Study on the Development and Functional Characteristics of Salted Egg with Liquid Smoke

Putri Widyanti Harlina1,*, Tri Yuliana1, Fetriyuna1, Raheel Shahzad2,#, Meihu Ma3
Author Information & Copyright
1Department of Food Industrial Technology, Faculty of Agro-Industrial Technology, Universitas Padjadjaran, Bandung 45363, Indonesia
2National Key Laboratory of Crop Genetic Improvement, Huazhong Agricultural University, Wuhan 430070, China
3College of Food Science and Technology, Huazhong Agricultural University, Wuhan 430070, China
*Corresponding author: Putri Widyanti Harlina, Department of Food Industrial Technology, Faculty of Agro-Industrial Technology, Universitas Padjadjaran, Bandung 45363, Indonesia, Tel: +62-22-7798844, E-mail:

# Current affiliation: Faculty of Agriculture, Universitas Padjadjaran, Bandung 45363, Indonesia and Bioresources Management, Graduate School, Universitas Padjadjaran, Bandung 45363, Indonesia

© Korean Society for Food Science of Animal Resources. This is an Open-Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License ( which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited.

Received: Jan 23, 2023 ; Revised: Feb 13, 2023 ; Accepted: Mar 02, 2023

Published Online: May 01, 2023


In this study, the duck eggs were salted with none or 2.5% and 5.0% (v/v) of liquid smoke (LS), respectively. As a control, samples salted without LS were used. The 2-thiobarbituric acid (TBA) values, 1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging ability, and reducing power of the three groups were tested at 0, 7, 14, and 21 and 28 days to determine the effects of LS on the antioxidant activity of treated eggs. In addition, gas chromatography-mass spectrometry (GC-MS) and electronic nose (E-Nose) were used to analyze the volatile flavor components of fresh duck eggs, LS, control, and salted duck eggs enriched with 2.5% (v/v) LS after 28 days of salting. The TBA value considerably increased with an increase in salting period, and the treated egg’s TBA value significantly associated with LS concentration. The TBA value decreased as the LS concentration increased. The amount of LS present was highly associated with their capacity to scavenge DPPH radicals. The reducing power of the samples was substantially correlated with the LS concentration, and the reducing power increased with increasing LS concentration. The GC-MS data revealed that phenols and ketones were the predominant chemicals present in the LS, and they were also found in the eggs added to the LS even though they were absent in the fresh eggs and control. The flavor of the control group and treated eggs with LS differed significantly, according to the principal component analysis and radar map of the E-nose. The texture study results revealed that the LS significantly impacted the hardness, cohesiveness, and chewiness of eggs.

Keywords: liquid smoke; salted egg; antioxidant activity; gas chromatography-mass spectrometry (GC-MS); electronic nose (E-nose)


Salted egg is a common preserved egg product, also known as salted duck egg. It is usually pickled in brine or mixed with yellow mud, plant ash and salt and is a popular traditional pickled egg product in Indonesia. During pickling, the egg yolks gradually become solidified and hardened. Egg whites lose viscosity and become diluted (Li et al., 2022). The rate of salt penetration of the egg whites and yolks may have an effect on changes in the composition and characteristics of eggs, especially yolks, during pickling. In addition, the marinating time also plays an important role in the formation of salted eggs desired by consumers (Kaewmanee et al., 2011).

During storage, there are many factors that reduce the quality of salted eggs. The most important factor is the oxidation of oil, which not only affects the flavor of salted eggs, but also affects the nutritional value of salted eggs. The oil in salted egg mainly exists in the egg yolk; the main reason for the reduction of the shelf life of salted egg is the oxidation of oil in the egg yolk and the overall quality of the salted egg (Ahn et al., 1995; Harlina et al., 2015). Therefore, it is necessary to reduce the oxidation of oil to prolong the storage time of salted eggs. The oxidation of oil can be reduced by adding synthetic or natural additives (Hayat et al., 2010), and the liquid smoke (LS) with good antioxidant properties can be used as an additive for pickling salted duck eggs.

Many natural antioxidants are based on phenolic compounds. LS contains a lot of phenolic compounds. The constituents in LS include many different compounds such as phenols, ketones, alcohols, esters, aldehydes, acids, furan and pyran derivatives (Montazeri et al., 2013). Among them, phenolic derivatives probably represent the most important one in terms of quality, and phenolic compounds are used to optimize antimicrobial performance, antioxidant potential and sensory properties (Milly et al., 2005). The antioxidant properties of phenols can reduce chronic diseases, degenerative diseases, heart disease, eye diseases, etc. (Hasler, 2000). Adding LS to the product can delay the lipid oxidation process (Estrada-Muñoz et al., 1998). They can act as hydrogen donors, reducing agents, singlet oxygen quenchers and metal atoms and free radicals, thereby neutralizing their toxic effects (Rice-Evans et al., 1996). In particular, methoxyphenols among phenolic compounds and their derivatives have been considered as major contributors to aroma in LS. In addition, they are also the main substances responsible for the antibacterial and antioxidant effects of smoked foods (Guillén and Ibargoitia, 1998; Suñen et al., 2003).

At present, in Indonesia, people’s living standards are gradually improving, and the requirements for consumer goods are getting higher and higher, and at the same time, the processing industry of egg products is gradually becoming more advanced and modern. Therefore, innovation in the processing of salted duck eggs, increasing the shelf life of salted duck eggs and developing salted egg products with more functional properties can be achieved and need to be achieved. At present, domestic scholars have developed many new pickling techniques, which have improved the flavor and storage time of salted eggs. In recent years, developed countries have been very advanced in food processing, and LS technology is basically used for popular smoked products such as bacon. Little research has been done on egg products, especially as food additives or new processing methods for preserved egg products.

The purpose of this study was to investigate the effects of LS as an additive for pickled salted duck eggs on the antioxidant properties, volatile flavor compounds, and texture of salted duck eggs. Studying the antioxidant properties of LS and the influence of its unique flavor in salted eggs is not only beneficial to provide new ideas for the study of extending the shelf life of salted duck eggs, but also to develop new types of salted duck eggs with smoked flavors to increase consumers’ choices and developed the new markets.

Materials and Methods


Methanol, ethanol, NaOH, NaCl, potassium ferricyanide, FeCl3, 2-thiobarbituric acid (TBA), trichloroacetic acid (TCA), 1-diphenyl-2-picrylhydrazyl (DPPH) were all Pro Analysis quality chemical reagents. LS were bought from Lubna Company (Semarang, Indonesia). LS was extracted from coconut shell pyrolysis that produces LS containing 4.13% phenolic compounds, 11.3% carbonyl and 10.2% organic acids.

