EP0637918A1

EP0637918A1 - Surface sterilisation by laser treatment

Info

Publication number: EP0637918A1
Application number: EP93911871A
Authority: EP
Inventors: Michael Francis 21 Scotsdown Road Foley; Robert Marc 11 Roman Court Clement; Neville Richard 61 Tan-Y-Lan Terrace Ledger
Original assignee: Minister of Agriculture Fisheries and Food UK
Current assignee: Minister of Agriculture Fisheries and Food UK
Priority date: 1992-04-27
Filing date: 1993-04-27
Publication date: 1995-02-15
Also published as: BG99133A; KR950701193A; FI945035A0; ZA932956B; AU5155293A; GB9420400D0; SK128294A3; BR9306293A; IL105522A0; HUT71647A; JPH07506744A; GB9303841D0; GB2280371B; NZ252710A; GB9209103D0; FI945035A; BG61377B1; GB2280371A; HU9403018D0; CN1079626A

Abstract

The present invention relates to a method of treating substrates for the purpose of reducing the population of contaminant organisms associated with them; particularly to treatment of foodstuffs, propagative materials and items intended for use in veterinary and medical applications. The method directs laser radiation at the substrate whereby the type and amount of laser radiation are selected such as to render organisms associated with the substrate inviable while leaving the desired properties of the substrate itself substantially unchanged. Apparatus suitable for treating a variety of substrates are disclosed, with a source of laser radiation (9, 28) and means (26, 27, 29) for handling the substrate (24).

Description

SURFACE STERILISATION BY LASER TREATMENT

The present invention relates to a method of treating substrates for the purpose of reducing the population of contaminant organisms associated with them; particularly to treatment of foodstuffs, propagation materials and items for veterinary and medical end uses.

Extensive fungicidal and pesticidal treatment of plant materials, eg. fruit, vegetables and grains, is presently carried out for the purpose of precluding unwanted contamination. The treatment is often environmentally undesirable, potentially hazardous to the consumer of the product and is somewhat inefficient in eradicating certain parasitic growth, particularly of fungi. Similarly many animal products must be treated prior to sale to reduce the numbers of contaminating microorganisms to an acceptable level for the intended final use. For example eggs and poultry products are often dipped in bactericidal solutions for eliminating bacteria such as salmonella and listeria.

Further to these chemical treatments, physical sterilization treatment are routinely applied to products for use in consumer, veterinary or medical applications. For example, sterilization using microwaves has been applied to treatment of mushroom casing, while high pressure steam treatment forms the basis for treatment of medical instruments in autoclaves. These treatments are all potentially hazardous and/or require significant amounts of time to achieve optimal effect. Furthermore where the end product is a foodstuff or chemical entity its structure may be altered to the detriment of desirable qualities such as flavour, texture, efficacy and, eg for seeds, viability.

US 3817703 uses high powered lasers to sterilise laser transmitting liquids, wherein the power denisty used is at least 10⁵ Watts cm^"2 and is preferably 10⁸-10¹⁰ Watts cm^"2. Such method is applicable to light transparent materials such as wines, but is completely inappropriate

SUBSTITUTE SHEET for application to materials which are light absorbent, particularly those substantially opaque to laser light or which absorb it in part.

The present inventors have now provided a novel method capable of being applied to all the above substrates and others, whereby contaminant organisms are rendered inviable in short time without the disadvantages of the aforesaid methods and without affecting the desired qualities of the end product or leaving environmentally or physiologically damaging residues thereon. Furthermore, in certain applications, such as in the inhibition of some parasites, eg. fungal growth, the method is more efficient than previously used treatments.

The present method differs from the known laser approach in that it uses thermal laser effect to raise a contaminant organisms temperature above a critical level for a sufficient time to render it inviable. This temperature will vary from organism to organism, but is approximately 45°C for many bacteria and fungi. Using heated media such as steam, or using radiation eg. microwaves, the temperature of the substrate will also be raised to levels which are inappropriate for end product use. In the present method the substrate, with the optional exception of its surface, remains unaffected by the treatment while surface organisms are heated to the aforesaid inviability.

