Recent Developments in Non-thermal Processess - Food and Industrial Bioproducts and Bioprocessing - page 316

from soybeans and extraction of carbohydrates, polysaccharides and other functional
compounds such as hemicelluloses (Bates and Patist, 2009; Demirdoven and Baysal, 2009).
Thereby, ultrasound may reduce the dependence on solvents and enable the use of alternative
solvents which may provide more attractive economics, environmental and health and safety
benefits (Vilkhu et al ., 2008 ).
An ultrasound processing system consists of three basic parts: (i) generator; (ii) trans-
ducer; and (iii) coupler. Ultrasonic generators transform electrical energy into ultrasound
energy (a type of mechanical energy) via a transducer, with piezoelectric transducers the
most commonly used in commercial-scale applications due to their scalability (Bates and
Patist, 2009). The intensity of the ultrasound treatments can be measured in terms of power
(Demirdoven and Baysal, 2009). The scale-up of an ultrasonic treatment system can be
achieved by integrating flow-cell modules, either in series or in parallel, providing 2-16 kW
of power, with amplitudes ranging from 1 to 150 micron peak-to-peak displacement, and
flows ranging from 1 to 1000 l/min, with an energy efficiency of 90-95% depending on the
application (Feng et al ., 2008; Bates and Patist, 2009). Companies such as Cavitus Pty Ltd.
(Australia) provide a wide range of high power ultrasonic equipment for different food appli-
cations, such as extraction, emulsification/homogenization, viscosity alteration, de-foaming
and cleaning/sanitation in the wine industry with a payback less than two years (Bates and
Patist, 2009 ).
13.2.8 Hurdle approach
All non-thermal technologies cited in this chapter have several drawbacks. In general,
high production costs, the unavailability of industrial-scale equipment, the inability to
reduce spores and the lack of effective communication to the consumers about the
principles and benefits of these technologies are the main limitations. Taking into account
all of these limitations, the hurdle approach has been proposed as the most efficient way
to improve overall effectiveness. The combination of temperature and/or low pH with
other stress factors, such as pressure, electric field or radiation, has been demonstrated to
have a synergistic effect on microbial and enzyme inactivation in numerous studies.
Research on high pressure treatment at either elevated temperature for high pressure
assisted sterilization or low temperature for high pressure assisted quick freezing and
combination of ultrasound and temperature treatment (thermosonication) are some
examples. In addition, the use of a combination of different non-thermal processes by
applying them consecutively, that is HPP + PEF, HPP + irradiation, and PEF + ultrasound,
may represent a new approach to improve the efficacy of the entire process by decreasing
the intensity of treatments required for any process alone. Lowering pH, oxygen
concentration and water activity during storage have also been used as a barrier to control
the growth of microorganisms and preventing the recovery of any sublethally injured cell
during storage.
The use of biopreservatives in combination with non-thermal technologies has also been
proposed to enhance the effectiveness of these processes against vegetative cells and
bacterial spores and help to control microbial growth during storage under chilled conditions.
In this sense, bacteriocins and natural antimicrobial compounds, such as nisin, lysozyme,
lactoferrin, lactoperoxidase system, chitosan and essential oils from diverse plants, have
been successfully applied. Lately, there has been a growing interest in using natural
ingredients as biopreservatives. In addition to providing interesting flavors and colors,