Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
2 1 0 3 7 7 Ll
This invention relates to a heat treatment
process for a food product, to an apparatus for carrying
out the process and to applications of the process.
US 3,494,724 describes a process for destroying
or inactivating microorganisms or enzymes in solid or
liquid materials/ in which the material in question
accommodated in a confined zone permeable to microwave
and infrared radiation is simultaneously subjected to
radiation of the two types through an atmosphere of
steam under pressure, the steam under pressure being
intended to prevent rupture of the walls of the confined
zone, more particularly in the form of a pack of thermo-
plastic film.
US 3,537,862 describes a process for the produc-
tion of pastas intended for rapid cooking in which thin-
walled pastas are precooked ~lith steam while, at the
same time, being kept moist by intermittent or con-
tinuous spraying with water from above.
The problem addressed by the present invention
was to provide a process and an apparatus which would
enable a food product to be heat-treated, more particu-
larly for pasteurization, sterilization, blanching or
cooking, directly, i.e. without the product having to be
accommodated in a confined zone, such as a pack, effec-
tively, i.e. intensively and rapidly, and under control,i.e. without any adverse effect upon the texture,
colour, water content or organoleptic qualities of the
product.
To this end, the process according to the inven-
tion for the heat treatment of a food product is charac-
terized in that the product is su~jected to infrared
radiation in a steam atmosphere.
The apparatus for carrying out the process
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according to the invention comprises a heat treatment
tunnel, a perforated conveyor belt passing through the
tunnel, infrared elements above and below the conveyor
belt in the tunnel and steam injection nozzles above
and/or below the conveyor belt in the tunnel.
By virtue of the process and apparatus according
to the invention, food products intended in particular
to be subsequently packed in sterile packs, such as for
example finished or semifinished confectionery and
bakery products, fresh pastas, fruits, vegetables or
mushrooms, can be heat-treated, more particularly
pasteurized, sterilized, blanched or cooked, in a
direct, effective and controlled manner.
In the context of the invention, the expression
"in a steam atmosphere at a temperature of 170C, for
example, at atmospheric pressure" is understood to be
the atmosphere which prevails, for example, in a tunnel
open at both ends into which saturated steam is injected
at atmospheric pressure, the steam then being brought to
the temperature of 170~C under the effect of the infra-
red radiation.
T~ carry out the process according to the inven-
tion, the product may be subjected, for example, to
infrared radiation of 0.05 to 2 kWh and preferably 0.1
to 1 kWh per kg of product for 5 to 300 s in a steam
atmosphere at 100 to 200C under atmospheric pressure.
The treatment is preferably carried out continuously by
passing the product through a tunnel in which infrared
radiation and a steam atmosphere are simultaneously
maintained.
In one particular embodiment of the process
according to the invention, sterile water is also
sprayed simultaneously onto the product. Accordingly,
the product may be simultaneously sub~ected to sprayinq
with droplets of water in contact with steam and infra-
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red radiation. The water thus sprayed may be cold, warm
or hot, for example depending on whether it is desired
to cool or moisten the surface of the product.
The process according to the invention is parti-
cularly suitable for the pasteurization of, for example,
confectionery products, such as sliced ~ake or pastry
bases intended to be subsequently used for the prepara-
tion of refrigerated desserts, or bakery products, such
as long-life bread, particularly in the form of sandwich
loaves.
The process according to the invention enables
such products to be pasteurized without their appearance
being altered, i.e. without browning, and without their
texture being affected, more particularly without the
products drying out.
The process according to the invention is also
particularly suitable for the blanching of pastas, more
particularly filled pastas, such as for example freshly
prepared ravioli or tortellini.
The process according to the invention enables
such products to be blanched without an adsorption of
moisture so that their surface does not become crackly,
nor does their colour change, thus enabling the time
required for subsequent drying, for example, to be
reduced.
Accordingly, the apparatus according to the
invention comprises a heat treatment tunnel and a
perforated conveyor belt passing through the tunnel from
end to end. This conveyor belt may be formed, for
example, by pivotally interconnected metal grill ele-
ments or by a steel wire mesh.
