The material presented inthis publication has beenprepared for the generalinformation of the readerand should not be used orrelied on for specificapplications without firstsecuring competent advice.The Nickel DevelopmentInstitute, its members, staffand consultants do notrepresent or warrant itssuitability for any general orspecific use and assume noliability or responsibility ofany kind in connection withthe information herein.
Journal of Applied Bacteriology 1993, 75, 91-94The effect of wiping and spray-wash temperature on bacterialretention on abraded domestic sink surffacesR.A. Stevens and J.T. HolahFood Hygiene Department, Campden Food and Drink Research Association, Chipping Campden, Gloucestershire4207/05/92: accepted 8 February 1993R.A. STEVENS AND J.T. HOLAH. 1993. The relative cleanability of artificially abraded stainlesssteel, enamelled steel, mineral resin and polycarbonate domestic sinks was assessed byexamining bacterial retention after cleaning. Two cleaning regimes were used: the mechanicalaction of wiping combined with a spray-rinse, and spray-washing at a range of temperatures.After wiping, stainless steel retained O' 5-1 log order fewer bacteria than the enamel sinkswhich in turn were O' 5 log order cleaner than the mineral resin and polycarbonate sinks. Afterspray-washing, stainless steel retained O' 5 log order fewer bacteria than enamel which in turnwas O' 5 log order cleaner than the polycarbonate and mineral resin. Extending the number ofwipes or increasing spray-wash temperature enhanced bacterial removal but, in general, didnot change the relative cleanability of the sink materials. As a cleaning technique, wiping wasshown to be more effective than spray-washing in reducing bacterial numbers. SEM studiesshowed that bacteria were typically retained in surface imperfections, particularly pits andcrevices such that surfaces which sustained the most extensive damage due to abrasionretained higher numbers of bacteria.INTRODUCTIONFactors to be considered in the comparison of materials tobe used as food contact surfaces include durability, cost andcleanability. Surface hygiene is a critical consideration forfood preparation areas because of the possibility of contamination of food. Kitchen and catering sinks are sourcesof contamination by food spoilage and/or pathogenic bacteria. Sink materials that retain fewer numbers of bacteriaafter cleaning would be the hygienic choice and present theleast risk of contamination.A previous investigation (Holah and Thorpe 1990)assessed the cleanability of stainless steel, enamelled steel,mineral resin and polycarbonate sinks both before and afterartificial abrasion. No difference in cleanability of unusedsink surfaces was found but stainless steel, abraded toproduce a finish not dissimilar to that observed on naturallyworn domestic stainless steel sinks, was approximately 10times more cleanable than the other sink materials subjected to the same treatment. Further to this, extending thecleaning time did not enhance bacterial removal from theother surfaces as compared with stainless steel. This difference in cleanability was thought to be caused by the characCorrespondence to: Dr J. 1". Holah, Food Hygiene Department, CampdenFood and Drink Research Assol"iatllin, Chipping Campden, GloucestershlreGLSS 6LD.teristic surface changes due to the abrasion, with stainlesssteel being most resistant to surface change.This work sought to determine the relative retention ofbacteria on the same abraded sink materials by investigatingadditional cleaning factors. These were the influence ofwiping, a mechanical cleaning force, combined with aspray-rinse and the effect of spray-wash temperature.MATERIALS AND METHODSPreparation of sink samplesTwo examples, from different manufacturers of the following sink material types were purchased: austenitic stainlesssteel (sinks I and 2), polycarbonate (sinks 3 and 4),enamelled stecl (sinks 5 and 6) and mineral resin (sinks 7and 8). Sinks 1 to 8, inclusive, were the same makes andmodels as purchased for earlier studies (Holah and Thorpe1990). A ferritic stainless steel sink was also purchased (sink9). Sample pieces, 40 x 20 mm and 80 x 60 mm in size,were removed from the sink bases and abraded as describedby Holah and Thorpe (1990). Surface roughness wasassessed before and after abrasion using a surface roughnessmeasuring instrument (Rank Taylor Hobson Surtronic 3P,Leicester, CK) (Anon. 1984a,b).
