CA2118516A1 - Surface sterilisation by laser treatment - Google Patents

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

. Wo 93/21787 ~? 1 18 5 1 ~ P~/GB93/0~72 SURFA~E STERILISATION BY LASER TR~A~MENT

The presPnt invention ~elates to a method of treating substrates ~or the purpose of reducing ~he population of contaminant organisms ~sociated with them; particularly to treatment of ~oods~uffs, propagation materials and items for veterinary and medical end u~es.

E~tensive fungicidal and pesticidal treatment of plant materials, eg.
fruit, vegetables and grains, i6 presently carried out for the purpose of precluding unwented contamina~ion. The treatment is often environmentally undeæirable, potentially hazardous to the consumer of the product and is somewhat inefficient in eradicating certain para&itic growth0 particul~rly 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 iisteria.

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Further to these chemical treatments, physical sterilization treatments are routinely applied to products for use in consumer, veterinary or medical applications. For example, sterilization using microwaves has been applied~to trea Oent of mushroom casing, while high pressure steam treatment ~orms the basis for treatment of medical instruments in autoclaves. These~treatments are all potentially haz~rdous and/or require significant amounts of ti~e to achieve op~imal efPect.
Furthermore where the~end product is a foodstu~f or chemical entity its structure may be altered to the detriment of desirable qualities such as flavour, texture, efficacy and, eg for seeds, viabili~y.

US 3817703 uses hlgh powered lasers to sterilise laser transmitting liquids, wherein the power denisty used is at least 105 Watts cm~2 and is preferably 108-101 Watts cm~2. Such method is applicable to light tr&nsparent materials such as wines, but is completely inappropriate :

S~BSTITVTE SHEET

W O 93/21787 PC~/GB93/00872 2118~

for application to materials which are light absorbPnt, particularly those fiubs~antially opaque to laser light or which absorb it in part.

The present inventors have now provided a novel method capa~le of being applied to all the above substrates and others, whereby contamin~nt organisms are rendered inviable in short time without the disadvantages of the afore6sid methods and without affecting the desired qualities of *he end product or leaving environmentPlly or physiologically damaging residues thereon. Furthermore, in certain ~pplications, such as in the inhibition of ~ome 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 u~es thermal laser e~fect to raise a contaminAnt organisms temperature above ~ c~itical level ~or a sufficient time to render it inviable.
This temperature will vary from organism to organism, but is , ~ .
appr~ximately 45C for many bacteria and fungi. Using heated media such as ste~m, or using radiation eg. microwaves, the temperature of the substrate will also be raised to level~ 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 level~ of cont~minating organisms associated with its surface, comprixing 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 prop~rties of the substrate itself ~ubstantially unchsnged.

In a preferred method of the first aspect vf the invention the substrate and laser radiation are moved relative to each other such ~ 0 ~3/21787 PCT/GB93/Q0872 ` 211~51~

as to ensure that a ~ubstantial propor~ion of the substrat~ surface iB exposed to the radiation. Preferably this relative ~ovement of the substrate involves turning of ~he substrate, eg. elements of food material. relative to the laser rsdiation, more preferably by tumbling. Thus successive tu~bling movements of elements such ~g those achieved on a c~nventional roller type con~eyor belt may be used. Other conv~nient movements will be exemplified by reference to the further provided apparatus o~ ~he invention as described below.

The laser radiation ~y 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 co~veniently an infra-red laser, ~uch as a C2 or YA5 l~ser source, but may be any laser capable of heating the surface org~nisms, thus W lAsers are included. Power density of less than 105 Watts :: :
cm~2 i5 used, more~pre~erably less than 103 Watts cm~2 and most preferably le~s 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 o~ generating laser radiation at a power outpuSs of about 10 to 250 watts, but other outputs will be capAble of use, particularly on substrates of more resilient composition ~s may be appreciated by those ækilled in the art.

Conve~ient YAG laser source units uæe in the examples and ~pparatus described below are~neodymium doped Yttrium Aluminiu~ ~arnet (Nd:YAG). The CO2 and YA~ lasers emit light at different wavelengths;
C2 at 10.6~ and YAG at 1.06~m. Due to the different absorption levels of obj0cts being illuminated the type of laser used needs to be chosen for each. For example, the preferred laser for tuber trea~ment is Nd:YAa while that for eggs is the CO2. It is found tha~
the l~sers are conveniently both operated in CW (Continuous Wave) -mode but pulsed mode may be applied with appropriate laser sources.
.

