Effects of drying and grinding in production of fruit and vegetable powders: A review

Food process innovation through new technologies: Use of ultrasound

Drying of ultrasound pretreated apple and its selected physical properties

The drying of foods is hugely important technique for the food industry and offers possibilities for ingredient development and novel products to consumers In recent years, there have been many advances in technology associated with the industrial drying of food including pre-treatments, techniques, equipment and quality Recent research has revealed that novel drying approaches such as microwave- or ultrasound-assisted drying, high electric field drying, heat pump drying and refractance window drying can be now taken to improve the efficiency and efficacy of drying so that energy consumption can be reduced whilst at the same time preserving the quality of the end product However, whilst research has showed these technologies to be successful, commercial practitioners do not often know what techniques have the greatest potential in industry The current work highlights recent developments of valuable novel drying techniques to promote sustainability in the food industry and points towards

Novel Drying Techniques for the Food Industry

Background Drying is one of the most popular methods of preserving a wide variety of food and agricultural products. Unfortunately, this unit operation may negatively influence product quality. Moreover, due to the high heat capacity of water, drying is usually a long-lasting and energy-intensive process, thus new drying techniques are continuously being sought. Scope and approach This review presents the current state of art in ultrasonic-assisted drying. Despite immense knowledge on the principles of ultrasound generation and action, this technology has found no practical application in industrial drying yet. In this paper we tried to find the reasons for this state of affairs. Up-to-date designs of dryers using ultrasound to enhance the drying process and the various possible mechanisms of accelerating the drying process with the application of ultrasonic waves are discussed. The influence of ultrasound on the product's quality (dried food) is judged and described. Key findings and conclusions The analysis of the results presented by the researchers here allows to state that applying ultrasound to drying caused a shortening of the drying time and could reduce total energy consumption. Moreover, due to the small “temperature effect”, the quality of the obtained products was noticeably better as compared to the control processes (without ultrasound enhancement). The lack of an effective technology for generating power ultrasound in air was distinguished as the primary constraint for industrial application of this technology. The necessity of conducting detailed studies on ultrasound application in drying was emphasized.

Food drying enhancement by ultrasound – A review

Influence of power ultrasound application on mass transport and microstructure of orange peel during hot air drying

The use of ultrasound for drying, degassing and defoaming of foods

This paper in memory of Leif Bjorno deals with the non-linear acoustic problems linked to high-intensity ultrasonics, an area that he deeply cultivated. The generation, propagation and measurement of high intensity ultrasonic waves in air is highly conditioned by the nonlinearities that are inherent with high intensities such as wave distortion and saturation. Particularly in air the propagation of high-intensity ultrasonic waves is greatly affected by the strong non-linearity introduced by the medium itself which notably limits the attainable acoustic pressure levels. On the other hand the power capacity of the sources is also limited by nonlinear effects such as modal interactions and fatigue failure of its components. Finally, the characterization and measurement of the acoustic field of finite amplitude waves by means of probes of very small diameter with respect to the wavelength poses specific issues on the signal capture and the distortion introduced by the probe itself. All these problems will be reported and analyzed in this paper in light of the experimental work developed, partly on collaboration with Leif Bjorno.This paper in memory of Leif Bjorno deals with the non-linear acoustic problems linked to high-intensity ultrasonics, an area that he deeply cultivated. The generation, propagation and measurement of high intensity ultrasonic waves in air is highly conditioned by the nonlinearities that are inherent with high intensities such as wave distortion and saturation. Particularly in air the propagation of high-intensity ultrasonic waves is greatly affected by the strong non-linearity introduced by the medium itself which notably limits the attainable acoustic pressure levels. On the other hand the power capacity of the sources is also limited by nonlinear effects such as modal interactions and fatigue failure of its components. Finally, the characterization and measurement of the acoustic field of finite amplitude waves by means of probes of very small diameter with respect to the wavelength poses specific issues on the signal capture and the distortion introduced by the probe itself. All these problems will be ...

Nonlinear problems in the generation, propagation and measurement of high intensity ultrasonic waves in air

Power ultrasound application on convective drying of foodstuffs may be considered an emergent technology. Acoustic energy may improve drying rate without significantly heating the material due to phenomena affecting mass transfer resistances. As a consequence, ultrasound application on the drying of heat sensitive materials or in process carried out at low temperatures is quite interesting. The aim of this work was to address the influence of the main processing variables on the convective drying assisted by power ultrasound (21.7 kHz) of different foodstuffs. The influence of air velocity and temperature, raw material characteristics, mass load density and ultrasonic power applied was addressed. From the experimental results, a significant influence of the application of power ultrasound on both external and internal resistance to mass transfer has been found. Nevertheless, the ultrasonic effects depended strongly on the experimental conditions used. In the case of carrot drying at different temperatures, the application of power ultrasound increased the effective moisture diffusivity by 55 % at experiments carried out at 30 oC, however the improvement was non significant at experiments conducted at 70 oC. INTRODUCTION Convective drying constitutes a traditional dehydration method. Although it has been widely studied, it still present some limitations which difficult its application in some specific fields [1]. Among other things, the drying rate is low mainly during the falling rate period or in processes carried out at low temperatures. Drying process may be improved by application of complementary energy sources to hot air. In comparison to other technologies, like microwave or infrared radiation, power ultrasound does not significantly heat the product, thus avoiding quality loss during drying [2]. As a consequence, ultrasound present a high potential use to dry heat sensitive materials or to be applied in drying process carried out at low temperatures, like atmospheric freeze drying. A series of effects associated to acoustic energy are responsible for increasing drying rate [2]. Power ultrasound introduces pressure variations at interfaces gas/solid and causes oscillating velocities and microstreaming which may affect the diffusion boundary layer characteristics. Furthermore, ultrasonic waves also produce rapid series of alternative contractions and expansions (sponge effect) of the material in which they are travelling; which may make the moisture removal easier. Ultrasonic applications on gas-solid systems, like convective drying, are quite difficult [3] due to the high impedance mismatch between ultrasound generating systems and air and also the high energy absorption of this medium. In literature, ultrasonic systems with direct contact between the vibrating element and the material being dried have been shown [2]. Despite their high efficiency, the adaptability to traditional convective driers is quite difficult. The development of a new and efficient ultrasonic technology has already been the matter of previous research [4].

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Influence of process variables on hot air drying assisted by power ultrasound

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Procedimiento y dispositivo para mejorar la transferencia de materia en procesos a baja temperatura mediante el uso de ultrasonidos de elevada intensidad.

Enrique Riera

Papers

Influence of power ultrasound application on mass transport and microstructure of orange peel during hot air drying

The use of ultrasound for drying, degassing and defoaming of foods

Nonlinear problems in the generation, propagation and measurement of high intensity ultrasonic waves in air

Influence of process variables on hot air drying assisted by power ultrasound

Procedimiento y dispositivo para mejorar la transferencia de materia en procesos a baja temperatura mediante el uso de ultrasonidos de elevada intensidad.