Electricity: measuring and testing – Determining nonelectric properties by measuring electric...
Reexamination Certificate
2001-09-28
2003-07-29
Le, N. (Department: 2858)
Electricity: measuring and testing
Determining nonelectric properties by measuring electric...
C324S423000, C324S444000
Reexamination Certificate
active
06600306
ABSTRACT:
CROSS-REFERENCES TO RELATED APPLICATIONS
This application claims the benefit of International Application No. PCT/FR00/00871 filed Apr. 13, 1999.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to the in-situ monitoring of the degradation of frying oils and fats (in practice in the food sector).
2. Description of the Related Art
Food oils and fats used in cooking and frying operations undergo a thermo-oxidative alteration leading to a progressive degradation of the oil with the formation of polar compounds.
In France, decree 86-857 of Jul. 18
th
, 1986 amending the decree of Mar. 11
th
, 1908 stipulates that fats and oils with a polar compound content greater than 25% are unsuitable for human consumption and provides for the fixing by order of a reference analytical method for determining the polar compound content.
The current standardized reference analytical method is a liquid chromatography at atmospheric pressure followed by a solvent evaporation and a weighing (duration 3 hours). This method cannot be used for routine monitoring.
Moreover, a subjective assessment involving monitoring of the browning of the oil, the viscosity, the appearance of foam or the presence of smoke is not reliable because these criteria can appear well after the 25% limit.
More rapid methods have been developed or envisaged:
A. Methods Based on Colorimetric Reactions
“LRSM” test from 3M: this involves soaking a reactive paper in the oil. The criterion defining the end of use of an oil is the number of strips of the reactive paper that have changed color.
“OXYFRITEST” test from MERCK-CLEVENOT laboratories: a test tube is filled with oil using a syringe and some drops of reagent are added to it. After a few seconds, the color is modified according to the polar compound content. The limit of use is defined by comparison of the color obtained with a scale of reference colors.
French Patent No. FR 2 513 765 (OIL PROCESS SYSTEMS INC.) for: “Kit and process for the analysis of alkaline substances in fatty foodstuffs”; the analysis is based on a mixture of fatty material with a titration solution containing a solvent and a colorant.
B. Methods Based on the Measurement of Conductivity or Specific Resistance
U.S. Pat. No. 5,239,258 (KAUFFMAN) for: “Freshness and Stability Test Using Oxidative Degradation”; the analysis is based on the development of the current passing through a specimen relative to the voltage applied.
U.S. Pat. No. 5,594,327 (SAGREDOS et al.) for: “Method For Determining the Degree of Deterioration of Oils or Fats Used for Frying Foods”; the analysis is based on specimens introduced into a measurement cell in which, at a voltage of 100V and a temperature of 75° C., the specific ohmic resistance of the material constituting the specimen is measured.
C. Methods Based on the Measurement of the Dielectric Constant
Various scientific articles have already dealt with the problem of degradation of oils, for example:
“Changes in Dielectric Constant as a Measure of Frying Oil Deterioration”, by C. W. FRITSCH et al., published in “Journal of The American Oil Chemists' Society”, Vol. 56, August 1979,
“Measurements of Frying Fat Deterioration. A Brief Review” by C. W. FRITSCH et al. published in JAOCS, March 1981.
These articles showed a strong correlation between the variation in the dielectric constant and the percentage of polar compounds formed. This is exploited in the German Patent Application No. DE 30 06 696 5 (NORTHERN INSTRUMENTS CORP.) providing a device for measuring dielectric properties. The device for measuring dielectric properties which is described therein is sometimes referred to by the name “Food Oil Sensor”.
In practice, only the 3M and MERCK-CLEVENOT tests are used. The duration of a test is approximately one minute per deep fryer. The reliability of these tests, however, remains poor because it depends on 3 factors which are difficult to control:
1. storage conditions of the reagents: temperature, time, ambient light;
2. their use:
the reactive papers must not be brought into contact with other objects and must be immersed for a precise time (a few seconds) in the homogenized oil; and
it is vital that the quantity of reagent (a few drops) be observed; and
3. measurement and interpretation:
this must be carried out after a precise period (about ten seconds) and is valid only for a fixed period (about 30 seconds); and
the color changes are progressive and require a degree of experience in order to be read correctly.
As a general rule, all the tests available or mentioned in the literature have the disadvantage of involving sampling, i.e. the taking of samples which are analyzed outside the mass of the fatty material in use. The reliability of the monitoring therefore depends on the periodicity and regularity of the tests.
Of course, the overall reliability also depends on the reliability of the conclusions drawn from the results of the test operations.
All the methods which require prior preparation (chemical, colorimetric, or even electric, U.S. Pat. No. 5,239,258) cannot be used for in-situ monitoring and are hardly suitable for frequent monitoring (typically several times during a heating cycle).
U.S. Pat. No. 5,594,327 describes a method of measuring the variation in conductivity using a DC voltage of 100 V, a method inapplicable for monitoring in a commercial cooking vat (problem of safety voltage).
It must be noted with regard to this latter document that it mentions, among other monitoring techniques, measurement of the dielectric constant of the cooking bath, but considers this method to be complex and costly in terms of monitoring time, without stating a reason. However, the following comments can be made:
A. With Regard to Complexity
The composition of frying oils and fats is always changing, according to clients' needs and/or the purchase price of the raw materials. For example, an oil can contain animal fats (suet for example), vegetable fats (palm for example), an anti-oxidant (Exxx), and/or an anti-foaming agent (Eyyy). However, the permittivity of such an oil at 180° C. (typical usage temperature) does not appear in any publication, including the manufacturer's technical specifications, nor do its dispersion during successive production stages, or its variation when it contains 25% of polar compounds.
Moreover, each catering group uses an oil or a fat the composition of which it has determined itself.
B. With Regard to the Cost in Terms of Monitoring Time
The above-mentioned patent doubtless refers to the Food Oil Sensor which proceeds by sampling and that has clearly proven to be long and complex.
BRIEF SUMMARY OF THE INVENTION
An object of the present invention is to overcome the disadvantages of the known solutions, providing a process for monitoring that is at once reliable and repetitive, and that lends itself to automation so as to be able to guarantee in particular the consequences of the detection of too large a quantity of polar compounds.
To this end, the present invention proposes a process for monitoring a frying vat containing a bath of frying oil or fat intended to follow a plurality of heating cycles, according to which:
A. In a zone of the vat suitable for immersion in the bath, a capacitive probe is arranged, the dielectric space of which is constituted by a portion of the bath, and, after filling the vat with this bath, an initialization procedure is triggered during which an initial value of a characteristic representative of the dielectric constant of this bath in heating conditions is measured, and a shutdown criterion is fixed.
B. A measurement of this characteristic is repeatedly detected during the following heating cycles, and a shutdown procedure is triggered when it is detected that the shutdown criterion is met by this measurement.
The invention thus teaches the use of a capacitive, in practice permanent, probe in the cooking vat. The probe must therefore withstand an average temperature of 180° C. and its construction must satisfy the food and electric standards. The requirements for the prob
Le Henaff Denis
Pernot Christian
Benson Walter
Le N.
Metatron
VanOphem & VanOphem P.C.
LandOfFree
Method and device for controlling a vat containing oil or... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Method and device for controlling a vat containing oil or..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Method and device for controlling a vat containing oil or... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3092652