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Influence of bio-active terpenes on the characteristics and functional properties of egg yolk

Egg yolk is a high nutritional source for humans in which it widely used in food processing for its technological properties and health effects (Gouda, Zhang, Liu, Sheng, & Ma, 2017). Moreover, its hygienic quality is of major concern, especially when used as a raw nutrient. In addition, yolk protects itself by numerous proteins like immune globulin Y in which they have antimicrobial properties with a positive impact on its hygienic quality (Bedrani, Helloin, Guyot, Rehault-Godbert, & Nys, 2013). On the other hand, yolk protein functionality is directly based on its structure. In addition, in foams and emulsions, they can increase stability by either being part of the interface or forming structures in the continuous phase. Also, its surface hydrophobicity is playing an important role in its stability and functionality (Foegeding, 2015). Moreover, protein particle size has a great effect on stability in which the smaller protein particle size, the greater will be yolk stability (Foegeding, Plundrich, Schneider, Campbell, & Lila, 2017). Salmonella typhimurium DT104 and Escherichia coli O157:H7 are two major food-borne pathogens often identified as primary sources of food-borne disease in humans (Si et al., 2006). Moreover, the public health concern over the use of synthetic preservatives against them in processed foods has increased the demand to develop alternatives natural way. Furthermore, the design of using naturally active antimicrobial compounds in the bulk of liquids instead of synthetic ones is a creative approach to extending the microbial shelf life of foods with generally improving human health (Ahmed et al., 2017; Fouad, Moustafa, Hussein, Romeilah, & Gouda, 2014; Gouda, Moustafa, Hussein, & Hamza, 2016; Kashiri et al., 2017). Terpenes, such as trans-cinnamaldehyde, thymol, menthol, and vanillin, are a natural secondary metabolites isolated from various

plants and generally recognized as safe compounds (GRAS) by the US Food and Drug Administration (Gouda et al., 2017). Moreover, they are used as bactericidal, virucidal and fungicidal agents, in which they widely used as promising natural food preservatives (Kashiri et al., 2017). In addition, these compounds have strong antimicrobial activity against Salmonella typhimurium and E. coli as gram-negative, and Listeria monocytogenes as gram-positive bacteria (Si et al., 2006). Furthermore, It has been showed that they have inhibitory activity against trypanosomatid protozoa, Crithidia fasciculata, Leishmania spp., and Trypanosoma cruzi (Azeredo & Soares, 2013). Also, most of their antimicrobial activity is related to their phenolic structure, as phenolic compounds often exhibit high antimicrobial activity (Yu, Chao, Chang, Chang, & Lee, 2016). Yolk as oil in water emulsion is effectively protecting the degradation of terpenes loaded in it through the interaction with lipophilic compounds like lecithin. Furthermore, these compounds can be used to improve the stability of emulsion delivery systems (Guan, Wu, & Zhong, 2016). In addition, many studies observed synergistic surface activity when hydrophobic lecithin was used in combination with other proteins to prepare nanoemulsions or microemulsions with terpenes in which they change their physical properties, dimension, storage stability, zeta-potential, and morphology of emulsion droplets (Chen, Guan, & Zhong, 2015; Ma, Davidson, & Zhong, 2016; Xue & Zhong, 2014). A recent study has proved the significant effects of terpenes on stability, size, charge and rheological properties of emulsions in which it showed better physical and oxidative stability during storage as compared to “Purity Gum 2000” as a commonly used emulsion stabilizer. This was attributed to the role of terpenes as high antimicrobial, antioxidant, low molecular weight and density molecules for improving physical and functional properties of yolk (Sharif et al., 2017). Moreover, these compounds by themselves have demonstrated an ability to stabilize protein foam structures in which associated with catechin induced cross-linking in the protein interfacial layer. A structure-based mechanism implies that protein terpenes mixtures can be used to enhance a desired food structure and stability (Dickinson, 2017). In addition, our previous study showed that different concentrations from trans-cinnamaldehyde, thymol, menthol, and vanillin were significant antioxidant agents against yolk lipid oxidation. Moreover, they significantly increased the emulsion activity (EA) with increasing oil peak surface area, viscosity, stress, viscoelastic properties and decreasing the droplet size distribution (d3,2), in which it means that these four compounds have the ability to change the physical and chemical properties of egg yolk (Gouda et al., 2017). The aim of the present study was to evaluate the enhancement of antimicrobial effects of trans-cinnamaldehyde, thymol, menthol, and vanillin, as a high antimicrobial agents, with egg yolk against Salmonella typhimurium and E. coli; In addition, to evaluate the suitable concentration with using three different concentrations of them and to study some of their structure and functional characteristics, such as hydrophobicity, zeta-potential, in vitro antimicrobial activity, foaming and color properties; and thus to provide evidence of their applicability in the design of yolk hydrocolloidal system as a very simple drug deliver method for human health.

For the first time, evaluation of trans-cinnamaldehyde, thymol, menthol, and vanillin effects onto yolk general structure, secondary protein structure, surface hydrophobicity, zeta-potential, antimicrobial activity, foaming and color properties as a simple and nontoxic procedure for enhancing food preservation ability by these natural bio-active molecules with developing a new thinking idea through using yolk as a drug deliver agent. The four compounds showed different effects onto yolk structure through their effects on the secondary protein structure, surface hydrophobicity, and zeta-potential. Also, the different concentrations have been used for purifying and more clarifying these four compounds relationships with changing the antimicrobial activity, general structure, secondary protein structure, surface hydrophobicity, electrostatic negativity and color properties with studying the possible principles correlated with the functional activities like foaming and emulsion properties. Therefore, it has been concluded that different concentrations from trans-cinnamaldehyde, thymol, menthol, and vanillin are making cross-links with yolk proteins in which it changes its structure with increasing the antimicrobial activity, surface hydrophobicity, foaming properties and decreasing the electrostatic negativity with slight changes in color properties. Our study is providing a new thinking approach in applying yolk as colloidal media in the protection of health benefit compounds through the cross-links with its proteins and changing in the surface hydrophobicity. Moreover, the using of these compounds help to improve some important technological properties. Mostafa Gouda, Linlin Zu, Sumin Ma, Long Sheng, Meihu Ma.(2018) Influence of bio-active terpenes on the characteristics and functional properties of egg yolk. Food Hydrocolloids J, 80 (2018) 222-230.

Gouda, M., Shisi, Z., Yuanyuan, L., Sheng, L., Ma, M. (2017) Effects of four natural antioxidant phenyl terpenes on emulsifying and rheological properties of egg yolk, LWT - Food Science and Technology, 83,56-63. doi: 10.1016/j.lwt.2017.04.075.

Shankar V, Gouda M, Moncivaiz J, Gordon A, Reo NV, Hussein L, Paliy O. (2017). Differences in gut metabolites and microbial composition and functions between Egyptian and U.S. children are consistent with their diets. mSystems 2:00169-16. https://doi.org/ 10.1128/mSystems.00169-16.

Farid E. Ahmed, Mostafa M. Gouda, Laila A. Hussein, Nancy C. Ahmed, Paul W. Vos  and Mahmoud A. Mohammad (2017). Role of melt curve analysis in interpretation of nutrigenomics' microrna expression data. Cancer genom & proteome J. 14 (6):110-124.