Whey proteins (WP) are widely used in a variety of food formulations and constitute a significant share of the dairy ingredients market. In this research WP functionalities were modified using a novel reactive supercritical fluid extrusion (SCFX) process. High pressure extrusion of WP under different pH conditions and in the presence of mineral salts, combined with a delicate control of heat, shear, and internal environments created by introduction of supercritical carbon dioxide (SCCO2), was used to texturize and develop unique functional properties in commercially available whey protein concentrate (WPC). A feed formulation comprising (w/w) 94% WPC-80, 6% pre-gelatinized corn starch, 0.6% (WP-starch basis) NaCl, and 0.6% (WP-starch basis) CaCl2 was texturized in a high-pressure extruder at 90 degree C and 60% (dry feed basis) moisture in the pH range of 2.89 to 8.16 with 1% (dry feed basis) SC-CO2 injected as a blowing agent. The average specific mechanical energy (SME) input for the process was 57 Wh/ kg. The resulting texturized WPC (tWPC) extrudates were dried, ground into powder, reconstituted in deionized water and evaluated for their rheological and physicochemical properties. The rheological behavior of tWPC was found to be strongly dependent on the pH and SC-CO2 levels used during extrusion. The highest apparent viscosity (nu =2.06 Pas) and elastic modulus (G'=10 kPa) values were observed in the tWPC produced at extremely acidic condition (pH 2.89) with SC-CO2 injection and were significantly higher than those exhibited by the unextruded control (nu = 0.008 Pas, and G'= 0.04 Pa). A 20% (w/w) tWPC dispersion exhibited a highly viscous and creamy texture with particle size in the micron-range (mean diameter ~ 5 mu-m) which could serve as a thickening/gelling agent or as a fat substitute in food formulations over a wide range of temperatures. The soluble protein content and free sulfhydryl groups of the tWPC decreased by approximately 20% and 16% relative to the unextruded control. The tWPC was completely soluble in the presence of urea (8 M) and sodium dodecyl sulfate (0.5%) without a reducing agent, indicating that the non-covalent interactions (hydrophobic interactions and hydrogen bonds) were mainly responsible for the structural formation of the tWPC. A homogeneous gel-like emulsion of creamy consistency was also successfully produced by incorporation of corn oil with tWPC dispersion in water serving as the continuous aqueous phase. Only 4% (w/w) tWPC was needed to emulsify 80% corn oil and it showed a higher thermal stability upon heating to 85 degree C. It also showed excellent emulsifying properties (emulsion activity index, EAI, = 431 m exp(-2) g exp(-1), emulsion stability index, ESI, = 13,500 h) compared to the commercial WPC-80 (EAI = 112 m exp(-2) g exp(-1), ESI = 32 h). Emulsions prepared with such small amounts of tWPC showed an enhanced adsorption of proteins at the oil-water interface which prevented flocculation and coalescence of the oil droplets, and an increase in the viscosity of the continuous phase which prevented creaming by trapping the oil droplets within the gel matrix. These attributes helped generate very stable oil-in-water emulsions of important utility in food formulations and should be useful in new product development.
展开▼
