MICROCOAGULATION OF PROTEINS FOR DEVELOPMENT OF CREAMINESS

Coagulation of proteins into moist particles of 0. 1-20 mum diameter constitutes the basis of several patents for producing protein-based replacers for fats and oil/water (O/W) emulsions. The thermomechanical coagulation of a whey protein concentrate at acid pH (US patent 4,734,287, 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, 1990, NutraSweet Co.) or from ethanol solutions (International Application WO 90/03,123, 1990, Enzytech Inc.) provides particles with a diameter below 10 mum, when carried out under controlled stirring conditions. Formation of complexes between electrically charged proteins and polysaccharides embedded in modified starch (US Patent 4,308,294, 1981, General Foods Corp.) or fragmented under high shear forces (European Application 0,340,035, 1989, Kraft Co.) can provide particles in the size range 0.5-15 mum. These and a few other patents are analyzed in terms of. coagulation and particulation mechanisms, optimal processing conditions, and food applications. For those patents that have led to the commercial fat replacers Simplesse 100 and 300, details are given concerning available structural, rheological, and nutritional characteristics of these products. However, their resistance to pH changes, heat processing, or freeze-thaw, before or after incorporation into various foods, has not yet been reported in a systematic manner. Our own studies deal with the thermomechanical coagulation of a whey protein isolate (free from fat and lactose) either at acid pH (3.5-3.9) or at neutral pH (6.5-6.7) in association with calcium caseinate, used as an inhibitor against extensive protein aggregation. The thermomechanical process is carried out in a long-barrel twin-screw extruder (water content almost-equal-to 77%; protein content almost-equal-to 20%; barrel temperature = 85-degrees-100-degrees-C; screw rotation speed = 100-200 rpm; feed rate = 20 kg/h). The resulting semisolid spreads displayed high nitrogen solubility: 4347% and 69-70% for the acid and the neutral products, 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 neutral product. Differential scanning calorimetry indicated 80% and 70% whey 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 rheometer. The texture of these fat replacers was only slightly affected by freezing and thawing. Their utilization for the preparation of given low-fat or fat-free foods showed that they were easily dispersed at a 5-10% level, developed desirable ''creaminess,'' and withstood to some extent the heat process given to the final food.