This chapter presents an evaluative review of advanced drying technologies relevant to the food industry specifically for drying of food materials at low temperatures under atmospheric pressure. It starts with a brief overview of the transport phenomena involved during drying of food materials. The chapter then describes various advanced drying technologies particularly applied for low temperature drying of food materials. These include details of the underlying drying mechanisms, operating principle, and industrial implementation of these technologies. The latter part of the chapter finally highlights the future outlook of these technologies for industrial adoption in the food industry.

This article deals with the application of ultrasound pretreatment prior to drying to enhance the drying process of waxy fruits. It starts with an overview of the pretreatment technology applied to waxy fruits. The article then presents the mechanisms of the ultrasound pretreatment. The latter part of this article focuses on the effects of ultrasound pretreatment on drying at different drying conditions and the impact on the quality of the dried products. Finally, it highlights the challenges and further work to be done for a successful adoption of the technology in industrial practice.

This chapter covers the development and application of thermal drying processes for food materials. It provides an overview of the drying mechanisms involved in conventional hot air-drying techniques and describes the drying equipment and design applicable to drying of foods and their limitations. The chapter also highlights the challenges in drying food materials and the R&D opportunities in drying, including the development of novel drying technologies and process improvements of existing drying techniques. In addition, the chapter presents a case study to demonstrate the application of computational modelling approach for optimisation in an industrial drying process. Finally, it highlights future directions in food drying research.

An ultrasonic design based on the indirect transmission of ultrasonic energy from the ultrasound emitter through to the material to be dried was investigated to assist in low temperature drying of food materials. The application of the improved design tested in this work was found to enhance the low temperature drying by shortening the overall drying time of up to 45% (i.e., lower energy consumption and may enable better retention of product quality). This offers a promising approach towards a better applicability of ultrasound in industrial operation, since no direct contact between the sample and the ultrasonic emitter is needed. Keywords: ultrasound; drying; low temperature; drying intensification

This article reviews the application of airborne ultrasound to intensify convectional drying processes. The basics of drying of food materials and common food drying processes are introduced. The influence of airborne ultrasound on the drying kinetics and on the changes of the product's structural and quality attributes, as well as the phenomena associated with the application of ultrasound responsible for these effects, are described.

This article provides an overview of the drying process of food materials. It starts with a brief history of food drying and then describes the techniques commonly used in the food industry. The latter part of this article focuses on the new/novel developments in food drying and finally highlights the future outlook of food drying.

The industrial production of palm oil concurrently generates a substantial amount of empty fruit bunch (EFB) fibers that could be used as a feedstock in a lignocellulose-based biorefinery. Lignin byproducts generated by this process may offer opportunities for the isolation of value-added products, such as p -hydroxybenzoate ( p Bz), to help offset operating costs. Analysis of the EFB lignin by nuclear magnetic resonance (NMR) spectroscopy clearly revealed the presence of bound acetate and p Bz, with saponification revealing that 1.1 wt% of the EFB was p Bz; with a lignin content of 22.7 %, 4.8 % of the lignin is p Bz that can be obtained as a pure component for use as a chemical feedstock. Analysis of EFB lignin by NMR and derivatization followed by reductive cleavage (DFRC) showed that p Bz selectively acylates the γ-hydroxyl group of S units. This selectivity suggests that p Bz, analogously with acetate in kenaf, p -coumarate in grasses, and ferulate in a transgenic poplar augmented with a feruloyl-CoA monolignol transferase (FMT), is incorporated into the growing lignin chain via its γ- p -hydroxybenzoylated monolignol conjugate. Involvement of such conjugates in palm lignification is proven by the observation of novel p -hydroxybenzoylated non-resinol β–β-coupled units in the lignins. Together, the data implicate the existence of p -hydroxybenzoyl-CoA:monolignol transferases that are involved in lignification in the various willows ( Salix spp.), poplars and aspen ( Populus spp., family Salicaceae), and palms (family Arecaceae) that have p -hydroxybenzoylated lignins. Even without enhancing the levels by breeding or genetic engineering, current palm oil EFB ‘wastes’ should be able to generate a sizeable stream of p -hydroxybenzoic acid that offers opportunities for the development of value-added products derived from the oil palm industry.

