Drying of Fruits and Vegetables: Retention of Nutritional/Functional Quality

In the past, research and development in drying has focused on the process and technology and food drying was performed mainly to extended the shelf life without much importance on retaining quality attributes. Recently, however, efforts have been made to develop high-quality dried foods. This is achieved by utilizing novel drying technologies, by improving and optimizing existing drying methods, and by maximizing quality attributes such as structure, color, flavor, nutrition, etc. In an effort to highlight quality aspect of dried foods and biomaterials, a special issue of Drying Technology [2005, 23(4)] was published. The objective of this article is to present an overview of quality attributes normally considered in the drying of food and biomaterials and highlight the recent advances in drying methods for the retention of nutritional and functional properties of fruits and vegetables.     

Drying of Fruits and Vegetables: Retention of Nutritional/Functional Quality

In the past, research and development in drying has focused on the process and technology and food drying was performed mainly to extended the shelf life without much importance on retaining quality attributes. Recently, however, efforts have been made to develop high-quality dried foods. This is achieved by utilizing novel drying technologies, by improving and optimizing existing drying methods, and by maximizing quality attributes such as structure, color, flavor, nutrition, etc. In an effort to highlight quality aspect of dried foods and biomaterials, a special issue of Drying Technology [2005, 23(4)] was published. The objective of this article is to present an overview of quality attributes normally considered in the drying of food and biomaterials and highlight the recent advances in drying methods for the retention of nutritional and functional properties of fruits and vegetables.     

Trends in Processing Technologies for Dried Aquatic Products

Fresh aquatic products are rich in nutritional compounds and are an important source of good protein for humans. Dehydration processing technologies of aquatic products used in practice are a mix of old and new technologies. With the rapid development of drying technologies and steadily increasing living standards, drying processing techniques as well as types of products produced have changed fundamentally. Two broad types of dried aquatic products are commercially available on a large scale: traditional products and snack foods. In this article, the development of dried aquatic product processing technologies will be expounded along with an overview of the necessary quality attributes and control strategies to produce high-quality dried products of aquatic origin.     

Energy and Quality Aspects of Food Drying

High energy consumption and increasing consumers interest in new products are two problems worthy of note in the drying of food. Difficulties in producing high-quality food and degrading transformations of the material during drying are mentioned. The kinetics of quality degradation due to drying is described. The role of water activity in maintaining product quality is emphasized. Examples of drying methods and tendencies toward a reduction in quality degradation of dried food products are shown.     

HIGHLIGHTS OF IDS'92

ABSTRACT

High energy consumption and increasing consumers interest in new products are two problems worthy of note in the drying of food. Difficulties in producing high-quality food and degrading transformations of the material during drying are mentioned. The kinetics of quality degradation due to drying is described. The role of water activity in maintaining product quality is emphasized. Examples of drying methods and tendencies toward a reduction in quality degradation of dried food products are shown.     

COMBINED INNOVATIVE HEAT PUMP DRYING TECHNOLOGIES AND NEW COLD EXTRUSION TECHNIQUES FOR PRODUCTION OF INSTANT FOODS

There is an increased demand for convenient foods including ready-to-eat and instant products. These products are desired with minimum concentration of synthetic chemicals. This creates challenges for the food industry and dryers manufactures to develop new technologies to process difficult-sensitive materials and to supply final products with high quality and improved properties. Fruits and vegetables are mainly composed of water, carbohydrates, proteins and lipids. Due to modification of chemical and physical bonds the compounds the material becomes viscous and sticky during processing. Conventional dryers have limitations in handling such sensitive materials. Heat pump dryers have been applied in the production of a diversity of ready-to-eat foods and dried instant products for the last five years at SINTEF-NTNU. Besides being energetically efficient and environmentally friendly, the heat pump drying technology provides a wide range of drying conditions as required to produce powders with improved characteristics. This work describes the new technologies and processing line for the production of instant foods as well as the measurements on the properties and quality attributes for raw, intermediate and final instant products.     

