WO2014181209A1

WO2014181209A1 - Method and device for measuring quality and freshness of vegetable oil using fluorescence spectrophotometry

Info

Publication number: WO2014181209A1
Application number: PCT/IB2014/060964
Authority: WO
Inventors: Ming Sun; Bin Yin
Original assignee: Koninklijke Philips N.V.
Priority date: 2013-05-06
Filing date: 2014-04-24
Publication date: 2014-11-13

Abstract

The present invention relates to a method for measuring quality and freshness of vegetable oil using fluorescence spectrophotometry and more particularly excitation - emission matrix (EEM) measurements, the method comprising steps of: exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s), such as vitamin E or chlorophyll derivatives, and/or anti-nutrient substance(s), such as oxidation products; detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and determining quality and freshness of said vegetable oil according to the detected fluorescence intensity. The present invention also relates to a device for measuring quality and freshness of vegetable oil. By selecting fluorophores as fluorescent markers, excitation spectrum and detection bandwidth can be preset in a relatively narrow range, thus the disturbance of unconcerned components will be eliminated, which makes the measurement more rapid and more accurate.

Description

METHOD AND DEVICE FOR MEASURING QUALITY AND FRESHNESS OF VEGETABLE OIL USING FLUORESCENCE SPECTROPHOTOMETRY

FIELD OF THE INVENTION

The invention relates to a method and a device for determining quality of cooking oil, in particular, to a method and a device for measuring quality and freshness of vegetable oil.

BACKGROUND OF THE INVENTION

Vegetable oils, which contain significant amounts of energy as well as essential micronutrients for health, are important components for human daily diet. Vegetable oils comprise of triacylglycerols, free fatty acids and various minor compounds. Among these minor compounds, phenols, tocopherols, carotenes and chlorophyll derivatives are the most important as they designate the nutrition and organoleptic (e.g. color, flavor, taste) characteristics of oils.

Phenols, especially tocopherols (vitamin E), are essential fat-soluble micronutrients for higher mammals and function as an antioxidant for lipids and also as a regulator of gene expression and a modulator of cell signalling and proliferation. Tocopherols and tocotrienols comprise the vitamin E family and can only be synthesized by plants and other photosynthetic organisms. For human beings, vitamin E is mainly ingested from vegetable oils, nut/seed oils, and cereals (or grains). Tocopherols are present in oils in variable amounts, from 70 to 1900 mg/kg, depending on the type of oil. Furthermore, vitamin E is being widely labeled as the lipophilic antioxidant and free radical scavenger, which will protect lipids from being oxidatively damaged. When the vitamin E is consumed, the oxidation process of unsaturated fatty acids will be accelerated, chlorophyll derivatives are also reported to exhibit antioxidant activity under certain conditions and may be beneficial in the prevention of cancer.

For long-term stored and repeatedly used oils, antioxidants and micronutrient will be consumed and destroyed completely. Especially, frying oil, which is used continuously at high temperatures, is subject to a series of complex chemical reactions, such as oxidation, polymerization, hydrolysis, cis/trans isomerization, conjugation, pyrolysis, and cyclization. More than 400 different chemical compounds, including 220 volatile products, have been identified in deteriorated frying oil. The degradation products have a negative effect on the flavor and nutritional value of fried products. Moreover, many degradation products of frying oil are harmful to human health because they destroy vitamins, inhibit enzymes, and can potentially cause mutations and gastrointestinal irritations.

For maximizing profitability, in restaurants cooking oils are sometimes over-repeatedly used, and the waste oils come back to the table after simple refinement instead of being recycled for industrial use, becoming so called 'hogwash oil' . Due to the frying/cooking processes these oils have undertaken, most nutrition components have been decomposed, and many degradation products are harmful to human health. Therefore, how to measure the quality (nutrition, freshness etc.) of edible oils and distinguish between normal and hogwash oils is becoming an increasing demand by consumers and authentic organizations to guarantee food quality and public health.