Sample preparation

Fresh duck eggs were harvested within three days of laying were purchased from local producers. After thoroughly cleaning numerous duck eggs with water, place the eggs in a solution of salt that is 18% (w/w; salt solution:duck eggs=1:1, w/w), the egg samples were then treated with LS (Liquid Smoke Food Grade A, Lubna Company) at concentrations of 2.5% and 5% (v/v) and curing them for 28 days.

Determination of lipid oxidation

According to Harlina et al. (2018), oxidative rancidity of fat was assessed using a thiobarbituric acid reactive substances (TBARS) assay of malondialdehyde (MDA). Briefly, 5 g of the sample was combined with 25 mL of TCA 7.5%, homogenized, and left at room temperature for 1 hour. The solution was centrifuged (model 3,740, Kubota, Osaka, Japan) at 2,000×g for 10 min. The filtrate was then added 50 mL of purified water. 5 mL of the prepared solution and 5 mL of 0.02 M TBA were combined. A UV-vis spectrophotometer was used to test the reaction mixture’s absorbance at 532 nm after being maintained in a water bath at 100°C for 15 min. In a 50-mL volumetric flask, distilled water was added to 25 mL of 7.5% TCA, and the resulting solution (5 mL) was combined with 5 mL of 0.02 M TBA to create the blank sample. Malondialdehyde standard curve data was used to determine TBARS value, which was then represented as mg MDA/g sample.

Sample preparation for antioxidant activity assay

Combining egg white and yolk with 95% ethanol at a ratio of 1:10 (w/v), the mixture was extracted for 2 h at 60°C while being continuously shaken at a speed of 170×g. The resulting slurry was centrifuged for 10 min at 10,000×g. The antioxidant activity of the supernatant was examined. Salted duck eggs treated with LS were examined in vitro for their antioxidant properties, including DPPH radical scavenging activity and reducing power assay.

Determination of the ability to scavenge 1-diphenyl-2-picrylhydrazyl (DPPH) free radicals

Free radical scavenging activity was used to measure the antioxidant activity (DPPH method). It was made with a 0.002% concentration of DPPH. Supernatant samples were obtained at various concentrations and formed up to 2 mL quantities in each test tube. Each test tube was then filled with 2 mL of the DPPH solution, which was then left in the dark for 30 min. Each sample was examined three times. Using a UV-Visible spectrophotometer, optical density was later measured at 517 nm. As a control, ethanol combined with DPPH was employed. With a small modification, the procedure was the same as that employed by Harlina et al. (2019). The formula was:

% Inhibition of DPPH activity =  [ ( A B ) ] ÷ A × 100 

Where: A=Optical density of control; B=Optical density of sample.

Determination of reducing power

The reducing power assay was evaluated described by Harlina et al. (2018). In a summary, 2.0 mL of sample was combined with 2.0 mL of 1% (w/v) potassium ferricyanide and 2.0 mL of 0.2 mol/L sodium phosphate buffer (pH 6.6). The aforementioned combination was incubated for 20 min at 50°C. Two milliliters of 10% TCA was then added after cooling. The supernatant was recovered after centrifugation at 3,000×g for 10 min, and 2.0 mL was combined with 2.0 mL of distilled water and 0.4 mL of 0.1% (w/v) FeCl3. After 10 min of mixtures standing at room temperature, the absorbance at 700 nm was measured. As a blank, the same amount of distilled water was used.

Determination of volatile flavor compounds using gas chromatography-mass spectrometry (GC-MS)

The control and treated eggs were put in 20 mL headspace extraction bottles. CAR/PDMS Fused Silica 24 Ga (Manual Holder, 3pk; Supelco, Bellefonte, PA, USA) extracted for 2 h, desorbed in the GC-MS inlet for 5 min, and determined volatile flavor compounds. GC-MS conditions: Agilent 7890B/5977A (Agilent, Santa Clara, CA, USA) GC-MS, HP-5 (30 m ×0.25 mm×0.25 mm) column, inlet temperature 230°C, split less injection. Heating program: the initial temperature was 40°C, maintained for 6 min, increased to 135°C at a heating rate of 3°C/min, and then increased to 230°C at a heating rate of 6°C/min and held for 10 min. Mass spectrometry conditions: EI ion source, ion source temperature 200°C, electron capacity 70 ev, filament current 150 μA, scanning mass range 33–450 u.

Determination of volatile flavor substances using an electronic nose

FOX-3000 electronic nose (E-nose; Alpha MOS, Toulouse, France) was used to collect and evaluate data. It contains an HS-100 autosampler, sensor array, air generator tool, sampling instrument, and software called Alpha Soft V11. Eighteen metal oxide sensors are put in the sensor array, which is separated into three series chambers called T, P, and LY (Li et al., 2012). Take 2–3 g of the egg yolk sample into a 10 mL headspace vial, seal and equilibrate for 30 min. Using pure air as the carrier gas, the vial was put into an autosampler and equilibrated at 50°C for 10 min at a flow rate of 200 mL/min. The stirring speed was 250×g, the injection volume was 2,500 mL, and the injection time was 3 s. The injection delay time was 180 s, while the acquisition time was 50 s. Analysis was conducted using the electronic nasal maximum response point that was automatically recorded with each of the 18 sensors (Song et al., 2013). Three different evaluation samples were used.

Texture profile analysis (TPA) of egg yolk

Texture analysis can be used to determine a product’s texture. A TA.XT Plus texture analyzer was used to determine the texture of salted egg yolk. Samples of egg yolks were divided in half before texture analysis with a compressed 36 mm diameter cylindrical probe. Each sample is compressed after being sandwiched between specific stainless steel plates (using a texture analyzer at room temperature). Prior to and during the test, the texture analyzer’s speed was 2 and 5 mm/s, respectively. At an intermediate speed of 3 mm/s, the torque-deformation curves were captured. Evaluations included hardness, cohesiveness, elasticity, tackiness, chewiness, and recovery. The software Micro Stable was used to obtain these parameters (Stable Micro System, Godalming, UK). Three replicates were used on average.

Data processing

Experiments were performed in triplicate. Data are presented as SD. One-way analysis of variance (ANOVA) was performed using SPSS 20.0 software (SPSS, Chicago, IL, USA). Means were compared using Duncan’s multiple range test to determine the least significant difference between methods at a significance level of 0.05.


The effect of liquid smoke (LS) on the antioxidant activity of salted duck eggs
The effect of liquid smoke (LS) on lipid oxidation

Malondialdehyde, a result of lipid peroxidation that can be represented by TBA values, can be created from polyunsaturated fatty acids with at least three double bonds (Ayala et al., 2014). The concentration of the reaction product, TBARS was calculated by reacting the peroxidation product in the sample with thiobarbituric acid. Due to the presence of TBA reactive substance resulting from the oxidation of peroxides to aldehydes and ketones during the second stage of autoxidation, the TBA value has been commonly employed to quantify the extent of lipid oxidation (Song et al., 2011). The equation derived from the standard curve was used to compute the TBA value, which was then represented as mg (MDA)/kg. Fig. 1 displays the findings of the TBA values for the control group and the LS-treated salted eggs during the duration of the 28 day curing period.

