A new test method for in-place cleanability of foodprocessing equipment

T. Beeneezech *, C. Lelieevre, J.M. Membree, A.-F. Viet, C. FailleINRA Laboratoire de Geenie des Proceedees et Technologie Alimentaires, 369 rue Jules-Guesde, B.P. 39, 59651 Villeneuve dAscq, France

Received 3 June 2001; accepted 14 September 2001

Abstract

A practical and quantitative method for assessing complex food equipment cleanability is described. After soiling a positive

displacement pump by a composite model food made of custard and Bacillus cereus spores isolated from a food processing line, a

mild cleaning-in-place procedure was carried out using basic detergents such as sodium hydroxide and nitric acid. After cleaning,

surfaces potentially in contact with the contaminated food were overlaid with nutrient agar containing a tetrazolium salt. Residual

contaminants appeared as small red colonies and contamination levels could be dened. A non-parametric statistical analysis was

performed to compare the dierent areas in the pump and three cleanability levels were dened. Geometry appeared to be one of the

main factors in hygiene, emphasised by the way the equipment is connected to the CIP circuit. 2002 Elsevier Science Ltd. Allrights reserved.

Keywords: In place cleanability assessment; Food industries; Bacillus spores; Hygienic design; Pump

1. Introduction

Liquid food treatments which are intended to inac-tivate unwanted micro-organisms (pasteurisation andsterilisation) can adversely aect avour and damagemany nutrients. This trend appears to conict withthe new consumer demands for fresher foods of highorganoleptic and nutritional quality, which suggestslighter preservation methods. Of course, low heattreatment conditions imply that hygienic processing re-quirements must be correctly and consistently met(Moster & Lelieveld, 2000). Since 1998 in Europe, thedesign of food processing equipment must meet theMachinery Directive (European Council Directive 98/37/EC on machinery, 1998). The Directive includes ashort section dealing with hygiene and design require-ments which states that machinery intended for thepreparation and processing of foods must be designedand constructed so as to avoid health risks and thissection consists of hygiene rules that must be observed.These rules concern the suitability and cleanabilityof materials in contact with food. Recent international

standards such as ISO 14159 for food, cosmetics andpharmaceutical industries (International Organisationfor standardisation (ISO), 1999) and CEN EN 1672-2for food industries (Comitee Europeeen de Normalisation(CEN), 1997) give details on hygiene requirements forprocessing machines associated with a risk assessmentprocedure. Within the requirements set out in the stan-dard EN 1672, it was noticed that cleanability and/orcapability of being disinfected should be checked bymeans of visual inspection (on drawing(s) or machiner-ies) and/or a practical test, microbiological test orfunctional test. In addition, according to ISO 14159,most closed product processing machinery are consid-ered cleanable if the cleaning procedure eciency can beveried by means of a practical test for the entire plantor its individual components. Machines designed to bepasteurised, sterilised or for aseptic production, usuallyfor closed product processing, shall require practicaltesting. However, no practical way of testing is eitherindicated or referred to.

A new standard prEN 197-042 specic to liquidpumps is under preparation by CEN to dene designrules to ensure hygiene in use (Comitee Europeeen deNormalisation (CEN), 1999). Pumps complying withthis standard shall achieve or have veried one ofthe specied categories of cleanability which shall be

Journal of Food Engineering 54 (2002) 715

www.elsevier.com/locate/jfoodeng

*Corresponding author. Fax: +33-3-20-43-64-26.

E-mail address: benezech@lille.inra.fr (T. Beeneezech).

0260-8774/02/$ - see front matter 2002 Elsevier Science Ltd. All rights reserved.PII: S0260-8774 (01 )00171-6

identied by the manufacturer in the instruction hand-book, and may be related to specic types of processesand cleaning procedures. Four cleanability categoriesare identied in the standard, based on the potential useof the pump in factories. Only one category species alevel of remaining micro-organisms after cleaning de-ned by a relevant test to be chosen. This should beassessed by applying tests established by the manufac-turer or by a laboratory and shall comprise a visible soiltest and a micro-organism test. The standard EN 12462referring to the standard EN 1672-2, indicates that thecleanability of pumps used in biotechnological processesis one major element of the performance criteria to betaken into account. As explained in the standard, anyprescribed cleanability threshold value should be basedon the required safety level and can be the detectionlimit of an approved test method (e.g. European Hy-gienic Equipment Design Group (EHEDG)).