In the context of the present invention, "quality" represents properties in favor of health, such as the content of nutrient substance(s) and/or anti-nutrient substance(s), as well as the purity of the cooking (vegetable) oil. Currently, a variety of methods are available for assessing the oils quality. Traditional chemical analyses, such as gas and liquid chromatography, are reliable ways for oil analysis. However, these chemical analyses are often time-consuming, expensive, and destructive to the sample. In addition, they require potentially hazardous reagents and also require reasonable analytical expertise.

To date, there are few quick test devices available for real-time in situ oil analysis. Spectroscopic methods present alternatives to chemical analyses, which can be applied quickly, conveniently and inexpensively, especially when only limited numbers of optical bands are needed for a specific sensing purpose. Infrared spectroscopic techniques, such as near infrared spectroscopy (NIR) and mid infrared spectroscopy (MIR), have been used for testing authenticity of foods. The main disadvantage of IR spectroscopic methods is their lack of selectivity; hence, the data on qualitative and quantitative composition often have to be extracted using advanced multivariate procedures.

SUMMARY OF THE INVENTION

It is thus desired to provide a method and a device for measuring quality and freshness of vegetable oil more rapidly and more accurately.

Most of abovementioned micronutrients and degradation products possess unique optical spectroscopy properties (e.g. fluorescence, absorption, reflection), which can be used, after optically detected, as multi natural intrinsic markers for monitoring the nutrition and freshness of edible oils. In this invention, fluorescence spectroscopy is selected, due to its high sensitivity and specificity. Besides, Fluorescence technology is simple, fast and has relatively low instrumentation cost. For tocopherols and phenols, the emission spectrum region lies between 300 and 400 nm, with excitation wavelength at -250-300 nm. Some derivatives of vitamin E are also associated with the emission spectrum region 400-600 nm. For chlorophyll derivatives, the emission bands lie in the region of 625-775 nm with excitation wavelength at -300-625 nm. For degradation or oxidation compounds, the emission bands lie in the region of 350-550 nm with excitation wavelength at -300-500 nm.

In order to achieve the desired obj ect, an embodiment of the invention provides a method for measuring quality and freshness of vegetable oil, the method comprising steps of: exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and determining quality and freshness of said vegetable oil according to the detected fluorescence intensity.

In the embodiment of the invention, a new fluorescence based spectrophotometric method is presented for the rapid assessment of oil quality. Multi-intrinsic fluorophores are explored from the excitation-emission matrix (EEM), e.g. phenols & tocopherols (vitamin E), chlorophylls & pheophytins and oxidative compounds. These fluorophores are sensitive to oxygen, light and thermal, and thereby can be used as intrinsic molecular markers for monitoring the nutrition, freshness and frying process of edible oils. By selecting these fluorophores as fluorescent markers, excitation spectrum and detection bandwidth (corresponding to the emission bandwidth of the selected fluorophores) can be preset in a relatively narrow range, thus the disturbance of unconcerned components will be eliminated, which makes the measurement more rapid and more accurate.

Alternatively, a heating process monitoring mode is also presented. Sigmoid (Boltzmann function) fitting curves can be derived from the fluorescence intensity evolution process of fluorescence markers in various vegetable oils from ~ 25 °C to 350°C. By using the parameters of sigmoid fitting function, the oils quality can be evaluated more accurately.

Therefore, to provide a more reliable testing result, another embodiment of the invention provides a method for measuring quality and freshness of vegetable oil, the method comprising steps of: heating said vegetable oil from a first temperature to a second temperature; wherein at different temperature points between said first temperature and said second temperature: exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and determining quality and freshness of said vegetable oil by fitting an evolution curve with a predetermined function, wherein said evolution curve is composed of the detected fluorescence intensity of said predetermined fluorescent marker(s) at different temperature points.

In such a dynamic method, fluorescence intensities of markers evolving in a thermal process are analyzed, which may increase the accuracy of oil quality assessment.

