| The salted egg yolk(SEY)is especially popular in China because of its pleasant flavor(gritty texture,oil exudation and orange color).However,the production cycle of traditional pickling is too long limiting its industrialization.On this ground,a new method combining enzyme hydrolysis and microwave treatment is used to generate the SEY flavor from fresh egg yolk without pickling.The main odorants of generated egg yolk flavoring as well as the major formation pathways were studied.The results are as follows:Egg yolk liquid was co-hydrolyzed,then heated and microwave treated to achieve products.The optimal conditions of hydrolysis were determined by degree of hydrolysis(DH)and sensory analysis as follows: The pH of the egg yolk solution was about 6.20.The optimal additive amount of neutralzyme was 2000 U/g and that of flavoryzme was 600 U/g.The hydrolysis was commited at 40°C for 2 h and the DH was 10.17%.Heating conditioin: 15 min at 80°C.Microwave condition: 50%(w/w)water,addition of salt in 2%(w/w).Sample weight 14 g/batch and suitable microwave treatment time 80 s.In order to explain flavor formation mechanism,a headspace solid-phase micro-extraction gas-mass spectrometry was used to study the odorants of egg yolk flavoring combining with lipid oxidation.11 kinds of potent volatile compounds were identified.By correlation analysis,hexanal,haptanal,benzaldehyde and 2-pentyl-furan were possibly related to SEY flavor.Benzyl alcohol,3-methylbutanal,benzaldehyde and phenyl acetaldehyde were possibly related to egg-puff flavor.And 1-octen-3-ol and 2-pentyl-furan was possibly related to rancidity flavor.With the increase of DH,lipid oxidation and the contents of volatile compounds grew higher.Lipid oxidation maybe the major pathway of flavor formation.Flavor characteristic of egg yolk was related to the chemical properties of egg yolk liquid.Hydrolysis and heatment destroyed the gelation and emulsion system,leading to the formation of flavor precursors such as amino acids and the freedom of egg yolk oil droplets.It is a requirement for flavor formation.Results showed that bitter amino acids were important precursors of the egg yolk flavoring.Sulfur-containing amino acids were possibly related to egg yolk off-flavor.The relative molecule weight of peptides was mainly ranging from 100 to 500.The PLSR analysis showed that leucine,isoleucine,valine,lysine,methionine and phenylalanine were possibly related to the formation of SEY flavor.Strecker degradation might be another important pathway for flavor formation.Microwave treatment induce the lipid oxidation and Strecker degradation of egg yolk directly leading to the formation of flavor compounds.With the increase of microwave treatment time,the hue angle and lightness decreased,the moisture content of egg yolk fell,the exudation of egg yolk oil rose.And the multibound water molecule transferred into single bound leading to a decrease in the interaction between water and lipids.The change of amount of free thiol content was possibly related to sulfur-containing amino acids.Meanwhile lipid oxidation of linoleic acid,arachidonic acid and DHA was the reason of flavor formation.Enose results showed that change of odor profile of egg yolk was due to the sharp increase of certain kinds of volatile compounds. |
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