The conveyor belt preferably follows a flat upper
path which extends of this side of and beyond the tunnel
for the loading and unloading of the product to be
treated which is preferably in the form of separate
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articles. The conveyor belt may follow a lower path
which passes, for example, through fixed drive means on
a frame.
Inside, the tunnel may be provided, for example,
with a row of infrared elements above the belt and with
another row of infrared elements below the belt. These
elements may be quartz tubes accommodating tungsten
coils each arranged, for example, in a parabolic groove
of a metal reflector.
In one particular embodiment of the apparatus
accoxding to the invention, infrared elements are also
provided above and/or below the conveyor belt just after
the tunnel exit so that an additional treatment step,
more particularly drying, can be carried out solely with
infrared radiation.
The tunnel may be equipped with steam injection
nozzles in the form of transverse horizontal tubes each
drilled with a row of holes which may be directed
towards the entrance, exit, top or bottom of the tunnel,
for example depending on the position of the tubes.
Similarly, one or more nozzles for spraying
sterile water may be provided above and/or below the
conveyor belt in the tunnel.
In one preferred embodiment of the apparatus
according to the invention, separation elements perme-
able to infrared radiation, but impermeable to water and
steam, for example pyroceramic plates, are provided
between the infrared elements and the conveyor belt in
the tunnel, thus horizontally defining a heat treatment
chamber.
In one variant of this preferred embodiment,
channels may be provided beneath the heat treatment
chamber in an extension of walls vertically defining
this chamber for the removal of condensates which can
trickle along the inner surface of the walls mentioned.
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In this variant, the separation element provided
below the conveyor belt may have a slightly recessed
periphery relative to the lower edge of the walls for
removal of the condensates which can drip into the
interior of the heat treatment chamber.
The apparatus according to the invention is
described in detail in the following with reference to
the accompanying drawings, wherein:
Figure 1 is an oblique semitransparent perspec-
tive view of a preferred embodiment of the apparatus.
Figure 2 is an oblique perspective view of oneparticular embodiment of the apparatus according to the
invention.
Figure 3 is an oblique perspective view of one
variant of the preferred embodiment of the apparatus
according to the invention.
Referring to Fig. l, the apparatus according to
the invention comprises a heat treatment tunnel l and a
perforated conveyor belt 2 which passes through the
tunnel from end to end, entering through an entry gate
3 and leaving through an exit gate 4.
The conveyor belt 2 is made of steel wire mesh.
It follows a flat upper path which extends on this side
of the entry gate of the tunnel 3 for loading the
product treated and beyond the exit gate 4 of the tunnel
for unloading the treated product. That part of the
flat upper path which is situated in the tunnel and
which has not been shown in the interests of clarity of
the drawing is situated at the same level and in the
axis of these extensions. The belt follows a lower path
(no~ shown) which passes through drive means fixed to a
frame.
In the tunnel l, a row of transverse infrared
elements 5 is provided above the belt and another row of
transverse infrared elements 6 is provided below the
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belt. Each infrared element is a quartz tube 7 which
encloses a tungsten coil and which is arranged in a
parabolic groove of a metal reflector 8. These elements
emit infrared radiation having a wave length of 0.7 to
25 u.
In the tunnel 1, steam injection nozzles 9-14 are
provided above and below the conveyor belt 2 in the form
of transverse horizontal tubes each drilled with a row
of holes. These holes are horizontally directed up-
stream for two tubes 11 and 14 provided near the exit
gate 4, horizontally dowstream for two tubes 9 and 12
provided near the entry gate 3, vertically upwards for
one tube 10 provided below the belt in the middle of the
tunnel and vertically downwards for one tube 13 provided
above the belt in the middle of the tunnel.
A water spray nozzle 15 is provided in the tunnel
1 near the entry gate 3 above the conveyor belt 2. This
nozzle is directed in such a way as to project a hori-
zontal curtain of water droplets downstream.