By analyzing fitting curves of the markers, existence of these markers can be determined qualitatively and quantitatively with high reliability.

In the embodiments of the invention, ranges of said excitation spectrum and said detection bandwidth are 250-300 nm, 300-400 nm respectively, or 300-625 nm, 625-775 nm respectively, or 300-500 nm, 350-550 nm respectively. Preferably, said nutrient substance(s) comprises vitamin E and/or chlorophyll derivatives; and/or said anti-nutrient substance(s) comprises oxidation compounds.

The invention also discloses a device for measuring quality and freshness of vegetable oil. Said device comprises: a light emitting unit for exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); a fluorescence detection unit for detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; an optical interface; an output light path for transmitting excitation light from said light emitting unit to said optical interface; an input light path for transmitting emission light of said predetermined fluorescent marker(s) from said optical interface to said fluorescence detection unit; and an electronic signal processing unit for receiving the detected fluorescence intensity of said predetermined fluorescent marker(s), and determining quality and freshness of said vegetable oil according to said detected fluorescence intensity.

By preselecting fluorescent marker(s) corresponding to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s), excitation spectrum and detection bandwidth (corresponding to the emission bandwidth of the selected fluorophores) can be preset in a relatively narrow range, thus the disturbance of unconcerned components will be eliminated, which makes the measurement more rapid and more accurate.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter. However, the invention is not limited to these exemplary embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described based on various embodiments with reference to the accompanying drawings, in which:

Figs. 1A, IB show total fluorescence Excitation/Emission spectra of peanut oil at 25°C and 280°C respectively; Figs. 2A, 2B show total fluorescence Excitation/Emission spectra of olive oil at 25°C and 280°C respectively;

Figs. 3A-D show fluorescence evolution of vitamin E in different kinds of peanut oils (fresh, storage in darkness, thermal treated) at different heating rate from 25 °C to 350°C respectively;

Fig. 4A shows a schematic diagram of a device according to an embodiment of the invention;

Fig. 4B shows a schematic diagram of a device according to another embodiment of the invention;

Fig. 5 shows fluorescence evolution of chlorophyll derivatives (emission wavelength 670 nm) and oxidation compounds (emission wavelength 502 nm) in olive oil from 25°C to 310°C.

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made to embodiments of the disclosure, one or more examples of which are illustrated in the figures. The embodiments are provided by way of explanation of the disclosure, and are not meant as a limitation of the disclosure. For example, features illustrated or described as part of one embodiment may be used with another embodiment to yield still a further embodiment. It is intended that the disclosure encompass these and other modifications and variations as come within the scope and spirit of the disclosure.

Figs. 1A, IB show total fluorescence Excitation/Emission spectra of peanut oil at 25°C and 280°C respectively; Figs. 2A, 2B show total fluorescence Excitation/Emission spectra of olive oil at 25°C and 280°C respectively. Wherein X axis indicates the excitation wavelength, Y axis indicates the emission wavelength, and Z axis indicates the fluorescence intensity with arbitrary unit (a.u.).

In Fig. 1A and Fig. 2 A, the total fluorescence excitation/emission spectra (room temperature) of fresh and thermal-treated (280°C, heated by induction cooker) peanut oil / olive oil are plotted. For the fresh samples, the vitamin E (circle indicated with reference number 1) and chlorophyll derivatives peaks (circle indicated as 2) are both strong. The oxidation compounds peaks (circle indicated as 3) are visible but lower, which may be resulted during the produce process (crushing, milling, beating, stir-frying processes, pH-changes etc.). During thermal treating process (as shown in Fig. IB and Fig. 2B), the peaks intensity of vitamin E and chlorophyll derivatives (circles 1, 2) will decrease, and oxidation compounds peaks (circle 3) will increase continuously. Based on the fluorescence intensity and the ratios between vitamin E (or chlorophyll derivatives) and oxidation compounds, the nutrition and freshness of oils can be determined.