Fig. 1. TBARS value of egg yolk of salted duck egg during salting. TBARS, thiobarbituric acid reactive substances; MDA, malondialdehyde.
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During the 28 day marinating period, TBA value of the salted egg yolk considerably increased over time (p<0.05). The steady increase in the degree of partial oxidation and dehydration of unsaturated fatty acids may be responsible for the rise in TBA value. The TBA value of the control sample was considerably different from the samples that had been treated with LS (p<0.05). The TBA value of the control sample was higher than that of the salted egg treated with LS, and the TBA value decreased with increasing LS concentration. The oxidation reaction is inhibited by the high LS concentration of phenolic compounds and their derivatives, which have good antioxidant activity and can be employed as antioxidants. According to Estrada-Muñoz et al. (1998), the instability of the generated MDA or the oxidation of various lipid populations at various intervals could both account for the rise and fall in TBA values at different storage times.

Effects of liquid smoke (LS) on the ability of scavenging 1-diphenyl-2-picrylhydrazyl (DPPH) free radicals

Fig. 2 displays the changes in the free radical scavenging rate of the salted eggs treated with the LS and the control group throughout the duration of the 28 day curing period. According to the findings, during the first 14 days of curing, salted duck eggs treated with LS considerably improved over time at scavenging DPPH free radicals in the yolk and protein (p<0.05). After the 14th day, the amount of the increased protein capacity to scavenge free radicals reduced with time and tended to stabilize in the salted egg yolk treated with LS. During the 28-day curing period, free radical scavenging rate of the control group did not rise significantly (p>0.05).

Fig. 2. Radical scavenging ability of egg yolk and egg white of salted duck egg during salting.
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Salted eggs supplemented with LS 2.5% and 5.0%, (v/v) considerably outperformed the control sample in terms of their ability to scavenge free radicals (p<0.05), and it was found that the concentration of LS was inversely correlated with the rate of free radical scavenging. Egg yolks often scavenge free radicals at a higher rate than egg whites.

The effect of liquid smoke (LS) on reducing power

Fig. 3 illustrates changes in the reduction power of the salted eggs in the control group and the salted eggs treated with LS over the duration of the 28-day curing period. The results indicated that reduction power of salted egg yolk significantly increased over the duration of the 28-day pickling period (p< 0.05). After the first seven days (p<0.05), the reducing power of the control of salted egg white and the 2.5% (v/v) LS increased dramatically with time and then progressively stabilized. With the exception of the second week during the 28 curing cycles, the reducing power of salted egg white in 5.0% (v/v) LS increased significantly over time (p<0.05). The reducing power of salted eggs added with LS (2.5% and 5.0%, v/v) was significantly higher than that of the control samples (p<0.05). The reducing power of egg yolk is overall higher than that of egg white.

Fig. 3. Reducing power of egg yolk and egg white of salted duck egg during salting.
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Phenolic compounds, which compose the majority of LS, act as reducing and antioxidant agents by chelating metal ions or providing hydrogen to prevent the oxidation chain reaction (Bursal and Köksal, 2011). The electrons provided by natural antioxidants are frequently calculated using the reducing force (Dorman et al., 2003). According to You et al. (2010), antioxidants cause Fe3+/FeSCN complexes to degrade into the Fe2+ form, which results in the formation of reducing power in the samples. The strongest reducing power is demonstrated by the absorbance at 700 nm (Duh, 1998; Memarpoor-Yazdi et al., 2013). Yellow color of sample reagent turns green or blue-green during the test. Antioxidants that act as a reducing agent transform ferricyanide from its complicated state to its simple ferrous form. As a result, Fe2+ content can be determined by observing Prussian blue absorption at 700 nm. The ability of a phenolic antioxidant to provide electrons is key, and its indication, the valence reduction of Fe(III), is frequently used (Dorman et al., 2003).

Effect of liquid smoke (LS) on volatile flavor compounds of salted duck eggs
Volatile flavor compounds identified by gas chromatography-mass spectrometry (GC-MS)

Lipid oxidation is the main reaction that produces volatile flavor compounds, which can improve flavor. The volatile substances found on fresh duck eggs and control salted duck eggs by GC-MS are listed in Table 1. There are 3 esters, 5 acids, 1 ketone, 3 aldehydes, 5 nitrogenous compounds, 1 ether, 2 hybrid cyclic compounds, 3 hydrocarbons, and 1 other substance among the 24 volatile compounds found in fresh duck eggs, which are classified into 9 groups. The salted duck eggs of the control group included 21 volatile components that could be categorized into 10 different groups. These included 1 ester, 5 acids, 3 alcohols, 1 ketone, 4 aldehydes, 5 nitrogenous compounds, 1 ether, 1 heterocyclic compound, 3 hydrocarbons, and 1 other substance.

Table 1. Analysis of volatile flavor substances from egg yolk of fresh egg and salted duck egg by GC-MS
Fresh duck egg yolk Control group salted duck egg yolk
Retention time (min) Compound name Retention time (min) Compound name
Esters Esters
 1 20.937 Methyl benzoate  1 20.960 Methyl benzoate
 2 17.872 Succinic acid, decyl tetrahydrofurfuryl ester
 3 22.708 1-Alanine, N-pentanoyl, myristyl ester
Acids Acids
 1 2.476 Acetic acid  1 2.720 Acetic acid
 2 22.255 5-(1,1-Dimethylethoxy)-2-thiophenecarboxylic acid  2 21.477 4-(Methylamino)butanoic acid
 3 25.123 Propyl-malonic acid  3 33.831 Pterin-6-carboxylic acid
 4 36.937 Octadec-9-enoic acid  4 36.930 6-Octadecenoic acid
 5 44.514 n-Hexadecanoic acid  5 44.507 n-Hexadecanoic acid
Alcohols Alcohols
nd nd  1 3.993 Ethanol
 2 7.138 2-Methyl-1-propanol
 3 10.103 3-Methyl-1-butanol
Ketones Ketones
 1 33.783 2’,4’-Dihydroxypropiophenone  1 23.324 (+)-2-Furanone
Aldehydes Aldehydes
 1 7.514 Furfural  1 7.554 3-Furfural
 2 7.631 3-Furfural  2 7.590 Furfural
 3 14.240 5-Methyl-2-furfuraldehyde  3 9.104 3-Methyl-butyraldehyde
 4 17.773 Benzaldehyde
Nitrogen compounds Nitrogen
 1 20.387 Methylpent-4-enylamine  1 35.336 Dimethylamine
 2 23.118 2,2-Dinitro-N-methylbutylamine
 3 24.376 Propionamide
 4 27.359 2-(Adamantan-1-yl)-1-methyl-ethylethylamine
 5 28.982 N-Formyl DL-alanine
Ethers Ethers
 1 41.176 Polyethylene glycol monolauryl ether  1 38.329 Octaethylene glycol monolauryl ether
Heterocyclic Heterocyclic
 1 7.469 3,5-Dimethylpyrazole  1 7.554 3,5-Dimethylpyrazole
 2 7.609 1,4-Dimethyl-pyrazole
Hydrocarbons Hydrocarbons
 1 25.632 3-Azabicyclo[3.2.2]nonane  1 30.798 2-Methylaminomethyl-1,3-dioxolane
 2 29.477 2-Methylaminomethyl-1,3-dioxolane  2 31.007 3-Azabicyclo[3.2.2]nonane
 3 28.071 2-Methylbicyclo[4.3.0]non-1(6)-ene  3 35.189 4-Methyl-1,3-dioxolane
Others Others
 1 8.702 Methyl cyanogen chloride  1 22.852 Naphthalene

