Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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METHOD AND APPARATUS FOR P~STEURISATION OR STliR~T.T.';~TION
OF HERBS AND SPICES
This invention relates to a method and apparatus for paste-lrising or
sterilising lherbs, spices and other materials prone to microbial spoilage.
Attempts have been made to develop methods for pasteurising or
sterilising herbs and spices involving heat treatment. Ho~/ve~t:r, these
methods have been found to be impracticable as the heat treatment step
results in tlhe mobilisatioll and/or destruction of the volatile substances
which give the herbs and spices their functionality and appeal.
Traditionally, therefore, herbs and spices have been treated by exposure to
ethylene oxide.
Un~ortunately, such ethylene oxide processes have certain
disadvantages. For example, it has been found that while such processing
can result in a reduction in the bacterial numbers in the product, they have
the disadvaLntages that bacterial and fungal spores commonly have a natural
resistance l:o this sterilant, so its effect is concentration dependant and longexposure times are required for penetration. Further, the exposure to
ethylene oxide of foods with high salt concelltrations has been reported to
produce reaction products, such as epichlorhydrin. which are potentially
toxogenic.
Thus, it is one object of the present invention to provide a method
and apparatus for effectively pasteurising or sterilising herbs, spices and
other materials prone to microbial spoilage, which has little or no adverse
effect on their functionality.
Accordingly, in a first aspect, the present invention provides a
3method for pasteurising or sterilising herbs, spices and other materials prone
to microbial spoilage comprising the steps of:
(1) cooling said herbs, spices or other materials to a temperature
less than about 0~C,
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(2) rapidly heating said cooled herbs, spices or other materials to
a pasteurising or sterilising temperature, and
(3) recooling said herbs, spices or other materials to about room
temperahlre,
wherein at least steps (2) and (3) are performed in an enviromnent(s) having
a pressure of greater than 1 Bar.
Perfornling steps (2) and (3) under pressures greater than 1 Bar,
prevents loss of volatiles from the materials being treated. In addition, use
of such pressure in these steps is believed to positively contribute to colour
fastness and the reduction of microbe numbers. Preferably, the pressures
applied in steps (Z) and (3) are greater than 3 Bar. Once step (3) is
concluded, the environment within which the materials are contained, may
be returned to atmospheric pressure.
Step (1) is preferably a rapid cooling step and may be completed in
0.05 to 5.0 minutes, more preferably 0.5 to 3.0 minutes. During step (1) the
herbs, spices or other materials are preferably cooled to a temperature less
than about-70~C, more preferably, to a temperature of about-170~C. It is
also preferred that step (1) be performed in an environment(s) having a
pressure greater than 1 Bar.
2 0 The rapid heating step (2) may be achieved by the application of
heat from any source, radiative, conductive or convective, which may be
generated by combustion! by induction or dielectric heating with
electromagnetic radiation, microwave, by infra red irradiation, or any other
means. The heat is preferably applied for 0.05 to 5.0 minutes, more
preferably 0.1 to 3.0 minutes or longer dependent on the material and its
microbial bioburden.
The recooling step (3) is also preferably a rapid cooling step and may
be completed in 0.05 to 5.0 minutes, more preferably 0.1 to 2.0 minutes.
In a second aspect, the present invention provides apparatus for
3 0 conducting the method of the first aspect of the invention.
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The method may be performed on batches of materials or
continuously. Thus, an apparatus according to the invention for batch
treatments may comprise;
a vessel comprising,
an ilnlet means through which a batch of herbs, spices or other
materials susceptible to microbial spoilage may be introduced,
means for cooling said batch to a temperature less than about 0~C,
means for rapidly heating said cooled batch to a pasteurising or
sterilising temperature,
means for recooling said batch to about room temperature,
means for applying and/or regulating a pressure within the vessel
during heating and recooling of greater than 1 Bar, and
outlet means for removfilg the treated batch from said vessel.
Prei~erably, the apparatus for batch treatments comprises a pressure
15 ~essel constructed to sanitary standards which feeds out through a valve to
an aseptic filer sourced commercially. A batch of material for treatment is
introduced through an infeed hopper equipped with a valve into the vessel
were stirring is instigated by a motorised stirrer. The product is rapidly
cooled to less than O"C by the cooling effects of expallding coolant, sparged
20 through the material being treated, which may be liquefied nitrogen,
liquefied carbon dioxide or a mixture of both, or other gas, either in
combinatiom or alone and may be humidified prior to application.
Immediately the desired cooling step temperature (e.g. temperature of
between -70~C and -170~C) and pressure (e.g. pressure greater than 1 Bar) is
2s reached, a pressure regulating valve is closed, the inflow of coolant reducedand then controlled to maintain a pressure of greater than 1 Bar, more
preferably greater than 3 Bar. While this pressure is maintained, the
material is exposed to heating for a treatment duration sufficient to reduce
the total microbial content by the desired factorr dependant on the bacterial
30 and fungal bioburden of the infeed material.