Based on the abovementioned properties of the vegetable oil, according to a first aspect of the invention, a method for measuring quality and freshness of vegetable oil is proposed. Said method comprises steps of: exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and determining quality and freshness of said vegetable oil according to the detected fluorescence intensity.

According to the fluorescent properties of the representative nutrient substances and anti-nutrient substances of vegetable oil, preferably, ranges of said excitation spectrum and said detection bandwidth are 250-300 nm, 300-400 nm respectively, or 300-625 nm, 625-775 nm respectively, or 300-500 nm, 350-550 nm respectively. With such a configuration, representative nutrient substances and anti-nutrient substances of vegetable oil can be excited and detected without disturbance of unconcerned materials.

According to a preferred embodiment of the invention, said nutrient substance(s) comprises vitamin E and/or chlorophyll derivatives; and/or said anti-nutrient substance(s) comprises oxidation compounds.

Tocopherols and tocotrienols comprise the vitamin E family and can only be synthesized by plants and other photosynthetic organisms, chlorophyll derivatives are also involved in complex biochemical processes and their compositions are complicated for different vegetable oils. Both of them are sensitive to oxygen, light and heat, and will be destroyed irreversibly. Therefore, vitamin E, chlorophyll derivatives and oxidation compounds may be used as reliable intrinsic markers for the oil quality assessment. By measuring the fluorescence intensity or calculating the ratios between vitamin E (or chlorophyll derivatives) and oxidative compounds, the nutrition and freshness of oil can be assessed. However, as can be understood by those skilled in the art, other representative nutrient substances (such as flavones, phaeophyll, etc.) and/or anti-nutrient substances (such as aspergillus flavus, polycyclic aromatic hydrocarbon, cholesterol, etc.) can also be selected as the fluorescent markers. With the idea of the invention, once the fluorescent marker(s) is replaced with new fluorescent marker(s), the excitation spectrum and detection bandwidth can be preset according to fluorescent properties of the new fluorescent marker(s) conveniently.

Preferably, the method according to the first aspect of the invention can further comprise steps after said step of detecting: calculating fluorescence intensity ratio between said fluorophore(s) of nutrient substance(s) and said fluorophore(s) of anti-nutrient substance(s); and comparing the calculated result with a prestored value.

By calculating such a fluorescence intensity ratio and comparing the calculated result with a prestored value (which corresponds to a fresh or standard sample of vegetable oil), quality and freshness of said vegetable oil can be assessed quickly and accurately.

According to a second aspect of the invention, besides the above "static" fluorescence intensity based method, a dynamic method in which fluorescence intensities of markers (such as vitamin E, chlorophyll derivatives etc.) evolving in a thermal process get analyzed may increase the accuracy of oil quality assessment. The dynamic method inspects a thermal evolution curve of the fluorescence intensity of a marker in a heating process, extracts features from the morphology of the curve and makes decision based on the extracted features. This method, therefore, will be insensitive to intrinsic and external factors, such as biological species, geographic regions, extraction methods, storage time, instrument parameters etc.

In an embodiment according to the second aspect of the invention, a method for measuring quality and freshness of vegetable oil is proposed. Said method comprises steps of:

- heating said vegetable oil from a first temperature to a second temperature; wherein at different temperature points between said first temperature and said second temperature:

- exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); and

- detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and

- determining quality and freshness of said vegetable oil by fitting an evolution curve with a predetermined function, wherein said evolution curve is composed of the detected fluorescence intensity of said predetermined fluorescent marker(s) at different temperature points.

According to the fluorescent properties of the representative nutrient substances and anti-nutrient substances of vegetable oil, preferably, said excitation spectrum comprises at least one excitation wavelength of said predetermined fluorescent marker(s); and said detection bandwidth comprises at least one emission wavelength of said predetermined fluorescent marker(s). With such a configuration, one substance in vegetable oil can be excited and detected separately without disturbance of unconcerned materials.

