Effects of Bioactive Terpenes on the Functional Properties of Egg Yolk and It’s Mechanism

Author:Mostafa Mahmoud Abdulhakeem Gouda

Supervisor:ma mei hu


Degree Year:2018





This study investigated the effects of natural safe and highly antioxidant and antimicrobial terpenes on functional properties,physicochemical properties,volatile components and microstructure of egg yolk.To clarify the molecular mechanisms of natural active terpenes for improving the functional properties of egg yolk from the macroscopic,microscopic and molecular levels,in which is intended to provide a theoretical basis and practical technical support for these combinations applications in the food industry field;and also to enhance the use of biologically active molecules in human nutrition field.Moreover,it provides new thinking ideas for their functions in food processing.The main findings are as follows:It was found that the addition of trans-cinnamaldehyde,thymol,menthol and vanillin increased the antioxidant activity of egg yolk.The effect of 0.1% vanillin and thymol was the most significant,and the anti-lipid oxidation effects were 70.21 ± 0.14 AI% and 51.37 ± 0.09 AI%,respectively.At the same time,the addition of 0.1% thymol and transcinnamaldehyde can significantly improve the antimicrobial activity of egg yolk,with inhibiting Salmonella effect by 92.18 ± 3.26% and 98.95 ± 3.16%,and inhibiting E.coli effect by 103.30 ± 4.58% and 101.34 ± 1.82%,respectively.In addition,the 0.1% concentration of thymol can significantly improve the emulsification activity of the egg yolk by changing the structure of the egg yolk protein.The addition of 0.1% vanillin can significantly improve the emulsion stability of the egg yolk by reducing the surface tension.Moreover,0.1% concentration of trans-cinnamaldehyde,thymol,menthol and vanillin can significantly increase the foaming capacity of egg yolk to 95.83 ± 3.54%;79.67 ± 0.47%;78.17 ± 2.60% and 100.00 ± 0.00%,respectively.The improvement of the functional properties of egg yolk is mainly due to the slight change of secondary structure protein after the interaction of protein and terpenes,which can form a better interface protein network structure.The study found that the Herschel-Bulkley model is the best model for viscosity calculation.The viscosity of egg yolk added with 0.1% thymol increased to 18.09 ± 0.08 Pa.s,and d3,2 decreased to 2.48 ± 0.01 μm.The addition of 0.1% trans-cinnamaldehyde reduced the d3,2 of egg yolk to 1.61 ± 0.12 μm,while increased the viscosity,stress and viscoelasticity.Egg yolk with 0.1% thymol was found to have the largest oil peak area(13.88 ± 0.04 k.au)by low field NMR compared to control group.The storage modulus of vanillin and thyme yolk group was higher than the loss modulus,which made the egg yolk tend to be gel-like media.Also,compared to control group(20.01 ± 0.15 g),the yolk firmness of 0.1% concentration of thymol was 21.46 ± 1.23 g.0.1% thymol and transcinnamaldehyde highly increased the consistency of egg yolk,reached to 242.12 ± 21.23 g.sec and 221.64 ± 1.76 g.sec,respectively.In addition,the cohesiveness of egg yolk with 0.1% thymol was significantly increased to 58.32 ± 2.46 g compared to the control group(51.51 ± 0.44 g).However menthol itself is colorless,the yolk lightness L* and yellowness b* values of 0.1% concentration menthol increased from 80.15 ± 0.44 and 47.92 ± 0.14 to 83.67 ± 0.14;50.01 ± 0.05,respectively.Fourier transform infrared spectroscopy and circular dichroism revealed that transcinnamaldehyde,thymol and menthol(0.1%)increased the α-helix of egg yolk from 32.70 ± 0.14% to 34.00 ± 0.85%;34.05 ± 0.21% and 34.15 ± 0.35 %.Also,XRD results showed that a new diffraction peak appeared at 2θ = 33° with egg yolk mixed with 0.1% menthol,and asymmetric peak shape at 2θ = 0° to 2θ = 15° in all groups of mixed terpenes.In which,it revealed that the amorphous structure of the egg yolk has been changed.Raman spectra showed that the intensity of the absorption peak at 1329 cm-1 of the egg yolk with 0.05% of trans-cinnamaldehyde,0.01% of thymol,and 0.1% of menthol was significantly increased compared to the control group.The surface hydrophobicity of the yolk with 0.1% trans-cinnamaldehyde and thymol