Microwave ashing procedure for determination of inorganic ash in food samples

The ashing test on food samples is commonly used for evaluation of mineral content. The minerals constituents include potassium, sodium, calcium and magnesium, which are present in larger amounts as well as smaller quantities of aluminum, iron, copper, manganese or zinc, arsenic, iodine, fluorine and other elements present in traces. Determination of ash content is very important for several reasons. Mineral content in food play an important role from a physicochemical and nutritional point of view. Ash content analysis is also an accepted index of refinement of foods, such as wheat flour or sugar production, since the ash test is a reliable indicator of efficiency of which the separation of bran and germ from the rest of the wheat kernel. Traditional tools like electrical muffle furnaces, have their own set of limitations – long ashing time, long cooling, high power consumption and low aspiration efficiency. Milestone PYRO system incorporates all of the benefits of a microwave system working with special fast heating/cooling crucibles while making the ashing application fast, easy, effective, and in complete safety.

The new Milestone PYRO is an advanced microwave muffle furnace, suitable for food ashing applications. It is equipped with a full stainless-steel door and the cavity has a volume in excess of 70 liters, thus allowing the use of a large muffle which in turn enhances the sample throughput. PYRO system is equipped with two 950 Watt magnetrons for a total of 1900 Watt making it the most powerful microwave muffle furnace system available in the market. The system additionally employs a rotating diffuser that evenly distributes the microwaves throughout the cavity, assuring a uniform temperature improving the reproducibility.
PYRO enables the analysts to perform the ashing test of a wide variety of samples. A unique ceramic muffle allows microwave radiation to pass through and rapidly raise the temperature of a silicon carbide plate. Sample crucibles are placed on a large clean quartz plate and an airflow is induced by a built-in exhaust system. Any type of crucible (metal, porcelain, quartz, etc.) can be used and for this test we have used the Milestone UltraFAST crucibles (Picture on the right).
The UltraFAST crucibles are made of an innovative material that, although chemically and thermally resistant, allows the samples to be surrounded by a constant airflow which accelerates the ashing process. Furthermore, just 30 seconds are enough for the UltraFAST crucibles to go from 1000°C to room temperature.

We have weighed accurately 4 g of Wheat flour and 1 g of BCR-380R (Milk powder) in UltraFAST crucibles (see details in Table 1). The crucibles were initially preconditioned at constant weight (preconditioning step time is reduced thanks to the short cooling time of UltraFAST crucibles).
Crucibles were here placed into PYRO microwave ashing unit and ashed with the microwave program.

The samples were completely ashed, obtaining a white residue of inorganic material. The crucibles were weighted and percentage of residue was then recalculated. Results are reported in the tables on the left.