GC-MS, gas chromatography-mass spectrometry.

Download Excel Table

The volatile flavor components found on salted duck eggs that were cured in LS 2.5% (v/v) that analyzed by GC-MS are listed in Table 2. 53 phenols, 8 esters, 3 acids, 4 alcohols, 32 ketones, 11 aldehydes, 6 nitrogen-containing compounds, 3 ethers, 7 heterocyclic compounds, 18 hydrocarbons, and 2 others are among the 147 volatile substances in LS, which are subdivided into 11 categories. A total of 63 volatile compounds, subdivided into 8 categories, were found in salted duck eggs that were cured in LS at a 2.5% (v/v) concentration. These included 23 phenols, 2 esters, 1 acid, 2 alcohols, 13 types of ketones, 4 types of aldehydes, 2 types of heterocyclic compounds, and 16 types of hydrocarbons. For total ion chromatogram of volatile flavor component from these samples can be seen in Supplementary Fig. S1.

Table 2. Analysis of volatile flavor substances from liquid smoke and egg yolk of salted duck egg supplemented with LS by GC-MS
LS Salted duck egg yolk supplemented with 2.5% (v/v) LS
Retention/min Compound name Retention/min Compound name
Esters Esters
 1 12.192 Methyl caproate  1 16.512 Glycine, N-(2-furylcarbonyl)-methyl ester
 2 14.811 Methyl 2-furoate  2 20.937 Methyl benzoate
 3 21.286 Methyl benzoate
 4 22.704 Methyl octanoate
 5 26.845 4-Methyl-benzoic acid methyl ester
 6 32.130 2-Sec-butylphenylmethylcarbamate
 7 32.584 3-Methoxy-benzoic acid methyl ester
 8 35.098 2’-Hydroxy-5’-methoxyacetophenone, acetate
Acids Acids
 1 2.674 Acetic acid  1 2.291 Acetic acid
 2 6.688 Butyric acid
 3 6.884 (E)-2-Butenoic acid
Alcohols Alcohols
 1 29.098 O-Methoxy-α-methylbenzyl alcohol  1 8.597 3-Furanmethanol
 2 35.098 6-Methyl-5-(1-methylethyl)-5-hepten-3-yn-2-ol  2 8.597 2-Furanmethanol
 3 39.710 Dihydroartemisinin
 4 40.082 5-Tert-butylpyrrolidinol
Ketones Ketones
 1 10.968 2-Methyl-2-cyclopent-1-one  1 10.972 2-Methyl-2-cyclopent-1-one
 2 10.968 3-Methyl-2-cyclopent-1-one  2 10.972 3-Methyl-2-cyclopent-1-one
 3 11.225 1-(2-Furyl)-ethanone  3 11.280 1-(2-Furyl)-ethanone
 4 13.213 2,3-Dimethyl-2-cyclopent-1-one  4 11.362 1-(1H-pyrazol-4-yl)-ethanone
 5 15.941 3,4-Dimethyl-2-cyclopent-1-one  5 12.688 3,4-Dimethyl-2-cyclopent-1-one
 6 16.585 1-(2-Furyl)-1-propanone  6 15.920 2,3-Dimethyl-2-cyclopent-1-ene
 7 18.351 2,3,5-Trimethyl-2-cyclopent-1-one  7 17.133 4,4-Dimethyl-2-cyclopenten-1-one
 8 18.351 3,4,4-Trimethyl-2-cyclopent-1-one  8 17.366 2,3,4-Trimethyl-2-cyclopent-1-one
 9 19.565 Acetophenone  9 19.385 Acetophenone
 10 21.408 1-(2-Furyl)-ethanone  10 19.951 3-Ethyl-2-cyclopent-1-one
 11 23.084 1-(2-Methylphenyl)-ethanone  11 23.578 2,3,4,5-Tetramethyl-2-cyclopent-1-one
 12 23.172 2,3,4-Trimethyl-2-cyclopent-1-one  12 33.778 2’,4’-Dihydroxypropiophenone
 13 24.144 2,3-Dimethylhydroquinone  13 33.778 2,5-Dihydroxypropiophenone
 14 24.293 4’-Hydroxy-acetophenone
 15 24.293 1-(2-Hydroxyphenyl)-ethanone
 16 26.598 Spiro[4.5]decan-2-one
 17 27.139 4-Hydroxy-2,4,5-trimethyl-2,5-cyclohexadien-1-one
 18 28.460 4-Hydroxy-3-methylacetophenone
 19 30.818 1-(2,5-Dihydroxyphenyl)-ethanone
 20 31.014 1-Methylinden-2-one
 21 31.014 2,3-Dihydro-2-methyl-1H-inden-1-one
 22 32.008 2’,6’-Dihydroxy-3’-methylacetophenone
 23 32.008 1-(2-Hydroxy-4-methoxyphenyl)-ethanone
 24 32.200 1-(2-Hydroxy-6-methoxyphenyl)-ethanone
 25 33.552 1-(4-Hydroxy-3-methoxyphenyl)ethanone
 26 33.552 Tert-butyl hydroquinone
 27 34.470 2,3-Dihydro-3,3-dimethyl-1H-inden-1-one
 28 34.470 1-(2,3-Dihydro-1H-inden-5-yl)-ethanone
 29 34.649 7-Methylinden-1-one
 30 36.606 1-(3,4-Dimethoxyphenyl)-ethanone
 31 37.243 4-(4-Methoxyphenyl)3-buten-2-one
 32 38.685 6,7-Dimethoxy-1(3H)-benzofuranone
Aldehydes Aldehydes
 1 7.630 Furfural  1 7.405 Furfural
 2 7.630 3-Furfural  2 7.438 3-Furfural
 3 13.794 Benzaldehyde  3 13.765 Benzaldehyde
 4 14.080 5-Methyl-2-furfuraldehyde  4 14.063 5-Methyl-2-furfuraldehyde
 5 18.138 2-Hydroxy-benzaldehyde
 6 18.138 3-Hydroxy-benzaldehyde
 7 22.801 2-Hydroxy-4-methylbenzaldehyde
 8 22.801 2-Hydroxy-3-methylbenzaldehyde
 9 22.801 2-Hydroxy-6-methyl-benzaldehyde
 10 35.667 2-Ethoxy-4-anisaldehyde
 11 36.889 3-Ethoxy-4-methoxybenzaldehyde
Nitrogenous Nitrogenous
 1 22.050 4-Methoxy-1,3-phenylenediamine nd nd
 2 34.368 N-(Adamantan-1-yl)methyl-2,5-dichloro-benzenesulfonamide
 3 38.000 1-Methyl-N-vanillyl-(+)-s-2-phenethylamine
 4 41.291 1-Methyl-N-vanillyl-(+)-S-2-phenethylamine
 5 41.291 1-Methyl-N-(-)-R-phenethylamine