WO93/21787 ~118 5 16 PCT/GB93/00872~

Examples of l~ser ~uitable for the CW mode are CO2 lasers available from Synrsd Inc, California, USA ~s D48/5 (60 W) ~nd Nd:YAG lasers available from SpectrDn Laser Systems. Rugby, UK as model SL901 (90 W); these may be operated at various powers up to their maximum.

The configuration o~ the laser radiation may vary but is conveniently provided a~ 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 moun~ed 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 sc~nning mirror, eg a General Scanning (USA) M3 scanner, or by use of a cylindrical cptic. The scenning mirror is used to reflect the beam, which for the exe~plified l~sers is parallel of approx. 5 to 6mm di~meter, while rotating about a central axis. This operation c~n be computer controlled to give a predefined scan angle and ~peed~ 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 ~ gle governed by the optic geometry.

The distance at which ~he laser source is placed from the ~ubstrate to be treated ~ay vary. This distance is of course made up of two co~mponents: ~i) the distance~from the laser to the ~anning mechanism and ~ii) the distance from the fanning mechaniRm to the object. For (i) the beam is parallel and can be remotely transmitted by reflection to the fanning mechanism.~ This distance could be ~rom centimetres to tens o~ metre~ but in the pre~ent 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 Z0 degrees respectively~ but many others are possible.

W O g3/21787 ~ I 18 516 PCT/GB93/00872 The ~tructures of the parts of the treatment apparstus used to mount the substrate iteo~ and all parts supporting that which are capable of being impinged upon by the laser energy sre constructed of materialg which allow heat build up to be avoided. Thus u~e of met~ls connected to suitable heat 8ink systems ~s recommended to avoid ind~rect heating of the substrate through conveying and mounting structures. Otherwise all po~sible ~tep~ ~re taken to avoid the beams heating anything oth~r than the surf~ce 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 microorgani~ms, to be rendered inviable while allowing the substrate, having relatively low surface to volume r~tio, ~o remain at a temperature that h~s substantially no lRsting effect on its desired properties. Appropriate cooling mechanisns will occur to those skilled in the art of temperature control.

Any substrate may have it~ Rurface treated by the method of the present inveDtion~ but most advantageously treated are those that might be adversely affected by other treat~e~ts. To this end certain plastics and otherwise he~t and chemicAlly sensitive materials intended for sterile end use will be advantageously treated. However, a ~ost appropriate substrate will be any consumable or propagative material that might;have its taste, te~ture, viability or other desirable quality af~ected by known treat~ents. For example, combinable crops (seeds and grn ns~, 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 ;

W O 93/21787 ~ 1 18 5 16 PCT/GB93/0087~ ~

viru~es. Eggs are sn exa~ple of substrate, susceptible to s~l~onel}a, that can be ~ucce~sfu}ly treated. Typically fungal, parasitic, growth undesirable on consuMer goods is fungal growth on potatoes.

m e present invention further provides apparatus for la~er treatnent of substrates by the method of the ~nvention comprising (a) a source of laser radiation; (b) a means for handling the subs~rate, eg as ite~s or elements, whereby the laser radiation is caused to impinge upon the substrate handled by the handling ~eans and is of type and ~mount ~uch that contaminating organisms are rendered inviable while desirable properties of the substrate remain unchanged.

The apparatus prePerably comprises a means for effecting relative movement of the substrate and laser radiation to irradiate a substantial portion of the surface of each ele~ent, 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.
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Substrates are preferably transferred as items, eg. elements of plant ~ , , aterial, 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 8S
fluid pa~hs defined in~part by laser transmitting walls passing through~laser irradiations; paths defined by a series of deflecting means such that~subs~trate is caused to be reoriented in the path of laser radiation to en ure that a substantial area of it is exposed to :
an ~ppropriate level of laser light to achieve the desired effect.
Individu~l items may be treated without relative movement if moun~ed such that one or~ re 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.

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.~W O 93~21787 PCr/GB93/OOX72 ~ ~118516 The appar~tus of the pr~sent invention thus will take a form appropriate to the substrate that i8 to be treated. As the substrates only have their outer surface treated. and do not allow la3er illumination to pass therethrough, it will be appreciated that many different produce will be treatable by the ame apparatus with only the laser type (C2 or YAG), duration of exposure and power level requiring altering to values appropriate to contaminant to be rendered inviable and susceptability of sub~trate to damage. Factory floor machines may eg. use ~ources of 60 to 250 Watts maximum output. The power density required will vary but is exemplified in the Exa~ples.
Mech~nisms of cooling the surfaces of the apparatus that come into contact with the substrate will occur to those skilled in the art, but ~hould be tailored to the end use of a particular apparatus.

