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Abstract
Moisture adsorption isotherms of spray-dried whole egg, microencapsulated with gelatin (G), lactose (L), pullulan (P), and their mixtures at equal ratios (gelatin + lactose [GL] and gelatin +pullulan [GP]), were determined using the standard static-gravimetric method at 25°C. The data were fitted to the various sorption models and the constants were estimated by nonlinear regression analysis. Among the sorption models tested, the Guggenheim-Andersen-de Boer (GAB) and Ferro Fontan equations were recommended for characterizing the adsorption behavior of spray-dried whole egg, either microencapsulated or unencapsulated, in the water activity range of 0.11–0.84. It was indicated that all of the egg powders were stable up to a water activity of 0.43. The oxidative stability of microencapsulated powders was investigated under storage conditions of 20°C and 50% relative humidity (RH). The microencapsulation process resulted in a decrease in the cholesterol oxidation level of egg powder during storage, where it followed a zero-order reaction kinetics and the t rej value representing the time required to reach total cholesterol oxidation products (TCOP) = 384.2 µg/g egg fat as the upper limit of acceptability for fat oxidation was calculated as 1,124 days at 20°C for egg powder microencapsulated with lactose. The relations among glass transition temperatures, oxidation rate constants, and monolayer moisture content values obtained by the GAB model are also highlighted.
ACKNOWLEDGMENTS
The authors acknowledge TUBITAK-TOVAG (Project No. 108 O 541); Ege University, Council of Scientific Research Projects (Project No. BAP 2008/MÜH/012); and Ege University, Science and Technology Center (Project No. EBİLTEM 09/BİL/014) for financial support. The authors also thank Mix Food Company, Izmir, Turkey, for material support.
Notes
GL = gelatin + lactose; L = lactose; GP = gelatin + pullulan; P = pullulan; G = gelatin; E = egg powder without wall material.
GL = gelatin + lactose; L = lactose; GP = gelatin + pullulan; P = pullulan; G = gelatin; E = egg powder without wall material.