This chapter covers the basic concepts of the drying process of food materials, detailing the transport mechanisms involved in the drying process and the drying techniques commonly used in the food industry. It describes the different approaches employed for modelling various drying processes and the developmental steps involved in modelling the drying process of food materials. The chapter also presents a case study to demonstrate the application of modelling approach for optimisation of an industrial drying process. Finally, it highlights future development and application of modelling in food drying.

The process of drying food materials is extremely complex involving coupled transient mechanisms of heat, mass and momentum transfer phenomena accompanied by physical, chemical and phase change transformations. It is an energy-intensive operation that usually imparts significant alterations in product quality and functionality attributes. With increasing fuel prices, large energy consumption is a major concern in industrial drying not only due to the cost and increasing scarcity of fuel but also for the associated environmental impact as the necessity to reduce greenhouse gas emissions is critical for a sustainable future. This is coupled with an increasing consumer demand for healthy and high quality processed foods which offer more convenience. There is a significant interest to develop and optimise drying operations that will accelerate the process (increased throughput) and reduce energy consumption without compromising the quality of the dried products. This paper discusses the development and validation of a computational drying model and its application in optimising the design and process conditions of an industrial fruit drying system.

Aqueous ultrasound-assisted extraction (UAE) of grape pomace was investigated by Response Surface Methodology (RSM) to evaluate the effect of acoustic frequency (40, 80, 120 kHz), ultrasonic power density (50, 100, 150 W/L) and extraction time (5, 15, 25 min) on total phenolics, total flavonols and antioxidant capacity. All the process variables showed a significant effect on the aqueous UAE of grape pomace (p < 0.05). The Box-Behnken Design (BBD) generated satisfactory mathematical models which accurately explain the behavior of the system; allowing to predict both the extraction yield of phenolic and flavonol compounds, and also the antioxidant capacity of the grape pomace extracts. The optimal UAE conditions for all response factors were a frequency of 40 kHz, a power density of 150 W/L and 25 min of extraction time. Under these conditions, the aqueous UAE would achieve a maximum of 32.31 mg GA/100 g fw for total phenolics and 2.04 mg quercetin/100 g fw for total flavonols. Regarding the antioxidant capacity, the maximum predicted values were 53.47 and 43.66 mg Trolox/100 g fw for CUPRAC and FRAP assays, respectively. When comparing with organic UAE, in the present research, from 12% to 38% of total phenolic bibliographic values were obtained, but using only water as the extraction solvent, and applying lower temperatures and shorter extraction times. To the best of the authors' knowledge, no studies specifically addressing the optimization of both acoustic frequency and power density during aqueous-UAE of plant materials have been previously published. (C) 2014 Elsevier B.V. All rights reserved.

Drying is one of the oldest and most commonly used processes in the food manufacturing industry. The conventional way of drying is by forced convection at elevated temperatures. However, this process step often requires a very long treatment time, is highly energy consuming and detrimental to the product quality. Therefore, an investigation of whether the drying time and temperature can be reduced with the assistance of an airborne ultrasound intervention is of interest. Previous studies have shown that contact ultrasound can accelerate the drying process. It is assumed that mechanical vibrations, creating micro channels in the food matrix or keeping these channels from collapsing upon drying, are responsible for the faster water removal. In food samples, due to their natural origin, drying is also influenced by fluctuations in tissue structure, varying between different trials. For this reason, a model food system with thermo-physical properties and composition (water, cellulose, starch, fructose) similar to those of plant-based foods has been used in this study. The main objective was, therefore, to investigate the influence of airborne ultrasound conditions on the drying behaviour of the model food. The impact of airborne ultrasound at various power levels, drying temperature, relative humidity of the drying air, and the air speed was analysed. To examine possible interactions between these parameters, the experiments were designed with a Response Surface Method using Minitab 16 Statistical Software (Minitab Inc., State College, PA, USA). In addition, a first attempt at improving the process conditions and performance for better suitability and applicability in industrial scale processing was undertaken by non-continuous/intermittent sonication.

A mathematical model for simulation of simultaneous heat and mass transport was developed to describe the drying kinetics during finish drying of trellis-dried sultanas. In this model, the governing partial differential equations for heat and mass transfer for a solid spherical body were numerically solved using a finite difference technique. In addition, a kinetic model was coupled to the heat and mass transfer calculations to simultaneously predict the evolution of product color during the drying process. This allows predictions of moisture content, temperature, and color profiles of the product in a space–time domain during the drying process as a function of various operating conditions. Predictions compared well with the experimental values, implying that the proposed numerical model can be used with confidence for the simulation of the important transport phenomena in optimizing the design and operation of a drying system for sultanas that maximizes the retention of the desired product color. The work has demonstrated the importance of establishing optimal and closely controlled drying conditions because significant effects of the key operational parameters on drying kinetics and the associated changes of product color were found. The modeling approach proposed here can be extended to other products and for incorporation of other product quality indices.