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It should be noted that apparatus that subject~ 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. Par~icularly the la~ers 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.

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Figure 1 shows a plan view of an apparatus a6 provided by the present inventlon which is suitable for the treatment of relatively large substrate items such as potatoes or eggæ.
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Figure 2 shows a per~pective view of the interior of thP laser treatment unit of the apparatus of Figure 1 showing the arrangement of laser sources, longitudinally extending conveyor rollers and substra~e items. Figure 2A shows a cross section through the end of rollers and WO 93/21787 PCT/GB93/0~872~
.~ 1 1 8 ~

substrate ite~s thereon.

Figure 3 shows a vsriant of the interior of Figure 2 wherein the rollers are transver~e to the direction of travel of the ite~s.
Figure 3A shows a cross ~ection through the end of the rollers and substrate items thereon.
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Figure 4 shows plan view a variant of the appar~tus of Figure l 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 5 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.~

8AX~LE~L~ DISINPLCTION OF EGGSHELLS USING VARIQUS LA~ER LI~HT

Hens eggs conta inated artificially with Sbl~L~e~ eneesi~ldi bacteria and spores~of~the fungus ~ g - were subjected to various enerlgy 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 4 cm2 of the blunt end of 700 hens eggs were contaminated wlth suæpensions o~Sal~onella enteritidis ~nd spores of the fungu~
_ . An overnight broth of s. _- e -i5 ~i was prepared in bufPered peptone water and ~h_fgmLgD~ wa~ grown on mal~
agar plates until prolific sporulation had taken place. A suspension of spores was prepared by washing the plates with Maximum Recovery ` Diluent (MRD). A lO~l 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 templat2 and the eggs stored overnight at ~: .

~ W O 93/21787 PCT/G~93/00872 , ~
~J~ 1 85~(;

room temperature.

Six batches of lOO contaminated egg~ were subjected to a disinfectant treatment by scanning a laser bea~ over the contaminated areas. each egg being positioned by hand before scanning. Three energy levels were applied with each laser (a CO2 source and an Yttrium Aluminium Garnet source). The energy levels imparted to the egg surface were controlled by Altering bo~h the power setting of the laser and the scan ~peed. The number of surviving S. enteri~idi~ and ~, ~umigatus spores on treated eggs and on lOO untreated control eggs were determined.

Bacteria and fungal spores werP 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 b~g 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 SL_~n~ri~ and OAES Agar ~or the enumeration of the fungal spores of ~,_fg~idlL~s. XLD plates were incubated at 37C
for 4 days and visible colonies of both organisms were counted and the number of viable organisms per egg calculated. Mean values were calculated ~nd~the~results ~nalysed using a MINITAB computer software statistics ~ackage; these are shown in Tables 1 and 2 below.

No salmonella bacteria were recovered from 57 ~ut of lOO treated eggx after treatment~C3.~ The carbon dioxide (C2) source proved to be more effective than~the Yttrium Aluminium Garnet (YAG) source at similar energy levels.~Ae~i~ts highest energy setting the C2 laser reduced mean numbers of the contaminating Salmonella by 99.72% and the more re~istant A. fu~igatus 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 substratest particularly on egg shells.

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W O g3~21787 ~ 516 P ~ ~GB93/00872 : ~ . - .
Treatment Power Parameters Mean Counts/Egg Density Watt~/sc~n W cm~2 speed mm/sec S. ent A~ fum : . . __ Yl 0.4 1.85/193.5 16000 3400 . . .- _ ;~ Y2 2.7 12.5/193.5 ~6000 4300 - ~ .
Y3 27.0 23/60 11000 æoo _ : : :: _ __ Cl 0.2 1.6/193.5 29000 5400 :~ ~ : .; : :
C2 1.65 10.5/162.5 8600 6700 _ C3 ~ 3O.o Il/34 81 640 Control ~ 29000 540 . :
TA~LE 2 ~ ~

~ : I~a~.~ne ~ ~ XRe uction in V~able orgam sms (rounded to nearest whole number).
~; ~5~ sm~o~GLLLiiE A~ fmmi~atu~

Yl ~ ~ 44.82 ~ 30.61 . ~ _ Y2 62.06 55.10 : - _ _ Cl 0 0 . _ :~
C2 70.34 0 : _ _ ~ C3 99.72 8609 ~ ~ .