Influence of Structure on Saltiness and Sweetness of Dehydrated Food Products

Pore structure of foods influences the quality and texture of dehydrated food products. The development of food products with different pore structures and its effect on the sensory characteristics of the products were investigated. Potatoes and bananas were osmotically pre-treated using salt and sucrose solutions, respectively, and dehydrated with various drying methods, such as air drying, freeze drying, and vacuum drying, in order to obtain different pore structures. Simple mathematical models were developed in order to correlate the structural properties with process conditions. Depending on the drying method, porosity varied from 5% to 75% for potatoes and from 15% to 60% for bananas. Porosity was higher for the samples that were freeze-dried at lower pressures, followed by samples freeze-dried at higher pressures and, finally, vacuum- and air-dried samples. The surface areas of the dried samples varied between 0.961 and 3.040 m²/g, which are typical values for dehydrated foods. Freeze-dried potatoes and bananas were found to be saltier and sweeter (Score 6.5–7.8), respectively, than air- and vacuum-dried products (Score 4.8–5.8). Bananas and potatoes with the highest porosity and the highest specific surface areas presented more intense taste, providing the opportunity of reducing the levels of salt and sugar of the produced products without affecting the salty or sweet taste.     

Solids Rheology for Dehydrated Food and Biological Materials

Mechanical properties of food products and biological materials are greatly affected by the drying process and are considered one of the most important quality attributes of dehydrated products. The aim of this work was to review theoretical principles and mathematical modeling, analyzing the measurement techniques and major experimental results that exist in the literature about rheological properties of dehydrated foods and biological materials. Different methods of measuring rheological parameters (fundamental and empiric or imitative) are discussed and major experimental results, as well as the rheological models used in their analysis, published in recent years are presented.     

Effect of Water on the Quality of Dehydrated Products: A Review of Novel Characterization Methods and Hybrid Drying Technologies

The effect of water on the quality of dried products is reviewed in light of recent applications of novel characterization methods (nuclear magnetic resonance (NMR), X-ray spectroscopy, and Raman spectroscopy) in quantifying the state and mobility of water in dried products. The mechanical configuration and ability of a number of hybrid drying technologies that use novel heating sources (microwave, infrared, radiofrequency) and/or sub-atmospheric pressure in producing better-quality products are reviewed in considerable detail. The drying kinetics models, especially those related to the quality loss, are also reviewed. It appears that more and more drying research is now focused on the development of novel hybrid technologies to produce better-quality products and for energy savings. The novel characterization technologies listed above are capable of quantifying the dynamic mobility and state of water in dried food products; this information can be used to design more efficient drying processes.     

COMBINED INNOVATIVE HEAT PUMP DRYING TECHNOLOGIES AND NEW COLD EXTRUSION TECHNIQUES FOR PRODUCTION OF INSTANT FOODS

ABSTRACT

There is an increased demand for convenient foods including ready-to-eat and instant products. These products are desired with minimum concentration of synthetic chemicals. This creates challenges for the food industry and dryers manufactures to develop new technologies to process difficult-sensitive materials and to supply final products with high quality and improved properties. Fruits and vegetables are mainly composed of water, carbohydrates, proteins and lipids. Due to modification of chemical and physical bonds the compounds the material becomes viscous and sticky during processing. Conventional dryers have limitations in handling such sensitive materials. Heat pump dryers have been applied in the production of a diversity of ready-to-eat foods and dried instant products for the last five years at SINTEF-NTNU. Besides being energetically efficient and environmentally friendly, the heat pump drying technology provides a wide range of drying conditions as required to produce powders with improved characteristics. This work describes the new technologies and processing line for the production of instant foods as well as the measurements on the properties and quality attributes for raw, intermediate and final instant products.     

An Overview of Recent Developments and Some R&D Challenges Related to Drying of Foods

Thermal dehydration is the most common and cost-effective technique for preservation of foods and for the production of traditional as well as innovative processed products such as snacks with desired functionalities. The basic intent of this article is to provide a global overview of emerging and innovative thermal drying technologies that are already commercialized or show potential of industrial exploitation upon successful R&D to sort out some limitations. New drying technologies are needed to enhance quality, reduce energy consumption, improve safety, and reduce environmental impact. Mathematical modeling can be used for cost-effective development of untested novel designs to reduce the cost and time required for innovation. As examples of emerging drying technologies we consider selected dehydration techniques with imminent commercialization potential. These include heat pump–assisted drying, microwave-assisted drying, low-pressure superheated steam drying, pulse combustion spray drying, pulsed and ultrasound-assisted osmotic dehydration, as well as novel gas–particle contactors such as impinging streams and pulsed fluidized beds. Multistage drying, intermittent drying, and the use of hybrid drying technologies—which combine advantages of different dryers without some of their limitations—will be outlined. This article also discusses various methods of energy minimization, and the potential for use of renewable energy will also be discussed briefly. Although this overview emphasizes food dehydration, the themes covered are applicable to other materials as well.     

