Transcript Applications of hurdle technology - E-Course

ΠΑΝΕΠΙΣΤΗΜΙΟ ΙΩΑΝΝΙΝΩΝ
ΑΝΟΙΚΤΑ ΑΚΑΔΗΜΑΪΚΑ
ΜΑΘΗΜΑΤΑ
Προχωρημένα Μαθήματα
Επεξεργασίας και Συντήρησης
Τροφίμων
Νεοφανείς μέθοδοι επεξεργασίας & συντήρησης
τροφίμων (NOVEL METHODS OF FOOD PROCESSING AND
PRESERVATION)
Διδάσκοντες: Κ. Ακρίδα, Π. Δεμερτζής, Κ.
Ρηγανάκος, Ι. Σαββαΐδης
Άδειες Χρήσης
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• Για εκπαιδευτικό υλικό, όπως εικόνες, που
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B. NOVEL METHODS OF FOOD
PROCESSING AND
PRESERVATION
1. HURDLE TECHNOLOGY
The concept of Hurdle technology
Applications of hurdle technology
The future of hurdle technology
2. HIGH-PRESSURE TREATMENT OF
FOODS
Principles of High- Pressure
Processing
Effect of Pressure on Biomoleculs
Industrial applications of
h.- p. technology.
3. OHMIC HEATING
(a) Ohmic heating principle.
(b) Processing applications.
1. HURDLE TECHNOLOGY
The concept of Hurdle technology
The problem of achieving preservation procedures that have
less of an impact on product quality while assuring food
safety has led to the rediscovery of an old concept: hurdle
technology.
Hurdle technology (also called combined processes, combination
processing, combination preservation, combination techniques, or
barrier technology) advocates the use of different preservation
techniques in combination. Individually, the strength or intensity of
the individual hurdles would not be sufficient to preserve the food,
but in concert they have the desired level of effect. Individual
hurdles used are, for instance, temperature, water activity (aw), pH,
redox potential (Eh), and preservatives. It requires a certain amount
of effort from a micro-organism to overcome each hurdle. The
higher a hurdle, the greater this effort is. Some hurdles, such as
pasteurization, can be high for a large number of different types of
microorganisms, whereas others, such as salt content, have a less
strong effect or the effect is limited in the range of types of
microorganisms it affects.
This Figure gives an example of the hurdle technology
effect. t, chilling during storage; aw, low water activity; pH,
acidity; Eh, low redox potential; pres., preservatives.
Applications of hurdle technology
Hurdle techniques of food preservation were developed
empirically many centuries ago, and consequently many
different types of food preserved in this way are commonly
produced and marketed.
For instance, fermented food products (sausages,
cheeses, vegetables) are actually made safe and shelf-stable
for long periods through a sequence of hurdles that arise at
different stages of the ripening/fermentation process. With
salami-type fermented sausages, salt and nitrite inhibit
many microorganisms in the batter and are thus important
hurdles in the early stage of the ripening process.
Other bacteria multiply and use up oxygen. This reduces the
redox potential of the product and enhances the Eh hurdle.
This reduces growth of aerobic microorganisms and favors
the selection of lactic acid bacteria. They are a competitive
flora and cause acidification of the product, thus increasing
the pH hurdle.
Also with non-fermented foods, such as ready-to-eat
products that are composed of different types of raw or
minimally processed (washed, trimmed, sliced) vegetables,
hurdle technology has been used to assure proper safety.
Refrigeration and modified-atmosphere packaging are the
main hurdles used to stabilize these perishable foods.
The future of hurdle technology
With the increasing popularity of minimally processed
foods, which are highly convenient for the consumer but
preserved only by relatively mild techniques, the
environmental conditions in foods as a habitat for
microorganisms have changed dramatically, giving many
new options for their survival and growth compared with
traditionally preserved foods. In order to control food
poisoning and spoilage microorganisms in these new food
habitats, while keeping loss of product quality to a minimum,
a hurdle technology approach is advocated which involves
the educated selection and use of a set of preservative
factors that can adequately ensure product stability and
safety.
Minimal processing, however, should not lead to minimum
food safety. It is appreciated that combined processes used
today do not eliminate micro-organisms but rather inactivate
them.
The proper use of hurdle technology needs to include sound
information on factors affecting the survival and growth of
target micro-organisms at both the macroscopic and the
microscopic level.