In its broadest aspect the present invention provides a method of treating a substrate substantially opaque to laser radiation or unable to transmit laser radiation without absorbing substantial amounts thereof, for the purpose of reducing levels of contaminating organisms associated with its surface, comprising directing laser radiation at the substrate wherein the type and amount of laser radiation are selected to render organisms on the substrate inviable while leaving the desired properties of the substrate itself substantially unchanged.

In a preferred method of the first aspect of the invention the substrate and laser radiation are moved relative to each other such as to ensure that a substantial proportion of the substrate surface is exposed to the radiation. Preferably this relative movement of the substrate involves turning of the substrate, eg. elements of food material, relative to the laser radiation, more preferably by tumbling. Thus successive tumbling movements of elements such as those achieved on a conventional roller type conveyor belt may be used. Other convenient movements will be exemplified by reference to the further provided apparatus of the invention as described below.

The laser radiation may be supplied from any source capable of achieving the required heating of organisms to inviability without permanently changing the desired properties of the substrate. The source is conveniently an infra-red laser, such as a C0₂ or YAG laser source, but may be any laser capable of heating the surface organisms, thus UV lasers are included. Power density of less than 10⁵ Watts cm^"2 is used, more preferably less than 10³ Watts cm^"2 and most preferably less than 120 Watts cm^"2. In the examples herein power densities of the order of 10-120 watts cm^"2, preferably about 30, are found to be most effective for eradicating bacteria while retaining substrate integrity, eg. for egg or potato their ability to develop and grow. Conveniently such laser sources are capable of generating laser radiation at a power outputs of about 10 to 250 watts, but other outputs will be capable of use, particularly on substrates of more resilient composition as may be appreciated by those skilled in the art

Convenient YAG laser source units use in the examples and apparatus described below are neodymium doped Yttrium Aluminium Garnet (Nd.YAG). The C0₂ and YAG lasers emit light at different wavelengths; C0₂ at 10.6μm and YAG at 1.06μm. Due to the different absorption levels of objects being illuminated the type of laser used needs to be chosen for each. For example, the preferred laser for tuber treatment is Nd.YAG while that for eggs is the C0₂. It is found that the lasers are conveniently both operated in CW (Continuous Wave) mode but pulsed mode may be applied with appropriate laser sources. Examples of lasers suitable for the CW mode are C0₂ lasers available from Synrad Inc. California, USA as D48/5 (60 W) and Nd.YAG lasers available from Spectron Laser Systems, Rugby, UK as model SLQOl (90 W) ; these may be operated at various powers up to their maximum.

The configuration of the laser radiation may vary but is conveniently provided as a diverging fan like beam or beams from one or more sources. These beams are conveniently directed across a path of conveyance of the substrate, but the substrate may be mounted such that one or more sources provide irradiation of substantially its entire surface without it being moved.

The laser beam may be fanned by a variety of methods, notably by use of a scanning mirror, eg a General Scanning (USA) M3 scanner, or by use of a cylindrical optic. The scanning mirror is used to reflect the beam, which for the exemplified lasers is parallel of approx. 5 to 6mm diameter, while rotating about a central axis. This operation can be computer controlled to give a predefined scan angle and speed. The cylindrical optic method places an optic in the beam path prior to illuminating the object thus causing it to be deflected to create a fan of light at an angle governed by the optic geometry.

The distance at which the laser source is placed from the substrate to be treated may vary. This distance is of course made up of two components: (i) the distance from the laser to the fanning mechanism and (ii) the distance from the fanning mechanism to the object. For (i) the beam is parallel and can be remotely transmitted by reflection to the fanning mechanism. This distance could be from centimetres to tens of metres but in the present examples is about 50cm. For (ii) the distance from the 'fanning' mechanism and the angle of fan that this provides defines the area covered by the fanned beam. It is desirable that substrate items are completely exposed to the laser light; one convenient distance and angle of fanning combination is about 50cm and 20 degrees respectively, but many others are possible. The structures of the parts of the treatment apparatus used to mount the substrate items and all parts supporting that which are capable of being impinged upon by the laser energy are constructed of materials which allow heat build up to be avoided. Thus use of metals connected to suitable heat sink systems is recommended to avoid indirect heating of the substrate through conveying and mounting structures. Otherwise all possible steps are taken to avoid the beams heating anything other than the surface of the substrate or the organisms thereon.

