MICROCOAGULATION OF PROTEINS FOR DEVELOPMENT OF CREAMINESS

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.