Aw Theory 수분활성도 이론 > Hurdle
|Several years ago, hurdle technology was
developed as a new concept for the realization of safe, stable,
nutritious, tasty, and economical foods. It employs the intelligent
combination of different preservation factors or techniques
to achieve multi-target, mild but reliable preservation effects.
Mild processing of foods with hurdle technology.
Many promising hurdles have been identified so far, although
application of the idea in the food industry has been largely
restricted to the meat sector. Recent studies, however, emphasize
a much wider potential application, e.g., in bakery products,
fish, and dairy products. More specifically, the concept was
introduced into mild processing of fruits and vegetables. The
design of new hurdles such as gas packaging, bioconservation,
bacterocins, ultra-high pressure treatment, and edible coatings
aided this development.
Consumers want fresher food products.
Consumers demand fresher and more natural products. This prompts
food manufacturers to use milder preservation techniques and
could be stimulating the current trend to hurdle technology.
There is an urgent need for new or improved methods producing
stable and safe foods. The concept of hurdle technology addresses
Preservation factors are hurdles
to inhibit microorganisms.
Hurdle technology deliberately combines existing and new preservation
techniques to establish a series of preservative factors (hurdles)
that the microorganisms in question are unable to overcome (jump
over). These hurdles may be temperature, water activity, acidity,
redox potential, preservatives, and others. A crucial phenomenon
in hurdle technology is known as the homeostasis of microorganisms.
Hurdles disturb homeostasis.
Homeostasis is the constant tendency of microorganisms to maintain
a stable and balanced (uniform) internal environment. Preservative
factors functioning as hurdles can disturb one or more of the
homeostasis mechanisms, thereby preventing microorganisms from
multiplying and causing them to remain inactive or even die.
Food preservation is achieved by disturbing the homeostasis
of microorganisms. The best way to do this is to deliberately
disturb several homeostasis mechanisms simultaneously.
Multiple hurdles affect product
This multi-targeted approach is the essence of hurdle technology.
It is more effective than single targeting and allows hurdles
of lower intensity, improving product quality. There is the
further possibility that different hurdles in a food not only
have an added effect on stability, but can act synergistically.
Shelf-life of fermented sausage--an
Using hurdle technology, salami-type fermented sausages are
produced that are stable at ambient temperature for extended
periods. A sequence of hurdles is important at different stages
of the ripening process. The first hurdles used are the preservatives,
salt and nitrite, which inhibit many of the bacteria present
in the batter. Other bacteria multiply, use up oxygen and thereby
cause a drop in redox potential, which inhibits aerobic organisms
and favors the selection of lactic-acid bacteria. These bacteria
then proliferate, causing product acidification and an increase
of the pH hurdle. During the long ripening process of salami,
the initial hurdles gradually become weaker: nitrite is depleted,
the number of lactic-acid bacteria decreases, redox potential
and pH increase. However, since water activity decreases with
time it becomes the main hurdle.
An increasing list of hurdles.
Up to now, about 50 different hurdles have been identified in
food preservation. Apart from the most important and commonly
used hurdles such as temperature, pH, and water activity, there
are many others of potential value. Other hurdles include: ultrahigh
pressure, mano-thermo-sonication, photodynamic inactivation,
modified atmosphere packaging of both non-respiring and respiring
products, edible coatings, ethanol, maillard reaction products
and bacteriocins. Examples of foods preserved by combined processes
are fruit juices and heat-processed, cured meat products.