Enyymatic Oxidation Of Egg Yolk Phospholipids And Its Application

In this paper,the oxidation changes of egg yolk phospholipids before and after enzymatic oxidation and their effects on the aroma of chicken were studied.The composition and oxidation process of phospholipids were determined by ³¹P NMR and ¹H NMR techniques and spectrophotometry,and then the relative content and aroma changes of volatile flavor compounds in chicken samples were studied by HS-SPME-GC-MS technique and sensory evaluation.The results of the study are as follows:（1）³¹P NMR results showed that the fresh egg yolk phospholipids contained 80.02±0.76%PC（Phosphatidylcholine）and 14.37±0.54%PE（Phosphatidylethanolamine）.There were 76.96±0.80%and 13.24±0.65%in enzymatic oxidized phospholipids,respectively.Enzymatic hydrolysis increased the hemolytic phospholipids,LPC（lysophosphatidylcholine）increased from1.27±0.16%to 2.14±0.41%,and 1.57±0.10%LPE（lysophosphatidyl-ethanolamine）appeared.Its main components have not changed.¹H NMR monitored six groups of phospholipid samples:fresh phospholipids,water bath heated phospholipids,enzymatic oxidation（p H=6）phospholipids,enzymatic oxidation（p H=9）phospholipids,enzymatic（p H=6）water bath heated phospholipids,and enzymatic（p H=9）water bath heated phospholipids.Combined with cluster analysis results,the content of unsaturated fatty acids in all oxidized samples decreased,while the content of saturated fatty acids increased,The content of polyunsaturated fatty acids in phospholipids treated by enzymatic oxidation is lower.（2）Combined with ¹H NMR and the determination of conjugated diene,conjugated triene and TBA values,it was found that the specific oxidation of egg yolk phospholipids by lipoxygenase at p H=6 could produce more hydroperoxides,and after heating,more desired flavor compounds（E,Z）2,4-dienal were generated,indicating that under the action of LOX,although linoleic acid in egg yolk phospholipids was oxidized at C9 and C13 positions,more oxidation occurred at C9 position than self oxidation;Under the condition of more active p H=9,LOX is degraded after the egg yolk phospholipids synthesize hydroperoxide quickly due to the longer enzymatic reaction time,and it is mainly oxidized at C13 position,so more n-alkaldehyde is generated after heating.（3）QDA experiment was used to evaluate the flavor of three groups of samples:pure chicken,chicken with fresh phospholipids and chicken with enzymatic phospholipids.The results showed that the chicken samples treated with enzymatic phospholipids scored the highest in all aroma attributes,while the pure chicken samples scored the lowest.The samples added with enzymatic phospholipids scored higher in"chicken flavor","fat flavor"and"barbecue flavor"attributes than the samples added with fresh phospholipids,indicating that the enzymatic oxidized phospholipids have a stronger flavor enhancing effect than the fresh phospholipids without oxidation treatment.In this experiment,less phospholipids（0.5%of the chicken quality）were added.Compared with other studies,adding 1%or 2%phospholipids,the amount was less,but it could also achieve the purpose of aroma enhancement.（4）The volatile substances in two groups of phospholipid samples and three groups of chicken samples were extracted and identified by HS-SPME-GC-MS.The results showed that the addition of phospholipids significantly increased the contents of characteristic flavor compounds（E,E）and（E,Z）-2,4-decene aldehyde,1-octene-3-ol,2-amyl-furan,etc.in chicken samples.The samples added with enzymatic phospholipids have more key flavor substances than those added with fresh phospholipids.The presence of enzymes makes linoleic acid in phospholipids produce more C9 hydroperoxide,thus producing more（E,E）-2,4-decene aldehyde,and relatively less hexanal,which plays a key role in producing more chicken aroma substances.This paper proved that the hydroperoxide of egg yolk phospholipids increased significantly after enzymatic oxidation,and adding enzymatic oxidized phospholipids to chicken had a stronger flavor enhancing effect.