable;

(b) detecting the fluorescence intensity produced by the skin; and

(c) estimating the quality of the fruit or vegetable as a function of the intensity of the fluorescence detected, wherein when the fruit or vegetable has a first level of the fluorescence of the chlorophyll in the skin when the fluorescence intensity is relatively high which is indicative of an acceptable quality and wherein the intensity of the fluorescence of the chlorophyll at a second level which is decreased and which is indicative of an unacceptable quality.

2. The method of claim 1 wherein the quality is selected from the group consisting of firmness, texture, color and aroma.

3. The method of claim 1 wherein the red light wavelength is at least about 690 nm and the fluorescence intensity is measured at wavelengths between about 710 and 740 nm.

4. The method of claim 1 wherein the source of the red light is part of a spectrum of a white light.

5. The method of claim 1 wherein the source of light is monochromatic.

6. The method of claim 5 wherein the light source generates a pulse of light.

7. The method of claim 1 wherein the source of light is continuous.

8. The method of claim 1 wherein the source of light is modulated.

9. A method for indirectly estimating quality of a fruit or vegetable having a skip which comprises:

(a) exposing the skin of the fruit or vegetable to an applied continuous first source of light including red light which induces a background fluorescence intensity (F_o) and to a second source of light which provides a maximal fluorescence intensity (F_m) from the skin of the fruit or vegetable at longer wavelengths than the first light source;

(b) detecting the fluorescence intensities F_o and F_m produced by the skin;

(c) determining a fluorescence intensity ratio of ##EQU3## wherein F_m -F_o Fo is equal to a variable fluorescence intensity F_v ; and

(d) estimating the firmness of the fruit or vegetable as a function of the ratio, wherein the fruit or vegetable which has a first level of the chlorophyll in the skin as determined by the fluorescence intensity ratio has an acceptable quality and wherein the florescence intensity ratio is at a second level which is decreased and which is indicative of an unacceptable quality.

10. The method of claim 9 wherein the red light is at 690 nm and the fluorescence intensity is measured at about 710 to 740 nm.

11. The method of claim 9 wherein the quality is selected from the groups consisting of firmness, texture, color and aroma.

12. The method of claim 9 wherein the fruit is a red fruit.

13. An apparatus for indirectly estimating quality of a harvested, edible fruit or vegetable which comprises:

(a) light source means for exposing the fruit or vegetable to a red light which induces a fluorescence intensity at a wavelength greater than that of the red light from the skin of the fruit or vegetable;

(b) detection means for detecting the fluorescence intensity from the fruit or vegetable; and

(c) calculator means for converting the intensity of the fluorescence into a measure of the quality of the fruit or vegetable, wherein the fruit or vegetable which has a first level of chlorophyll in the skin as determined by the fluorescence intensity which is indicative of an acceptable quality and wherein the fluorescence intensity is at a second level which is decreased and which is indicative of an unacceptable quality.

14. The apparatus of claim 13 wherein the calculator means is a computer.

15. The apparatus of any one of claims 13 or 14 wherein the light source means and detection means are mounted adjacent to a conveyor for the fruit or vegetable.

16. The apparatus of claim 13 wherein the quality is selected from the group consisting of firmness, texture, color and aroma.

17. The apparatus of claim 13 wherein the wavelength red light is at least about 690 nm and the fluorescence intensity is measured at wavelengths between about 710 and 740 nm.

18. The apparatus of claim 13 wherein the source of the red light is in a spectrum of white light.

19. The apparatus of claim 13 wherein the source of the red light is monochromatic.

20. The apparatus of claim 13 wherein the light source produces a light pulse.

21. The apparatus of claim 13 wherein the light source produces a continuous light.

22. An apparatus for estimating quality of fruit or vegetable having a skin which comprises:

(a) a first light source of red light which is modulated and is a monochromatic;

(b) a second light source which is continuous and produces an actinic light including red light;

(c) fiber optic means comprising individual fibers in a bundle of a group of fibers with one end in a spaced apart relationship with a fruit or vegetable, wherein a first of the group of the fibers are illuminated by the second light source to provide the actinic light at the one end and on the fruit or vegetable, a second of the group of the fibers which are periodically illuminated by the first light source to provide the modulated and monochromatic light at the one end and on the fruit or vegetable and a third of the group of the fibers which directs fluorescent light from the fruit or vegetable produced by each of the first or second light sources at the one end; and

(d) detection means connected to the third group of the fibers with circuit means for determining a first fluorescence intensity (F_o) produced by the second light source and for determining a fluorescence intensity (F_m) produced by the first light source for calculating a fluorescence intensity ratio of ##EQU4## which when F_m -F_o is equal to a variable fluorescence intensity (F_v), wherein the fruit or vegetable has chlorophyll in the skin as determined by the fluorescence intensity ratio which is at a first level indicative of an acceptable quality and wherein the fluorescence intensity ratio is at a second level which is decreased and which is indicative of an unacceptable quality.

23. The apparatus of claim 22 wherein the red light wavelength is at about 690 nm and the fluorescence intensity is measured at wavelengths in the range of 710 to 740 nm.

24. The apparatus of claim 22 wherein the quality is selected from the group consisting of firmness, texture, color and aroma.