BLBS102-c39 BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come
39 Minimally Processed Foods 7511000 MPa (Cheftel 1995). There is a long list of spore-forming
bacterium that spoils food such as milk, cheese, meat, juices,
etc. The spores ofBacillusandClostridiumspecies have been
cited as the common reason for food-borne diseases (Shapiro
et al. 1998, Salkinoja-Salonen et al. 1999, Borge et al. 2001,
Brown 2000). An elaborate review of studies on spore inactiva-
tion has been given by Black et al. (2007). Although HPP has
shown great potential as a reliable processing technique, very
high pressures may result in poor quality. Thus, in some cases,
combination of HPP with other factors (such as temperature, pH,
water activity, etc.) may be beneficial. There is increasing inter-
est in the high pressure, high temperature or Pressure-Assisted
Thermal Sterilization or Pressure-Assisted Thermal Processing
(PATP) for development of shelf-stable low-acid food products
(Barbosa-Canovas and Juliano 2007, Zhu et al. 2008).Pulse Electric Field ProcessingPulse electric field (PEF) processing of foods is growing in im-
portance as a technique for producing microbiologically safe,
nutritious, fresh-like, and high-quality products (Mittal 2009).
There are also economic and energy-saving advantages associ-
ated with the technology. It has been used for processing liquid
food products like fruit juices, alcoholic beverages, soups, liquid
eggs, and milk. It can be used in continuous for pumpable fluids
or in batch modes for both liquids and solids.
PEF processing is based on the principle of application of
electric field (20–80 kV/cm) on a food product contained be-
tween two electrodes in short pulses (1–100μs). Microbial cells
present in the food are inactivated and drastically reduced in
count. Electric breakdown of cells and electroporation are the
two mechanisms of microbial destruction during PEF (Zimmer-
mann 1986, Harrison et al. 1997, Barbosa-Canovas and Sepul-
veda 2005). In electric breakdown mechanism, application of
external electric field causes development of electrical potential
difference across cell membrane, also called as transmembrane
potential. When the transmembrane potential is higher than the
natural potential of the cell (nearly 1 V), pores are formed, re-
ducing the thickness of cell membrane. With higher potential,
the cell membrane is eventually disrupted permanently, leading
to cell destruction. With respect to the electroporation mech-
anism, lipid bilayers and proteins are destabilized, increasing
membrane permeability and number of pores. The pores cause
the cell membrane to rupture, cytoplasmic material oozes out,
and finally cell dies (Vega-Mercado et al. 1997). Effective ap-
plication of PEF depends on the type of pulse (monopolar and
bipolar) and waveform (sinusoidal, square, or exponentially de-
caying) used (Ho and Mittal 2000, Ngadi and Bazhal 2004).
Earlier application of PEF in food processing in North Amer-
ica focused on pasteurization of liquid or semi-liquid products.
Some of the foods that have been processed using the technology
include milk (Evrendilek and Zhang 2005), apple juice (Vega-
Mercado et al. 1997, Sanchez-Vega et al. 2009), orange juice (Ri-
vas et al. 2006), liquid egg (Martin-Belloso et al. 1997, Amiali
et al. 2006, Amiali et al. 2007), and egg yolk (Bazhal et al. 2006).
These studies and others showed that PEF can be used to success-
fully inactivate pathogenic and food spoilage microorganisms aswell as selected enzymes, resulting in better retention of flavors,
nutrients, and fresher taste compared to heat-pasteurized prod-
ucts. Mosqueda-Melgar et al. (2007) reported efficacy of PEF
in decreasingSalmonellaspp.,E. coliandL. monocytogenes
in melon and watermelon fruit juices. A reduction in the bac-
terial yeast and mould count in naturally contaminated orange
juice was observed. The color, aroma, and flavor features were
better than as in conventional HTST treatments. PEF was also
effective in inactivating yeast (Saccharomyces cerevisae)and
bacteria (Kloeckera apiculata, Lactobacillus plantarum, Lacto-
bacillus hilgardii, and Gluconobacter oxydans) present in grape
juice (Marsell ́es-Fontanet et al. 2009). Many factors influence
effectiveness of PEF processing. These include process factors
(electric field strength, number of pulses, treatment time, treat-
ment temperature, pulse shape, pulse width, pulse polarization,
frequency, specific energy, treatment chamber design, etc.), mi-
crobial factors (cell concentration, microorganism resistance to
environmental factors, type and species of the microorganism,
as well as growth conditions such as medium composition, tem-
perature and oxygen concentration and other stress conditions),
and product parameters (product composition, presence or ab-
sence of particles, sugars, salt and thickeners, conductivity, ionic
strength, pH, water activity, etc.). Optimal application of PEF
often involves appropriate control of these factors. There has
been effort to develop mathematical models that will describe
the complex mechanism of microbial inactivation using PEF.
Research is still ongoing to discover suitable models. However,
typical inactivation characteristics tend to follow the sigmoidal
shape and may be described using kinetic-based or probability-
based models. Table 39.2 indicates how different parameters
might influence microbial inactivation using PEF.
Although the influence of PEF on microbial inactivation is
well established, there are varying reports on its effect on quality
of processed liquids. There was high retention of lycopene and
vitamin C in water melon juice (Oms-Oliu et al. 2009), higher vi-
tamin A in orange–carrot juices (Torregrosa et al. 2006), higher
phenolic content and antioxidant capacity in strawberry juice
(Odriozola-Serrano et al. 2008), and no change in phenolic con-
tent of tomato juice (Odriozola-Serrano et al. 2009) with PEF
processing. A new orange juice-milk beverage was developed
by insertion of bioactive components (n-3 fatty acids and oleic
acid) as an alternative to soft drinks. The effect of PEF at two
levels, namely 35 and 40 kV/cm, was used to study effects on
physicochemical properties, pH, degree Brix, and peroxide in-
dex. The study concluded that there was no significance effect of
PEF treatment on saturated and unsaturated fatty acid contents,
with no detection of peroxide and tolerable levels of furfurals
(Zulueta et al. 2007).
PEF treatment may influence physical and chemical prop-
erties of products. The nature and extent of PEF influence on
quality changes are still being actively discussed. Ngadi et al.
(2010) provided an excellent review of quality aspects of PEF
processing. Barsotti et al. (2002) indicated that PEF treatment
of model emulsions and liquid dairy cream may result in dis-
persal of oil droplets and dissociation of fat globule aggre-
gates. Qin et al. (1995) reported no apparent change in the
physical and chemical attributes of PEF-processed milk. PEF