 6 41.291 1-Methyl-N-vanillyl-(+-)-2-phenylethylamine
Ethers Ethers
 1 29.098 3,4-Methylenedioxyanisole nd nd
 2 31.489 O-Isopropyl anisole
 3 36.606 3-Tert-butyl-4-hydroxyanisole
Heterocyclic Heterocyclic
 1 8.920 2,4-Dimethylfuran  1 7.438 3,5-Dimethylpyrazole
 2 9.741 3,5-Dimethylpyrazole  2 15.689 2-Ethyl-5-methyl-furan
 3 20.044 2,3-Dihydro-benzofuran
 4 24.197 1,3,5-Trimethyl-1H-pyrazole
 5 36.167 1,3-Dihydro-5,6-dimethyl-2-benzothiophene
 6 37.243 2-Ethyl-7-methyl-benzo[b]thiophene
 7 38.000 2,5-Dibutyl-furan
Hydrocarbons Hydrocarbons
 1 9.439 1-Cyclohexyl-2,5-diene  1 12.688 1,3-Dimethyl-1-cyclohexene
 2 12.682 1-Methylcycloheptene  2 12.756 Tetramethylmethylenecyclopropane
 3 12.703 1,2-Dimethyl-cyclohexene  3 12.792 5,5-Dimethyl-1,3-hexadiene
 4 17.022 1-Methoxy-3-methyl-benzene  4 12.792 2,3-Dimethyl-2,4-hexadiene
 5 18.351 3-Fluoro-o-xylene  5 12.792 2,5-Dimethyl-2,4-hexadiene
 6 22.487 1,1,2-Trimethyl-3-(2-methyl-1-propenyl)-cyclopropane  6 13.113 1-Methylcycloheptene
 7 28.849 2-Methoxy-1,3,5-trimethylbenzene  7 13.195 1,6-Dimethyl-cyclohexene
 8 29.332 2,6-Dimethoxytoluene  8 17.133 3,4-Dimethyl-(Z,Z)-2,4-hexadiene
 9 29.332 3,5-Dimethoxytoluene  9 17.709 1-Methylcyclooctene
 10 30.541 1-Methoxy-4-(1-methylethyl)-benzene  10 21.336 1-Isopropylcyclohex-1-ene
 11 30.818 1,4-Dimethoxy-2-methyl-benzene  11 22.284 1,1,2-Trimethyl-3-(2-methyl-1-propenyl)-cyclopropane
 12 31.567 1,2,3-Trimethoxybenzene  12 22.808 2,6-Dimethyl-2,4-heptadiene
 13 32.008 4-Ethyl-1,2-dimethoxy-benzene  13 27.597 1,2,3,4,5-Pentamethyl-1,3-cyclopentadiene
 14 34.368 1-Ethyl-1(1-cyclobutylethylene)cyclobutane  14 28.125 2,3-Dimethoxytoluene
 15 34.368 1-Methoxy-4-(1-methylpropyl)-benzene  15 28.125 3,4-Dimethoxytoluene
 16 35.481 1,2,3-Trimethoxy-5-methylbenzene  16 31.525 1,2,3-Trimethoxybenzene
 17 35.667 1,2-Dimethoxy-4-n-propylbenzene
 18 39.710 9-Ethylfluorene
Phenolics Phenolics
 1 15.570 Phenol  1 15.325 Phenol
 2 19.409 p-Cresol  2 19.091 2-Methyl-phenol
 3 19.409 2-Methyl-phenol  3 20.198 p-Cresol
 4 20.703 3-Methyl-phenol  4 20.198 3-Methyl-phenol
 5 20.782 Methoxyphene  5 20.666 2-Methoxy-phenol
 6 20.782 2-Methoxy-phenol  6 20.666 Methoxyphene
 7 21.730 2,6-Dimethyl-phenol  7 21.536 2,6-Dimethyl-phenol
 8 22.050 Methoxycresol  8 22.284 2,6-Dimethyl-1,4-benzenediol
 9 23.439 2-Ethyl-phenol  9 23.319 2-Ethyl-phenol
 10 23.973 2,3-Dimethyl-phenol  10 23.755 2,3-Dimethyl-phenol
 11 23.973 3,5-Dimethyl-phenol  11 23.755 2,4-Dimethyl-phenol
 12 23.973 2,4-Dimethyl-phenol  12 23.755 3,5-Dimethyl-phenol
 13 24.931 3-Ethyl-phenol  13 25.104 2-Methoxy-6-methylphenol
 14 24.931 4-Ethyl-phenol  14 25.104 2-Methoxy-3-methyl-phenol
 15 25.248 2-Methoxy-6-methylphenol  15 25.104 4-Methoxy-3-methyl-phenol
 16 25.248 2-Methoxy-3-methyl-phenol  16 25.472 2-Methoxy-5-methylphenol
 17 25.248 4-Methoxy-3-methyl-phenol  17 25.472 Cresol
 18 26.456 2,4,5-Trimethyl-phenol  18 25.665 2,5-Dimethyl-1,4-benzenediol
 19 26.456 2,4,7-Trimethyl-phenol  19 26.297 2,4,6-Trimethyl-phenol
 20 27.021 m-Tert-butyl-phenol  20 27.597 2-Ethyl-4-methyl-phenol
 21 27.021 p-Tert-butyl-phenol  21 27.597 3-Ethyl-5-methyl-phenol
 22 27.392 2-Propyl-phenol  22 29.844 4-Ethyl-2-methoxy-phenol
 23 27.695 2-Ethyl-4-methyl-phenol  23 33.778 2-Methoxy-4-propyl-phenol
 24 27.695 2-Ethyl-6-methyl-phenol
 25 27.695 3-Ethyl-5-methyl-phenol
 26 28.200 2-(1-Methylethyl)-phenol
 27 28.200 3-(1-Methylethyl)-phenol
 28 28.460 3,4-Diethylphenol
 29 28.460 3-Methyl-5-(1-methylethyl)-methylcarbamatephenol
 30 29.503 2,3,5-Trimethyl-phenol
 31 29.747 2,4,6-Trimethyl-phenol
 32 30.090 4-Ethyl-2-methoxy-phenol
 33 30.541 3-Methyl-4-isopropylphenol
 34 30.541 Thymol
 35 30.750 2-Methyl-5-(1-methylethyl)phenol
 36 31.170 2,3,4,6-Tetramethyl-phenol
 37 31.170 2-Ethyl-4,5-dimethyl-phenol
 38 31.356 2,3,5-Trimethyl-1,4-benzenediol
 39 31.356 3-Isopropylthiophenol
 40 31.489 2-Methyl-5-(1-methylethyl)phenol
 41 32.130 2-(1-Methylpropyl)-phenol
 42 32.200 P-Tert-butylcatechol
 43 33.149 2,6-Dimethoxy-phenol
 44 33.392 3-Allyl-6-methoxyphenol
 45 33.392 Eugenol
 46 33.552 4-(1,1-Dimethylethyl)-thiophenol
 47 33.685 2,3,5,6-Tetramethyl-phenol
 48 33.883 2-Methoxy-4-propyl-phenol
 49 37.328 2-Ethyl-5-n-propylphenol
 50 39.635 2,5-Bis(1,1-dimethylethyl)phenol
 51 39.635 2,4-Bis(1,1-dimethylethyl)phenol
 52 39.710 4,6-Dimethoxy-phthalide
 53 43.170 2,6-Bis(1,1-dimethylethyl)-4-(1-oxopropyl)phenol
Others Others
 1 25.561 Dimethylphenylphosphine nd nd
 2 32.584 M-Phenylhydrazide

