| Egg flavor primarily originates from the yolk and is a key factor in determining egg quality.However,there is lack in the accurate and systematic evaluation system of the egg flavor and few research in the formation mechanism for the egg characteristic flavor.The objective of this study was to pinpoint the key volatile compounds in egg yolk,investigate the relationship between the hydrophilic and hydrophobic metabolites and flavors,and explore the regulation of egg flavor based on the change of flavor precursors and the deposition of essential oils through adding Sacha inchi oil and Rosemary oil to feeds.The specific findings are as follows:(1)Characterization of flavor precursors and volatile compounds in Taihe black-boned silky fowl(TS)and Hy-line Brown(HL)egg yolksBased on the comparison of TS and HL eggs,sensory panel evaluation indicated that TS egg yolks had the stronger odor and better acceptance.Gas chromatography-olfactometry-mass spectrometry analysis showed that a total of 28 volatile compounds were identified.Among them,8 volatile compounds contributed to the egg flavor.Four substances including 3-methyl-butanal had significant differences(P< 0.05).Metabolomic and lipidomics analysis unveiled 112 metabolites had significant variations,these differential metabolites were significantly enriched(P < 0.05)in pathways such as the biosynthesis pathways of phenylalanine,tyrosine,and tryptophan and so on.147 Lipids were significantly up-regulated in TS egg yolks.Partial least squares regression analysis of lipids and flavor demonstrated that 48 differential lipids(VIP > 1)were highly involved in the odor discrimination.(2)Effect of Sacha inchi oil(SIO)on volatile compounds in egg yolksA total of 270 Hy-line Brown laying hens at the age of 40 weeks with similar egg production rates were selected and fed with SIO in different levels of 0,0.5%,1% for 8 weeks.A combined multi-omics approach was utilized to assess the impact of SIO concentrations on volatile compounds and flavor precursors in egg yolks.The introduction of SIO did not generate any off-flavor but improved the consumer preference.A total of 38 volatile compounds were identified.Compared to the control group,thirty-five volatiles’ levels were significantly increased(P < 0.05),resulting in the overall olfactory enhancement in the SIO groups.Fatty acid analysis results demonstrated that the addition of SIO could increase the content of ω-3 polyunsaturated fatty acids in egg yolks.Based on the lipidomics analyses in the 0.5% SIO and control groups,the content of triglycerides was significantly increased in the 0.5% SIO group.The unsaturated fatty acids such as linoleic,linolenic,and oleic acid were correlated with the flavor differences between the two groups.(3)Effect of Rosemary essential oil(RO)on aroma compounds in egg yolksA total of 450 Hy-line Brown laying hens at the age of 42 weeks with similar egg production rates were selected and fed with RO in different level of 100 mg/kg,200 mg/kg,300 mg/kg and 400 mg/kg for8 weeks.The impact of RO on both of the laying hens and eggs was examined.It was observed that only eggshell strength was significantly increased(P < 0.05)when RO was added.However,there were no significant differences in performance,egg quality,hydrophilic and hydrophobic precursors between the RO group and the control group.The sensory evaluation results demonstrated that 100 mg/kg of rosemary oil eggs were the most acceptable.In addition,biomimetic sensory analysis revealed that the yolk aroma and taste profile in the RO group could be clearly distinguished from the control group.Notably,1,8-Cineole,one of the key aroma compounds in RO,was directly retained in the egg yolk and made a significant contribution to the yolks’ flavor.In this paper,we conducted a multidimensional evaluation of the flavor and flavor precursors of egg yolks from TS chicken and HL eggs and screened and identified four different flavor substances,including3-methyl-butanal and 48 lipid molecules with important contributions to the flavor.On this basis,the effect of adding SIO on the flavor of Hy-line Brown eggs was investigated,and it was found that the addition of 0.5% SIO in feed could increase the content of unsaturated fatty acids such as linolenic acid,and further influence the egg flavor through the oxidative degradation of fatty acids.Besides,the addition of RO to the feed could lead to the direct deposition of 1,8-cineole,a characteristic substance of the essential oil,in the egg yolk.The above results provide valuable data for regulating egg flavor. |
