Coagulation of proteins into moist particles of 0. 1-20 mum diameter c
onstitutes the basis of several patents for producing protein-based re
placers for fats and oil/water (O/W) emulsions. The thermomechanical c
oagulation of a whey protein concentrate at acid pH (US patent 4,734,2
87, 1988, J. Labatt Ltd.) or that of egg white proteins on the surface
of casein micelles at neutral pH (International Application WO 89/05,
587, 1989, NutraSweet Co.) provides in both cases spherical particles
with a diameter ranging from 0.1 to 2.0 mum. Precipitation of soluble
proteins at their isoelectric point (European Application 0,400,714, 1
990, NutraSweet Co.) or from ethanol solutions (International Applicat
ion WO 90/03,123, 1990, Enzytech Inc.) provides particles with a diame
ter below 10 mum, when carried out under controlled stirring condition
s. Formation of complexes between electrically charged proteins and po
lysaccharides embedded in modified starch (US Patent 4,308,294, 1981,
General Foods Corp.) or fragmented under high shear forces (European A
pplication 0,340,035, 1989, Kraft Co.) can provide particles in the si
ze range 0.5-15 mum. These and a few other patents are analyzed in ter
ms of. coagulation and particulation mechanisms, optimal processing co
nditions, and food applications. For those patents that have led to th
e commercial fat replacers Simplesse 100 and 300, details are given co
ncerning available structural, rheological, and nutritional characteri
stics of these products. However, their resistance to pH changes, heat
processing, or freeze-thaw, before or after incorporation into variou
s foods, has not yet been reported in a systematic manner. Our own stu
dies deal with the thermomechanical coagulation of a whey protein isol
ate (free from fat and lactose) either at acid pH (3.5-3.9) or at neut
ral pH (6.5-6.7) in association with calcium caseinate, used as an inh
ibitor against extensive protein aggregation. The thermomechanical pro
cess is carried out in a long-barrel twin-screw extruder (water conten
t almost-equal-to 77%; protein content almost-equal-to 20%; barrel tem
perature = 85-degrees-100-degrees-C; screw rotation speed = 100-200 rp
m; feed rate = 20 kg/h). The resulting semisolid spreads displayed hig
h nitrogen solubility: 4347% and 69-70% for the acid and the neutral p
roducts, respectively. The beta-lactoglobulin constituent was totally
soluble in 1% SDS in the case of the acid product, while the degree of
solubility depended on the process conditions in the case of the neut
ral product. Differential scanning calorimetry indicated 80% and 70% w
hey protein unfolding for the acid and neutral products, respectively.
Laser diffractometry revealed for both products that over 50% of the
particles had a diameter range within 6 and 11 mum (on a volume basis)
. Viscoelasticity characteristics were studied with an oscillatory rhe
ometer. The texture of these fat replacers was only slightly affected
by freezing and thawing. Their utilization for the preparation of give
n low-fat or fat-free foods showed that they were easily dispersed at
a 5-10% level, developed desirable ''creaminess,'' and withstood to so
me extent the heat process given to the final food.