It will be appreciated that appropriate temperature control of all surfaces which contact the substrate will allow relatively high surface area to volume organisms, particularly microorganisms, to be rendered inviable while allowing the substrate, having relatively low surface to volume ratio, to remain at a temperature that has substantially no lasting effect on its desired properties. Appropriate cooling mechanisms will occur to those skilled in the art of temperature control.

Any substrate may have its surface treated by the method of the present invention, but most advantageously treated are those that might be adversely affected by other treatments. To this end certain plastics and otherwise heat and chemically sensitive materials intended for sterile end use will be advantageously treated. However, a most appropriate substrate will be any consumable or propagative material that might have its taste, texture, viability or other desirable quality affected by known treatments. For example, combinable crops (seeds and grains), vegetables, root crops, fruit, fodder, ornamental plants, leaves and beans (tea, tobacco, coffee) and dairy produce can all be treated, pre-planting/sowing or post harvest. Thus substrates such as grasses that transmit laser light, but not without absorbing substantial amounts, are treatable without damage.

Organisms to be rendered inviable, or eradicated, will typically and most effectively be microorganisms such as bacteria, fungi, algae and viruses. Eggs are an example of substrate, susceptible to salmonella, that can be successfully treated. Typically fungal, parasitic, growth undesirable on consumer goods is fungal growth on potatoes.

The present invention further provides apparatus for laser treatment of substrates by the method of the invention comprising (a) a source of laser radiation; (b) a means for handling the substrate, eg as items or elements, whereby the laser radiation is caused to impinge upon the substrate handled by the handling means and is of type and amount such that contaminating organisms are rendered inviable while desirable properties of the substrate remain unchanged.

The apparatus preferably comprises a means for effecting relative movement of the substrate and laser radiation to irradiate a substantial portion of the surface of each element, preferably involving the rotation of the substrate about one or more of its axes as it passes through the radiation, ie, the illumination of the laser.

Substrates are preferably transferred as items, eg. elements of plant material, moving along a treatment path, typically on a conveyor belt eg. a roller conveyor belt which helps achieve relative movement of the elements and the laser radiation and can transport them to successive treatment zones. Other paths may be provided, such as fluid paths defined in part by laser transmitting walls passing through laser irradiations; paths defined by a series of deflecting means such that substrate is caused to be reoriented in the path of laser radiation to ensure that a substantial area of it is exposed to an appropriate level of laser light to achieve the desired effect. Individual items may be treated without relative movement if mounted such that one or more laser beams can cover substantially their entire outer surface. Preferably a series of laser beams are directed at respective receiving points along the belt, typically as fan-like beams as above, typically emanating from one source via fanning units. The apparatus of the present invention thus will take a form appropriate to the substrate that is to be treated. As the substrates only have their outer surface treated, and do not allow laser illumination to pass therethrough, it will be appreciated that many different produce will be treatable by the same apparatus with only the laser type (C0₂ or YAG) , duration of exposure and power level requiring altering to values appropriate to contaminant to be rendered inviable and susceptability of substrate to damage. Factory floor machines may eg. use sources of 60 to 250 Watts maximum output. The power density required will vary but is exemplified in the Examples. Mechanisms of cooling the surfaces of the apparatus that come into contact with the substrate will occur to those skilled in the art, but should be tailored to the end use of a particular apparatus.

It should be noted that apparatus that subjects substrate on conveyor belts to laser radiations are known, eg. see EP0231027 and GB2195438, but that these are used for detection purposes only and are not suitable for the present purpose. Particularly the lasers are not configured to induce thermal effect and no substrate rotation occurs.

The method and apparatus of the present invention will now be described by way of illustration only by reference to the following Examples and Figures; other embodiments will occur to those skilled in the art in the light of these.

FIGURES

Figure 1 shows a plan view of an apparatus as provided by the present invention which is suitable for the treatment of relatively large substrate items such as potatoes or eggs.

Figure 2 shows a perspective view of the interior of the laser treatment unit of the apparatus of Figure 1 showing the arrangement of laser sources, longitudinally extending conveyor rollers and substrate items. Figure 2A shows a cross section through the end of rollers and substrate items thereon.

