∑ the soil removalproperties should be more or less similar to those in
practice.
Testcoupons with soilscomplyingwiththeserequirements wereproduced in a
heatingplant on a laboratoryscale(Grasshoff, 1999).In a heatingtrial overfour
hours, foulings frommilkcomponents wereformedon the metallic coupons.
Theirchemical compositionwas verysimilarto that occurringin practicein
milkpasteurizingplants. At the end of the heatingthe couponswereremoved
fromthe plant, rinsedwithdistilledwater, and air-dried. For a longer period
(several weeks), theycouldbe storedwithouta measurable modification of the
scaling-offpropertiesof the fouling in subsequentcleaningprocesses.
The cleaningtrialswereperformedin a flowchannelwithrectangularcross-
section 3 65 mm^2 and a frontagefromacrylicglass,throughwhichthe cleaning
solutionsto be testedunderdefinedconditions(temperature,concentration,flow
velocity)werepumped.The test couponsto be cleanedwereinsertedin the rear ward
channelwall.The scaling-off operationof the foulingswas observed fromthe front
side witha videocamerathe outputsignalof whichwas connectedto a computer.
Figure32.1displaysthe experimentalset-upof the trial.On individualimages,
whichweresavedat regularintervals,the surfacedepositswerequantitatively
detectedvia electronicimageanalysiswithinthe `areaof interest'on the test
coupons,in whichthe foulinghad beenremovedup to the metallicsurface.
32.3.2 Availableenzymes and enzyme-containingready-maderecipes
Theenzymesavailable for laboratory tests as wellas their operatingdata
deliveredby the enzymeproducerare presented in Table32.1.For detailsabout
the enzymes, pleasereferto Grasshoff (1999).
For practicaluse, two ready-maderecipeswith the enzymesSavinase’16.0
and Properase’L 1600(ChemischeFabrikDr. Weigert,Germany)wereused.
Apartfromthe enzymes, theycontainedstabilizers for improving storability
and/orfor pH regulation. The two recipescontained5% enzymeand had to be
appliedin a 1% solution.In the first recipe,the pH value had to be adjusted to
the recommended pH optimum for the enzyme by adding Na 2 HPO 4 as a buffer
substance and NaOH.The secondrecipewas adjustedto the processwater(type
and concentrationof the watersalts) availablefor the application,and contained,
apartfromthe enzymestabilizers, special surfactants, so that the solutioncould
be produced directly, without anyother measures, except for temperature
adjustment, withthe availableprocess water.
32.3.3 Descriptionof the enzyme`Savinase'
A detaileddescriptionof the enzyme Savinase and of Savinase-containing
recipeswill followas the enzymehad proven its highefficiency at the laboratory
scalefor the cleaningof milkheatexchangers (cf. resultspresentedbelow).
Technically, it is produced by submersefermentationof genetically modified
Bacillusstrains. Its efficiency is basedon its abilityto hydrolyse water-insoluble
Enzymatic cleaning in foodprocessing 523