Recent Developments in Non-thermal Processess - Food and Industrial Bioproducts and Bioprocessing - page 312

PEF by the juice processing industry became a reality in the USA where several types of
fruit juices treated by PEF were commercialized (Clark, 2006). In addition, several
companies manufacturing PEF processing units have appeared in recent years. Among
them, Diversified Technologies Inc. and PurePulse Technologies Inc. in the USA and
ScandiNova Systems AB in Sweden manufacture PEF units with an overall flow rate of
400-8000 l/h. The cost of a PEF-processed product by these units is estimated in $0.04
per liter (Huang and Wang, 2009). It is expected that the high number of research studies
and industrial efforts will lead to new industrial applications of PEF technology in the
near future.
13.2.5 Ultraviolet Light (UV)
The use of ultraviolet light (UV) for air and water treatment and surface decontamination
has been well established for nearly 50 years (Masschelein, 2002). As a physical preservation
method, UV irradiation has a positive consumer image (non-ionizing radiation) and is of
interest to the food industry as a low cost technology. UV irradiation of foods does not
produce chemical residues, by-products or radiation and it is a simple, dry and low
temperature process (Bachmann, 1975 ; Morgan, 1989 ). The UV light wavelength range
used for food processing varies from 200 to 280 nm, which is known as UV-C or germicidal
range, since it effectively inactivates bacteria and viruses (Guerrero-Beltrán and Barbosa-
Cánovas, 2004). Typically, three general types of mercury UV lamps are used: low pressure
mercury lamps (LPM), low pressure high output (LPMHO), and medium pressure mercury
lamps (MPM). These terms are based on the vapor pressure of mercury when the lamps are
operating. The FDA has approved the use of LPM lamps for juice processing and the process
has already been successfully commercialized (Koutchma, 2009).
Liquid foods absorb UV radiation. The presence of dissolved organic and suspended solids
and high initial microbial populations (such as yeast cells) in liquid foods leads to strong UV
attenuation effects (penetration of only 1 mm is required for absorption of 90% of the light)
(Sizer and Balasubramaniam, 1999). Penetration of light through the system decreases as
color or turbidity increases because of high light absorption (Tran and Farid, 2004). The UV-C
dose emitted from a lamp is usually measured using UV sensors in W/m 2 units. It has been
lately proposed that a turbulent flow increases UV light penetration (Koutchma, 2009). UV-C
light is also applied to fresh fruits, vegetables and roots before being stored to reduce the initial
count of microorganisms on the surface of the product and to induce host resistance to the
microorganisms (Guerrero-Beltrán and Barbosa-Cánovas, 2004).
Microorganisms that are exposed to UV light are affected at the DNA level. The UV-C
light absorbed by DNA causes a physical shifting of electrons to render splitting of the
DNA bonds, delay of reproduction or cell death (Wright et al ., 2000 ). In addition, DNA
transcription and replication are blocked, compromising cellular functions and eventually
leading to cell death (Sastry et al ., 2000). The highest germicidal effect against bacteria is
obtained at wavelengths near 254 nm (UV-C, generated by LPM lamps) (Guerrero-Beltrán
and Barbosa-Cánovas, 2006). Photoreactivation is a phenomenon that must be taken into
account when the UV-C injured cells are subsequently exposed to wavelengths within the
range of 330-480 nm (Liltved and Landfald, 2000). The damage occurring at the DNA
level could be repaired, increasing the number of viable microorganisms during storage if
light-transmitting packages are used. The variation of microbial resistance is believed to be
due to the presence of UV absorbing proteins or differences in the structure of the nucleic
acids as well as the ability of the microorganisms to repair UV damage (Guerrero-Beltrán