LS, liquid smoke; GC-MS, gas chromatography-mass spectrometry.

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Antibacterial, antioxidant, and organoleptic qualities are connected to phenols and their derivatives. Numerous phenolic substances, primarily phenol, guaiacol, eugenol, etc., are present in LS. When phenolic compounds are thermally degraded, they sometimes contain dihydroxybenzene derivatives, which have a high antioxidant activity (Guillén and Manzanos, 2002). Macromolecular polymers that are randomly cross-linked make up lignin. It is composed of a disorganized collection of hydroxyl groups with various linkages and methoxy-substituted phenylpropane units. Pyrolysis involves competing thermal degradation reactions that, depending on the bond energies involved, lead to various bond breakage. The considerable structural variety of lignin allows for a wide range of compounds to be produced during pyrolysis (Guillén and Ibargoitia, 1998).

Salted duck eggs marinated in 2.5% (v/v) LS contained a significant amount of phenolic chemicals. Fresh duck egg and salted duck egg without LS did not contain phenolic substances. Additionally, only a very little number of ketones were identified in fresh duck eggs and salted duck eggs without LS but there were 32 and 13 ketones in the LS and treated eggs with LS 2.5% (v/v), respectively. The primary element responsible for the color and flavor of smoked goods is ketone. Carbonyl groups found in ketones can interact with amino groups in protein molecules to produce a distinctive smoky color.

Fresh duck eggs, salted duck eggs in the control group, and salted egg yolks cured in 2.5% (v/v) LS, they all contained trace amounts of esters, alcohols, and aldehydes. Esterification is the process by which fatty acids and alcohols are converted into esters. Alcohols often make minor contributions to food taste (Barclay et al., 1997). Aldehydes are mostly produced as a result of the oxidation of fats and oils during heating (Mensink et al., 2003). Therefore, fresh duck eggs, the control group, and salted egg yolks treated with LS did not contain a significant amount of aldehydes. Salted duck eggs were cured in 2.5% (v/v) LS, and significant amounts of hydrocarbons were found in both. Alkenes dominate the liquid-cured, salted duck egg yolks.

Discrimination of volatile flavor substances by electronic nose

The electronic nose (E-nose) imitates the olfactory system of mammals by employing a number of sensors that react to volatile substances (Cramp et al., 2009). The E-nose is a device that combines a gas sensor structure and an air sample tool with a personal computer. The ability of sensor array function of the E-nose device to react differently to distinct flavors sets it apart from other devices used for flavor characterization. Hundreds or even thousands of distinct volatile flavor components can be found in each flavor. The identification and measurement of numerous flavor constituents in a single flavor sample is accomplished by widely used analytical techniques like GC-MS. However, unlike the human nose, which analyzes flavors as a whole and detects them by our brains (for example, by identifying patterns of flavors in memory), the E-nose can react to a sample of total flavor compounds. This is because the human olfactory system does not require isolation of individual compounds as part of the sample analysis process (Cramp et al., 2009).

Figs. 4 and 5 show the PCA analysis and radar chart of the volatile flavor E-nose in fresh duck eggs, the control group, and the eggs treated with LS (2.5% and 5.0%, v/v), respectively. In the PCA principal component analysis graph, the abscissa represents the first principal component and the ordinate represents the second principal component, both of which show that salted duck eggs differ significantly from fresh duck eggs and those treated with LS. The radar chart demonstrates that fresh duck eggs had considerably lower relative values of T40/2, P30/2, P40/2, P30/1, PA/2, T70/2, P40/1, P10/2, and P10/1 than a sample of treated eggs. Salted eggs supplemented with LS (2.5% and 5.0%, v/v) had significantly lower PA/2, T70/2, P40/1, P10/2, P10/1, and T30/1 values than the control samples. E-nose sensor intensity for volatile compounds of these samples is shown in Supplementary Fig. S2.