Therefore, there is an obvious need for the creation ofstandardised cleanability test methods. Over recent lastyears, a research programme funded by the Europeancommission (AIR 1-CT92-0091) was undertaken to de-velop test protocols on a practical basis to assess thecleanability of equipment intended for food production(Holah, 2000). A standardised cleanability test method(Timperley et al., 2000), recently published by theEHEDG is based on the comparison, in laboratoryconditions, of the cleanability of a test item (closedprocessing equipment) with that of a straight piece ofpipe with a dened surface nish. A previous version ofthe Timperley et al. (2000) procedure is therefore quotedin the standard NF EN 1296-X 42 120, as an example ofthe application of a relevant methodology (Comitee Eu-ropeeen de Normalisation (CEN), 1995). The chosen soilwas made of a suspension of Bacillus stearothermophilusspores in soured milk, spores being a tracer of the milksoil as demonstrated by Galesloot, Radema, Kooy, andHup (1967) and Carpentier and Kobilinsky (1993). Thepresence of the soil after cleaning is detected after directgrowth of the remaining micro-organisms on the sur-faces. Four successive steps are required and could besummarised as follows:

1. soiling of the surface of the equipment to be tested to-gether with a standard component (a length of pipe);

2. cleaning the surface of the soiled equipment underappropriate conditions;

3. detecting the remaining soil and, when possible,quantifying it and;

4. comparing with the standard component.

Other practical methods have been proposed basedon the use of mixed soil containing a milk product andrelevant bacteria such as Bacillus spores (Huusmark,Faille, Roonner, & Beeneezech, 1999; Holah, 2000) for as-sessing the cleanability of pieces of equipment such as

at surfaces and pipes. Indeed Bacillus species are im-portant as food-spoilage organisms, and can be isolatedfrom a great range of food products such as spices,vegetables, meat, milk and dairy products (Goepfert,Spira, & Kim, 1972; Johnson, 1984). B. cereus is note-worthy a predominant organism that determines thekeeping quality of pasteurised milk products (Stewart,1975). Such a risk remains today as reported by TeGiel, Beumer, Leijendekkers, and Rombouts (1996).Food contamination of these thermo-resistant micro-organisms may originate from raw materials, but alsofrom fouled processing equipment surfaces (Wong,1998). Indeed, spores of Bacillus species such as B. ce-reus or B. thuringiensis were demonstrated to be highlyadherent to various surfaces (Huusmark & Roonner, 1990,1992; Faille, Dennin, Bellon-Fontaine, & Beeneezech,1999).

The aim of this study was to propose a detailed testmethod to assess the cleanability (soiling and cleaningability) of food processing equipment designed for spe-cic heat, chemical or physical treatment to free themachinery from relevant micro-organisms. A B. cereusstrain isolated from a dairy processing line and dem-onstrated to be a relevant test organism in dening thepotential risk of contamination in dairy processing lines(Faille, Fontaine, & Beeneezech, 2001) was proposed.Spore adhesion was obtained by circulating a contami-nated dairy desert throughout the equipment to be tes-ted. A positive displacement pump was chosen as anexample of complex food processing machinery used forthe processing of viscous and/or fragile products (eggs,custard, stirred yoghurt). The design of such an appa-ratus could be considered as complex due to the pres-ence of various hydraulic diameters, moving parts,dierent materials and the various ways it can be in-stalled in processing lines.

2. Materials and methods

2.1. Equipment and test rig

The progressive-cavity pump used to carry out thecleanability test method (Fig. 1) was chosen for its highoccurrence in the food industry. It is mainly composedof a rotor and a stator with two internal spiral bearings.In any cross-section, the rotor is in contact with thestator. The rotational movement causes a shift, alongthe axis from the inlet to the discharge, of the sealed cellsmarked o by the rotor and stator. Body and suctionports are made of 316 L stainless steel and the stator ofchlorosulfonated polyethylene (CSPE)-based syntheticrubber.

Two ways of connecting the pump to the CIP circuitwere tested using two dierent pump bodies with anaxial exit pipe or a tangential exit pipe. Exit pipes thus

8 T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715

were horizontally (axial) or side (tangential) oriented.Tangential connection allows the pump to be selfdrained.

The pump was installed in a soiling circuit (Fig. 2).The model food as the soiling suspension was main-tained at 50 C in a tank and circulated in the loopconsisting of the pump to be tested, stainless steel 304 Lpipes (0.15 m length, 0.38 m diameter and an average

roughness of 0.4 lm) and a three way seat valve (Alpha Laval, Sweden) for the CIP connection. Between thedierent ttings, rubber gaskets (Nitrile) specic to thefood industry, were used. The cleanability of the dier-ent parts of the equipment tested was compared to re-sults obtained for the 304 L pipes used as references.