is increased to 3033.60 ± 19.31 Ho and 3051.25 ± 9.77 Ho,respectively.In which,the increase of surface hydrophobicity was related to the change of protein α helix.The zeta-potential of the yolk group with 0.1% trans-cinnamaldehyde,thymol,menthol and vanillin was-6.73 ± 0.30 m V;-6.30 ± 0.49 m V;-6.90 ± 0.57 m V and-6.19 ± 0.80 m V,which were significantly lower than the control group(-5.02 ± 0.37 m V).A total of 111 different components were identified by analyzing the volatile components by HS-SPME-GC/MS.Some ketones,amines,nitro and organic acid compounds such as hexanone,1-phenyl-1H-pyrazol-3-amine,4-methylthiocyanobenzene,3,4-dimethylbenzoylamide,acetophenone and 3,5-di-tert-butyl-4-hydroxyacetophenone were significantly reduced in all egg yolk groups with added terpenes.In the egg yolk group supplemented with 0.1% trans-cinnamaldehyde,thymol and menthol,the content of D-limonene decreased from 14.16 ± 4.95 MPA(control group)to 3.90 ± 1.83 MPA,4.82 ± 3.48 MPA and 4.65 ± 0.49 MPA,respectively.The content of hydrocarbon compounds such as 7-hexadecene is decreased from 0.88 ± 0.30 MPA to 0.25 ± 0.05 MPA in the egg yolk with 0.1% trans-cinnamaldehyde.The electronic nose P10/1 sensor detected a hydrocarbon content in the egg yolk groups with 0.01% and 0.1% added thymol from 0.473 ± 0.042 to 0.446 ± 0.007 and 0.448 ± 0.005,respectively.In addition,for 0.1% menthol and vanillin it decreased to 0.431 ± 0.005 and 0.406 ± 0.002,respectively.P30/2 and TA/2 sensors values,which detect organic compounds such as ethanol,combustion,hydrogen sulfide and ketone content,decreased from 0.204 ± 0.034 and 0.413 ± 0.080 to 0.169 ± 0.010 and 0.344 ± 0.010 in the egg yolk supplemented with 0.1% vanillin group,respectively.Scanning electron microscope and fluorescent microscope showed that the microscopic morphology of the control group presented a relatively homogeneous structure,whereas in yolk with terpenes exhibited more heterogeneous with the surface covered by small aggregates and possibly originated by changing in fat distribution and protein interactions.At SEM,100 X magnification,the egg yolk group with 0.1% vanillin had the greatest morphological changes,which correlated with the protein secondary structure,oil peak area,foaming properties,and XRD results.At 1000 X and 2000 X magnifications,the particle size of yolk with 0.1% menthol group was observed to be decreased,and some interactions were also observed in the 0.01% menthol yolk group.After the dyeing of Nile red,some larger aggregates were observed by the red filter in egg yolk with 0.05% trans-cinnamaldehyde group.And,in egg yolk with 0.05% and 0.1% trans-cinnamaldehyde groups which observed by the blue filter,some bright green dots appear in the red structure area,which means that the hydrophobicity of the protein has changed,and the protein-bound oil droplets have separated and dissolved.Egg yolk with 0.1% concentration from each compound from the four studied terpenes was used to prepare ice cream product.The sensory,physical and structural characteristics of the final product were evaluated.In terms of taste,compared to the control(6.70 ± 1.42),the vanillin group score was the highest(8.40 ± 0.97)(P < 0.05).In the color evaluation,the menthol group was significantly(P < 0.05)higher than the control.In the overall score,the vanillin group and the thymol group scored the highest(7.90 ± 0.99 and 7.20 ± 1.48,respectively).The overrun of the menthol group was significantly higher than control group,reaching 32.25 ± 7.98%.In addition,the density of the menthol group was reduced to 0.71 ± 0.00 g/cm3,and the firmness of the thymol group was increased to 457 ± 53.56 g(P < 0.05)compared to control group(21.24 ± 0.15 Pa.s).The viscosity of the thymol group was significantly increased(P < 0.05)to 27.92 ±5.25 Pa.s.Also,the addition of menthol has the greatest effect on the lightness of ice cream(80.88 ± 0.10).The spread ability of the menthol and vanillin groups was significantly different increased from the control group from 6 min to 12 min.On the other hand,by using magnetic resonance imaging technique,it was found that the water distribution of thymol group ice cream was significantly changed compared to the control group.