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. W O 93/21787 PCT/GB93/00872 ' ' '' j.118~516 ;

The suitQbility of using laser light to disinfect the surface of eggs wa~ assessed, with particular attentio~ to the effect of the treatment ; on the interior of the egg being determined by monitoring the effect on ea~ly developme~t of chick embryos. For this assess~ent a rot~ting platform in the path of 8 5mm 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~revoIution 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 surfsces were subjected corresponded to levels~C2 and C3 in the experiments outlined above.
Table 3 sets out;parAmeters of the scan.

;Egg Rotation rpm Laser power output Watts ; C2 ~ ~ 78 ~ 10.6 C ~
3 ~ ~ 3o , ~ ~ ~ ~

Treated eggs and~;l50 untreated control eggs were stored overnight before incubation~in~'Western' hatchers. Egual 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 aIl eggs were opened~and the state of the embryo development expertly assessed. The results of this assessment are given in Table 4 below.

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W O 93/217B7 PCT/GB93/00872,~
~118~1~

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Treatment Incubator No of e~gs Infertiles DeAd ~erm Live Ger~
_ _ .. . _ ~ . . , _, . . .

~ __ ~; Tota1s 150 23 7 119 C3 1 90 ~8 4 68 , _ .
: . .. 2 60 5 8 47 . _ . ,,_ ~ Tot~ls : 150: 23 12 115 ~ . . .. . . , Control 1 90 15 3 72 : ~ . _ _ ,, ... -_ 2 _ 60 _ 11 2 47 T b--ls : _ 150 26 119 , me treatments:C2 and C3 thus appear to show no si0~ificant adverse ef~ects o~ the number of viable embryos resulting from eggs treated in :: this manner.

; : : As shown in Figure 1, a number of conveyor rollers (1) are arr~nged : : parallel to each other along a conveyance direction of the apparatus, : having spiral gripping elements (2) arranged on their surfaces such ;~ that on ro~ation they cause items (3) placed in upper recesses (4) :

~ W 0 93/21787 ,~118 51 ~ PCT/GB93/0~872 between adjacent rollers to be prGpelled forward. m ese recesses ~4), referred to herein as lanes, extend the length of the conveyance path through an intake station (5), a laser treatment unit (6) ~nd 3n o~take to a grading ~nd packing s~at~on (7). The rollers, or at least the gripping elemen~s, are nade from resilient material æuch as rubber and cause the items to rotate about an axis transverce to the direction of truvel 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 C2 sourced, mounted to direct laser radiation toward respective lanes. The laser illuminatlon is ,. ~ .
configured as fans (9~ (10) with their planes parallel to the rollers such that they impinge on the items to be trea~ed 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~ e~. 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 humber 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 c~use the eggs to rotate and expose previously unexposed surface to laser light fans (9) tlO). 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.

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W O 93/21787 PCT/~B93/00872 `6~

EXAMPLE 4:_CoNTRoL OF POTATO PATHOGENS USING LASER_LI9ET~

Potato seed tubers are a source of inoculum of several important diseases including black scur~ ( ), black dot (Colletotrichu~_cn55Q~es), silver scurf (~lminthosporium solanii), powdery scab (S~ongo~ora ~ubterranea), skin ~pot (Polvscvtalum ustulans), gangrene (PhQmeLf9~ea~). dry rot (E~rlL~L~e~Y~o-) ~nd blackleg ~Erwinia caroto~n~ ss~_a~roseDtica). 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 applica~ions 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. mere is on~oing pressure to reduce dose and number of agrochemicals to potato crops and use alternative methods to reduce these diseases.

For as}essment 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 ~o the particular di~ease being ~tudied; these varying as shown by studies of the tuber, transferred lesions or trans~erred organism after exposure to laser light.

Tests were carried out such tha~ laser-travelling speed across the tuber surface v~ried widely in order to detect energies that might cause skin d~mage 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 t@sts used C. coccodes as the indicator pathogen, whereby a {~ W O 93/2l787 ~ 516 PCT/GB93/00872 relative travelling speed between potato and beam of 612 mm ~ec~l at 30 Watts resulted in nearly 50% of the lesion pieces detached Prom tuber skin failing to produce fungal growth when transferred to agar plates. At a relative speed of 214 m sec~l control was 100% while speeds greater than 612 mm sec~l (eg 1010 mm 6ec~l And above) g~ve poor control.

The tests using d~fferent power levels showed no differences in the viability of R, ~ol~ni used as the indicator pathogen. Control of this was good~st longer durations of illumination. Considerable control of ~ni~ 9~ development after incubation was also scored.
A rotary table~gpun at~various rpm 50co 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.