After soiling the test equipment, the three-way valvewas opened to by-pass and clean in place the tested

Fig. 2. Soiling [1] and CIP [2] circuits; A: agitator; CP: centrifugal pump; FI: ow indicator; PS: pressure sensor; TH: tank heating; TI: temperature

indicator; V: valves (Ma: manual; 2W: 2 ways; 3W: 3 ways; MD: motorised drive; PR: pressure relief); VP: volumetric pump.

Fig. 1. General drawings of a progressive cavity pump: 1 axial connection, 2 tangential connection.

T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715 9

pump (Fig. 2). An automatic CIP unit was used. Simplelaboratory made software, was run on an IPC 486computer connected to a module, containing 16 auto-matic switches (action in the centrifugal pump and theCIP valves). In addition, the signals of dierent sensors(temperature, ow-rate and pressure) were acquired bymeans of a Hewlett Packard 39970 data acquisitionswitch unit.

2.2. Testing protocol

2.2.1. Soil and soil detectionB. cereus CUETM 98/4 (Collection Unitee Eco Toxi-

cologie Microbienne, Villeneuve dAscq, France) wasused throughout this study. This strain was isolatedfrom a dairy processing line. Spores were obtained aspreviously described (Faille, Lebret, Gavini, & Main-gonnat, 1997).

Commercially available custard containing fat, starch,sucrose, cocoa and skimmed milk was used. Around105 CFU ml1 of B. cereus spores were added to thecustard.

The TTC-nutrient agar was made of 13 g l1 nutrientbroth (Biorad, France) and 15 g l1 agar type E (BiokarDiagnostics) supplemented by 0:1 w/w 2,3,5 triphe-nyltetrazoliumchloride (TTC). This soluble non-col-oured salt which is an electron acceptor, will be reducedin the bacterial cells to formazan which is non-solubleand red. The colonies will be coloured red and easilycounted.

2.2.2. Test methodDuring the soiling step, 12 kg of the contaminated

custard were poured into the tank 60 1 C and cir-culated by means of the pump through connecting pipesfor 1 h at a ow rate of 300 l h1.

The custard was then removed and the CIP wasconnected to the rig. The power of the tested pump wasset at its maximum ow rate of 600 l h1 and the fol-lowing steps were completed:

1. Rinsing with cold tap-water for 2 min, at a ow veloc-ity of 0:5 m s1. A pipe was removed to evaluate thesoiling rate (soiling control or SC) and an unsoiledreference pipe (deposit control or DC) was set intothe test rig.

2. Rinsing with cold tap-water for 6 min, at a ow veloc-ity of 0:5 m s1.

3. Circulating 0.2% NaOH at 60 C for 10 min, at a owvelocity of 1.5 m s1.

4. Rinsing with cold tap-water for 6 min, at a ow veloc-ity of 0:5 m s1.

5. Circulating 0.2% HNO3 at 60 C for 10 min, at a owvelocity of 1.5 m s1.

6. Rinsing with cold tap-water for 6 min, at a ow veloc-ity of 0.5 m s1.

Flow velocities were indicated for the connectingpipes and the entry and exit of the tested pump. Thepump was then completely dismantled, drained and allparts to be tested were protected with aluminium foil toprevent airborne contamination.

All the relevant surfaces were covered with or par-tially immersed in the TTC-nutrient-agar. The volumeof the molten agar poured was chosen to obtain a mouldof a representative part of the internal surface. Thesetest items were incubated for 4 h at room temperature.Removal of the solid TTC-nutrient-agar from pipes andpump pieces was done carefully in order to avoidsmearing the young colonies growing on the agar sur-face in contact with the tested surfaces and to avoiddamaging the moulds. These were then placed in vessels,covered by an aluminium foil to prevent any agar dryingout or contamination and further incubated for 16 h at37 C. The small, red colonies grown on the agar surfacewere counted on photographs, taken using a digitalOlympus camedia C-2020 Z camera.

At least four trials were required to properly analysethe results. The mohnopump was tested four times withan axial CIP connection or six times with a tangentialCIP connection mainly due to some diculties in han-dling the agar moulds.

