Effects of pectin and guar gum on food protein functionality

In this study, the effect of hydrocolloids (pectin, guar gum, iota-carrageenan) onfunctional properties of whey protein isolate (WPI) and egg proteins (egg white, eggyolk plasma, egg yolk granule) were investigated. In protein-polysaccharide mixtures,phase separation behavior and thermal properties of these proteins were determined. Inaddition, the influence of hydrocolloids on emulsifying properties, foaming propertiesand rheological properties was investigated. And also the effect of heat treatment onfoaming properties of egg white and emulsifying properties of egg yolk proteins andWPI was also studied. The presence of hydrocolloids did not affect the thermal stabilityof egg white but increased thermal stability of WPI and egg yolk plasma. WPI-pectinand WPI-guar gum systems exhibited phase separation but no phase separation wasobserved in WPI-i-carr systems. Except for plasma-pectin mixtures, all other eggprotein-hydrocolloid mixtures occupied a two-phase system; the top phase was definedas protein-rich phase and the bottom phase was defined as polysaccharide-rich phase.Therefore, emulsions were prepared below the phase separation threshold and theemulsifying activity and emulsion stability were determined spectrophotometrically bymeasuring time-dependent changes in turbidity. Emulsion activity of egg yolk granulestabilized emulsions without the addition of hydrocolloids was determined as 2.61m2/mg. While the addition of pectin slightly caused a slight change in emulsion activityiiof these emulsions, addition of guar gum (0.5%) increased it to 3.41 m2/mg. Emulsionstability was also observed to be changing with the concentration of hydrocolloids andmore stable emulsions were obtained at higher hydrocolloid concentrations. Onlytransient foaming (foam volume was 19.2 cm3 and collapsed within 9-10 sec) wasobserved with egg yolk plasma and granule. But quite stable foams were produced withWPI (80 s) and egg white (64 s) with a foam volume of 119.3 cm3 and 120.7 cm3,respectively, in the absence of hydrocolloids. Addition of hydrocolloids did not changefoam volume but increased foam stability. Emulsifying and foaming properties werealso studied by using heat-treated (65-80ºC) protein or protein-hydrocolloid mixtures.Foam volume of heat-treated egg white decreased as compared to that of non-heated eggwhite. Foam stability of egg white increased as heating temperature was increased from65ºC to 75ºC. However, it reduced when the protein solution was treated at 80ºC. Asthe temperature was increased emulsifying properties of both egg yolk proteins and WPIalso decreased. Finally, rheological behavior of these proteins was determined inemulsion systems. Elastic modulus and viscous modulus increased with increasingfrequency and they were regarded as frequency dependent. Emulsions prepared in theabsence of hydrocolloids showed Newtonian behavior (n ≅ 1.0). Generally addition ofpectin increased viscosity slightly but did not change flow type. Addition of higheramounts of guar gum (0.5%) changed rheological properties of these emulsions and theyshowed pseudoplastic behavior (n < 1.0).Key words: Whey protein isolate, Egg proteins, Hydrocolloids, Emulsion, Foam, DSC,Heat treatment, Rheologyiii