Figure 3 shows a variant of the interior of Figure 2 wherein the rollers are transverse to the direction of travel of the items. Figure 3A shows a cross section through the end of the rollers and substrate items thereon.

Figure 4 shows plan view a variant of the apparatus of Figure 1 that is specially configured for treating potatoes. Figure 4A shows a perspective view of the interior of the laser treatment unit of this apparatus.

Figure shows a cross section through an apparatus of the present invention which is suitable for treating flowable substrates such as granular material, eg. whole grains.

EXAMPLE 1: DISINFECTION OF EGGSHELLS USING VARIOUS LASER LIGHT ENERGIES.

Hens eggs contaminated artificially with Salmonella enteritidis bacteria and spores of the fungus Aspergillus fumigatus were subjected to various energy levels of laser light from two individual sources. The disinfectant effect of the lasers were compared by determining residual levels of the contamination after treatment.

Areas of cm² of the blunt end of 700 hens eggs were contaminated with suspensions of Salmonella enteritidis and spores of the fungus Aspergillus fumigatus. An overnight broth of S, enteritidis was prepared in buffered peptone water and A. fumigatus was grown on malt agar plates until prolific sporulation had taken place. A suspension of spores was prepared by washing the plates with Maximum Recovery Diluent (MRD) . A lOμl volume of each suspension was spread sequentially over a 4cm² area of the blunt end of each egg using an inoculating loop and a 2x2cm template and the eggs stored overnight at room temperature.

Six batches of 100 contaminated eggs were subjected to a disinfectant treatment by scanning a laser beam over the contaminated areas, each egg being positioned by hand before scanning. Three energy levels were applied with each laser (a C0₂ source and an Yttrium Aluminium Garnet source) . The energy levels imparted to the egg surface were controlled by altering both the power setting of the laser and the scan speed. The number of surviving S. enteritidis and A_^ fumigatus spores on treated eggs and on 100 untreated control eggs were determine

Bacteria and fungal spores were removed from the egg surface by placing each egg in a sterile plastic bag with lOmls of MRM and gently rubbing the contaminated surface through the bag for two minutes. Ten fold serial dilutions were made of the washings and Appropriate dilutions plated out onto XLD Agar (Oxoid CM469) for the enumeration of S. enteritidis and OAES Agar for the enumeration of the fungal spores of A. fumigatus. XLD plates were incubated at 37°C for 4 days and visible colonies of both organisms were counted and the number of viable organisms per egg calculated. Mean values were calculated and the results analysed using a MINITAB computer software statistics package: these are shown in Tables 1 and 2 below.

No salmonella bacteria were recovered from 57 out of 100 treated eggs after treatment C3« The carbon dioxide (C0₂) source proved to be more effective than the Yttrium Aluminium Garnet (YAG) source at similar energy levels. At its highest energy setting the C0₂ laser reduced mean numbers of the contaminating Salmonella by 99-72 and the more resistant A. fumi^gatus spores by 86.9 . An analysis of the variance data indicates that differences in the mean for each treatment were significant at the 5% level and not due to variation within each sample, thus demonstrating that laser light can be used to effectively reduce both bacteria and fungal spores on substrates, particularly on egg shells. TABLE 1

TABLE 2

EXAMPLE 2: EFFECT OF DISINFECTING LEVELS OF LASER LIGHT ON EGG INTERIOR.

The suitability of using laser light to disinfect the surface of eggs was assessed, with particular attention to the effect of the treatment on the interior of the egg being determined by monitoring the effect on early development of chick embryos. For this assessment a rotating platform in the path of a 5ωm width C0₂ sourced laser beam was used to mount individual eggs on their blunt ends.

Eggs were obtained from 450 hens from broiler breeder stock; two batches of 150 eggs being exposed to the laser disinfection procedure by scanning their surfaces. The 5mm beam was stepped sequentially so that after each whole revolution of the egg the beam was moved down resulting in treatment of sequential circumferences of the egg shell. The levels of laser energy to which the surfaces were subjected corresponded to levels C2 and C3 in the experiments outlined above. Table 3 sets out parameters of the scan.