According to a preferred embodiment of the invention, said predetermined function is: Y=A₂ + (Ai - A₂) / (1 + exp ((X - ¾) / d_x)),

in which Ai and A₂ are the detected fluorescence intensity of said predetermined fluorescent marker(s) before and after heating respectively; X is dynamic heating temperature; X₀ is the heating temperature for the fastest decomposition; d_x is a decomposition slope; wherein X₀ and d_x can be preset according to type of said vegetable oil. However, other suitable functions can also be prestored and applied for performing the fitting.

Optionally, an adjusted R-square value indicates the goodness of fitting, which is proportional to the quality and freshness of vegetable oil. A value closer to 1 indicates a good fit.

The following examples explain how this method works with reference to Figs.

3A-D.

Figs. 3A-D show fluorescence evolution of vitamin E in different kinds of peanut oils (fresh, storage in darkness, thermal treated) at different heating rate from 25 °C to 350°C respectively, wherein the horizontal axis indicates the temperature, and the vertical axis indicates the detected fluorescence intensity of said predetermined fluorescent marker(s). The evolution curves are composed of the detected fluorescence intensity of said predetermined fluorescent marker(s) at different temperature points. In Figs. 3A-D, a sigmoidal (Boltzmann function) template is used to fit the fluorescence intensity evolution process of vitamin E in different peanut oils from ~ 25°C to 350°C. The used Sigmoidal (Boltzmann) function is Y=A₂ + (Ai - A₂) / (1 + exp ((X - Xo) / d_x)). The type of vegetable oil, heating time and the adjusted R-square value of the corresponding curves in Figs. 3 A-D respectively are:

Fig. 3A: peanut oil (fresh), ~15minutes, adjusted R-square=0.9929;

Fig. 3B: peanut oil (storage), ~40minutes, adjusted R-square=0.9945;

Fig. 3C: peanut oil (storage), ~5minutes, adjusted R-square=0.9929;

Fig. 3D: peanut oil (320°C thermal treated), ~20minutes, adjusted R-square=0.8813.

For short term stored oils, although the initial fluorescent intensity will decrease, the sigmoidal curves will not change significantly. The heating rate also has little influence on the sigmoidal curves. However, for the cooked oils, most of vitamin E will be thermally destroyed and the thermal evolution curve will be significantly different (the right bottom plot in Figure 3). The shape of sigmoidal fitting curve is different from that of fresh oil, which possesses larger fluorescence signal noise and lower Adjusted R-square (0.8813). And, the fastest decomposition temperature (¾ = 310°C) is much higher than the decomposition temperature of vitamin E. By evaluating the parameters of sigmoidal fitting curves, certain thresholds may be derived so that the nutrition and freshness of oils can be determined more accurately. For instance, for fresh oils, large amount of markers (vitamin E, chlorophyll derivatives etc) are present, the fluorescence change will be significant at certain temperature conditions. On the contrary, for cooked oils, most of markers are vanishing, and the fluorescence will not change with temperature as dramatically. Therefore, for fresh oils, the initial fluorescence intensity (Ai) should be larger than a certain threshold, the fastest decomposition temperature (¾) and decomposition slope (d_x) should be smaller than certain thresholds, and the Adjusted R-square should be closer to 1.

In a summary, prior to actual detection, the optical spectroscopy database of various fresh vegetable oils and their corresponding thermal evolution process should be established.

The spectroscopy parameters, such as peak positions, peak intensities, FWFDVI (full wide at half maximum), intensity ratios, and sigmoidal function parameters, are derived and to be used as references for qualitative and quantification analysis. The reference preparation step is completed offline by using professional spectrometer, and the established database is stored in a storage medium that can be accessed during actual detection.

For special oil types or mixtures, their specific thermal evolution process could be established in a customized manner, by making use of the heating accessory in the heating process monitoring mode.

