1. Field of the Invention
The present invention relates to a process and apparatus plant for treating food products with ozone, aiming especially to bleach or decolorize, sanitize and deodorize the products thus treated.
2. Description of the Related Art
The literature relating to the ozone treatment of food products, in particular in the field of seafood (fish, crustacea, etc.) is known to be very extensive, and the reader may be referred for instance to documents FR-385,815, EP-294,502, FR-797,928 or else U.S. Pat. No. 4,559,902.
The use of ozone has thus been most particularly described in the case of the treatment of fish meat with the objective of sterilizing and deodorizing the meat, the treated fish meat coming from the recovery of the residues remaining on the bones and the head after filleting the fish, from fillet cutting scraps or even from actual fillets, the meat in question being eventually used as raw material for the manufacture of various products, such as surimi seafood products or other fish pastes, terrines or steaks.
A typical apparatus for the recovery and treatment of such fish meat for producing what those skilled in the art call "base surimi" seafood therefore comprises the following steps:
a step of separating the meat from the bones and heads (resulting in a first crude pulp, which is ready to use if necessary); PA1 one or more operations of washing in water which optionally is slightly acidified, each washing operation being followed by a draining step (resulting in a washed pulp ready to use for some applications); PA1 a refining step making it possible, by passing the material over a screen, to separate the proteins from the impurities (skin residues, etc.); PA1 a final operation of mechanical water/meat separation carried out by centrifugal sedimentation or screw pressing, resulting in washed and refined fish meat ready to use (base surimi seafood). PA1 to improve the productivity of ozone-treated food products; PA1 to improve the quality of the transfer of ozone to the food product to be treated (it is known in practice that at the present time only 15 to 60%--depending on the plants available--of the ozone injected is actually transferred to the food product in question); PA1 to avoid, nevertheless, the risk of impairing the product (by way of illustration, mention may be made here of the risk of impairing fish meat by turning it brown because of local overdosing); PA1 to reduce overall the number of washing steps carried out in the user treatment chain; PA1 to achieve higher quality in the product. PA1 a) a supply of the initial solution containing the product is used; PA1 b) a pumping device is used which allows the initial solution to be taken under pressure to a contactor; PA1 c) an ozone-containing treatment gas mixture is injected into the initial solution, the injection taking place at one or simultaneously at several of the following locations: PA1 the ozone dose used for the treatment, expressed in grams of ozone per kilo of treated product, lies within the range going from 0.2 to 2 g/kg (taking into account not only the specificity of the treated product and of the desired treatment, but also, for example, the national legislation governing each user site). PA1 The ozone content in the treatment gas mixture lies within the range going from 10 to 200 g/m.sup.3, preferably lies within the range going from 20 to 120 g/m.sup.3 and more preferably within the range going from 40 to 100 g/m.sup.3 of mixture. PA1 The composition of the initial solution treated satisfies a degree of dilution corresponding to 1 volume of product per 0.5 to 10 volumes of water, but preferably to a degree of dilution corresponding to 1 volume of product per 1 to 5 volumes of water and even more preferably to a degree of dilution corresponding to 1 volume of product per 3 to 5 volumes of water. PA1 a) a supply of the initial solution to be treated; PA1 b) a pumping device suitable for the initial solution to be taken under pressure to a contactor; PA1 c) a supply of a treatment gas mixture which contains ozone; PA1 d) means for injecting the treatment gas mixture into the solution, allowing the mixture to be injected at one or simultaneously at several of the following locations:
The results of animal meat bleaching are commonly monitored by industrial sites by color measurements, called colorimetry, with readings of the brightness or whiteness, of the red/blue index and the yellow/green index, for example using the conventional L*/a*/b* system (CIE 1976 reference), the factor L being expressed in %.
For reasons of simplification, throughout the following text reference will be made, indiscriminately, to the L/a/b or L,a,b system or to their results, clearly keeping in mind that such references pertain to the abovementioned evaluation system.
The desired objectives, in terms of colorimetry, throughout the various washing operations carried out, are generally (depending on the product in question) an increase in the whiteness, a decrease in the redness and the absence of any change in yellows/browns or even a reduction in the latter.
The aforementioned document EP-A-284,502 describes in particular an apparatus for treating animal meat, consisting of a shell in which a hollow tube provided with a helical partition rotates, the whole assembly constituting a transverse screw, the free volume existing between the internal walls of the outer shell and the external helical partition of the hollow tube constituting a splashing chamber through which the meat/water mixture to be treated travels, the gas mixture containing ozone being injected into the hollow tube and diffusing outward into the splashing chamber through a plurality of diffusers located along the transfer screw.
The example provided by the document indicates a meat transfer rate inside the system of about 1 cm/s, which gives, taking into account the geometrical characteristics of the apparatus, a meat output of about 1 liter/minute.
Apart from the complexity of the system described in that document, work successfully carried out by the Applicants has allowed them to show that, because of the dynamics created in such an apparatus, the performance in terms of contact between the fish meat and the dissolved ozone is insufficient (no intimate mixing between the meat and the gas), leading to solid/gas demixing, but also, as a consequence, a lack of effectiveness over the entire diameter of the screw.
It may also be added that the use of gas injection pores for injecting the gas seems not to be very compatible with the cleanability requirements commonly practiced in the food industry (zones of the screw that are difficult to reach by a cleaning agent and potential blocking of the porous injectors with food material).