92 RA STEVENS AND J.T. HOLAHCleaning studiesBiofilms of Acinetobacter calcoaceticus (Campden Food andDrink Research Association Culture Collection-CRA 296)were attached to sink samples using techniques describedby Holah et al. (1989). The samples were wiped with an80 x 60 x 25 mm synthetic open pore sponge held in astainless steel casing to which a steel block was attached.The combined weight of the casing and the block was 692 gwhich simulated the mean force measured when volunteersproduced a wiping action on a balance pan. For each80 x 60 mm sink piece, a sponge was moistened with 5 mldistilled water. A O' 5 ml volume of a domestic washing-upliquid (Velvet, Maigret Chemicals Ltd, Daventry, UK) wasthen pipetted on the centre of the sponge. The sponge/weight was placed on the edge of the sink piece and pulledacross its length. For multiple wipes (two, three or fivewipes), the sponge was lifted off the sample after the firstwipe and placed back on the starting edge for the nextwipe. The sink pieces were rinsed with a purpose-builtcleaning rig which produced spraying conditions as previously used (Holah and Thorpe 1990). The rig consistedof a 20 I tank, feeding into a centrifugal pump (StuartTurner, Henley-on-Thames, Oxon), a needle valve for flowcontrol and a relief valve to return surplus flow to the tank.The main cleaning flow passed through a braided hose to asprinkler head under which samples to be sprayed werepositioned. Samples that had been wiped and rinsed wererinsed for 10 s with potable water (II QC). Samples thatwere spray cleaned were sprayed with a 0·33% v/vaqueoussolution of Velvet at a range of temperatures for 5 s. Detergent residues were rinsed off with distilled water from awash bottle before attached bacteria were enumerated.Bacteria were enumerated on sink samples by direct epifluorescent microscopy (DEM) (Holah et al. 1989).Samples were examined under oil at 1000 x magnificationwith an epifluorescent microscope linked via a video camerato an Optomax V Image Analysis System (Analytical Measuring Systems, UK). The total surface area covered byfluorescing bacteria was measured for each field and converted to bacteria per cm 2 by dividing the area of coverageby the area of one bacterium and multiplying by thenumber of field areas in one cm 2. The area of one bacterium was determined by selecting 'Edit Mode' and initiating a measurement of the area of a single cell. This wasrepeated 20 times and the mean value, 1·4p 2, was employedin a user-defined parameter which converted total bacterialcount to count per cm 2 . An enumeration of 20 fields ofview was undertaken for each sample and results expressedas colony-forming units (cfu) per cm 2 .Two-way analysis of variance (ANOVA) was used to testwhether there were significant differences between sinkmaterials and whether there was an effect of number ofwipes or spray-wash temperature. An interaction term wasincluded in the ANOVA to assess whether the number ofwipes or spray-wash temperature had any effect on therelative performance of the sink materials. Conventionalsignificance levels (P 0'05) were used. When theANOVA test indicated a significant difference be weenmaterials, a Newman-Keuls multiple range test (Snedecorand Cochran 1980) was carried out. This test was employedto categorize the sink materials into groups for whichsimilar cleanability was obtained.RESUL 1S AND DISCUSSIONSurface roughness measurements (not shown) and visualexaminations by scanning electron microscopy (SEM) indicated that there was little difference, before and after abrasion, in the sink materials used in this and the previousstudy (Holah and Thorpe 1990).For the wiping trials control counts of biofilm development on all sink samples indicated little difference betweenthe sink types, with counts ca 5 x 10 6 cfu per cm 2 . Meanlog counts from 15 wiping trials each at one, two, three andfive wipes are shown in Fig. I. Two-way analysis ofvariance with interaction (number of wipes x material)showed that extended wiping enhanced cleanability of thesink surfaces (P 0·00 I) and showed a significant difference in cleanability for the different sink materials(P 0,001). Where significance was obtained, NewmanKeuls multiple range tests were performed on each set ofwiping trial results to categorize the sink materials intogroups of similar cleanability using 5% significance levels(Table 1).The results in Table I indicated that stainless steel sinkswere significantly more cleanable than the enamel, poly-3L- .L. ----lo2.l.- --J. - - l345Number of wipesFig. 1 Mean (n 15) log cfu per cm 2 vs number of wipes for arange of abraded domestic sink materials. SS, Stainless steel; E,enamelled steel; MR, mineral resin; P, polycarbonate; . "',SS I; . D. ., SS 2;·" 0 "', SS 9; - --, P 3; -D.--,P 4; - -, E 5; -D.-, E 6; - -, MR 7; --D.-, MR 8