Fig. 4. PCA analysis for egg yolk of duck egg. FE, fresh duck eggs; CK, salted duck eggs of the control group after 28 days of curing; 2.5%, salted duck eggs with 2.5% (v/v) liquid smoke added after 28 days of curing; 5.0%, salted duck eggs after 28 days of curing salted duck eggs with 5.0% (v/v) liquid smoke.
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Fig. 5. The electronic-nose radar profile of egg yolk of duck egg. FE, fresh duck eggs; CK, salted duck eggs of the control group after 28 days of curing; 2.5%, salted duck eggs with 2.5% (v/v) liquid smoke added after 28 days of curing; 5.0%, salted duck eggs after 28 days of curing salted duck eggs with 5.0% (v/v) liquid smoke.
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Effects of liquid smoke (LS) on the texture of salted duck eggs

Salted egg quality is correlated with the product texture. Table 3 summarizes the texture of salted eggs enriched with LS (2.5% and 5.0%, v/v) and the control group after 28 days of curing. Significant changes in hardness may be seen between control samples and salted egg yolks treated with various concentrations of LS (p<0.05). The results showed that the structure of the salted duck egg yolk became more solidified in the eggs treated with LS, but the hardness of the egg yolk was reduced if the concentration of the LS was too high. Kaewmanee et al. (2009a) and Kaewmanee et al. (2009b) have reported that the hardness of salted duck egg yolk is associated with an increase in the hardening rate. The hardening rate of the yolk is defined as the ratio of the hard outer yolk to the weight and is used as an indicator of the completion of the pickling. The more dehydrated the marinated egg yolks are, the rougher the texture will be.

Table 3. Texture profile analysis of egg yolk of salted duck egg
Variable Control 2.5% 5.0%
Hardness (g) 3,342.97±154.82b 3,659.51±99.87a 1,874.17±111.10c
Springiness (mm) 0.338±0.043a 0.269±0.027a 0.240±0.081a
Cohesiveness 0.411±0.012a 0.363±0.021b 0.251±0.009c
Gumminess (N) 1,375.32±84.60a 1,328.52±90.58a 469.19±34.62b
Chewiness 462.53±40.05a 359.14±57.50b 114.27±46.10c
Resilience 0.180±0.011a 0.172±0.008a 0.109±0.006b

a–c Different lowercase letters indicate significant differences between salted duck eggs with different treatments (p<0.05).

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Between the control group and the LS-treated salted yolk, there was no noticeable change in terms of elasticity (p>0.05). The three groups of salted duck eggs varied significantly (p<0.05) in terms of cohesion and chewiness. In addition, the control and 2.5% (v/v) LS-treated eggs were significantly different from the 5.0% (v/v) LS-treated egg for gumminess and resilience (p<0.05), the gumminess and resilience of eggs control and 2.5% (v/v) LS were higher than those of egg treated with 5.0% (v/v) LS. It is possible that the excessively high concentration of LS causes the protein in the egg yolk to denature and alter its structure, making it flakier and lowering its viscosity and recovery. The picture of control and treated of salted duck eggs after 28 days of salting can be seen in Fig. 6.

Fig. 6. The picture of salted duck egg control and salted duck egg supplemented with liquid smoke (2.5% and 5.0%, v/v) after 28 days of salting.
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In recent years, the use of LS as a flavor enhancer and preservative in food products has increased. Salted duck eggs, in particular, are a popular traditional food product in many cultures, and the addition of LS to this product has intrigued the interest of researchers due to its potential effect on the antioxidant activity and lipid oxidation of the eggs. LS contain a variety of compounds with antioxidant properties, including phenols and polyphenols (Montazeri et al., 2013). These compounds may contribute to the overall antioxidant capacity of salted duck eggs, preventing lipid oxidation and maintaining egg quality (Li et al., 2022). LS can improve the antioxidant properties of salted duck eggs by increasing their DPPH scavenging activity and reducing power (Soldera et al., 2008). This is most likely because LS contains phenols and polyphenols, both of which have been shown to have powerful antioxidant properties.

The fact that the hydroxyl group of the phenolic component in LS can provide stable free radicals and reduce fat oxidation caused by the interaction of free radicals and fatty acids may explain its high antioxidant activity. Phenols and their derivatives are most likely the primary class of chemicals in LS that act as antioxidants and free radical scavengers (Montazeri et al., 2013). Polyphenolic substances such as flavonoids and phenols have also been studied and found to have a variety of biological effects, including antioxidant activity (Kumar and Pandey, 2013; Shahidi and Ambigaipalan, 2015; Tungmunnithum et al., 2018).

According to Barclay et al. (1997), the antioxidant properties of phenolics and their derivatives are derived from lignin (4-propylguaiacol, eugenol, isoeugenol, and 4-allyl-2,6-dimethoxyphenol). These substances, according to reports, have greater antioxidant potential than commercially available 2,6-di-tert-butyl-4-methylphenol (BHT). The primary goal of anti-oxidation is to delay oxidation by avoiding and limiting free radical production. Antioxidants can be formed from phenolic compounds and their derivatives. As a result, using LS as a good source of phenolic chemicals can benefit functional foods. Antioxidant properties can also be used to inhibit oxidative food reactions (Albishi et al., 2013).

The addition of LS to salted duck eggs can alter their volatile flavor profile significantly. LS can improve the overall flavor of the eggs while also adding a smoky, woody aroma. This is most likely because the LS contain volatile flavor compounds such as phenols, aldehydes, and ketones (Guillén and Ibargoitia, 1998; Suñen et al., 2003). It can make the eggs more tender and juicy by improving their texture. Because the presence of volatile flavor compounds in the LS is likely, this can improve the sensory properties of the eggs and increase their overall appeal.


Comprehensive analysis of the experimental findings revealed that the LS did have a significant impact on the antioxidant properties of salted duck eggs, which may have the potential to enhance the antioxidant capacity of these eggs to some extent and alleviate the oxidation of the lipids in the egg yolk. In addition, GC-MS detected several phenolic compounds in both the LS and the salted duck eggs treated with LS groups. These compounds may be the primary factors contributing to the eggs treated with LS having increased antioxidant activity. Additionally, LS can alter the physical characteristics of the salted duck eggs, such as hardness, cohesiveness, chewiness, oil exudation, color, etc., for the egg yolks. Therefore, LS may be beneficial to increase the sensory quality of salted duck eggs.


Supplementary materials are only available online from:



Conflicts of Interest

The authors declare no potential conflicts of interest.


This article was supported by Universitas Padjadjaran, Indonesia.

Author Contributions

Conceptualization: Harlina PW, Ma M. Data curation: Yuliana T, Fetriyuna. Methodology: Harlina PW, Yuliana T, Fetriyuna, Shahzad R. Validation: Harlina PW, Ma M. Investigation: Harlina PW. Writing - original draft: Harlina PW, Ma M. Writing - review & editing: Harlina PW, Yuliana T, Fetriyuna, Shahzad R, Ma M.

Ethics Approval

This article does not require IRB/IACUC approval because there are no human and animal participants.