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The applied heat source is preferably arranged on the vessel so as to
optimise the application and penehration of the heat, thus minimi.sing the
treatment time needed and the resultant product damage. Fast response
sensitive pressure and temperature sensors may be provided to monitor
5 progression of the hreahnent and the outputs from these are feed to a control
circuit which in turn regulates the application of heat and pressure. The
control circuit typically includes a progrRmm~hle logic conhroller and a
supervising, control and data acquisition computer.
An apparatus according to the invention for continuous treatments
10 may comprise:
a first vessel comprising. an inlet means through which herbs, spices
or other materials susceptible to microbial spoilage may be continuously
introduced, and means for cooling said herbs. spices or other materials to a
temperature less than about 0~C;
a second vessel comprising, means for rapidly heating said cooled
herbs, spices or other materials, and means for applying and/or regulating a
pressure of greater than 1 Bar; and
a third vessel comprising means for recooling the herbs, spices or
other materials to about room temperature, means for applying and/or
2 0 regulating a pressure of greater than 1 Bar, and outlet means for removing
the treated herbs, spices or other materials from said vessel,
wherein said first vessel is connected to said second vessel and said second
vessel is connected to said third vessel, the arrangement being such that the
herbs, spices or other materials inhoduced into the first vessel may be
25 continuously and progressively transferred to the second and then third
vessels.
The material treated by this invention may be, in addihon to herbs
and spices, for which it was specifically developed, other foods,
pharmaceuticals, leaf material in various forms for example tobacco or
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various free flowing powdered materials which are prone to microbial
spoilage.
The inventioll will llOW be further described by way of the following,
non-limiting examples and accompanying ffgures.
lBrief Description of Accompanvin~ Fi~ures
Figure 1 provides a schematic elevational representation of a
preferred apparatus according to the invention for batch treatments of herbs
and spices.
Figure 2 provides a schematic elevational representation of a
preferred apparatus according to the invention for continuous flow
treatments of herbs and spices.
EXAMPLE 1: Batch Apparatus
As shown in FiEsure 1, the sanitary designed pressure vessel (1) has a
tapered conical base, is equipped with a motorised stirrer (2), infeed
hopper/valve (3) and outfeed hopper/valve (4). A safety vent (7) is also
lProvided.
A preweighed batch of material to be treated is introduced through
2 0 ;,nfeed hopper/valve (3) and stirring commenced with stirrer (Z). Coolant is introduced through sparging ports (10) and allowed to escape through a
lpressure regulator valve (6) until the desired cooling step temperature is
recorded by the thermocouple (9) in contact with the material being treated.
In the next stage, coolant gas flow is reduced and the pressure
25 regulating valve (6) is servo driven to maintain the desired pressure (greater
than 3 Bar), sensed by a pressure transducer (8). Heating is then
commenced, applied from heaters (5) to a temperature of between 70-90~C
i~or pasteurisation and between 105-150~C for sterilisation. The duration of
exposure is optimised to provide the maximum reduction in bioburden
3 0 while maximising the flavour and other functionality of the material being
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treated. Typically, heating energy/batch mass can be balanced to attain
treahnent times of only 0.1-3.0 minutes. This short time/high temperature
processing yields at least 4 and often 6 log reductions in microbial
bioburden.
At the end of the penetrative heat treatment stage the protective post
treatment cooling is comlllenced. This is mandatory to protect the delicate
aromatic flavour and functional components. Cooling is immediately
effected while still under pressure by again controlling cooling inflow at
sparging ports (10) and its release at the pressure regulator valve (6). Rapid
cooling reduces the temperature of the material being treated to less than
20~C and then coolant inflow is ceased and the pressure within the vessel is
allowed to return to atmospheric pressure.
Stirring is continued throughout the process and until the material is
discharged directly into the aseptic filler located at (11).
EXAMPLE 2: Continuous Flow Apparatus
In an alternative arrangement the steps of the method according to
the invention may be applied to material conveyed through three vessels
sirmilarly equipped to the batch process so that each stage of the treatment
2 0 can be applied in a continuous manner. Each vessel is separated by rotary
locks and each vessel has a discrete conveyor mechanism. A suitable
apparatus is depicted in Figure 2.
The apparatus shown in Figure 2 employs open conveyor belts,
however, it is to be understood that screw conveyor(s) could be used as an
2 5 alternative.
The components (3)-(6), (9) and (10) shown in Figure 2 are as
described in Example 1.
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: 7
E~A~IPLE 3 - Preli-ninRrv Tests
Test A
Aim:
To assess the potential of applying heat to herbs and spices to reduce
5 the microbial bioburden.