ABRADED SINK MATERIAL CLEANABILITY 93Table 1 Analysis of wiping trial resultsSink material1 Wipesubscript2 Wipessubscript3 Wipessubscript5 WipessubscriptStainless steel 1Stainless steel 2Stainless steel 9Enamelled steel 5Enamelled steel 6Mineral resin 7Mineral resin 8Polycarbonate 3Polycarbonate 4abcdeffggabaccdedeffabacceddeaaabccbbcccNote: Subscript labels range from a (best) to g (worst), withintermediate materials labelled ab, bc, etc. Materials with nocommon subscript were found to be significantly differentwhereas those with a common subscript did not differ significantly.Materials were graded according to bacterial removal after cleaning with Newman-Keuls multiple range tests (5% significance).Results for each of 1, 2, 3 and 5 wipes were treated independently.less steel sinks after one wipe was not achieved after fivewipes by the other materials.For the spray-wash temperature trials, control counts ofbiofilm development on all sink pieces indicated little difference between the sinks with counts ca 10 7 cfu per cm 2 Mean log counts from IS spray-wash trials each at lOoe,25 C, 40 e and 55 e are shown in Fig. 2. Two-wayanalysis of variance with interaction (spray-washtemperature x material) showed a significant difference(P 0,001) for both material type and temperature withthe most significant differences for temperature notedbetween 25 e and 40 C. Sinks were categorized accordingto cleanability at each temperature using Newman-Keulsmultiple range tests at the 5% significance level (Table 2).Results in Table 2 showed that the stainless steel sinkswere significantly more cleanable than enamel sink 6, both07"'E 6'"0.-t'"S'carbonate and mineral resin sinks after one, two, three andfive wipes. The enamelled steel sinks ranked next in orderof cleanability, with enamel sink 5 performing better at onewipe than enamel sink 6. The enamel sinks were 0·5 toI log order less cleanable than the stainless steel sinks butwere approximately O' 5 log order more cleanable than themineral resin and polycarbonate sinks, which achievedsimilar levels of cleanability.Sink surface cleanability increased with the number ofwipes (Fig. I) though the rank order of the sinks remainedthe same. The degree of cleanability achieved by the stain-Table 2 Analysis of spray-wash trial§ 5'"::;;;\0'-----::10:--:1 -5-2:-'0::- 2'::"5---:3:'::0:--- 3':"5--:4.L:0-4-:l:5:---5L.0-5.J.5-.I60Spray-wash temperature (Oe)15) log cfu per cm 2 vs spray-wash temperaturefor a range of abraded domestic sink materials. SS, Stainless steel;E, enamelled steel; MR, mineral resin; P, polycarbonate;. ., SS 1; . 6"', SS 2; . 0"', SS 9; - --, P 3;-6--, P4;- -, E 5;-6-, E 6;- -, MR 7;-6-,MR8Fig. 2 Mean (n Sink materiallOoespray-washsubscript25 espray-washsubscript40 espray-washsubscript55 espray-washsubscriptStainless steel IStainless steel 2Stainless steel 9Enamelled steel 5Enamelled steel 6Mineral resin 7Mineral resin 8Polycarbonate 3Polycarbonate lts0See footnote to Table 1.Materials were graded according to bacterial removal after 5s spray-wash cleaning withNewman-Keuls multiple range tests (5% significance). Data obtained at each temperature were treated independently.
94 R.A. STEVENS AND J.T HOLAHmineral resin sinks and both polycarbonate sinks at lOoCand 25 C, and all of the sinks at 40 C and 55 C. No significant difference was shown between the polycarbonate sinksand mineral resin sink 7 at the four test temperatures. At55 C, enamel sink 6, both mineral resin sinks and bothpolycarbonate sinks achieved similar levels of cleanability.Two effects were seen with increasing spray-wash watertemperature. First, all of the sink materials showedenhanced cleanability with increased temperature. Secondly, the difference in cleanability between stainless steeland the other materials became more pronounced as thespray-wash temperature was increased. For example, thiseffect was shown for enamel sink 5 which, although notsignificantly different from the stainless steel sinks at lOoCand 25 C, was significantly less cleanable than stainlesssteel at 40 C and 55 C.Overall results suggest that five wipes followed by a 10 srinse removed more bacteria per cm 2 than did spraywashing at the highest test temperature (55 C) (Figs 1 and2). Wiping five times followed by a 10 s rinse removedapproximately 1 log order more bacteria than did spraywashing at 55 C for each of the sinks. Similar conclusionswere observed by Offiler (1990) who suggested that of thefour cleaning factors, mechanical