Humberto Vega-Mercado

Advances in dehydration of foods

Food dehydration is still one of the most relevant and challenging unit operations in food processing, although the art of food preservation through the partial removal of water content dates back several centuries. This article provides essential information on the fundamental, including psychrometry, and applied engineering aspects of food dehydration with up-to-date available commercial applications. The evolution of drying technology, divided into four generations, is thoroughly reviewed, from tray drying to the combination of some drying technologies (the hurdle technology approach in drying) in order to optimize the process in terms of final food quality and energy consumption. The study of each generation covered numerous examples of different dryers, including their principles of operation, basic configurations and most common applications, as well as their main advantages and disadvantages.

Non-thermal food preservation: Pulsed electric fields

The use of electric discharges to inactivate microorganisms and enzymes in food products has evolved since the 1920s from the ‘ElectroPure process’ (ohmic heating process) to the use of high-intensity pulsed electric fields in the 1990s. The non-thermal inactivation of microorganisms and enzymes using electric fields was demonstrated in the 1960s with a variety of microorganisms suspended in simulated food systems. A variety of liquid foods and beverages, including orange, apple and peach juices, pea soup, beaten eggs and skim milk, has been successfully processed during the 1980s and 1990s by several research groups. Little by little, the food industry is demonstrating increasing interest in this promising emerging technology; furthermore, it is expected that it will soon be adopted to process several liquid food products.

Inactivation of Escherichia coli by combining pH, ionic strength and pulsed electric fields hurdles

Abstract The use of pulsed electric fields is reported as a nonthermal process in the inactivation of bacteria and yeast. The inactivation of microorganisms is caused mainly by an increase in their membrane permeability due to compression and poration. Up to 2.2 log reductions in plate counts are observed when both pH and electric field are modified: pH from 6.8 to 5.7 and electric field from 20 to 55 kV/cm. Similar results are obtained when the ionic strength is reduced from 168 mM to 28 mM. The electric field and ionic strength are more likely related to the poration rate and physical damage of the cell membranes, while pH is more likely related to changes in the cytoplasmic conditions due to the osmotic imbalance caused by the poration. In this context, pulsed electric fields can be considered a hurdle which, combined with additional parameters such as pH, ionic strength, temperature and antimicrobial agents, can be effectively used in the inactivation of microorganisms.

Other Methods of Dehydration of Foods and Packaging Aspects

There are other drying techniques in addition to the ones already discussed in Chapters 5, 6, 7, and 8 based on similar concepts and used in the food industry. This chapter covers drying techniques such as sun drying, vacuum drying, drum drying, microwave drying, extrusion cooking, fluidized bed drying, and pneumatic drying. In addition, this chapter includes some important aspects related to the packaging of dried foods: mechanical damage, permeability, temperature effect, light transmission and, compatibility of packaging materials.

Non-thermal Processing Technologies

Every food manufacturing and processing operation has inherent risks affecting the safety of food products. Non-thermally processed foods are not exempt of those risks. This chapter provides the reader with an overview of various non-thermal technologies (e.g. irradiation, pulsed electric fields, high hydrostatic pressure, intense pulsed lights, membrane filtration and hurdle technology). Each of these technologies has specific critical process parameters that must be monitored as part of critical control points. In-depth understanding of these technologies is the key while considering their implementation. The main challenge on non-thermal processes is standardization when compared to thermal treatments. Non-thermal processes seem to be product specific resulting in additional research work to define process parameters. Nevertheless, a significant amount of research data are available and specific process conditions can be found in the literature.

Introduction to Dehydration of Food

It is not known when the preservation of foods by dehydration began, but history does show that our ancestors learned how to dry foods by trial and error. Food dehydration eventually evolved within a scientific based environment and made possible the establishment of a worldwide industry, capable of providing a convenient and nutritious food supply.

Cabinet and Bed Dryers

The main purpose of food dehydration is to extend the shelf life of the final product. The process meets this objective by reducing the moisture content of the product to a level that limits microbial growth and chemical reactions. Hot air is used in most drying operations and air dryers have been in use for several years around the world.

Fundamentals of Air-Water Mixtures and Ideal Dryers

Air—water mixtures are used in most drying operations. The thermodynamic properties of this type of mixture are reported elsewhere (Himmelblau, 1982), but we consider it important to include in this chapter fundamental aspects of an air—water mixture before entering into the details of drying operations such as spray drying, fluidized bed drying, or atmospheric drying.