The Effect Of Different Processing On Lipid Oxidation And Fatty Acid Composition Of Eggs

In order to study the lipid component change in poultry eggs during processing and storage, chicken and duck eggs were chosen to be the raw materials. Microwave heating, different ways of drying, different concentration of salt and alkali pickling wer e used in this study to reveal lipid oxidation, change of fatty acid profile and other related lipid index. The main results are as follows:(1) In the chapter of microwave heating, the CDA of Hailan grey egg ascended from 0.12±0.01% to 0.37±0.03% after 5 min microwave heating, and ascended from 0.12±0.01% to 0.27 ± 0.01% after 5 min light/microwave combination heating. While microwave heating and light/microwave combination heating have slight impact on Bailaihang white egg. P-AV in fresh Hailan grey egg and fresh Bailaihang white egg were respectively 3.19±0.45 and 7.64±1.62, and it has elevated in all groups after heating process. After 5 min of light/microwave combination heating, the P-AV reached to 71.57±12.2 and 61.09±3.9 respectively. Besides the type of chicken eggs, heating method and heating time, lipid oxidation has a significant relationship with the amount of PUFA in raw eggs. The relative content of Palmitic acid C16:1 in Hailan grey egg descended from 4.32% to 2.56% and 4.02% respectively after 5 min microwave heating and light/microwave combination heating. In conclusion, short-time microwave heating has slight impact on fatty acid change of chicken eggs.(2) In the chapter of egg powder drying, spray drying induced more intense lipid oxidation than vacuum freeze drying did. CDA in fresh egg yolk was 0.175±0.006%, and it reached to 0.177±0.009% in whole egg powder and 0.216±0.027% in egg yolk powder respectively after vacuum freeze drying. While it reached to 0.299±0.007% in whole egg powder and 0.233±0.002% in egg yolk powder respectively after spray drying. CDA changes in all groups during storage were slight. p-AV change showed the same trend with CDA. Spray drying brought more intense damage to PUFA than vacuum freeze drying did, especially AA,DHA and DPA(respectively 1.88±0.02%,0.61±0.03% and 0.49±0.03% in fresh egg yolk). The relative content of these PUFA descended to 0.95±0.01%, 0.38±0.03% and 0.23±0.02% in whole egg powder produced by spray drying. These PUFA content all descended with the extension of storage time.(3) In the chapter of duck egg salt pickling(0%,10%,20%,26%) for 49 days, it can be observed that CDA in all groups ascended before 35 days pickling, it reached to 0.246±0.009% in 26% group. Since 35 day to 49 day, it showed a trend of decrease in 4 groups. P-AV in all groups ascended before 35 days pickling(142.67±2.65 in 0% group), and it showed a trend of decrease in 10%,20% and 26% group(68.59±9.41 in 20% group at 49 day) and remained stable in 0% group. Salt pickling slightly influenced the change of duck egg fatty acid.(4) In the chapter of duck egg alkali pickling(0%,4%,6%) for 30 days, CDA in three groups ascended before 15 days pickling(in 15 day, 0.242±0.010% for 0%,0.228±0.004% for 4%,0.213±0.014% for 6%). Since 15 day to 30 day, it showed a trend of decrease(in 30 day, 0.180±0.001 for 0%,0.185±0.008 for 4%, 0.155±0.001 for 6%). The PUFA decreased with the increase of alkali concentration and extension of pickling time, especially AA( in the 30 th day, C20:4 decreased from 4.18±0.13% to 2.30±0.06% in 0% group, 1.59±0.02% in 4% group, and 1.55±0.03% in 6% group), DPA and DHA showed the same trend. PI decreased the most in 6% group. Aldehydes, ketones, acids and alcohols were detected in 3 groups using GC-MS for volatile compounds analysis.(5) In the chapter of duck egg salt pickling(10%,20%) and alkali pickling(4%,6%) for 30 days, it can be observed that compared to fresh duck egg yolk(Cholesterol 2.357 ±0.069g/100 g lipid), salt and alkali pickling both increased the amount of Cholesterol in duck egg yolk. In the 30 th day, it reached to 3.799±0.077 g/100 g lipid and 3.199±0.088g/100 g lipid respectively in 10% and 20% salt pickling groups. Phospholipid change was not obvious. Egg yolk ratio in salt pickling groups decreased(35.84±2.21% in fresh duck egg, 28.54±3.05% in 20% in 30 th day), while it increased in alkali pickling groups(45.52±1.51% in 6% in 30 th day).