Modification Of Gelling Properties Of Egg White Powder

Egg White (EW) is an additive widely used in food processing because of its excellentgelling ability, but fresh EW can not be stored for a long time and its gel property is easilyaffected by pH and NaCl concentration of the medium. EW powder can be stored for a muchlonger time than fresh EW, but the gel property will be damaged due to the pH adjusting beforespray drying. So it is necessary to futher study the medium and processing conditions affectingthe gelling property of EW/SDEW (spray dried egg white) and the modification methods toimprove the gel property of SDEW so as to widen its application in food industry.The effects of medium on the gelling property of fresh EWwas firstly discussed in this paper.The gel strength increased with the incresement of protein concentration, heating temperature andheating time, and had higher strengths when the pH of EW solutions was adjusted to 4.0, 9.0 and11.0. However, the gel fromed at pH 6.0 was the softest. The gel strength was dramaticallydecreased by the addition of NaCl at pH 4.0 and 9.0. The gel strength of the desugarizedEW/SDEW (DSDEW) was higher than that of native EW/SDEW (NSDEW).Several modification methods were applied to improve the gel strength of SDEW. For themethod of microbial transglutaminase (MTG), the gel strength could be increased by 90.5% if theDSPEW solution was mixed with 15U MTG/g DSDEW and incubated at 37℃ for 1 hour. For themethod of Maillard reaction, the DSDEW modified by the hydralysate of guar gum could form agel whose strength was 1207% higher than that of NSDEW. However the color of themodification DSDEW was not as good as that of NSDEW because of the unavoidably browningreaction. For the the dry-heating method, DSDEW could form a gel whose hardness wasincreased by 10-13 times after being dry-deated at 80-100℃ for several days.The gelmicrostructure was also much finer and more homogeneous. Meanwhile the dry-heated DSDEWhad a better digistibilty and a higher tollarance to NaCl and pH.The dry heating method has a brighter application prospect for its better modification effectand its cheaper cost. So its modification mechanism was also studied in this paper. The graphs ofDSC, SDS-PAGE and HPLC as well as the changes of hrophobicity, free amino and sulfhydrxylgroups and glucose content of the dry-heated DSDEW indicated that the DSDEW proteins werepartly denatured and polymerrized during dry heating process. The partly denaturation contributedto the increasement of hydrophobicity and the exposure of the surface SH. The proteinpolymerization was properbly induced by intermolecular S-S or other covalent bonds. TheMaillard reaction occurred between proteins and the residue glucose in DSDEW might also havean effect on the polymerization process.