The porosity and structure of cereal products have been evaluated using an indirect method of acoustic echolocation and an acoustic level meter with a special measurement vessel. First, the construction of the measurement vessel of the non-contact acoustic level meter was improved. Then by determining the amount of absorbed water and its water absorption dynamics, an accurate method to evaluate the structure of porous cereal products has been developed. Links between the indices of ring-shaped roll structure parameters (total amount of absorbed water and water absorption dynamics) and the standard weighing method were established. The quality of baked products such as ring-shaped rolls is related to the total amount of water absorbed and the water absorption dynamics. Linear or exponential dependences indicate good quality while exponential or composite dependences indicate average quality and composite dependences poor quality. The results show that the echolocation method gives additional information on the structure parameters of porous cereal products. The application of this method to the optimization of technological processes has been proven. In comparison with analogue methods such as the weighing method the proposed method is non-destructive. We can, therefore, repeat the investigations several times using the same sample. In this way the accuracy of measurements can be improved. Additionally the acoustic method is rapid and simple.

Deoxynivalenol (DON) is a natural and ubiquitous toxic metabolite produced by filamentous fungi of the genus Fusarium. Approximately one quarter of the world's food crops (mainly cereals) are affected by mycotoxins such as DON. A rapid and non-destructive method to evaluate the quality and safety of grains is therefore required to eliminate these toxins from the food chain. The first portable acoustic device that predicts the concentration of DON in cereal grains has been developed using a broadband capacitive ultrasonic transducer. An acoustic method was optimised for the rapid prediction of DON in wheat. To measure the performance of this method, a model system comprising 0-100% scabby wheat grains was prepared and a single laboratory validation was carried out. The best regression model between DON concentrations determined by the reference ELISA method and the acoustic technique was obtained at an acoustic frequency of 32.2 kHz, with a correlation coefficient of 0.9852 and a repeatability coefficient of variation of 2.1-9.3%, which is much better than the results achieved by prototype acoustic spectrometers. These data show that acoustic technology allows the online monitoring of DON in cereal grains, such as wheat, because it is possible to analyse multilayer grain beds. Sound absorption depends on the grain size and moisture content, so it is advisable to use the equipment at the point of harvest, where one strain of cereals usually dominates and the grains have a more homogeneous morphology and uniform moisture content.

In this article application of direct and indirect ultrasonic methods for evaluating and measuring porous materials are reviewed. Ultrasonic waves, due to their physical properties and wide frequency range can successfully be applied when evaluating the porosity of materials. Ultrasonic methods have many advantages when comparing them with other, non-acoustic measurement methods, which are also briefly reviewed in this article. We examine application of the proposed acoustic echolocation method when evaluating porous materials directly and indirectly. The possibilities to apply Lamb waves for evaluation of porous structures are also examined. The application of ultrasonic echolocation measurement method to evaluate porous structures indirectly is presented in depth, along with the process description and various possible implementations. The basic principle along with advantages and shortcomings of such methods are explained. Physical-mechanical properties of porous materials are also described, along with mathematical equations, which are necessary for their theoretical analysis. The ability to determine porosity of various materials is necessary to insure the quality of the final product. We also present a working real-world system, which implements an indirect ultrasonic porosity evaluation method. For indirect porosity determination, we use a very accurate ultrasonic echolocation-based distance meter. Block diagram for such unit is presented. The most important component in the acoustic porosity evaluation system is the electro-acoustic transducer. We describe the most suitable transducers for use in this case, along with acoustic antennas constructed using such transducers. Antennas, designed for measurements in air, consist of transducers vibrating in a flexural mode, which give the best possibility to match acoustic impedances between air and the transducer. Specific type of transducers for acoustic antennas is described, along with their schematic diagrams. The necessary expressions for calculating radiations patterns are also supplied. Schematic diagrams of actual antennas, along with their directivity patterns are presented. A method for eliminating peripheral radiation of these antennas is also described.

No abstract