2.3. Evaluation of the results

The equipment was arbitrarily divided into elemen-tary areas. The partition presented in Fig. 6 was basedon the functional specicity such as the stator (ST),gasket (BB), pipe entry (EP) and exit (EXP) and CIPconnection pipe (EPCIP). In addition, larger areas weredivided into several parts such as 3 for the rotor (RO,AX and RS) and 6 from the motor to the stator/rotorarea for the pump body BC;Ba1; Ba2; Ba3; Bb1; Bb2.

For each part of the equipment tested, the number ofcolony forming units per square centimetre (cfu cm2)was determined after cleaning except for the soilingcontrol (SC). When it was not possible to count Bacilluscolonies due to extensive damage of the mould, an ar-bitrary value was given. This value was calculated asfollows: the median value obtained from the other rep-etitions for the same area was multiplied by the medianvalue from all counts of the same trial divided by theoverall median value of all the repetitions.

S-plus software (Seattle, USA) was used to performthe statistical analysis. Hartigan and Wongs clusteringmethod (1979) allowed us to identify groups of areasaccording to their hygienic level (Hartigan & Wong,1979). A partition of the observations with n groupsthat minimised the within-cluster sum of squares, wasobtained. The number of groups, n was found to beequal to 2 or 3 according to the data. Without assumingnormal distribution, the Friedman multiple comparisonstest (Conover, 1980) was then performed to conrm the

10 T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715

hygienic groups obtained. In addition, box plot dia-grams (Tukey, 1990) were produced: the box contains50% of the data, the horizontal line within the boxcorresponding to the median value. The vertical lines arean index of the data variability.

3. Results

The number of colonies counted on the moulds mayvary greatly between areas (from 1 to more than 40 cfucm2). Given that the largest dierence between soilingcontrol (SC) and cleaning control (CC) pipe data wasfound to be of this order of magnitude, the cleaning ofsome areas in the pump appeared to be as contaminatedas the non-cleaned reference pipe. Apart from any dif-culty in the cleaning ability, this could be due to ahigher amount of spores deposited during soiling. Theobservation of no spore deposition on the deposit con-trol (DC) pipe, allowed us to conclude on the absence ofsurface contamination during cleaning. On the pumpmoulds, such a cfu variation was illustrated in Fig. 3(a)(c). A wide variability was observed on the pump bodymoulds. The largest amount of colonies was found to beclose to the CIP connection (Fig. 3(a) and (b)). Con-versely, the stator mould (Fig. 3(c)) showed an homo-geneous repartition of the colonies.

According to Holah (2000), detection of B. thuringi-ensis by TTC on at surfaces probably covers a range of1100 cfu cm2 above which colonies become undistin-guishable (i.e. 2 log orders). Holah (2000) consideredsuch a range as sucient to both determine cleanabilitydierences by means of colony counts, or by visual as-sessment. On non-at surfaces, the enumeration of B.cereus of more than 40 cfu cm2 was found to be un-certain. This cfu count was thus arbitrarily given whenthe number of cfu was actually uncountable. This couldbe considered as a limit of the use of this technique, as agreat number of elementary surfaces cannot be enu-merated.

The variability between trials was easily visualisedthroughout box plot charts. Data obtained for the twoCIP connections tested are shown in Figs. 4 and 5.When the box plot chart was only based on three legibledata sets, no vertical lines were indicated as shown inFig. 4 ( Ba3; Bb1; Bb2, CE, ST and AX). It is noticeablethat the variability of the attachment of the spores to thesoiling control pipe (SC) was found to be dierent be-tween the data presented in Figs. 4 and 5. However, inboth situations, the soiling control median cfu valueswere similar and less than 10 cfu cm2. The SC vari-ability when testing the CIP axially connected pump,was found to be close to the variability of less hygienicareas. In addition, a high surface contamination alongwith a high variability was observed for the pump bodywhen axially connected to the CIP circuit. A slight

scattering of data was observed for areas such as BC,EP, EPCIP with a maximum of 10 cfu cm

2. The tan-gential connection drastically changed the results interms of variability and signicance of the number ofremaining spores after cleaning (Fig. 5): the highest datavariability, of up to 18 cfu cm2 was observed for Bb2,located at the CIP connection and the mean cfu cm2

values for all the areas remained under 10 cfu cm2.The results of grouping the dierent areas together

(Hartigan & Wong (1979) clustering method) are pre-sented in Figs. 6 and 7 (3 groups) and (2 groups). TheFriedman multiple comparison test P-values were foundto be 0.07 for the tangential CIP and 0.006 for the axialone. This means that the groups (colours) dened werehighly signicantly dierent.

