(2002)statethat the unfoldedmolecules, oligomers,dimersand monomers that
dissociate fromlargeraggregates by treatment withSDSwouldnot be predicted
by the Roefsand de Kruifmodel.
The difficulty of storageand cost of usingraw milkin researchled to the use
of whey protein concentrate(WPC)solutions by a numberof authors (suchas
Gillham, 1997;Robbinset al., 1999).Use of WPCavoidsthe naturalvariations
associated withmilkand enables reproduciblefoulingbehaviourto be obtained.
Heattreatmentof WPC solution causesa depositsimilar to Type A frommilk;
heavyprotein fouling of this typeoccurs at all temperaturesin the range85±
140 ÎC (Robbinset al., 1999). However, in contrast to WPCprocessing,milk
doesnot produce a depositbetween 100 and 120 ÎC. Also,unlikemilk,WPC
doesnot produce a mineralscale at UHTtemperatures.The extent of fouling
fromWPC solutionincreaseswithincreasing temperature.
Hegeand Kessler(1986b) notedthat afteran hour,whereTypeA depositis
initially formed, a mineral-rich layer (mainly calcium and phosphorus)
developednextto the heattransfer surface. The protein remained as an outer
layer,thusformingtwo distinct layerswithinthe deposit. Tissierand Lalande
(1986)suggested this was due to diffusionof minerals throughthe protein layer
and crystallisation of calciumphosphateat the heattransfer surface. Type B
depositis hardand granular rather thansoft and spongylike Type A (Lyster,
1965).A mineral-richlayer(calcium, phosphorus and magnesium) formsat the
heat exchanger surface(Fosterand Green,1990).The sameauthorsfoundthat,
despitethere not beingdistinct layerswithin the TypeB deposit, proteinwas
concentratednear the outside of the deposit. Lalandeet al. (1985)foundthat the
calcium phosphate depositedon surfaces withina plateheat exchanger(PHE) is
a mixture of dicalciumphosphate dihydrate (DCPD) (CaHPO 4 2H 2 O) and
octacalcium phosphate (OCP)(Ca 8 H 2 (PO 4 ) 6 5H 2 O).
Foulingfrommilkprocessing is thought to be due to a combination of a
number of different foulingmechanisms.Oftenthereis a lag (induction) period,
duringwhichno changein heattransfercoefficient of pressuredrop occurs,
beforefouling commences.Belmar-Beinyand Fryer(1992,1993)studiedthe
Table29.3 Compositionof depositsformedby milkat differenttemperatures.The
balanceof the percentagecomposition is madeup by other componentssuch as
carbohydrate(Burton,1968)
Processing Temperature Composition Appearance
conditionsTypeA Pasteurisation up to 100 ÎC Protein:50±60% Soft voluminous,curd-
Mineral:30±35% like material,white
Fat: 4±8% or creamin colour
TypeB UHT 100±140ÎC Protein:15±20% Brittle,grittyand grey
Mineral:70% in colour
Fat: 4±8%
Improvingthe cleaning of heatexchangers 473