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

Abstract

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.