Ahn DU, Sunwoo HH, Wolfe FH, Sim JS. 1995; Effects of dietary α-linolenic acid and strain of hen on the fatty acid composition, storage stability, and flavor characteristics of chicken eggs. Poult Sci. 74:1540-1547


Albishi T, John JA, Al-Khalifa AS, Shahidi F. 2013; Phenolic content and antioxidant activities of selected potato varieties and their processing by-products. J Funct Foods. 5:590-600


Ayala A, Muñoz MF, Argüelles S. 2014; Lipid peroxidation: Production, metabolism, and signaling mechanisms of malondialdehyde and 4-hydroxy-2-nonenal. Oxid Med Cell Longev. 2014:360438


Barclay LRC, Xi F, Norris JQ. 1997; Antioxidant properties of phenolic lignin model compounds. J Wood Chem Technol. 17:73-90


Bursal E, Köksal E. 2011; Evaluation of reducing power and radical scavenging activities of water and ethanol extracts from sumac (Rhus coriaria L.). Food Res Int. 44:2217-2221


Cramp AP, Sohn JH, James PJ. 2009; Detection of cutaneous myiasis in sheep using an ‘electronic nose’. Vet Parasitol. 166:293-298


Dorman HJD, Peltoketo A, Hiltunen R, Tikkanen MJ. 2003; Characterisation of the antioxidant properties of de-odourised aqueous extracts from selected lamiaceae herbs. Food Chem. 83:255-262


Duh PD. 1998; Antioxidant activity of burdock (Arctium lappa Linné): Its scavenging effect on free-radical and active oxygen. J Am Oil Chem Soc. 75:455-461


Estrada-Muñoz R, Boyle EAE, Marsden JL. 1998; Liquid smoke effects on Escherichia coli O157:H7, and its antioxidant properties in beef products. J Food Sci. 63:150-153


Guillén MD, Ibargoitia ML. 1998; New components with potential antioxidant and organoleptic properties, detected for the first time in liquid smoke flavoring preparations. J Agric Food Chem. 46:1276-1285


Guillén MD, Manzanos MJ. 2002; Study of the volatile composition of an aqueous oak smoke preparation. Food Chem. 79:283-292


Harlina PW, Ma M, Shahzad R, Gouda MM, Qiu N. 2018; Effect of clove extract on lipid oxidation, antioxidant activity, volatile compounds and fatty acid composition of salted duck eggs. J Food Sci Technol. 55:4719-4734


Harlina PW, Shahzad R, Ma M, Geng F, Wang Q, He L, Ding S, Qiu N. 2015; Effect of garlic oil on lipid oxidation, fatty acid profiles and microstructure of salted duck eggs. J Food Process Preserv. 39:2897-2911


Harlina PW, Shahzad R, Ma M, Wang N, Qiu N. 2019; Effects of galangal extract on lipid oxidation, antioxidant activity and fatty acid profiles of salted duck eggs. J Food Meas Charact. 13:1820-1830


Hasler CM. 2000; The changing face of functional foods. J Am Coll Nutr. 19:499S-506S


Hayat Z, Cherian G, Pasha TN, Khattak FM, Jabbar MA. 2010; Oxidative stability and lipid components of eggs from flax-fed hens: Effect of dietary antioxidants and storage. Poult Sci. 89:1285-1292


Kaewmanee T, Benjakul S, Visessanguan W. 2009a; Changes in chemical composition, physical properties and microstructure of duck egg as influenced by salting. Food Chem. 112:560-569


Kaewmanee T, Benjakul S, Visessanguan W. 2009b; Effect of salting processes on chemical composition, textural properties and microstructure of duck egg. J Sci Food Agric. 89:625-633


Kaewmanee T, Benjakul S, Visessanguan W. 2011; Effects of salting processes and time on the chemical composition, textural properties, and microstructure of cooked duck egg. J Food Sci. 76:S139-S147


Kumar S, Pandey AK. 2013; Chemistry and biological activities of flavonoids: An overview. Sci World J. 2013:162750


Li S, Li X, Wang G, Nie L, Yang Y, Wu H, Wei F, Zhang J, Tian J, Lin R. 2012; Rapid discrimination of Chinese red ginseng and Korean ginseng using an electronic nose coupled with chemometrics. J Pharm Biomed Anal. 70:605-608


Li X, Chen S, Yao Y, Wu N, Xu M, Zhao Y, Tu Y. 2022; The quality characteristics formation and control of salted eggs: A review. Foods. 11:2949


Memarpoor-Yazdi M, Mahaki H, Zare-Zardini H. 2013; Antioxidant activity of protein hydrolysates and purified peptides from Zizyphus jujuba fruits. J Funct Foods. 5:62-70


Mensink RP, Aro A, Den Hond E, German JB, Griffin BA, ten Meer HU, Mutanen M, Pannemans D, Stahl W. 2003; PASSCLAIM: Diet-related cardiovascular disease. Eur J Nutr. 42:i6-i27


Milly PJ, Toledo RT, Ramakrishnan S. 2005; Determination of minimum inhibitory concentrations of liquid smoke fractions. J Food Sci. 70:M12-M17


Montazeri N, Oliveira ACM, Himelbloom BH, Leigh MB, Crapo CA. 2013; Chemical characterization of commercial liquid smoke products. Food Sci Nutr. 1:102-115


Rice-Evans CA, Miller NJ, Paganga G. 1996; Structure-antioxidant activity relationships of flavonoids and phenolic acids. Free Radic Biol Med. 20:933-956


Shahidi F, Ambigaipalan P. 2015; Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects: A review. J Funct Foods. 18:820-897


Soldera S, Sebastianutto N, Bortolomeazzi R. 2008; Composition of phenolic compounds and antioxidant activity of commercial aqueous smoke flavorings. J Agric Food Chem. 56:2727-2734


Song S, Yuan L, Zhang X, Hayat K, Chen H, Liu F, Xiao Z, Niu Y. 2013; Rapid measuring and modelling flavour quality changes of oxidised chicken fat by electronic nose profiles through the partial least squares regression analysis. Food Chem. 141:4278-4288


Song Y, Liu L, Shen H, You J, Luo Y. 2011; Effect of sodium alginate-based edible coating containing different anti-oxidants on quality and shelf life of refrigerated bream (Megalobrama amblycephala). Food Control. 22:608-615


Suñen E, Aristimuño C, Fernandez-Galian B. 2003; Activity of smoke wood condensates against Aeromonas hydrophila and Listeria monocytogenes in vacuum-packaged, cold-smoked rainbow trout stored at 4°C. Food Res Int. 36:111-116


Tungmunnithum D, Thongboonyou A, Pholboon A, Yangsabai A. 2018; Flavonoids and other phenolic compounds from medicinal plants for pharmaceutical and medical aspects: An overview. Medicines. 5:93


You L, Zhao M, Regenstein JM, Ren J. 2010; Changes in the antioxidant activity of loach (Misgurnus anguillicaudatus) protein hydrolysates during a simulated gastrointestinal digestion. Food Chem. 120:810-816