Perfecting hurdle technology will enable food manufacturers
to improve food quality further without compromising on food
safety, at some stage achieving processing and preservation
treatments that are undetectable by the consumer.
2. HIGH-PRESSURE
TREATMENT OF FOODS
Principles of High- Pressure processing
The idea of using high hydrostatic pressure (HHP) as a
method of food processing is not new. Bert Hite, from West
Virginia University, reported in 1899 that high-pressure
treatment at ambient temperature could be used to preserve
milk. In later studies he also reported that some microorganisms, such as lactic acid bacteria and yeasts,
associated with sweet, ripe fruit were more susceptible to
pressure than spore-formers associated with vegetables.
Research did not progress as the equipment was not
available to routinely subject foods to the necessary
pressures. However, in recent years there has been renewed
scientific and commercial interest in the process.
High-pressure is generally a semi continuous bulk process
for liquid foods and a batch process for solid foods.
A typical high-pressure system consists of a pressure
vessel and a pressure generator. Food packages are loaded
into the vessel and the top closed. The pressure
transmission fluid, usually water, is pumped into the vessel
from the bottom. Once the desired pressure is reached, the
pumping is stopped, valves are closed and the pressure is
held without the need for further energy input.
Effect of Pressure on Biomolecules
There are two main principles involved in high-pressure
processing: the isostatic principle and the Le Chatelier
principle. The former states that pressure is transmitted
uniformly and instantaneously throughout the sample. This
process is independent of the volume or geometry of the
sample. This property gives HHP an important advantage
over conventional thermal processing. The Le Chatelier
principle states that the application of pressure to a system in
equilibrium will favour a reduction in volume to minimize the
effect of pressure. Thus, reactions that result in a volume
decrease are stimulated, while those causing a volume
increase are disrupted.
Hydrogen bonding tends to be favoured while ionic
bonds are broken. Hydrophobic interactions are
disrupted below 100 MPa but can be stabilized at higher
pressures. Covalent bonds appear to be unaffected by
high pressure, so low-molecular-weight molecules –
such as those responsible for the sensory and
nutritional qualities of food – are left intact. However,
the structure of high-molecular-weight molecules can be
significantly affected and this can result in altered
functionality of proteins and carbohydrates. These
changes result in micro-organisms being killed, as well
as the possibility of producing foods of improved
sensory and nutritional quality.
Industrial applications of h.- p. technology
The first commercial high-pressure processed product was a
high-acid jam, launched in 1990 by the Meida-ya Food
Factory Co., Japan. Since then several other pressuretreated products have been launched in the Japanese
market, including fruit sauces, juices and jellies. A highpressure processed orange juice is also available in France
and a pressure-treated avocado dip is available in the USA.
Pressurized fruit products are normally given a treatment of
around 400 MPa at 20°C.
It is claimed that the color and flavor of the fresh fruit is
maintained and there is only a slight decrease in vitamin
C content.
Yeasts and moulds, which are the main cause of
spoilage in fruit products, are relatively sensitive to
pressure, so the microbiological quality of the products
can be improved. However, enzymes such as
polyphenoloxidase, which causes browning, are
resistant to pressure and therefore can limit the shelf
life.
For these reasons the current commercial applications
of HHP as a preservation method have been limited to
high-acid, chilled foods where spore-forming bacteria
are unlikely to be a problem and enzymatic activity is
retarded by refrigerated storage.
However, extensive research and development
programmes are in progress in Japan, Europe and the
USA and it is likely that other foods, including fruit,
dairy, meat and fish products, will be launched into the
international market.
3. OHMIC HEATING
(a) Ohmic heating principle
Ohmic heating is the term used to describe direct
electrical resistance heating of food product by the
passage of mains frequency (50-60Hz) electric current
through the continuous flow of product (Fig. 3).
Fig. 3. Principle of ohmic heating
Depth of penetration is virtually unlimited and the extent
of heating is determined by the spatial uniformity of
electrical conductivity throughout the product and its
residence time in the heater.
The applicability of Ohmic heating is dependent on
product electrical conductivity. Most food preparations
contain a moderate percentage of free water with
dissolved ionic salts and hence conduct sufficiently well
for the Ohmic effect to be applied.
(b) Processing applications
The Ohmic heater was originally developed by the UK
Electricity Research and Development Center and in 1984,
APV Baker, secured a license for the heater system and
since then has undertaken substantial further development
with respect to the following specific applications within the
food processing industry:
- Aseptic processing of high added value ready prepared
meals for storage and distribution at ambient temperatures.