According to a further embodiment of the present invention, a device for measuring quality and freshness of vegetable oil is proposed. Fig. 4A shows a schematic diagram of a device according to an embodiment of the invention.

The device 400 comprises: a light emitting unit 401 for exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s); a fluorescence detection unit 403 for detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; an optical interface; an output light path 405 for transmitting excitation light from said light emitting unit 401 to said optical interface; an input light path 406 for transmitting emission light of said predetermined fluorescent marker(s) from said optical interface to said fluorescence detection unit 403 ; and an electronic signal processing unit 407 for receiving the detected fluorescence intensity of said predetermined fluorescent marker(s), and determining quality and freshness of said vegetable oil according to said detected fluorescence intensity. To transmit or receive light within a desired bandwidth, band pass (or high/low pass) filters 402, 404 can be inserted into the light paths. A rubber acetabulum 408 can be set around the optical interface to adhere the device 400 onto a container of the vegetable oil.

As can be understood by those skilled in the art, the output light path 405 and the input light path 406 can be integrated into one light path, i.e., the light emitting unit 401 , the fluorescence detection unit 403 and the optical interface can be coupled together with a T-joint mode. To eliminate the disturbance directly from the light emitting unit

401, a band pass or high/low pass filter can be applied in front of the fluorescence detection unit 403 according to the fluorescence band of selected markers.

According to still another embodiment of the present invention, a device for measuring quality and freshness of vegetable oil is proposed. Fig. 4B shows a schematic diagram of a device according to another embodiment of the invention.

As shown in Fig. 4B, in addition to those components in the device of former embodiment, the device 400 further comprises a heating accessory. Said heating accessory comprises: a container 409 for containing said vegetable oil; a transparent interface (not shown) on said container for coupling with said optical interface; a heating element 410 for heating said vegetable oil from a first temperature to a second temperature. The output light path 405 and the input light path 406 can have branches for connection with the transparent interface on said heating accessory. With such a configuration, the device 400 can be used to perform the abovementioned dynamic method.

By means of the device 400, various representative nutrient substances (such as flavones, phaeophyll, etc.) and/or anti-nutrient substances (such as aspergillus flavus, polycyclic aromatic hydrocarbon, cholesterol, etc.) can also be selected as the fluorescent markers. Fig. 5 shows fluorescence evolution of chlorophyll derivatives (emission wavelength 670 nm, indicated by reference number 501) and oxidation compounds (emission wavelength 502 nm, indicated by reference number 502) in olive oil from 25°C to 310°C. For fresh olive oil, the intensity of the peak of chlorophyll derivatives is up to 46000 fluorescence arbitrary units, and the intensity of the peak of oxidation compounds is below 1500 fluorescence arbitrary units. On the contrary, for thermo-treated olive oil, the intensity of the peak (670 nm) of chlorophyll derivatives is lower than 5000 fluorescence arbitrary units (the spectra feature is vanished), the intensity of the peak of oxidation compounds (502 nm) is up to 22000 fluorescence arbitrary units. The fluorescent intensity ratio between chlorophyll derivatives and oxidation compounds can be calculated for assessment. The fluorescent intensity evolution curves 501 and 502 can also be fitted with predetermined functions, so as to assess a single nutrient substance or anti-nutrient substance qualitatively and quantitatively with high reliability.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Other variations to the disclosed embodiments can be understood and effected by those skilled in the art in practicing the claimed invention, from a study of the drawings, the disclosure, and the appended claims. In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite article "a" or "an" does not exclude a plurality. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A method for measuring quality and freshness of vegetable oil, the method comprising steps of:

- exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s);

- determining quality and freshness of said vegetable oil according to the detected fluorescence intensity.

2. The method according to claim 1, wherein ranges of said excitation spectrum and said detection bandwidth are 250-300 nm, 300-400 nm respectively, or 300-625 nm, 625-775 nm respectively, or 300-500 nm, 350-550 nm respectively.

