BLBS102-c39 BLBS102-Simpson March 21, 2012 14:20 Trim: 276mm X 219mm Printer Name: Yet to Come
750 Part 7: Food Processingbelieved that the kinetics of microbial inactivation in microwave
processing is essentially same as the inactivation kinetics of
conventional thermal processing for the same heating rate. Re-
cent technological advancement, including development of new
chemical marker system for process monitoring and identifica-
tion of cold spots, techniques for achieving temperature unifor-
mity, computer modeling, and microbial inactivation validation,
has led to US FDA approval of microwave sterilization in 2009.
This clears the path for commercialization of the process. There
is no report of industrial application of RF sterilization (Ra-
maswamy and Tang 2008). There is a need to speed up research
and development efforts to enhance MF- and RF-based industrial
sterilization processes.NONTHERMAL PROCESSING
TECHNOLOGIESTraditional thermal processing technologies are well established
and proven to inactivate microorganism and prolong shelf life in
foods. However, some of the challenges associated with main-
taining product quality and freshness have been discussed in
the preceding sections. Nonthermal technologies that inactivate
microorganisms by means other than heat are being introduced
to mitigate some of the shortcomings of traditional processes.
These technologies include high pressure, pulsed electric fields,
irradiation and pulsed ultraviolet (UV) light, etc.High-Pressure ProcessingHigh-pressure processing (HPP) of foods is the application of
ultra high pressure (100–1000 MPa) on foods for short duration,
which may range from few seconds to minutes. The most impor-
tant aspect of HPP lies in its effectiveness in microbial control
in food products. HPP has shown its potential in keeping food
fresh for long time without the use of preservatives, in inactivat-
ing food-spoiling microbes, and most importantly in maintain-
ing minimally processed fresh-like texture. The technique was
initially commercialized in Japan in 1990s, but, historically, the
United States was the first country to use the HPP technology for
preserving products like juice, some fruits, milk, etc. The mone-
tary constraints and lack of expertise in high-pressure equipment
and package manufacturing emerged as a roadblock until Japan
reinitiated use of this technology in 1980s. There have been
an increasing number of HPP systems installed throughout the
world. In 2008, there were four systems (71 overall) systems in
North America (Campus 2010). A wide range of products includ-
ing juices, fruits and fruit related products, seafood, and meat
products have been successfully processed using the technology.
HPP operations can be conducted in three modes,
namely batch, semi-continuous, and continuous modes. Semi-
continuous or continuous modes typically apply to pumpable
products, in which case aseptic packaging is required. Products
can be processed in-package in batch mode. A flexible package
like a retort pouch or plastic bottle is introduced in a high-
pressure chamber, and pressure is transmitted to the food via
its package by the use of a hydraulic liquid. Water is preferred
as the hydraulic liquid because of operational ease and highcompatibility with the food components. HPP packages must be
airtight and capable of allowing about 19% decrease in volume
without losing seal integrity. Juliano et al. (2010) have provided
a good review on packaging concepts for HPP. Since pressure is
transmitted uniformly in all directions, the texture of processed
product, as well as nutritional and sensory attributes of the food
product, is preserved in HPP processing (Fernandez et al. 2001).
Typical HPP system comprises of four components, namely
pressure vessel, pressure generating device, pressure and tem-
perature control, and material handling units (Mertens 1995).
Pressure vessels are designed carefully to meet very strict safety
and operational standards of the American Society of Mechan-
ical Engineers (ASME) boiler and pressure vessel codes. To
withstand the high pressures used in HPP, prestressed multi-
layer or wire-wound vessels are used. High pressure can be
generated either by direct or indirect compression or simply by
heating the pressure fluid. In the more widely used indirect com-
pression, water (or other pressure transmitting fluid) is pumped
into a closed high-pressure vessel until the desired pressure is
achieved (Mertens 1995). Technological developments on de-
sign of pressure vessels and intensifiers are the major driving
advances in the HPP technology. Early HPP systems were oper-
ated with vertical vessels. Recently in 2000, NC Hyperbaric, one
of the leading HP manufactures introduced the first horizontal
HPP vessel. Information from the company suggests that instal-
lation and product handling in a horizontal system is reported
to be much easier and less expensive than the vertical system
(www.nchyperbaric.com). In particular, loading and unloading
motions in the horizontal machines are made at the waist level
and can be more easily done either manually or automatically
than in the vertical systems, which are typically several meters
high.
High pressure inactivates microorganisms by increasing the
permeability of the cell membrane, causing loss of intracellu-
lar fluids, thereby inhibiting biochemical reactions within the
cell and hampering cell growth (Cheftel 1995, Ananta et al.
2001). On application of high pressure, the acyl chains get
tightly packed with the phospholipid bilayer of membranes,
and it undergoes transition from liquid crystalline to gel phase,
hence modifying the internal microbial resistance. Variation in
time–pressure conditions affects the cytokinetic and mitotic ac-
tivity of the cell (Lopes et al. 2010). Presence of at least 40% free
moisture content is important for effective microbe destruction
(Earnshaw 1996). Gill and Ramaswamy (2008) used a pressure
of about 600 MPa with holding time of about 3 minutes on two
RTE meats (Hungarian salami and All beef salami) inoculated
with food-borne pathogenE. coliO157. It was observed that
there was reduction inE. colicount in both samples. However,
when samples were enriched with nutrient medium to recover
E. coli, there was increase in theE. colicount of Hungarian
salami, whereas stagnantE. colicount was found in all beef
salami that was conditioned in regulated pH and water activ-
ity. Bacterial spores are of small size, low in moisture content,
and impermeable to water, which makes them highly resistive
to intense pressure conditions. They are considered as poten-
tial danger in postprocessing storage, as they may germinate
and cause food toxification. Spores can tolerate pressure up to