~ethod:
Target Material: Basil
Whole peppercorns
both with known high bacterial bioburden
(greater than lo8 cfu/gram)
Equipment:
A device was constructed for these trials which consisted of a plastic
pressure tank from a garden spray with a volume of approx. 3 litres. This
was chosen so that it had adequate strength to allow for the pressures. The
15 pressure entry port was modified by the installation of a car tyre valve. A
screw downt O-ring sealed inlet port was present, normally for the addition
of spray and water. Also present was a safety pressure release valve which
was strengthelled appropriately.
The device, which appeared to be made from natural high or
2 0 ultrahigh density polyethylene or similar plastic, was tested at pressures
greater than intellded to be reached in the test and found to withstand in
excess of 3 Bar. even when heated.
Heating was effected in a 750 Watt domestic microwave oven
equipped with a rotating carousel. This was adapted to hold the plastic
25 vessel which was microwave transparent and did not heat appreciably when
exposed to microwave energy on its own. It was found that if it was loaded
with approx. 15ml of water and exposed for 5 minutes at 2 Bar overpressure
all contact surfaces were sterilised and then the vessel could be dried out
~ with the continuatioll of the heating at atmospheric pressure. This process
3 0 was employed before each new trial.
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To overcome some initial uneveness of heating a system was devised
to tilt the vessel as it was rotated by the carousel, thus mixing the target
material during exposure.
Exposur~s:
100 gram samples of each target material was exposed to varying
times and microwave powers and the temperatures achieved were taken
with an electronic thermometer equipped with a fast response
thermocouple.
This was repeated with 1 and 2 Bar overpressure generated with
compressed air and read by an external pressure gauge to assess the effect of
attained pressure on tlle temperatures achieved by varying the times and
microwave power.
From this data a range of exposures were chosen so that a spectrum
of attained temperatures ranging from 70 to 140 deg. C could be predicted
and duplicate exposures of each target material were made with 1 and z Bar
compressed air overpressure. This was released immediately after the
exposure was completed.
Results:
Observations: - condensation was present but minim~l.
2 0 -a noticeable volatile aroma was present on release
of the overpressure.
Target Material:
- loss of at least 30~/O of the organoleptic properties of
the material was estimated. Particularly effected
were the high flavour notes and after taste.
Microbiological Analyses:
- Reduction in microbial bioburden paralleled time
and temperature with greater than 6 log reductions in
Standard Plate Count achieved by the longer times
and temperatures employed.
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~Conclusion.s:
Significant reductions in microbial counts were observed, easily
~ achieving product pasteurisation and commercial sterility.
5 Test B
Aim:
To develop a means of preventing the loss of volatiles during heating
of the herbs and spices by the use of protective coolillg and overpressure.
Method:
Target l~laterial: As for Test A.
Equipment: As for Test A but employfilg overpressure
generated from bottled compressed food grade
carbon dioxide controlled by a regulator.
This was then used to assist with cooling, while
maintaininEs the overpressure, after the target
material had been exposed to heat. Additional
cooling was provided by immersing the vessel
in an ice bath.
Exposures: As for Test A.
Results:
Observations: - condensation was markedly reduced as was
the volatile aroma.
Target Material: - the material was now colour fast.
- there was a considerable reduction in the
2 5 organoleptic profiles.
Microbiological Analyses:
- Not significantly different from Test A
Conclusions:
~ Without losing microbial effect a definite improvement in the
3 o condition and functionality of the materials were seen following treahnent.
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While this was thought to be of some value, means by which the
losses of volatiles could be further reduced were sought.
Test C
5 Aim:
To further enhance the reduction of volatile loss by the use of a
precooling step in the process.
Method:
Target ~Iaterial: As for Test A.
Equipment: As for Tests A and B plus either;
- precooling with carbon dioxide sparging (-70
deg. C) in the vessel, or
- immersion in liquid nitrogen (-170 deg. C).
Exposures: As for Tests A and B.
Results:
Observations: - As for Test B.
Target ~Iaterial: - IlO discernible loss in volatiles or functionality
were detectable by organoleptic evaluation for
either means of precooling.
Microbiological Analyses:
- reductions in microbial bioburden of greater
than 7, approaching 8 log in the case of the
nitrogen precooled material.
Conclusions:
2 5 The aim of achieving a commercially significant reduction in the
loss of organoleptic functionality of herbs and spices, while maintaining
reductions in the microbial bioburden was achieved.
It will be appreciated by persons skilled in the art that numerous
variations and/or modifications may be made to the invention as shown in
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11
the specific embodimellts without departing from the spirit or scope of the
inventioll as broadly described. The present embodiments are, therefore, to
be considered in all respects as illustrative and not restrictive.