3. The method according to claim 1 , wherein said nutrient substance(s) comprises vitamin E and/or chlorophyll derivatives; and/or said anti-nutrient substance(s) comprises oxidation compounds.

4. The method according to one of claims 1-3, wherein the method further comprising steps after said step of detecting:

- calculating fluorescence intensity ratio between said fluorophore(s) of nutrient substance(s) and said fluorophore(s) of anti-nutrient substance(s); and

- comparing the calculated result with a prestored value.

5. A method for measuring quality and freshness of vegetable oil, the method comprising steps of:

- detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth; and - determining quality and freshness of said vegetable oil by fitting an evolution curve with a predetermined function, wherein said evolution curve is composed of the detected fluorescence intensity of said predetermined fluorescent marker(s) at different temperature points.

6. The method according to claim 5, wherein said excitation spectrum comprises at least one excitation wavelength of said predetermined fluorescent marker(s); and said detection bandwidth comprises at least one emission wavelength of said predetermined fluorescent marker(s).

7. The method according to claim 5, wherein said nutrient substance(s) comprises vitamin E and/or chlorophyll derivatives; and/or said anti-nutrient substance(s) comprises oxidation compounds.

8. The method according to one of claims 5-7, wherein said predetermined function is:

Y=A₂ + (Ai - A₂) / (1 + exp ((X - ¾) / d_x)),

in which Ai and A₂ are the detected fluorescence intensity of said predetermined fluorescent marker(s) before and after heating respectively; X is dynamic heating temperature; Xo is the heating temperature for the fastest decomposition; d_x is a decomposition slope;

wherein X₀ and d_x can be preset according to type of said vegetable oil.

9. The method according to one of claims 5-7, wherein an adjusted R-square value indicates the goodness of fitting, which is proportional to the quality and freshness of vegetable oil.

10. A device (400) for measuring quality and freshness of vegetable oil, the device comprising:

a light emitting unit (401) for exciting predetermined fluorescent marker(s) with an excitation spectrum, said predetermined fluorescent marker(s) corresponds to at least one fluorophore(s) of nutrient substance(s) and/or anti-nutrient substance(s);

a fluorescence detection unit (403) for detecting fluorescence intensity of said predetermined fluorescent marker(s) within a detection bandwidth;

an optical interface;

an output light path (405) for transmitting excitation light from said light emitting unit (401) to said optical interface;

an input light path (406) for transmitting emission light of said predetermined fluorescent marker(s) from said optical interface to said fluorescence detection unit (403); and

an electronic signal processing unit (407) for receiving the detected fluorescence intensity of said predetermined fluorescent marker(s), and determining quality and freshness of said vegetable oil according to said detected fluorescence intensity.

1 1. The device according to claim 10, wherein ranges of said excitation spectrum and said detection bandwidth are 250-300 nm, 300-400 nm respectively, or 300-625 nm, 625-775 nm respectively, or 300-500 nm, 350-550 nm respectively.

12. The device according to claim 10, wherein said nutrient substance(s) comprises vitamin E and/or chlorophyll derivatives; and/or said anti-nutrient substance(s) comprises oxidation compounds.

13. The device according to one of claims 10-12, wherein the device further comprising a heating accessory which comprises:

a container (409) for containing said vegetable oil;

a transparent interface on said container for coupling with said optical interface; a heating element (410) for heating said vegetable oil from a first temperature to a second temperature.

14. The device according to claim 13, wherein quality and freshness of said vegetable oil is determined by fitting an evolution curve with a predetermined function, said evolution curve is composed of the detected fluorescence intensity of said predetermined fluorescent marker(s) at different temperature points.

15. The device according to claim 14, wherein said predetermined function is:

Y=A₂ + (Ai - A₂) / (1 + exp ((X - ¾) / d_x)),

wherein X₀ and d_x can be preset according to type of said vegetable oil.