Finally, separation elements permeable to infra-
red radiation, but impermeable to water and steam are
provided in the form of pyroceramic plates 16 and 17
between the infrared elements 5 and 6 and the conveyor
belt 2 in the tunnel, thus horizontally defining a heat
treatment chamber 18.
In the particular embodiment shown in Fig. 2, the
apparatus further comprises infrared elements above (19)
and below (20) the conveyor belt 2 just after the exit
gate 4 of the tunnel 1.
In the variant of the preferred embodiment shown
in Fig. 3, the apparatus according to the invention
additionally comprises channels 21-24 beneath the heat
treatment chamber 18 in the vertical extension of walls
25-28 vertically defining that chamber. The ends of an
3S upstream transverse channel 23 open above the upstream
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ends of longitudinal channels 22 and 24 while the
downstream ends of the longitudinal channels open above
the ends of a downstream transverse channel 21. The
longitudinal channels are slightly inclined upstream
while the transverse channels are slightly inclined on
the same side to facilitate removal of the condensates
which can trickle along the inner surface of the walls
25-28.
Similarly, the separation element situated
beneath the conveyor belt (not shown) is slightly
inclined in relation to the horizontal plane both down-
stream and on the same side as the lateral channels 21
and 23 and has a periphery (not shown) slightly recessed
in relation to the lower edge of the walls 25-28 for
removal of the condensates ,which can drip into the
interior of the heat treatment chamber 18.
The process according to the invention is illus-
trated by the following Examples in which percentages
and parts are by weight, unless otherwise indicated.
ExampleR 1 and 2
Raviolis made from hard wheat pasta filled with
minced meat and having a water content of 33% are
blanched in an apparatus similar to that described with
reference to Fig. 3 of the accompanying drawing.
The conveyor belt has a width of 0.3 m. Above
and below the conveyor belt, th~ rows of infrared
elements have a length of 0.7 m. The raviolis are
arranged at regular intervals on the conveyor belt so
3~ that they do not overlap, which represents approximately
1 kg raviolis per m conveyor belt. The speed of travel
of the conveyor belt is adjusted in such a way that the
raviolis are subjected to the infrared radiation for 52
s or 76 s. The strength of the radiation is adjusted to
different values. In addition, an atmosphere of steam
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at approximately 120C under atmospheric pressure is
maintained in the tunnel.
After the treatment, the temperature reached at
the centre of the filling, the water content of the
raviolis and the weight losses undergone during the
treatment are determined. The results obtained are set
out in Table I below.
T~ble I
10 Example Dura- IR radi- Temper- Weight Water
No. tion ation ature of loss content
s power filling % %
kWh/kg C
1 52 0.13 77-80 0.4-0.5 32.5-33.0
2 76 0.14 87-90 0.8-0.9 31.9-32.2
The raviolis thus blanched show the same surface
state and the same organoleptic properties and absorb
hardly any water during the treatment.
The raviolis may then be dried in a controlled-
humidity hot air tunnel to reduce their water content
below 30% before being packed in sterile packs.
Ex~mples 3-5
Slices of Genoa cake approximately 9 mm thick and
approximately 60 mm in diameter and weighing approxi-
mately 6.2 to 6.4 g are pasteurized in an apparatus
similar to that described with reference to Fig. 3 of
the accompanying drawing, of which the conveyor belt has
a width of 0.3 m and of which the rows of infrared
elements have a length of 0.7 m. These slices are
intended to be packed in sterile packs before being used
in the preparation of desserts. ~efore the treatment,
they have a water content of 7.3 to 8.2% and a water
activity of 0.49 to 0.52. Their beige-brown colour is
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characterized by a component L of the system of coor-
dinates L, a, b of approximately 57 for the upper
surface and approximately 50 for the lower surface.
The slices are then arranged on the conveyor belt
Sat regular intervals without overlapping.
Three different treatments are carried out at
respective rates of 6, 12 and 32 kg product per h in an
atmosphere of steam at 170~C under atmospheric pressure
while approximately 4 l/h sterile water at ambient
10temperature is sprayed into the tunnel.
