application of alternative food-preservation - Bentham Science

Application of Alternative Food-Preservation Technologies to Enhance Food Safety & Stability, 2010, 143-160 143
Antonio Bevilacqua, Maria Rosaria Corbo and Milena Sinigaglia (Eds)
All rights reserved - © 2010 Bentham Science Publishers Ltd.
CHAPTER 9
Alternative Non-Thermal Approaches: Microwave, Ultrasound, Pulsed
Electric Fields, Irradiation
Nilde Di Benedetto, Marianne Perricone and Maria Rosaria Corbo*
Department of Food Science, Faculty of Agricultural Science, University of Foggia
Abstract: This chapter proposes a description of some non-thermal technologies (microwave, ultrasound,
pulsed technologies, irradiation) as suitable tools to inactivate foodborne pathogens and spoiling
microorganisms in heat-sensitive foods.
Ultrasound (US) is defined as pressure waves with a frequencies of 20 kHz or more; pulsed electric field
(PEF) processing involves treating foods placed between electrodes by high voltage pulses in the order of 20-
80 kV/cm (usually for a couple of microseconds); ionizing irradiation occurs when one or more electrons are
removed from the electronic orbital of the atom; and microwaves (MW) are defined as electromagnetic waves
in the range of infrared (IR) and radio waves (RF) with a wavelength ranging from 1 mm to 1 m and
operating at a frequency ranging from 300 Mhz to 300 Ghz. Each technique allows killing of vegetative
microorganisms but fail until now, when applied alone, to destroy spores.
This chapter reports some practical applications of the proposed approaches in food industry and also focuses
on their drawbacks and limitations.
Key-concepts: Microwave, Ultrasound, Pulsed electric fields, Irradiation, Food applications of non-thermal
approaches.
INTRODUCTION
Modern consumers are increasingly conscious of the health benefits and risks associated with consumption of
food. In addition, consumers demand for foods that are fresher, more natural and healthier and that at the same
time provide a high degree of safety have increased interest in non-thermal preservation techniques for
inactivating microorganisms and enzymes in foods.
For these reasons, the food industry is devoting considerable resources and expertise to the production of
wholesome and safe products, but it needs some unit operation such as scrutinizing materials, entering food
chain, suppressing microbial growth and reducing or eliminating the microbial load. The microbial destruction is
the principal aim to ascertain safety and stability of food. Heat treatments are traditionally applied to pasteurize
and sterilize food, generally at the expense of its sensory and nutritional qualities.
Microwave, high power ultrasound, irradiation, γ rays and pulsed electric field represent the alternative foodpreservation
technologies designed to obtain safe food, while maintaining its nutritional and sensory qualities.
Satisfactory evaluation of a new preservation technology depends on reliable estimation of its efficacy against
pathogenic and spoilage food-borne microorganisms. Moreover, the success of these new technologies depends
on the advances in understanding what happens to microbial cells during and after treatment.
Microorganisms are inactivated when they are exposed to factors that substantially alter their cellular structure or
physiological functions, such as DNA strand breakage, cell membrane breakdown or mechanical damage to cell
envelope. Furthermore, cell functions are altered when key enzymes are inactivated or membrane selectivity is
disabled. A preservation technology, e.g. heat, may cause cell death through multiple mechanisms, but limited
information is available about that.
For example, membrane structural or functional damage is, generally, the cause of cell death during exposure to
high-voltage electric field. Whereas, ionizing and UV radiations damage microbial DNA and to a lesser extent
denature proteins. Cells that are unable to repair their radiation-damaged DNA die.
Microorganisms are more likely stressed or injured than killed in food processed by alternative preservation
technologies, although adaptation of microorganisms to stress during processing constitutes a potential hazard.
*Address correspondence to this author Maria Rosaria Corbo at: Department of Food Science, Faculty of Agricultural Science,
University of Foggia, Italy; E-mail: m.corbo@unifg.it