METHOD AND KIT FOR DETERMINING THE CONCENTRATION OF COLOURED COMPOUNDS IN MEAT JUICE

Abstract: The invention concerns a method of monitoring the cooking temperature of meat patties. More specifically the present invention concerns a method of monitoring the cooking temperature of meat patties by determining the concentration of coloured compounds in meat juice.

Description: METHODANDKITFOR DETERMININGTHECONCENTRAΗONOFCOLOUREDCOMPOUNDS IN MEATJUICE The present invention concerns a method of monitor¬ ing the cooking temperature of meat patties. More spe¬ cifically the present invention concerns a method of monitoring the cooking temperature of meat patties by de- terminmg the concentration of coloured compounds m meat juice . Background In the US, rules for controlling meat have been strengthened since the incident with bacterial contamma- "ion of meat was discovered m a Jack n the Box restau¬ rant. Food Safety and Inspection Service (FSIS; equiva¬ lent to FDA) has in 1993 sent out directives which should be followed and inspections are carried out by local health units. Since 1996 similar directives in Europe prescribe that each food processing company should work m a preventive way. Listeria monocytogenes are the most serious contaminating bacteria but also Salmonella, E.coli 0157-.H7 and Staphylococcus aureus are of interest to monitor n all types of food. Since the first incident on bacterial contamination (Jack in the Box) , most fast- food chains like McDonalds, Burger King and Wendy's over¬ cook their hamburgers for safety reasons. Different methods to determine if patties have been well cooked have been used. FSIS recommends thermocouple thermometers inserted m the patties to verify that a certain temperature has been reached. In Europe meat samples are generally sent to external labs for bacterial analysis. Both temperature and cooking time are of impor¬ tance for killing bacteria. Measurements of correct temperature of cooked pat¬ ties are difficult mainly due to the heat transfer be¬ tween parts/spots of the patties during the cooking pro- cess. A better indicator of meat temperature would be a testing of a meat juice compound, flowing in the pores of the meat during cooking. Myoglobin and catalase (an enzyme) have been suggested for monitoring meat juice temperature. Myoglobin is the major pigment responsible for fresh meat colour. In fresh meat, the pigment can exist in three different forms: The reduced form of myoglobin is purplish, the oxygenated form is bright red and the oxi- dised form is brown. Fresh meat colour is determined by the relative abundance of these three forms. The consumer often associates the natural bright red colour to the freshness of the product, since brown colour of the oxi¬ dised pigment results from prolonged storage. Myoglobin is found in the muscle and is very similar in structure to haemoglobin. The difference in structure is the number of polypeptide chains. It is fairly insensitive to a change in pH. This is not a major problem with meat since the pH is fairly constant (pH 5.3-5.5) . It denatures at temperatures above 150°F (65.5°C) and might thus be of in¬ terest as a temperature indicator in processing of bovine meat (hamburgers) . One method for checking that meat has been heated to a temperature of about 80°C is disclosed in an article "Colour Determination of beef juices as an indication of beef cooking temperatures" by Nus movich, A.D. et al in Meat Science 1979 3(3) 233-244. This method is based on the measurement of the optical density at 10 nm intervals over the wave length range 380-770 nm. It is obvious that this method is comparatively labour-intensive and there¬ fore inadequate for industrial application. Additionally, this method is suggested for checking that a specific virus, the so called foot-and-mouth virus has been elimi¬ nated. It is furthermore stated that m this known method tne error of prediction is unacceptable large. An object of the present invention is to provide an industrially applicable method, wherein the error m the indirect end-point temperature measurement is negligible and amount of manual work is minimized. In brief, the method according to the present inven¬ tion provides a check for thorough cooking which is based on a measurement of myoglobin optionally in combination with other coloured compounds by filter photometry. The