TABLE 3

Treated eggs and 1 0 untreated control eggs were stored overnight before incubation in 'Western' hatchers. Equal numbers of untreated control eggs and eggs from the two treated batches were placed at random in each of five hatcher trays. After five days of incubation all eggs were opened and the state of the embryo development expertly assessed. The results of this assessment are given in Table 4 below. TABLE 4

The treatments C2 and C3 thus appear to show no significant adverse effects of the number of viable embryos resulting from eggs treated in this manner.

EXAMPLE . APPARATUS FOR STERILIZING TREATMENT OF EGG SURFACES.

As shown in Figure 1, a number of conveyor rollers (1) are arranged parallel to each other along a conveyance direction of the apparatus, having spiral gripping elements (2) arranged on their surfaces such that on rotation they cause items (3) placed in upper recesses (4) between adjacent rollers to be propelled forward. These recesses (4), referred to herein as lanes, extend the length of the conveyance path through an intake station (5), a laser treatment unit (6) and an offtake to a grading and packing station (7). The rollers, or at least the gripping elements, are made from resilient material such as rubber and cause the items to rotate about an axis transverse to the direction of travel as they are moved forward. In use substrate items, eg. eggs, are placed the lanes and the rollers driven to rotate about their longitudinal axes such that the items are propelled and rotated through the laser treatment unit to the grading and packing section. Rate of forward movement and rotation of eggs is adjusted to allow surface power density to be equivalent to C3 above.

The interior of the laser treatment unit, shown in Figure 2, has two fans of laser light (8) , preferably C0₂ sourced, mounted to direct laser radiation toward respective lanes. The laser illumination is configured as fans (9) (10) with their planes parallel to the rollers such that they impinge on the items to be treated as they rotate and move forward through the section, but do not substantially impinge upon any part of the rollers. Any radiation passing through the lanes is neutralised by a heat sink below the rollers, eg. a beam stop of light absorbing material placed opposite to the point from which he beam is emanating to catch any wasted laser light.

A variant of the conveyor mechanism is shown in Figure 3 where a number of powered rollers (11) are arranged transverse to the direction of travel with items, eg. eggs, held in recesses in between the upper surfaces of adjacent rollers. As the rollers rotate they cause the eggs to rotate and expose previously unexposed surface to laser light fans (9) (10). The rollers themselves are caused to travel through the laser treatment unit such as they thereby carry the items through it. In this case the rollers themselves do not remain in the unit and thus avoid the risk of overheating. In both these variants the fan angle is approx 20°, approx. 50cm from the items. EXAMPLE 4: CONTROL OF POTATO PATHOGENS USING LASER LIGHT.

Potato seed tubers are a source of inoculum of several important diseases including black scurf (Rhizoctonia solani) , black dot (Collβtotrichum coccodes. , silver scurf (Helminthosporium solani) , powdery scab (Spongospora subterranea) , skin spot (Polyscytalum pustulans) , gangrene (Phoma foveata) , dry rot (Fusarium caeruleum) and blackleg (Erwinia carotovora SSP atroseptica.. Control of these diseases in the progeny tubers of crop relies heavily upon suppression or kill of the pathogens residing in the seed stock. There is an expanding market for fungicide applications to be made to seed tubers in order to produce a healthier crop but most products do not give a broad spectrum activity and often more than one must be applied; fungicide resistance is furthermore becoming a worsening problem and new ones must be registered and approved in UK before they can be legally used. There is ongoing pressure to reduce dose and number of agrochemicals to potato crops and use alternative methods to reduce these diseases.

For assessment of the laser treatment, tubers were selected to have natural disease development over their skins and the viability of the organisms determined by a variety of methods appropriate to the particular disease being studied; these varying as shown by studies of the tuber, transferred lesions or transferred organism after exposure to laser light.

Tests were carried out such that laser-travelling speed across the tuber surface varied widely in order to detect energies that might cause skin damage and those which might be ineffective. Using three levels of power (wattage) within a smaller defined range of travelling speed interactions between these parameters were determined. 30 Watts was defined as an appropriate level of power.