In Fig. 6, for the axially CIP connected pump, mostof the pump elements appeared to be at a poor level,only one area being close to the levels of the pump entry(BC), the stator/rotor (ST, RO), exit pipe (EXP) and therotating parts (RS, AX and RO) being at a moderatelevel. According to Fig. 4, there is a gap between areas ata poor hygienic level and those at a moderate one, thusemphasising the poor hygienic level of the dark greyareas. The highest hygienic areas were found to be theones allowing the pump to be connected to the circuit(EP, EPCIP). In Fig. 7, the tangentially CIP connected

Fig. 3. Examples of the grown colonies on the incubated TTC-nutrient-

agar moulds (axial CIP connection); (a) Pump body; (b) CIP connec-

tion; (c) Stator.

T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715 11

pump, all the pump elements appeared to be at a highhygienic level, some of them clearly more hygienic: alarge part of the body (BC, Ba1; Ba2; Ba3), the stator/rotor area, the rotating parts and as in Fig. 6 the con-necting pipes EP and EPCIP.

4. Discussion

Cleanability tests are often suggested in recent stan-dards without any detail being provided. Only the EN

12462 for biotechnology industries gives general ele-ments on how to evaluate cleanability and explains thatany prescribed threshold value obtained from an ap-proved test should be based on a required safety level.This required safety level should be dened by the re-moval rate of a relevant bacteria. In this work, B. cereusCUETM 98/4 was isolated from milk products, so thatthe risk could be addressed of the processing of a milkyproduct to be pasteurised or sterilised. The chosen strainhad been previously demonstrated by Faille et al. (2001)to adhere to any kind of surfaces (polymer or stainless

Fig. 5. Box plot of the cleanability data for the tangential CIP connection.

Fig. 4. Box plot of the cleanability data for the axial CIP connection.

12 T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715

steel), the soiling level depending on the suspendingmedia. For example, custard as a suspending mediumwas shown to reduce by 100 fold the number of adherentspores when compared to media known to enhance thespore adhesion strength such as saline (Huusmark &Roonner, 1992; Faille et al., 1999). Consequently, a highlevel of spores in custard (105 cfu ml1) allowed a highlevel of adherent spores.

A mild cleaning procedure was chosen to allowcomparison of the hygienic status of the dierent areas.Nevertheless, the cleaning conditions were based onthose in use in industrial practice: sodium hydroxidefollowed by nitric acid (Grassho, 1995). In spite ofthe dierent experimental methods applied, Bird andBartlett (1995); Jeurnink and Brinkmann (1994) andLootscher, Henck, and Gallmann (1994) agreed that 0.51% NaOH was undoubtedly the optimum concentrationfor milk deposit removal. To obtain milder cleaningconditions, only NaOH 0.2% and HNO3 0.1% werechosen together with reasonable cleaning time (10 min)and temperature (60 C).

One of the main factors explaining the cleanability isthe material. The axially CIP connected pump did not

show any particular dierence between its ability to becleaned from that of polymers and stainless steel. TheCSPE stator was shown to be at a moderate hygieniclevel and not at a low one as was most of the pump. Therelatively good cleaning of this part could be explainedby the contact when cleaning between the rotor and thestator. Shear forces at the wall are much higher thanthose generated by the detergent uid ow. In addition,as shown recently by some authors (Huusmark &Roonner, 1992 and Faille et al., 1999) hydrophobicity ofthe material largely explains spore adhesion strength.The water sessile drop technique (Van Oss, 1994) used toevaluate water anity did not show any dierence in thehydrophobicity for stainless steel and CSPE, with awater contact angle below 60 for both materials. Itmust be noticed that the polymer tested here was a newone and the above conclusions could be slightly modi-ed after any ageing eect such as abrasion or scratch-ing. The entrapped micro-organisms would in this casebe highly protected from any sanitising process. Indeed,Holah and Thorpe (1990) on domestic sink materialspointed out the role of ageing on bacterial retention.Changes in surface nish due to abrasion did enhance

Fig. 7. Result of the grouping of the cleanability data for the tangential CIP connection: good (light grey), moderate (grey).

Fig. 6. Grouping of the cleanability data for the horizontal CIP connection: good (light grey), moderate (grey) and low (dark grey).

