Microwave Technology Optimizes Moisture and Fat Analysis

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Fat analysis: the sample must be dry

NMR technology for fat analysis is nothing new. It has been used for a number of years for dry samples such as nuts, chocolate and grain. However, early trials of fat analysis on very moist products such as meat & sausage, dairy products (ice cream, quark, yogurt, etc.), gourmet food, ketchup and mayonnaise were not successful. The reason was that water interfered with the fat signal. So, water must be removed from the sample priorly to fat analysis. However, drying in an oven can take several hours, making this idea unfeasible.

The logical way forward for the developers at CEM was first dry the samples in the Smart 6 microwave within 2 minutes before fat analysis. Microwave drying is the quickest drying method, and it is fast enough for process control. No calibration effort is needed for a large variety of products and product varieties at-line. The Smart 6 has been used for years as a microwave moisture/solids analysis system in various types of production. The sample is placed on special sample (glass fiber) pads and weighed on a balance which is built into the microwave dryer (see Fig. 2). The water molecules are heated in the microwave field and expelled without formation of crust on the surface which would prevent further evaporation of water.

The built-in temperature sensor provides controlled heating of the sample, minimizing the risk of sample decomposition. For high-precision moisture analysis, the microwave field must be uniform and continuously adjustable. The built-in balance constantly monitors the sample weight during the drying process and switches the dryer off when the weight no longer changes, often after only two minutes. Especially with substances for a high water content (up to 99.9%), this method is suitable for at-line process control because it is fast and accurate (precision ±0.1% dry weight). The dried sample is then placed into the NMR spectrometer (Oracle module). The sample is exposed to high-energy pulsed radiation in a magnetic field for 8 seconds.

The fat molecules emit a characteristic signal which the software directly converts into the fat content, and the value is displayed to the user. The results are not distorted by other ingredients such as sugar, salt, flavorings or preservatives. Color differences between the samples also do not affect the results, making the method suitable for general-purpose use. To make that possible, a universal calibration was carried out using a very wide variety of samples based on reference contents and reference methods. The results obtained from unknown samples are comparable with the results obtained using standard methods. As can be seen from Table 1, Oracle fat analysis produces results which are comparable with standard reference methods.

Fat analysis can be carried out directly on dry samples such as crackers, cookies, nuts, marzipan, whole milk powder, starch and baby food in the Oracle fat and moisture analysis systems.

Summary: Faster analysis increases throughput

The scope of what process control is expected to deliver has changed considerably in recent years. This is in part due to significant changes in laws and regulations. Demand has increased for analysis systems which can be operated right next to production (at-line). These applications place particular demands on safety and ease of use. Oracle fat and moisture analysis systems are the ideal choice. Skilled workers are not needed to operate the system. Fat analysis is fast and not dependent on the matrix, and the analyzer is ready to go as soon as it is installed. In contrast to organic measurement techniques, no elaborate product-specific calibration is necessary. Elimination of the need to handle acids and other solvents also enhances occupational safety. With high-speed moisture and fat analysis, food recipes can be kept very close to the allowable limits, increasing revenue generation.

Additional Information

Fat analysis

Traditional methods of fat analysis include Soxhlet solvent extraction and the Weibull-Stoldt method in which the sample is solubulized with hydrochloric acid prior to extraction. Besides standard manual equipment, automated solutions are also now on the market. In the past, fat analysis using NMR was limited to dry substances. By combining NMR with microwave drying, the method can now also be used for moist samples.

References

[1] „Analytik im Wandel – zwischen Labor und Prozess, Mensch und Methode“, H.-D. Isengard, Kompetenzmeeting Innovationen der Prozessanalytik und Feuchtemesstechnik, May 1995, Göttingen/Germany

* U. Sengutta: CEM GmbH, 47475 Kamp-Lintfort/Germany

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