RESPONSE SURFACE ANALYSIS OF EGG WHITE GELLING PROPERTIES IN A MEAT LOAF ANALOG

The effects of pH (5.0 to 7.0), salt content (0 to 3%), cooking time (15 to 75 min at 100°C), soy isolate and egg white level (both from 1 to 5%) on the gel strength of a model meat loaf analog system are investigated. An Instron Universal tester is used for evaluating the analog's strength of various compositions. The study indicates an insignificant influence of pH and soy isolate content on the analog's strength. Effects of egg white content, salt content, and cooking time are expressed in terms of a second order polynomial, where linear effects and interactions are shown to be significant. Egg white content and cooking time are exponentially related to the hardness, whereas, salt content is linearly proportional to the logarithm of hardness. Response surface analysis reveals that egg white usage can be greatly reduced if salt content and cooking time are manipulated. This study provides a model that can be used to optimize a process for producing meat loaf analogs.     

PICKLING TIME AND ELECTRODIALYSIS AFFECTS FUNCTIONAL PROPERTIES OF SALTED DUCK EGG WHITE

Salted duck egg was prepared by coating fresh duck egg with laterite and sodium chloride. The effects of different lengths of pickling time and electrodialysis desalination on foaming, emulsifying and gelation properties of salted duck egg white (SDEW) were investigated. The pH was decreased from 9.3 to 7.1, zeta potential was decreased from -48.3 to -26.4 (mV), NaCl content increased from 0.49% to 7.32% and surface hydrophobicity increased from 177 to 372 (So/100 mg protein) after pickling for 8 weeks. After electrodialysis desalination treatment, the pH of SDEW was slightly increased and zeta potential was decreased; however, the NaCl content was reduced by 95% and surface hydrophobicity decreased by 30as, the SDS-PAGE pattern showed the same distribution of protein molecules. Electrodialysis desalination treatment did not affect emulsifying properties. The foamability and foam stability of SDEW decreased with increasing pickling time, but increased with electrodialysis desalination treatment. The gel strength of SDEW decreased with pickling time, but decreased sharply after electrodialysis desalination treatment.     

RHEOLOGY OF FRESH, AGED AND GAMMA-IRRADIATED EGG WHITE

SUMMARY– Rheology of unmixed egg white at 2°C was studied with a narrow-gapped rotational viscometer over a 20-fold range of shear rates. For a constant shear rate, egg white consistency decreases with time and approaches an equilibrium value in a few minutes. Flow behavior is pseudoplastic at 2°C between shear rates of 8.1–147 sec^-1 and the shear stress-shear rate relation is accurately described by the power law and Casson models. The effects of gamma irradiation dose on Haugh unit score and equilibrium shear stress are discussed.     

SMALL DEFORMATION MEASUREMENTS OF SINGLE AND MIXED GELS OF LOW CHOLESTEROL YOLK AND EGG WHITE

Isolates of reduced-cholesterol egg yolk were prepared by extracting cholesterol from spray-dried yolk using the following solvents: (1) petroleum ether, (2) petroleum ether/ethanol, (3) ethanol/water and (4) supercritical carbon dioxide. Differential scanning calorimetry demonstrated that the temperature of minimum heat flow of the denatured isolates was about 75C. Mechanical properties of extracts were compared using small deformation oscillatory rheology. Ethanol/water and petroleum ether treated yolk had the strongest and weakest gelling characteristics respectively, following protein denaturation at 75C. When compared to egg white, yolk isolates formed stronger networks at 75C. Heating at higher temperatures denatured ovalbumin which produced slightly stronger gels than egg yolk. Binary mixtures of egg white and yolk formed phase separated gels. The best agreement between experimental data and calculated composite moduli by using isostrain and isostress Takayanagi models, was obtained for egg white keeping 37% more water per unit concentration than the egg yolk.     

EFFECT OF HEN EGG PRODUCTION AND PROTEIN COMPOSITION ON TEXTURAL PROPERTIES OF EGG ALBUMEN GELS

The effect of hen age, strain and dietary amino acid intake on the egg albumen gel textural properties was studied in two experiments by textural profile analysis (TPA) and uniaxial compression (UC) tests. In experiment 1, eggs from 4 different hen flocks were heat processed industrially. Egg rejection due to poor albumen gelling was correlated to hen age (r = 0.502), albumen dry matter (r =−0.632), gel hardness of 1^st compression (r =−0.765), and gel work of 1^st compression (r =−0.740) in TPA. In experiment 2 two hen strains, representing two levels of egg production, were fed diets with supplementation of L-lysine, methionine or both amino acids compared to a control diet. The lysine intake ranged from 818–1272 mg/hen/day and methionine intake from 377–575 mg/hen/day among hen groups, but without significant effect on the albumen gel texture parameters. The hen strains differed significantly in egg production (P<0.001), physical (P<0.001), chemical (P<0.05) and gel textural parameters of egg albumen (P<0.01). Hen age was essential, and correlated to the industrial egg rejection (r = 0.729), albumen dry matter (r =−0.902) and gel stress at fracture (r =−0.884). Albumen gels with high fracture stress values were found to contain a modified form of ovofransferrin.     

PREPARATION AND STORAGE PROPERTIES OF DRUM DRIED WHITE YAM (Dioscorea rotundata Poir) FLAKES

The white yam Dioscorea rotundata Poir was characterized, drum dried to different moisture levels, and stored at temperatures of 21.l °C, 29.4 °C and 37.8 °C for 90 days. Fresh and stored samples were analyzed for changes in color, ascorbic acid and organoleptic qualities. Freshly dried and reconstituted yam flakes were judged highly acceptable compared to conventionally mashed fresh yam and retained acceptability through storage. The taste panel consisted of persons from several West African countries. Changes in the flakes during storage are described.