J. García-Álvarez

Ultrasonic study of wheat flour properties

In this work, the wheat flour properties are investigated using ultrasound techniques. Moreover, the flour samples were also characterized by means of well established techniques such as protein content, Alveograph and Mixolab®. A set of 35 dough samples, made of wheat flours with diverse physical and quality properties, were studied. The obtained results shown that ultrasound measurements can detect changes in the dough consistency induced by proteins and also by gelatinization of the starch. Furthermore, ultrasound measurements can be related to parameters indicative of the proteolytic degradation or softening of the dough due to protease activity. Thus, ultrasound can be considered a low cost and rapid tool, complementary to conventional test, for wheat flour characterization.

Ultrasonic monitoring of malolactic fermentation in red wines

The progress of malolactic fermentation in red wines has been monitored by using ultrasonic techniques. The evolution of ultrasonic velocity of a tone burst 1MHz longitudinal wave was measured, analyzed and compared to those parameters of oenological interest obtained simultaneously by analytical methods. Semi-industrial tanks were used during measurements pretending to be in real industrial conditions. Results showed that the ultrasonic velocity mainly changes as a result of the conversion by lactic acid bacteria of malic acid into lactic acid and CO2. Overall, the present study has demonstrated the potential of the ultrasonic technique in monitoring the malolactic fermentation process.

Study of the time-dependence of the mechanical properties of doughs for flour strength evaluation

Both flour strength and dough processing affect the dough consistency that determines its potential for breadmaking purposes. Quick identification of poor dough quality would reduce problems with dough handling during further stages of the process and maximise productivity. Maintaining consistent production would contribute to better control of product quality and consequently lead to high levels of customer satisfaction. Ultrasonic measurements have already been carried out to characterise dough properties. The ultrasonic wave parameters generally measured include the velocity of propagation and the attenuation of the acoustic wave traveling through the sample. These measurements can be related to both viscoelastic and physical properties of the sample, providing the flour strength. However, due to the time-dependent nature of dough accurate measurements of the ultrasonic velocity and attenuation are sometimes difficult to attain especially in highly attenuating materials like dough. Furthermore, due to viscoelastic properties of dough when a sample is placed between both transducers it slowly flows away from the transducer surface producing changes in the values of the ultrasonic velocity and attenuation with time. The greater these changes are the softer the dough is. This makes necessary a settling time in order to get an accurate measurement. In this work, an alternative method for evaluating the flour strength using low intensity ultrasound is shown. The evolution with time of both velocity and attenuation is monitored and then related to the flour strength. Main advantage of this novel approach is that changes in time of ultrasonic velocity and attenuation are easy to monitor than carry out accurate measurements of them after a settling time. Experimental results on doughs with different flour strength are presented, compared and discussed. Automation of the food industry requires fast and reliable measurements of the physical properties of materials during processing. The mixture of wheat flour, water, yeast and other ingredients produces a dough with specific viscoelastic characteristics capable of retaining gas and producing aerated goods. Within the baking industry, the control of dough properties is required to achieve final product quality and consistency. Traditional methods for dough testing are slow and off-line and do not provide fundamental rheological information. There is therefore a need for the development of fast and on-line instruments capable of providing relevant data for baking. The ultrasonic wave parameters generally measured include the velocity of propagation and the attenuation of the acoustical wave traveling through the sample. These can be related to various of its physical properties. Sensors and instruments based on non-contact methods are especially attractive to the food industry to be employed in quality assurance, process control and non-destructive inspection (1-3), for being both hygienic and easy to maintain. However, there is still a need to develop new techniques that can perform precise evaluations of dough and flour quality. Currently, there are only a few studies using ultrasound for characterising flour-water systems (4-9). In this paper, the ultrasonic measurements of velocity and attenuation are used for the classification of flours intended for different purposes and are compared with conventional flour testing methods. The time-dependence of the mechanical properties of dough is also studied and the results are related to flour strength. The purpose of this study is to determine the potential of ultrasound for use to predict flour and dough quality by millers and bakers by means the determination of flour strength. Section II gives a short outline of the experimental procedure and set-up used during the experiments. In Section III the experimental results are explained and discussed in detail. Finally, conclusions are made in Section IV.

Resizing buffer rods for ultrasound testing of food products with acoustic noise considerations

Buffer rods can be used to perform non-destructive and on-line analysis of food and beverage products. These rods, usually solid cylinders, can be long and heavy for certain applications. In this paper, a resizing analytic procedure is described. Buffer rods designed following this new procedure can be several times shorter than the conventionally designed ones, optimising thus their weight and cost. The signal to noise ratio (SNR) of the resized buffers is also studied in order to determine their practical usability. To this effect, simulations and experiments are conducted using metal and plastic buffer rod materials appropriate for food and beverage testing such as aluminium and polyethylene.