Initial tests used C. coccodes as the indicator pathogen, whereby a relative travelling speed between potato and beam of 612 mm sec^"1 at 30 Watts resulted in nearly 0% of the lesion pieces detached from tuber skin failing to produce fungal growth when transferred to agar plates. At a relative speed of 214 mm sec^"1 control was 100 while speeds greater than 612 mm sec^"1 (eg 1010 mm sec^"1 and above) gave poor control.

The tests using different power levels showed no differences in the viability of R. solani used as the indicator pathogen. Control of this was good at longer durations of illumination. Considerable control of Penicillium development after incubation was also scored. A rotary table spun at various rpm 50cm away from a scanning mirror in line with centre of the side of the potato was used to scan it with vertical movements. Scan speed is given as travelling speed = Duration in the table. Spot size was 5-6mm diameter.

TABLE 5

TABLE contd.

Duration/Travelling speed. 0 = nil, 5 ⁼ longest, 1 = shortest. 5 = 106.7 mm sec^"1, 4 = 133-3 mm sec^"1, 3 = 160.0 mm sec^"1, 2 = 186.7 mm sec^"1, 1 > 186.7 mm sec^"1.

The results of application of laser energy on various organisms is shown in Table 6. 30 Watts was laser power.

TABLE 6

This trial also proved effective in controlling E.c.spp atroseptica. as well as those described above. Using these test conditions proved prone to the treated skin area becoming necrotic, but no secondary rotting occurred thus showing retention of desired properties with regard to storage and use for consumption. However, with YAG at least, experiments showed that parameters can be adjusted to avoid this effect while still controlling the organisms. Dormancy break of rose eye end of tubers and growth rate of sprouts was unaffected with retained numbers of compound leaves per stem.

EXAMPLE 5: LASER TREATMENT APPARATUS SUITABLE FOR APPROXIMATELY SPHERICAL PRODUCE SUCH AS POTATOES.

A treatment apparatus suitable for treating approximately spherical objects such as potato tubers is shown in Figure 4. A roller conveyor (12) travels through a laser treatment unit (13) between an intake hopper, grading screen, picking table (14, 1 t 16) and a box filler (17). Figure 4A shows the arrangement inside the the laser treatment unit wherein the 30 Watt YAG laser sources, approximately 50cm away from items on the conveyor and fanned by scanning mirror or optic into beams (9) (10) of 20° fan, are mounted. The fans impinge upon both rollers and items (18) carried thereon. The rollers (19) are arranged transverse to the direction of travel and rotate as they pass through the unit such as to cause the items to rotate and expose substantially their entire surfaces to the beams. The rollers (19) are of metal thus allowing rapid conductance of heat away from the items carried in the recesses between their adjacent upper surfaces. Drive of rollers is passive, as caused by contact with supports as the conveyor is driven around its path, or active by drive means acting on each and every roller individually.

EXAMPLE 6: LASER TREATMENT APPARATUS SUITABLE FOR FLOWABLE MATERIALS SUCH AS GRAINS.

A treatment apparatus suitable for laser illuminating flowable materials such as whole grains for rendering contaminating organisms thereon inviable is shown in Figure 5« In Figure 5 grains (24) are fed to a vertically oriented tubular housing (25) by a belt conveyor (26) whereupon dust and chaff are induced to separate upward by an extraction apparatus (26) while the grain falls under gravity into a laser treatment region below. Deflector means (27) made from material suitable for acting as a heat sink cause the grain to be sequentially tumbled and redirected while laser light fans (9) (10) of the type previously described impinges upon it from a number of points down the housing. The laser fan enters the housing through slots (28) from fanning mechanisms 0 cm away from the grain path. As in all these devices the source itself may be centimetres to metres away, but is conveniently 50 cm from the fanning source. All other parameters may be as described previously.

In this case it is possible to manipulate the fanned beam over a set area in order to cover as much grain as possible. For maintaining effective treatment duration and cover of substantially all the grain surface several fans are used through which the grain must pass before it exits onto conveyor (29) .

Claims

CLAIMS .

1. A method of treating a substrate substantially opaque to laser radiation or unable to transmit laser radiation without absorbing substantial amounts thereof, for the purpose of reducing levels of contaminating organisms associated with its surface, comprising directing laser radiation at the substrate, such that the type and amount of laser radiation are selected to render organisms on the substrate surface inviable while leaving the desired properties of the substrate itself substantially unchanged.

