Characterisation of Flavour Attributes in Egg White Protein Using HS-GC-IMS Combined with E-Nose and E-Tongue: Effect of High-Voltage Cold Plasma Treatment Time

Abstract

Egg white protein (EWP) is susceptible to denaturation and coagulation when exposed to high temperatures, adversely affecting its flavour, thereby influencing consumers' decisions. Here, we employ high-voltage cold plasma (HVCP) as a novel nonthermal technique to investigate its influence on the EWP's flavour attributes using E-nose, E-tongue, and headspace gas-chromatography-ion-mobilisation spectrometry (HS-GC-IMS) due to their rapidness and high sensitivity in identifying flavour fingerprints in foods. The EWP was investigated at 0, 60, 120, 180, 240, and 300 s of HVCP treatment time. The results revealed that HVCP significantly influences the odour and taste attributes of the EWP across all treatments, with a more significant influence at 60 and 120 s of HVCP treatment. Principal component analyses of the E-nose and E-tongue clearly distinguish the odour and taste sensors' responses. The HS-GC-IMS analysis identified 65 volatile compounds across the treatments. The volatile compounds' concentrations increased as the HVCP treatment time was increased from 0 to 300 s. The significant compounds contributing to EWP characterisation include heptanal, ethylbenzene, ethanol, acetic acid, nonanal, heptacosane, 5-octadecanal, decanal, p-xylene, and octanal. Thus, this study shows that HVCP could be utilised to modify and improve the EWP flavour attributes.

Keywords: E-nose; E-tongue; PCA; PLS-DA; egg white protein; flavour; high-voltage cold plasma; volatile compounds.

Figure 1

(a) PCA plot describing the variation in the odour fingerprints of HVCP treated EWP; (b) Loading plot describing the distribution of odour fingerprints across various HVCP treatments on the EWP; CK: Control; PC1: Principal component 1; PC2: Principal component 2; W1C: Aromatic compounds; W5S: Ammonia and aromatic molecules; W3C: Broad-nitrogen oxide; W6S: Hydrogen; W5C: Methane, propane and aliphatics; W1S: Broad-methane; W1W: Sulphur-containing organics; W2S: Broad-alcohols, broad-carbon chains; W2W: Aromatic, sulphur-and chlorine-containing organics and W3S: Methane and aliphatics.

Figure 2

(a) PCA plot describing the variation in the taste fingerprints of HVCP-treated EWP; (b) Loading plot describing the distribution of taste fingerprints across various HVCP treatment on the EWP.CK: Control; PC1: Principal component 1; PC2: Principal component 2; AAE: Umami; CTO: Saltiness; CAO: Sourness; COO: Bitterness and AEI: Astringency.

Figure 3

(a) Radar plot describing the influence of HVCP treatment on the odour fingerprints of the EWP; (b) Radar plot describing the influence of HVCP treatment on the taste fingerprints of the EWP.W1C: Aromatic compounds; W5S: Ammonia and aromatic molecules; W3C: Broad-nitrogen oxide; W6S: Hydrogen; W5C: Methane, propane and aliphatics; W1S: Broad-methane; W1W: Sulphur-containing organics; W2S: Broad-alcohols, broad-carbon chains; W2W: Aromatic, sulphur-and chlorine-containing organics and W3S: Methane and aliphatics. AAE: Umami; CTO: Saltiness; CAO: Sourness; COO: Bitterness and AEI: Astringency.

Figure 4

Heatmap showing individual concentration of volatile compounds identified in the HVCP-treated EWP at different treatment times.

Figure 5

(a) The number of volatile compounds identified in the HVCP-treated EWP using HS-GC-IMS. (b) The concentrations of volatile compounds classes identified in the HVCP treated EWP using HS-GC-IMS.

Figure 6

(a) PCA plot describing the variation in the volatile compounds’ fingerprints of HVCP-treated EWP; (b) Loading plot describing the distribution of volatile compounds’ fingerprints across various HVCP treatment on the EWP. PCA: Principal component analysis.

Figure 7

(a) The variable importance for the projection (VIP) predictive PLS-DA model of the volatile organic compounds (VOCs); (b) PLS-DA score plot showing the variation in the volatile compounds’ fingerprints of HVCP treated EWP; (c) PLS-DA loading plot showing the distribution of volatile compounds fingerprints across various HVCP treatment on the EWP. PLS-DA: Partial Least-Square Discriminant Analysis; X: represents the variable; Y: represents the PLS-DA models for the six classes.