Lignocellulosic biomass samples (wheat chaff) were pretreated by ultrasound (US) (40kHz/0.5Wcm(-2)/10min and 400kHz/0.5Wcm(-2)/10min applied sequentially) prior to digestion by enzyme extracts obtained from fermentation of the biomass with white rot fungi (Phanerochaete chrysosporium or Trametes sp.). The accessibility of the cellulosic components in wheat chaff was increased, as demonstrated by the increased concentration of sugars produced by exposure to the ultrasound treatment prior to enzyme addition. Pretreatment with ultrasound increased the concentration of lignin degradation products (guaiacol and syringol) obtained from wheat chaff after enzyme addition. In vitro digestibility of wheat chaff was also enhanced by the ultrasonics pretreatment in combination with treatment with enzyme extracts. Degradation was enhanced with the use of a mixture of the enzyme extracts compared to that for a single enzyme extract.

A mathematical model was developed to describe the coupled heat, mass and momentum transfer processes occurring in convective drying of prunes. In this model, the fruit is represented as a composite ellipsoidal body comprising of two materials (flesh and stone) having different properties. The model accounts for the variation of both air and food properties expressed as a function of temperature and moisture content. The resulting systems of transient non-linear partial differential equations (PDEs) in the space-time domain together with the set of initial and boundary conditions were numerically solved by utilising the finite element method (FEM) coupled to the Arbitrary Lagrange-Eulerian (ALE) procedure to account for the shrinkage phenomenon using a commercial package (COMSOL Multi-physics (TM), Comsol AB, Stockholm, Sweden).A series of laboratory drying experiments were undertaken using a computer-controlled dehydration system developed to obtain drying kinetics data under varying operating conditions for validation of the predicted results from the proposed model. Comparison of the model predictions against the experimental results has shown a very good agreement, implying that the proposed numerical model can be used with confidence as a tool in optimising the design and operation of the prune drying system. A parametric study performed using the modelling tool has demonstrated the impact of key operational parameters on the drying kinetics. It is expected that the model can be applied for other food products and processes involving similar phenomena. Crown Copyright (c) 2012 Published by Elsevier Ltd. All rights reserved.

A promising approach for the application of ultrasound to assistin convective food drying was developed and tested in this study. Theapplication of ultrasound is based on the transmission of ultrasonicenergy as a combination of airborne contacts and through a series ofsolid contacts between the ultrasound element and the product trayas the ultrasonic vibration transmitting surface. A computer-basedultrasonic drying setup was built to allow continuous recording ofthe process variables in real time and enabled simulation of dehy-dration to be accomplished under controlled conditions over a rangeof drying parameters. Apple slices were dried using the drying setupto study the influence of ultrasound in combination with conven-tional hot air drying on drying kinetics and product quality.The results from this work indicate that ultrasound can simul-taneously be applied to accelerate the processing time (i.e., reduceenergy consumption and increase production throughput) in con-ventional hot air drying without compromising product quality. Itappears that the magnitude of influence of ultrasound to enhancethe air-drying process depends on the process variables employed.In particular, the ability of ultrasound to improve the efficiency ofthe convective drying process appears to be maximized when usinglow temperature and high ultrasonic power level. This finding maybevery useful when there is a need to effectively dehydrate heat-sensitive products or when shorter drying times are required in orderto achieve better retention of the functional and nutritional proper-ties of the product.

This paper introduces a colour image segmentation algorithm for bicolour food products. The algorithm has been developed for colour quality measurement in manufacturing processes. a∗ and b∗ components of CIE L∗a∗b∗ colour space are sampled from pixels in the food product region in an image. A polynomial equation is obtained from this colour data by using a least square fitting method. All pixels in the image are tested with this equation, and pixels having colour values close to the polynomial equation are regarded as ones in the food product region in the image. This algorithm is useful when multiple products are captured in an image and the food region needs to be segmented. The procedures of the algorithm and its application using French fried chips and dried apple slices are presented.