During the first treatment, Example 3, the
product is first subjected to infrared radiation of 0.16
kWh/kg for 30 s and then to radiation of 0.12 kWh/kg for
90 s.
15During the second treatment, Example 4, the
product is first subjected to radiation of 0.22 kWh/kg
for 15 s and then to radiation of 0.06 kWh/kg for 45 s.
During the third treatment, Example 5, the prod-
uct is subjected to radiation of 0.28 kWh/kg for 23 s.
20The surface temperature of the slices on leaving
the tunnel, their water content, their water activity,
their weight and the component L of the colour of their
upper surface and their lower surface are all determined
for each treatment. The results obtained are set out in
25Table II below.
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o o
S ~O N
~rJ N t~ ~
X o ~ D O U)U~ ~
~n
U~
~1
U~
~D 3 3 ,N~ D o ,I~
N~D I 1 1` 1~tl`
ta ~ o ~ r ~ ~ ~
X ~ ~ o ~ N
O O ~ I` O~)
U~
O O
O ~t~
~ ~ ~ O
~a _I,1 co N ~ ~ ~
W o o ~/1~ o ~u~~r
O N ~ l~
N a~
F~ 6 ~ ~ N
U Uli
._
-
\" a~ ~D
O
O
a~ h
u~ S~ ~ ,1 h ~~1
.~ ~ OU~U~
a ~ h h
6 ~ ~ ~ VG~
/D ~ ~ h ~ ~ ~ 3
h O~ au ~ X
h E~~ ~ Q) 3 ,~ 3
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Measurements during the treatment also show that
a temperature of 100C at the centre of the slices is
reached very quickly, namely in 34 s, 20 s and 17 s for
Examples 3, 4 and 5, respectively.
5The results of strict microbiological examina-
tions show that particularly effective pasteurization is
obtained with each of the treatments of Examples 3 to 5.
As can clearly be seen from Table II, this
effective and rapid pasteurization is obtained without
10any significant effect on the physical and organoleptic
characteristics of the product or on its appearance.
Example 6 and 7 and Comparison Example
Using the apparatus described with reference to
15the accompanying drawing, as in the preceding Examples,
slices of Genoa cake are subjected to two treatments
under conditions similar to those described in Example
5, except that 5 l/h as opposed to 4 l/h sterile water
are sprayed in Example 6, no water at all is sprayed in
20Example 7 or in the Comparison Example and the ambient
atmosphere with no steam is used in the Comparison
Example.
The surface temperature of the slices on leaving
the tunnel, the weight losses undergone, the water
25content and the water activity are all determined, the
colour of the slices being visually evaluated. The
results obtained are set out in Table III.
2 1 0 3 7 7
x
o
~ U) h
D. I I ~ 3
E~ ~ I` I`r~ O
O t`l . h
t.) ~1 ~ ~ o
~n
o
~o
~ I` ~J
X
X
13 1~ a5 I h I t
X ~
O U~ ~1 ~ O
r7
C~
o . ~
~S r~ .,,
~D ~ h t~
3 ~ ~ O
--I X a~
3 1~
h I O ,~:
X ~ f~
o In v~ ~
0
r~ .
~ o
X
O ~ ~ ,1
a~ 0 ~ Q)
.~ 3 o ~r R
x ~ ~ I
h S~ ~ co h I ~ 3
E3 f~ ~1 0 C~ d' O
t: O ~ h
P u ~ o ~ D o m
dP
h :~
O
~
0 h ~1 ~ ~
H ~ ~
H ~ O ~ ~ O
o o\ U
E~ ~ U S~ h
O ~ .C h h:~
~4 ~ C: h ~ 0 ~ ~~1
~1 o ~ ~J ~ x ~ o(~,a o
U U~ ~ ~ o 3 rJ 3 ~
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The findings for the products of Examples 6 and
7 are the same as those for the products of Examples 3
to 5 above. By contrast, it can be seen from this Table
that the slices of the Comparison Example are distinctly
dryer and browner than they were before the treatment