force has a greater influence on cleaning action than solution temperature, chemicaltype or time of application.Observations with SEM revealed no apparent differencebetween areas of bacterial retention after the spray-washingand the wiping trials and bacteria were typically retained inareas that had been most affected by the abrasion process,e.g. pits and crevices. Results from this work, together withthose from the previous study, further suggest a relationship between surface topography and bacterial retentionafter cleaning. This is in agreement with other workers whohave demonstrated enhanced bacterial attachment associated with increasing surface roughness (Characklis 1973;Gibbons and Denton 1981) and conversely, reduced cleanability as measured by bacterial retention (Timperley andLawson 1980; Hoffmann and Reuter 1984).In conclusion, this and the previous study suggest thatpolycarbonate, mineral resin and enamelled steel sink surfaces are more readily damaged by abrasion such that theywould require a more stringent cleaning programme. Withextended cleaning, however, they may still not achieve adegree of surface hygiene comparable to abrasion-resistantmaterials such as stainless steel. It could be suggested,therefore, that for construction of domestic and cateringsinks (and also for other food handling equipment),abrasion-resistant materials would not only be moredurable but are also likely to remain more hygienicthroughout use.ACKNOWLEDGEMENTSCampden Food and Drink Research Association wishes tothank the Nickel Development Institute, Toronto, Canada,for their financial support and permission to publish thiswork.REFERENCESAnon. (1984a) ISO 4287-1: 1984 Surface RoughnessTerminology-·Part 1: Surface and its Parameters. Geneva:International Organisation for Standards.Anon. (1984b) ISO 4287-2: 1984 Surface RoughnessTerminology-Part 2: Measurements of Surface RoughnessParameters. Geneva: International Organisation for Standards.Characklis, W.G. (1973) Attached microbial growths; 1. Attachment and growth. Water Research 7, 1113.Gibbons, D.B. and Denton, P.H. (1981) Surface roughness andbiofouling. In Proceedings of the 2nd World Congress of ChemicalEngineerzng, Vol. I, pp. 430-441. Montreal, Canada: CanadianSociety for Chemical Engineering.Hoffman, W. and Reuter, H. (1984) Effect of surface roughnessand other factors on circulation cleaning of straight pipes.Chemis-Ingenieur-Technik 56, 328-329.Holah, J-T. and Thorpe, R.H. (1990) Cleanability in relation tobacterial retention on unused an abraded domestic sinkmaterials. Journal ofApplted Bacteriology 69, 599-608.Holah, J-T., Betts, R.P. and Thorpe, R.H. (1989) Thc use ofdirect epifluorescent microscopy to determine surface hygiene.International B/IIdeterioratlOn 25, 147-153.Offiler, M.T. (1990) Open plant cleaning: equipment andmethods. In Proceedings or H)'giene for the 90s, '\"oyember 7-X.Campden Food and Drink Research Association, UK.Snedecor, G.W. and Cochran, W.G. (1980) Statistlwl iHethods,6th edn, pp. 273-275. Ames, Iowa: State Lniyersity Press.Timperley, D.A. and Lawson, G.B. (1980) Test rigs for evaluation of hygiene in plant design. In HygieniC DeSign and Operation of Food Plant ed. Jowitt, R. Chichester: Ellis HorwoodLtd.
Journal ofApplied Bacteriology 1993, 75, 91-94 The effect of wiping and spray-washtemperature on bacterial retention on abraded domestic sink surffaces R.A. Stevens and J.T. Holah Food Hygiene Department, Campden Food andDrink Research Association, Chipping Campden, Gloucestershire 4207/05/92: accepted 8 February 1993 R.A. STEVENS AND J.T .
was some improvement. Removal of nickel from the spent electroless nickel bath was 81.81% at 5 A/dm 2 and pH 4.23. Under this condition, the content of nickel was reduced to 0.94 g/L from 5.16 g/L. with 62.97% current efficiency. Keywords: Electroless bath, Nickel, Electrolytic reduction, Nickel Recovery, Current efficiency. Introduction
The Journal of Bacteriology was first published in January 1916 and continues today. Abstracts of Bacteriology was published from February 1916 until December 1925. 9. Claude P. Brown, “Arthur Parker Hitchens, 1877–1949,” Journal of Bacteriology 60, no. 1 (1950): 2. 10. The Rockefeller Institute of Medical Research (RIMR), which opened in .
in the ASME Journal ofApplied Mechanics, Transactions ofthe American Society OfMechanical Engineers, September 1951, pages 293-297as described above. Discussion ofhis paper was reported in the ASMEJournal ofApplied Mechanics, Transactions ofthe American Society OfMechanical Engineers, June 1952, pages 233 234 as described on the following pages.
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