method includes the following steps: a) subjecting a meat sample to compressing for obtaining a meat juice sample; b) filtering said meat juice sample for removing sub¬ stances such as lipids which can interfere with the sub¬ sequent measurement; c) introducing the obtained meat juice sample into a microcuvette, preferably a capillary microcuvette having at least one cavity for receiving the sample, whereby the cavity is coated with a modifying additive for keeping the sample in a homogenous solution and for facilitating the introduction of the sample into the cuvette, and d) performing at least two absorption measurements directly on the sample at at least two predetermined wavelengths, whereby one measurement is a compensation measurement. The capillary microcuvette used for the measurement may be of the type generally described m the US patent 4 088 448. This microcuvette comprises a body member in¬ cluding two planar surfaces defining an optical path and placed at a predetermined distance e.g. at least 0.8 and preferably at least 0.7 mm from one another to determine the optical pathlength and to define at least one cavity having an inlet communicating the at least one cavity with the exterior of the body member, the predetermined distance being effective to permit the sample to enter the cavity by capillary force. Most preferably, the cuvette is of the type disclosed in our copending appli¬ cation PCT/SE96/00504, which is hereby incorporated Dy reference. In brief, the cuvette according to the PCT- application comprises a body member and a cavity mclud- ing a measuring zone within the body member, whereby the cavity is defined by two opposite, substantially parallel inner surfaces of the body member. The cavity is also de¬ fined by an outer peripheral edge including a sample in¬ let and an inner peripheral zone having a channel of higher capillary force than the measuring zone, whereby both ends of the channel communicate with the exterior of the microcuvette. The cuvette disclosed in the US patent 4 088 448 is intended and used for blood analysis, whereas according to the present invention the sample consists of meat juice and it is a critical feature of the invention that the cavity of the microcuvette is coated with a special modifying additive. The purpose of this additive is to keep the sample in a homogenous solution and to facilitate the introduction of the sample into the cavity. This agent could be a detergent selected from anionic agents such as caprylic acid, lauryl sulphate etc., cationic compounds such as cetyl pyridinium chlo¬ ride, zwitter ions, such as N-alkyl-N, -dimethylammonium- 1-propane sulphonate (CHAPS) and non-ionic agents, such as N-dodecyl-β-glucopyranoside. A preferred group of com¬ pounds is polyoxyethylene ethers, such as BRIJ52, BRIJ72 and BRU 92. Other preferred types are polyoxyethylene derivatives (stearate ethers) such as MYRJ. Another important feature of the invention is that an absorption measurement is carried out m order to eliminate the effect of optional turbidity in the sample and scratches on the cuvette walls. This compensation measurement is preferably carried out at 880 nm. According to an alternative embodiment the meat juice sample is introduced into a conventional non-capil¬ lary microcuvette having a distance between the cuvette walls less than about 5 mm. The invention is further illustrated by the follow¬ ing, non-limiting examples. Cooking procedure Frozen hamburgers (brand name Mulberry patties) were used, m which a hole was drilled for continuously measu¬ ring internal meat core temperature with a thermocouple. The hamburgers were cooked in a vertical oven. The cook¬ ing was stopped at pre-set temperatures. Sample preparation Cylindrical pieces of meat were cut out. The pieces were pressed and the meat juice obtained was filtered through a cellulose filter. Samples of juice were drawn for myo¬ globin determination. Samples were also taken from the top and bottom from the thermocouple locus to see if myo¬ globin concentration varied. A colour scale on juice and meat (Kansas State University) was used to grade the cooking. Preparation of microcuvette Microcuvettes of the type described m the PCT/SE96/00504 were filled with a detergent BRIJ 56 solu¬ tion and freeze-dπed. Measuring procedure By capillary action a few ml of each sample was drawn into each