T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715 13

bacterial retention. The greater the degree of surfaceirregularities, the greater the protection against shearforces during cleaning programmes. Recently, Strogaards,Simola, Sjooberg, and Wirtanen (1999a,b) came to simi-lar conclusions on food processing equipment. Physicaldeterioration was shown on the aged materials testedin industrial processes e.g. ethylene propylene dienemonomer rubber (EPDM), polytetrauoroethylene(PTFE), causing signicant reduction in cleanability.Conversely, no dierence was observed in the clean-ability of new EPDM, PTFE and stainless steel whenCIP parameters typical for dairies were used. In thiswork, for the most hygienic situation (tangential CIPconnection), the stator/rotor area appeared to be com-pletely cleaned. This would improve the hygienic statuseven after any ageing of the CSPE.

Cleanability dierences seemed to be mainly based onthe geometry and therefore on the mechanical eect ofthe detergent ow in the diering parts of the pump.According to Grassho (1992), of greatest importance isthe uid ow in connection with cleaning of deadspaces. Grassho (1980, 1983) found that the uid ex-change (rinsing behaviour) and the local wall shearstress (cleaning behaviour) decreased very rapidly withincreasing stagnant dead space depth. Thus, Ba1 Ba3areas being poorly hygienic, could not really be con-sidered as dead areas but in our cleaning conditions onlyas shadow areas (Fuggle et al., 1998). The detergent owvelocity of 1.5 m s1 in the connection pipes based on along industrial practice (International Association ofMilk Food, 1996; Deutsches Institut fuur Normung,1988) is clearly insucient to eciently ush out all ofthe Ba areas. However, in the axial CIP connectedpump, the BC area close to the pump entry was found tobe more cleanable than the immediate areas of the bodyprobably due to the mechanical action of the CIP owentering the pump. This is a good point for the cleaningof the mechanical shaft seal area, identied as a criticalarea by Fuggle et al. (1998). No particular contamina-tion was thus observed in this area despite the dicultiesin testing such a narrow place. The hygienic status of thebody of the pump appeared to be highly dependent onthe connection to the CIP circuit. The tangential con-nection would allow the detergent to ow through thepump body in a centrifugal pattern and signicantlyenhanced the cleaning eciency, the various areas thenbeing characterised by a high or very high hygienic level(cfu count below 18 per cm2). As far as we know, nowork has yet been done on the eect of an axial exit onthe ow pattern in a pipe. Legrand et al. (1991) de-scribed the swirling decaying ow induced by a tan-gential inlet in an annular space. They concluded thatthe application of a tangential component to the axialmovement leads to a signicant increase in the entrancelength. This phenomenon was associated with an in-crease in momentum transfer and values of the friction

factor were greater in the swirling ow thus inducedespecially at high Reynolds number values. In this work,cleaning was achieved at a Reynolds number of 10,800in the pump body, being above the range studied byLegrand et al. (1991) (up to 3800). It is worth statingthat the specic perturbation induced by the tangentialoutlet, would, in our work, explain this clear increase inthe Bacillus spores removal.

5. Conclusion

The use of spores of a relevant B. cereus strain asmicro-organism indicator in combination with the use ofTTC agar was demonstrated to give sensitive and ac-curate results when testing the cleanability of a positivedisplacement pump, a widely used piece of complexequipment. The use of custard for soiling made themethod even more realistic: besides other criteria, amicro-organisms attachment to equipment surfaces isdependent on environmental conditions. The possibilityof localising and counting the remaining contaminationpermitted an accurate evaluation of the cleaning processof the critical points. Any prescribed threshold value forthe cleanability should be based on a required safetylevel. The risk here is addressed to the processing ofmilky products to be pasteurised or sterilised based onthe micro-organism choice.

A statistical data analysis based on a non-parametricapproach allowed us to pinpoint the importance of thedesign of the connection of any equipment in the foodprocessing line. Geometry appeared here to be a deter-mining factor in the hygienic status of the food pro-cessing equipment. The tangential CIP connection wasshown to enhance the cleanability of the equipment as awhole and not only of the immediate areas. This em-phasised the fact that any equipment testing should takeinto account how the equipment is connected to the CIPloop in its industrial environment. This point is con-sidered as a major one in the EHEDG recommenda-tions.

However, such a technique could not be used on aroutine basis. The handling of nutrient agar when test-ing less accessible areas, e.g. small and/or hidden areasbut potentially in contact with food, is sometimes acritical task. Nevertheless, food processing equipmenthygiene should be rapidly improved in the near future ina practical way.

Acknowledgements

This work was supported by UNIR (UltrapropreNutrition Industrie Recherche) program, involving foodcompanies, the French Ministry of Agriculture, and theFrench Ministry of Research.

14 T. Beeneezech et al. / Journal of Food Engineering 54 (2002) 715

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