Emerging food drying technologies with energy-saving characteristics: A review

Abstract

Drying is one of the most vital preservation techniques used in the food industry. It demands different levels of energy to produce commercially high-quality-dried food products. Novel drying technologies minimize deterioration of the food ingredients and produce novel products for consumers. In recent years, there have been many developments in the technology connected with the industrial drying of foods. Recent research has shown that novel food drying technologies could be utilized to improve the efficiency of drying by lowering the energy consumption and also to enhance the product quality. This article reviews selected energy- saving techniques in drying and discusses some novel combined drying technologies. These include solar-assisted, infrared-assisted, microwave-assisted and similar hybrid drying methods for food drying. Recommendations are also made for future research and development.     

Production,health implications and applications of oleogels as fat replacer in food system: A review

Various food formulations widely utilized solid fats to provide specific textural properties and sensory attributes. Partially hydrogenated oil was commonly used as solid fat before being banned by FDA recently because of the existence of trans fats. Oleogels, semi-solid gel typically prepared from liquid vegetable oil and food-grade oleogelators, is developed as an alternative for solid fats that is free of trans fat and low in saturated fats. Oleogels are prepared via indirect or direct oleogelation technology by which the liquid oil is entrapped in a three-dimensional network with the aid of low molecular weight oleogelators (LMOGs) and high molecular weight oleogelators (HMOGs). Oleogels received tremendous attention from food scientists to be used in various food applications, particularly high-fat products such as comminuted meat, chocolates, ice cream, shortening and margarine and even as a deep-frying medium. They satisfy not only the current trends of consumers for healthy food products (free of trans fat and low in saturated fat) but also provide viscoelastic solid- and gel- like properties to structure high fat food products. More importantly, recent studies showed that oleogels tend to be metabolized differently from conventional fats and oils giving them an additional advantage in improving the nutritional value of high-fat foods. Therefore, this review aims to provide an overview that captures the latest studies on oleogels from their production via direct dispersion and indirect dispersion methods, processing conditions that influence the physical properties, metabolism and health attributes as well as recent application in food products.     

Swell Drying: Coupling Instant Controlled Pressure Drop DIC to Standard Convection Drying Processes to Intensify Transfer Phenomena and Improve Quality—An Overview

Increasing globalization is driving agricultural production in developing countries toward better recovery levels and high additional value. A great opportunity is thus offered to emerging economies. By adopting appropriate and improved methods that allow better preservation, transport, and storage and that conform to the rigorous requirements and standards of organoleptic and nutritional quality as well as stringent hygienic criteria, emerging economies can derive significant benefits.

Drying of biological materials usually results in shrinkage. The impact of shrinkage is often highly prejudicial for both the function and use of these materials. On the one hand, shrinkage results in a sharp decrease in water diffusivity through the porous structure (for dehydration and rehydration processes). On the other hand, the compact structure of dried biological material is usually unsuitable in terms of organoleptic quality and is inadequate for grinding. Thus, it is becoming very important to include retexturing and structure-expanding processes in standard drying processes. To this end, the instant controlled pressure drop (DIC) technology has been proposed and successfully tested as a texturing process for partially dried materials, which should normally intensify the whole operation. The quality of the final product as well as the performance of the drying process can also be dramatically improved. Finally, for a large category of dried fruits and vegetables, and even freeze-dried materials, microbiological contamination and the presence of insects and larvae are serious problems. DIC technology can be used as an ultra-high-temperature treatment for a controlled decontamination. Such dried, expanded, and completely decontaminated products can be used as highly nutritional snacks. They can easily be ground to produce expanded granulated powders with excellent sensory, nutritional, functional, and textural properties.     

Atmospheric Freeze Drying—Modeling and Simulation of a Tunnel Dryer

Drying is an important unit operation in processing of foods and other biotechnological products. Vacuum freeze drying is said to be the best drying technology regarding product quality of the end product, but the disadvantages are, among others, expensive operational costs and batch drying. Atmospheric freeze drying was introduced to lower the production costs of high-quality dried foods, and the need of simulation tools became important in estimations of the industrial drying processes.

