separator wereopenedfor control purposes. Oncemoreall the product flow
paths and the surfacesin touchwiththe productof the separator werevisually
clean. Noneof the microbiological samplestakenfromthe heated product
during the entiretrial periodrevealedabnormal findings.
32.5 Risks..
Apart fromthe function of the enzymes as cleaningagentsit is important for the
dairy, particularly for the manufacturers of yogurtor cheese,to understandthe
risks that may arise with the conversion from conventional cleaning to
enzymatic cleaning, e.g.,whethera change or disturbanceof the rennetting
ability of the process milkis to be expectedif the milkis contaminatedby
residues of the enzymesolution.To answer this question, the `worstcasein the
dairy', namelythe interminglingof cheese factory milkwithenzymeresidues
fromthe heat exchanger cleaning, was simulated in a laboratorytrial (Grasshoff,
1999).The trial was expressly donewithoutan acidactivationof the enzyme
residues, other thanin practice.It was presumedthat 10 L of a 1% enzyme
reciperemained in the heat exchangersystemand that thesewereintermingled
with10 000 L cheesefactorymilk.Thiscorresponds to a concentration of 1.0 mg
of the enzyme recipein 100 mL milk.In the laboratorytrialpasteurizedmilk
was mixedwitha differentlydilutedenzymerecipe,and was left for 30 min at
34 ÎC for simulation of pre-ripening.Afterwards, rennet enzyme was addedand
stirred. Fromthe mixture,1 mL was filledinto eachof two cuvettes of a lacto
dynamograph (devicefor measuringcoagulation; Hellige Thrombelastograph,
Germany).Withthis deviceoperating in a similar way to a rotationviscometer,
the periodsR 0 up to coagulation,andK 20 up to an amplitudeof 20 mm were
detected on the chartrecorder as wellas amplitudeA 10 in mm 10 min afterthe
beginningof coagulation.
Froman enzymepreparationcontaining5%Savinase,four differentdilutions
werepreparedand addedto a givenvolumeof the cheesefactory milk.The
samples contained0.1 mg, 0.5 mg, 1.0 mg and 10.0 mg of the enzyme recipeper
100 mL milk.In all the samplesthe coagulation behaviour was analysed, and
comparedwiththe results of a milksamplewithout enzymeadditionthat served
as a blindsamplebeforeand afterwards.Againstthe zero samplea shortenedR 0
period (11.0min insteadof 19.5min)was measuredup to the beginning of the
rennet coagulation onlyin the samplewith 10 mg of the Savinase recipe.The
K 20 andA 10 values displayed no modification against the referencesample. The
preparations with0.1, 0.5 and 1.0 mg enzyme recipe/100mL milkdisplayed no
significantdifferenceversusthe blindsample. Enzymesupplementsin this order
of magnitudemayhaveno influenceon the rennet behaviourof milk.
Coagulationtrials werealsoperformedwitha preparation containing5%
Properase 1,600L, namely withconcentrations1, 10 and 50 mg/100mL milk
related to the enzymerecipe.Hereby,the first dilutionshowedno deviationfrom
the zerosample.The additionof 10 mg enzyme recipeto 100 mL milkcaused a
534 Handbookof hygiene controlin the foodindustry