Handbook of Hygiene Control in the Food Industry

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whereA(m^2 ) is the disc surfacearea,and is the fractioncoveredby the sample
measured by imageanalysis as described above.The relationship betweenand
the actualadhesivestrengthbetweenthe surface and the deposit is not clear,as
the measuredforcenot only removesthe depositfromthe surfacebut also
deforms it.
Twotypesof measurementare possible:(i) totalremoval,in whichboth
adhesiveand cohesiveforcesare overcome,and (ii) partialremovalof deposit
to measurecohesivestrength.Thishas beendonefor fourdeposits.Figure
29.3comparesthe resultsfor full removal(adhesive)and partialremoval
(cohesive)for fourtypesof deposit.For tomatopaste(Fig.29.3a),the force
requiredfor partialremovalof the depositexceedsthat for the totalremoval,

Fig. 29.3(continued) Comparisonof the energyrequiredfor partialand totalremoval
of depositsof (c) breaddough,and (d) egg albuminshowingdifferencesin cohesiveand
adhesivebehaviour(Liuet al., 2005).

Improvingthe cleaning of heatexchangers 485