- Pasteurization of particulate fruit products for hot-filling.
- Pre-heating of food product prior to in-can sterilization.
- The hygienic production of high added value prepared
meals for storage and distribution at chilled temperatures.
A number of commercial systems are now
operating in the production of a range of high
added value food products. The benefits of
Ohmic heating are summarized in Table 1.
Table 1. Benefits of Ohmic Heating
-
Fresh tasting, high quality products with increased nutrient retention
due to minimal thermal and mechanical damage.
-
High levels of product safety due to minimum residence time
differences between liquids and particulates.
-
Low flow velocities and virtual absence of moving parts make Ohmic
heating the ideal process for delicate, shear sensitive products.
-
Low maintenance costs.
-
Continuous flow without hot heat transfer surfaces, thereby eliminating
plant fouling.
-
Rapid and even heating of both liquid and particles, minimizing heat
damage and giving vastly superior organoleptic properties.
-
Quietness of operation giving a better working environment.
-
Easy to control with fast start-up and shut down minimizing product
losses. A turndown facility is also available.
-
When combined with an aseptic filling system, product can be stored
and distributed at ambient temperatures, avoiding the need for costly
refrigeration.
• Brief description of:
OTHER NEW PROCESSING TECHNOLOGIES
(a) Dielectric Heating (Microwave or RF
Heating)
•
(b) Pulsed Electric Fields.
DIELECTRIC HEATING
• Dielectric heating: the techniques of Microwave
and radio frequency (RF) heating.
• Both are forms of electromagnetic energy
• Selection of RF (3 kHz-300 GHz) or Microwave (300
MHz-300 GHz) heating: depends on product
physical properties and process conditions
• Basic principle: If a material is placed in an electric
field alternating at radio or microwave frequencies,
heat is generating throughout the mass of the
material by the rapid reversal of polarization of
individual molecules.
•
Polarization types:
(a) Orientation (dipole) polarization (re-alignment of
molecules already permanently polarized due to
their chemical bonds).
(b) Space -charge (interfacial) polarization
(accumulation of charge at discontinuities within
the material due to the migration of charge
carriers under the influence of the applied
electromagnetic field.
•
Microwave or RF Heating?
Product’s physical properties, product’s shape,
products homogeneity, variation in loss factor
within the product and with temperature rise.
•
Applications of Microwave heating
1.
2.
3.
4.
•
Ready meal products.
Blanching.
Cooking.
Bulk product pasteurization.
Applications of RF heating
Typical application: Continuous
pasteurization of various products
(especially cooked meat products).
Advantages: reduced man powder, reduced
energy consumption, continuous
production, even heating, homogeneous
product, equipment savings.
PULSED ELECTRIC FIELD PROCESSING
• Electroporation: Pore formation (reversible or
irreversible in cell membranes exposed to highintensity pulsed electric field.
• Irreversible electroporation: the basis of the
pasteurization of food by means of PEF.
• PEF: Emerging technology (non thermal inactivation
of m/o) with a promising future (color, flavor, texture
& nutrients not affected).
• Can be used either as single technology or as a
hurdle in combination of various preservation
methods.
• Fundamental aspects of PEF
• PEF: Application of high-intensity electric field to food
product.
• Main application: pasteurization of a variety of
foods.
•
The PEF processing system consists of
1. A High Voltage power supply.
2. A Capacitor for Energy Storage.
3. A treatment Chamber.
•
The major technical drawback of PEF:
The dielectric breakdown of foods (when strength
of applied el. Field is equal to the dielectric strength
of the food).
Possible consequences: luminous spark, bubbles
generation, pressure increase, formation of pits on
the electrodes.
To avoid it: degassing and cooling of the food is
recommended.
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Σημείωμα Αναφοράς
Copyright Πανεπιστήμιο Ιωαννίνων, Διδάσκοντες: Κ.
Ακρίδα, Π. Δεμερτζής, Κ. Ρηγανάκος, Ι. Σαββαΐδης.
«Προχωρημένα Μαθήματα Επεξεργασίας και
Συντήρησης Τροφίμων. Νεοφανείς μέθοδοι
επεξεργασίας & συντήρησης τροφίμων (NOVEL
METHODS OF FOOD PROCESSING AND
PRESERVATION)». Έκδοση: 1.0. Ιωάννινα 2014.
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