TA~LE 5 ~

Power:of Duratlon %Recovery Relative Recovery Laser ~0-5~(see key) R. solani Penicillium ::~ ~o~ oo 49 30: 1~ : 79 46 :30 : ~2: ~ 32 13 :: 30 ~; 3~ o ~3 : 4 ~ 5~ ~:: O o ~: ~:
o 95 44 : 45 ~ 9 17 :

; ~ , W O 93J21787 ~118 ~ 1 ~ PCT/GB93/00872~

TABLE 5 contd.
. _ _ _ __ : 3 26 18 :

Duration~Travelling speed. 0 = nil, 5 = longest, 1 = shortest. 5 =
106.7 mm sec~l, 4 = 133.3 mm sec~l, 3 = 160.0 mm sec~l, 2 = 186.7 mm ~;~ sec~l, 1 > 186.7 mm sec~l.

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

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~ .
Travelling ~Relative recovery Speed C. coccodes H. solani E,_~8~ 5 P. foveata E~ Lsl~um , ~

~: 2 51 :38 o 20 o -; 3 9 : 6 o o o ; 4_ :; 6~ o o o o This trial also proved effective in controlling E.c~s~p atroseptica, as well as those described above. Using these test conditions proved prone to the treated skin area becoming necrotic, bu~ no secondary rotting occurred thus showing retention of desired properti~s with regard to storage and use for consumption. However, with YAG at : ~ i , W O 93/21787 PCTtGB93/~0872 ' ~i 1 18~1~

least, experiment~ showed that parameters can be adju~ted to avoid this effect while still controlling the organisms. Dor~ancy break of rose eye end of tubers and growth rate of sprouts was unaffected with retained number~ o~ compound leaves per st~m.

EXA~PLE ~ ~QSER T~EATMENT APPARATUS SUITABLE FOR APPROXIMATELY
SPHERICAL PRODUCE ~UCH AS POTATOES.

A treatment apparatus suitable for treating approximately spherical ob~ects such as potato tubers is shown in Figure 4. A roller conveyor (12) travels through a IAser treatment unit (13) between an intake :
hopper, grading screen, picking table (14, 15, 16) and a box filler (17). Figure 4A shows the arrangem2nt 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 bea~s (9) (10) of 20 ~an, 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 i8 passive, as caused~by contact with supports as the conveyor is driven around its~path,~or a~tive by drive means acting on each and every roller individually.

EXAMPLE ~_LASER~TREATMENT APPARATUS SUI~ABLE FQ~ FL~WABLE MATERIALS
.

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 vertic~lly oriented tubular housing (25) by a bel~ conveyor~ ~ (26) whereupon dust and ~haff are induced to separ~te upward by an :

W O 93t2178~ PCT~GB93/00872~.
, ;

~ 18 extraction apparatus (26) while the grain falls under gravity into a laser trea~ment 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 Or points down the housing. The laser fan enters the housing through slots (28) from fanning mechanis-s 50 cm away from the grain psth~ As in all these devices the source ltself may be centi-etres to metres away. but is conveniently 50 cm fro- 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 OE ain must pass before it exits onto conveyor (29).

Claims (27)

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 impinging laser radiation onto substantially all of the substrate's surface, such that the type and amount of laser radiation are selected to render organisms on the substrate surface inviable while allowing the substrate other than at its surface to remain substantially unaffected.

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 substantially all 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 250 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 50 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. 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 substantially all of the surface of the substrate handled by the handling means and is of type and amount such that contaminating organisms are rendered inviable while the substrate other than at its surface to remain substantially unaffected.
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14. An apparatus as claimed in claim 13 comprising a treatment path which passes through successive treatment zones.

15. An apparatus as claimed in claim 14 wherein the substrate is conveyed along the treatment path on a roller conveyor belt which effects relative movement between it and the laser radiation.

16. 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.

17. An apparatus as claimed in any one of claims 13 to 16 wherein the laser radiation is provided by a thermal laser source of between 10 and 250 Watts output.

18. An apparatus as claimed in any one of claims 13 to 17 wherein the laser source provides infra-red laser light.

19. An apparatus as claimed in claim 18 wherein the laser is a YAG or CO2 laser.

20. An apparatus as claimed in claim 18 or 19 wherein the apparatus is configured such that the power density provided at the substrate is between 10 and 120 Watts cm-2

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

22. An apparatus as claimed in any one of claims 13 to 21 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.

23. An apparatus as claimed in any one of claims 13 to 22, substantially as described in any one of Examples 3, 5 or 6.

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

25. 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.

26. 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.

27. A substrate as claimed in claim 25 or 26 further characterised in that it is a consumable, seedstock or is intended for veterinary or medical use.