2. A method as claimed in claim 1 wherein the substrate is a consumable and/or propagative material and the contaminating organisms are microorganisms.

3. A method as claimed in claim 1 or claim 2 wherein the substrate and laser radiation are moved relative to each other such as to ensure that a substantial proportion of the substrate surface is exposed to the radiation.

4. A method as claimed in claim 3 wherein the relative movement of the substrate involves turning of the substrate relative to the laser radiation.

5. A method as claimed in any one of claims 1 to 4 wherein the laser radiation is provided by an infra-red laser source.

6. A method as claimed in claim 5 wherein the laser source is capable of generating laser radiation at a power output of about 10 to 20 Watts.

7- A method as claimed in any one of the preceding claims wherein the laser source is operated in continuous wave mode.

8. A method as claimed in any one of the preceding claims wherein the power density of the laser on the substrate is between 10 and 120 Watts cm^"2.

9. A method as claimed in claim 8 wherein the power density of the laser on the substrate is between 20 and 0 Watts cm^"2.

10. A method as claimed in any one of the preceding claims wherein the laser radiation is provided in the form of a diverging fan like beam or beams from one or more sources.

11. A method as claimed in claim 9 or 10 wherein the beam is parallel and of approximately 5 to 6mm diameter before being fanned.

12. A method as claimed in any one of claims 9 to 11 wherein the distance from which the laser beam is fanned to the substrate to be treated is about 50cm.

13 A An apparatus for treatment of a substrate substantially opaque to laser radiation or unable to transmit laser radiation without absorbing substantial amounts thereof, for the purpose of reducing levels of contaminating organisms associated with its surface, comprising (a) a source of laser radiation and (b) a means for handling the substrate, whereby the laser radiation is caused to impinge upon substrate handled by the handling means and is of type and amount such that contaminating organisms are rendered inviable while desirable properties of the substrate remain unchanged.

14. An apparatus as claimed in claim 13 comprising a means for effecting relative movement of the substrate and laser radiation to irradiate a substantial portion of the surface of each element.

15. An apparatus as claimed in claim 13 or 14 comprising a a treatment path which passes through successive treatment zones.

16. An apparatus as claimed in claim 15 wherein the substrate is conveyed along the treatment path on a roller conveyor belt which effects relative movement between it and the laser radiation.

17. An apparatus as claimed in claim 15 wherein the path is defined by a series of deflecting means such that substrate is caused to be reoriented in the path of the laser radiation.

18. An apparatus as claimed in any one of claims 13 to 17 wherein the laser radiation is provided by a thermal laser source of between 10 and 250 Watts output.

19. An apparatus as claimed in any one of claims 13 to 18 wherein the laser source provides infra-red laser light.

20. An apparatus as claimed in claim 19 wherein the laser is a YAG or C0₂ laser.

21. An apparatus as claimed in claim 19 or 20 wherein the apparatus is configured such that the power density provided at the substrate is between 10 and 120 Watts cm^"2

22. An apparatus as claimed in claim 21 wherein the apparatus is configured such that the power density provided at the substrate is between 20 and 50 Watts cm^"2.

23. An apparatus as claimed in any one of claims 13 to 22 wherein the substrate is caused to rotate about one of its axes as it is conveyed through a station where the laser light impinges upon it.

24. An apparatus as claimed in any one of claims 13 to 23, substantially as described in any one of Examples 3» 5 or 6.

25. A method as claimed in any one of claims 1 to 12 substantially as described in any one of the Examples.

26. A substantially laser opaque substrate characterised in that organisms associated with its surface have been rendered inviable by being subjected to a treatment as claimed in any one of claims 1 to 12 or claim 24.

27. A substrate that does not transmit laser light without absorbing substantial amounts of laser energy characterised in that organisms associated with its surface have been rendered inviable by being subjected to a treatment as claimed in any one of claims 1 to 12 or claim 24.

28. A substrate as claimed in claim 26 or 27 further characterised in that it is a consumable, seedstock or is intended for veterinary or medical use.