A simplified mathematical model (AFDsim) is developed based on uniformly retreating ice front (URIF) considerations. The model is used to calculate theoretical drying curves of atmospheric freeze dried foods in a tunnel dryer. Studies of thermal and mass transfer properties during drying are essential for understanding the changes in product quality and for designing and dimensioning the drying process. The model can be used to simulate industrial atmospheric freeze drying of different foodstuff in a tunnel. The results from AFDsim modeling are in good accordance with the experimental results.     

The salmonella problem from an enforcement standpoint

The importance and significance of salmonella contamination in foods and drugs are discussed. Products presenting the greatest problems in the last two years have been dried milk, egg products, drug and enzyme substances of animal origin, basic protein feed ingredients of animal origin such as fish meal, meat scrap, rendered tankage and related substances. Prepared ready-to-eat foods, dried yeast, chocolate and similarly processed foods have more recently been identified as potential vectors, thus compounding the problem. Gaps in knowledge concerning mechanism of man to man, man to animal, and animal to man infections present handicaps to effective control measures. Lack of data on survival of the organism, conditions favorable to proliferation, and the avenues of contamination in various food and drug processes further complicate control. Presented at the AOCS-AACC Joint Meeting, Washington, D.C., April, 1968.     

Some Recent Research and Development in Drying Technologies: Product Perspective

Thermal drying is a major industrial energy consumer in developed economies. Efficient, energy-saving, low environmental impact drying processes to produce dried products of uniform quality that meet specific specifications are desired. This mini-review provides a nonexhaustive view of recent advances in drying technologies, particularly on product perspectives. Based on the listed studies, the challenges and ways forward are discussed.     

Atmospheric Freeze Drying—Modeling and Simulation of a Tunnel Dryer

Drying is an important unit operation in processing of foods and other biotechnological products. Vacuum freeze drying is said to be the best drying technology regarding product quality of the end product, but the disadvantages are, among others, expensive operational costs and batch drying. Atmospheric freeze drying was introduced to lower the production costs of high-quality dried foods, and the need of simulation tools became important in estimations of the industrial drying processes.

A simplified mathematical model (AFDsim) is developed based on uniformly retreating ice front (URIF) considerations. The model is used to calculate theoretical drying curves of atmospheric freeze dried foods in a tunnel dryer. Studies of thermal and mass transfer properties during drying are essential for understanding the changes in product quality and for designing and dimensioning the drying process. The model can be used to simulate industrial atmospheric freeze drying of different foodstuff in a tunnel. The results from AFDsim modeling are in good accordance with the experimental results.     

Relating the Stickiness Property of Foods Undergoing Drying and Dried Products to their Surface Energetics

Stickiness is a common problem encountered in food handling and processing, and also during consumption. Stickiness is observed as adhesion of the food to processing equipment surfaces or cohesion within the food particulate or mass. An important operation where this undesirable behavior of food is manifested is drying. This occurs particularly during drying of high-sugar and high-fat foods. To date, the stickiness of foods during drying or dried powder has been investigated in relation to their viscous and glass transition properties. The importance of contact surface energy of the equipment has been ignored in many analyses, despite the fact that some drying operations have reported using low-energy contact surfaces in drying equipment to avoid the problems caused by stickiness. This review discusses the fundamentals of adhesion and cohesion mechanisms and relates these phenomena to drying and dried products.     

Dried Food Properties: Challenges Ahead

In the last few decades, the knowledge of the properties of dried-food has increased tremendously. In fact drying research and development has extended beyond its limited chemical and mechanical engineering approach of heat and mass transfer. In the past drying was performed to preserve foods with less emphasis on multidimensional quality attributes. A recent trend is to develop dried-foods maintaining its quality, such as flavor, texture, convenience, and functionality with increased nutritional contents and reduced anti-nutritional factors or toxins. At present drying of foods has extreme focus on maintaining its bioactive and structural functionality. The main purpose of this paper is to give an overview on the food properties and to provide basic concepts of food properties and quality. A critical assessment is presented with emphasis on classifications, measurement techniques, data generation, prediction models and applications of food properties. An attempt is also made to answer the following questions: where are we now and where do we need to go or reach? What vicious circle needs to be broken? What efforts are being made around the globe?