microcuvette and the absorbance was measured by filter photometry at 570nm with a compensa¬ tion for turbidity at 880nm. A HemoCue Hemoglobin Pho¬ tometer available from HemoCue AB, Sweden was used. The following data were obtained on replicate experiments with meat juice from quaterpounder hamburgers: Temperature (°F) Temperature (°C) Myoglobi (g/1) at TC 133.2 56.22 5.0 133.2 56.22 4.9 140.6 60.33 5.0 140.6 60.33 4.5 150.6 65.89 4.1 150.6 65.89 3.5 158.8 70.44 1.3 158.8 70.44 1.3 170.6 77.00 1.6 170.6 77.00 1.5 174.9 79.39 1.2 174.9 79.39 1.2 Data from three studies at different occasions showed good reproducibility between meat core temperature measured with a thermocouple and the myoglobin concentra¬ tion. There is a drop in the myoglobin concentration be¬ tween 65-70°C (statistically significant; p<0.001) . This decrease in concentration might be due to a denaturation (or decomposition) of myoglobin. A couple of experiments on meat juice from McDonalds hamburgers gave myoglobin values around zero, which was interpreted as an extensive cooking time of those hamburgers. Tests have also been performed on imported beef, re- quiring a temperature of about 80°C according to FSIS. The decay m the myoglobin concentration can be seen in the following table Temperature 76 78 80 82 84 (°C) Experiment 1 1.6 0.7 0.3 0.2 0.1 (myoglobin g/1) Experiment 2 1.1 0.7 0.4 0.2 0.1 (myoglobin g/1) It can also be concluded that the precision is good and that myoglobin can be used as indicator for mean tem¬ perature.

Claims: CLAIMS 1. Method for determining the concentration of coloured compounds in meat juice, characterized by the steps of filtering a sample of meat juice, introducing the sample in a capillary microcuvette having at least one cavity for receiving the sample, whereby the cavity is coated with a modifying additive and performing at least two absorption measurements at at least two pre- determined wavelengths directly on the sample in the cuvette, whereby one measurement is a compensation measurement. 2. Method according to claim 1 characterized in that the modifying agent is used for keeping the sample in a homogenous solution and for facilitating the introduction of the sample into the cuvette. 3. Method according to claim 1 or 2 characterized in that the compensation measurement is carried out at 880 nm. 4. Method according to any of the claims 1 -3 characterized that the modifying agent is a detergent. 5. Method according to any of the claims 1-4 characterized m that the detergent is selected from the group consisting of caprylic acid, lauryl sulphate, cetyl pyridinium chloride, zwitter ions, such as N-alkyl- N,N-dιmethylammonιum-1-propane sulphonate, non-ionic agents, such as N-dodecyl-β-glucopyranoside. 6. Method according to claim 3 wherein the detergent is selected from polyoxyethylene ethers, such as BRIJ52, BRIJ72 and BRIJ 92 or polyoxyethylene derivatives. 7. Method according to claim 1, characterized in that the coloured compounds are selected from the αroup consisting of myoglobin and haemoglobin. 8. Method for checking thorough cooking of meat pat- ties comprising the steps of a) subjecting the meat patty to compressing for obtaining a meat juice sample b) filtering said meat juice sample c) introducing the obtained meat juice sample into a capillary microcuvette, comprising a body member includ¬ ing two planar surfaces defining an optical path and placed at a predetermined distance from one another to determine the optical pathlength and to define at least one cavity having an inlet communicating the at least one cavity with the exterior of the body member, the pre¬ determined distance being effective to permit the sample to enter the cavity by capillary force; d) measuring the absorption at at least two predetermined wavelengths directly on the sample whereby one measurement is a compensation measurement. 9. Disposable kit for checking thorough cooking in meat patties comprising a capillary microcuvette and a filtering system.

Inventors: LILJA JAN, NILSSON BERTIL, NILSSON SVEN-ERIK, WILLIAMSSON ANDERS, LILJA, JAN, NILSSON, BERTIL, NILSSON, SVEN-ERIK, WILLIAMSSON, ANDERS
Applicants: HEMOCUE AB, LILJA JAN, NILSSON BERTIL, NILSSON SVEN ERIK, WILLIAMSSON ANDERS, LILJA, JAN, NILSSON, BERTIL, NILSSON, SVEN-ERIK, WILLIAMSSON, ANDERS
Application year: 1997
Main classification: G01N33
IPC codes: G01N33