Effect of angle errors in conical tip buffer rods

Buffer rods are usually plastic or metallic solid cylinders of known acoustic properties, which are placed between the ultrasonic transducer and the sample under study. For some applications, the buffer rod end in contact with the sample under inspection is shaped in a form of a conical tip. If the cone angle is fixed to 45°, the components of the ultrasonic wave reflected at the buffer conical tip are received at the transducer in phase, forming thus a maximum amplitude signal. Otherwise, the components of the ultrasonic wave are received out of phase, composing thus a weaker signal. In this work, the effect of the buffer rod cone angle on the measurement signals has been studied by means of simulations and experiments. The simulations were performed using a two-dimensional finite differences tool and the measurements were conducted with the same operating conditions and buffer rod materials and dimensions than those defined for simulations. The influence of some aspects such as ultrasonic transducer operating frequency and diameter, and buffer rod material has also been analyzed.

Digital processing system for an air-coupled concave array NDT system

This work presents a processing subsystem for an air- coupled concave array NDT system, which uses Lamb waves. This processing system is able to equalize, delay and add the signals provided by a circular concave array used to receive Lamb waves in laminate materials, such as paper. A Field Programmable Gate Array (FPGA) is used in order to achieve shorter processing times and more flexibility than with DSP systems. The used array has circular concave shape and hence the delays used to get a plain wavefront are not lineal, thus a table with the delay values must be stored inside the FPGA. The Non-Destructive Testing is a growing field of interest for those industries where the high value of the developed components implies the need of a better quality control. In most of these cases the materials cannot be destroyed or altered, therefore a Non Destructive Test is needed. Ultrasonic testing is widely used to test a great variety of materials, but ultrasonic waves need a couplant to get a good transmission coefficient between the inspected material and the ultrasonic transducer. When air is used as couplant, new problems appear, like the higher attenuation that ultrasound suffers in this element. However, the greatest problem is the huge acoustic impedance mismatch that exists between air and the transducers. This mismatch, which is 40(PZT) to 0.006(Air), impedes a good transmission of the energy from the transducer to the inspected material. To improve the bad transmission coefficient, matching layers are included in the transducer (1) and improvements in the systems dynamic range are achieved (2). Lamb waves (3) are also widely used to inspect laminate materials. The main benefit which Lamb waves contribute in is the ability to inspect great portions of material in a short time, making them ideal for inspections where a great area has to be inspected. Moreover, the usefulness of Lamb waves in industrial applications where paper is tested has been demonstrated (4), (5). The usual way to produce a Lamb wave in a plate is to impact a plain wavefront with a certain angle respect to this plate. Lamb wave ultrasonic techniques are mostly based on the application of single element ultrasonic transducer with specific configurations, where the single element is specifically oriented to excite specific Lamb wave modes, see (6). The angular range where Lamb waves can be excited is very narrow in air (7), therefore a system that provides high angular resolution is needed. An array system would be a good solution to obtain this high angular resolution. It also has two main advantages, a transducer array will allow accurate beam steering, and the signal - to - noise ratio will improve. Furthermore, the array has a circular concave shape, so that it raises the angular steering margin of the array. The array used in this paper and its characteristics are deeply described in (8).

Ultrasonic analysis to discriminate bread dough of different types of flour

Many varieties of bread are prepared using flour coming from wheat. However, there are other types of flours milled from rice, legumes and some fruits and vegetables that are also suitable for baking purposes, used alone or in combination with wheat flour. The type of flour employed strongly influences the dough consistency, which is a relevant property for determining the dough potential for breadmaking purposes. Traditional methods for dough testing are relatively expensive, time-consuming, off-line and often require skilled operators. In this work, ultrasonic analysis are performed in order to obtain acoustic properties of bread dough samples prepared using two different types of flour, wheat flour and rice flour. The dough acoustic properties can be related to its viscoelastic characteristics, which in turn determine the dough feasibility for baking. The main advantages of the ultrasonic dough testing can be, among others, its low cost, fast, hygienic and on-line performance. The obtained results point out the potential of the ultrasonic analysis to discriminate doughs of different types of flour.

Ultrasonic preliminary measurements of oenological malolactic fermentation parameters in red wine

In the winemaking process, the malolactic fermentation is an essential process in the production of high quality red wines which concerns the conversion of malate into lactate. In this work, the ultrasonic velocity through wine samples with different concentrations of malate and lactate was measured using the pulse echo technique with 1 MHz tone burst signals. The evolution of these concentrations during malolactic fermentation was taken into account in order to determine the ratio between concentrations of malate and lactate of the different samples. These preliminary results have revealed that the ultrasonic velocity increases during the conversion of malate to lactate. In addition, measurements have been conducted to quantify the influence of variations in turbidity and temperature on test samples. Therefore, these results show the possibility of using ultrasonic velocity measurements for on-line monitoring the malolactic fermentation of red wine and may help to improve and contribute to the development of the winemaking process.