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This study investigated the impact of ultrasound pretreatment and phenolic binding on the structure characteristic and foaming properties of egg white (EW). EW treated without ultrasound (NEW) and with ultrasound (UEW) (power for 28% and time for 25 min: on-time 3 s and off-time 2 s) were incubated separately at 25 °C for 2 h with gallic acid (GA) and epigallocatechin gallate (EGCG) at pH 7.0. Phenolic treatment caused a significant loss of sulfhydryl content, with a more remarkable effect observed in UEW, especially at 120 μmol/g concentration. Both phenolics significantly decreased the surface hydrophobicity and slightly increased the disordered secondary structure of protein. Additionally, the microenvironment polarity of protein molecules was increased by phenolic treatment corroborated by UV absorption blue shift, especially for 240 μmol/g GA-UEW. After ultrasound pretreatment, low EGCG concentration (20 μmol/g) significantly increased the foaming ability. The 240 μmol/g EGCG treatment notably increased the reduced foaming stability by ultrasound from 81.00 to 95.10% (p < 0.05), which was due to high absolute ξ-potential value. This study has shed light on the mechanisms underlying the influence of unfolding structure by ultrasound treatment on phenolic binding. Image 1 • Phenolic treatment especially EGCG significantly decreased sulfhydryl content. • Protein surface hydrophobicity was obviously decreased by phenolic treatment. • EGCG treatment increased the foaming stability of egg white. • EGCG was stronger than GA in binding affinity with egg white. • Ultrasound pretreatment contributed to the binding of phenolic to protein. [ABSTRACT FROM AUTHOR]

The effects of shell egg cold storage (4 °C) on the foaming properties of its egg white were investigated by evaluating its physicochemical changes. The foaming ability decreased significantly (p < 0.05) while the foaming stability decreased slightly during cold storage. Specifically, the foam ability reached the minimum (25.17%) at 40 d of storage, which was decreased by 44.49% versus that at 0 d (45.33%). In the first 40 d, the decrease in foaming ability was mainly ascribed to the decreased surface hydrophobicity and the increased surface tension. Moreover, the exposed sulfhydryl groups tended to cause protein cross-linking probably by sulfhydryl-disulfide exchange reaction, leading to an increase of particle size and viscosity. However, during the 60–80 d storage, the decrease of sulfhydryl content and viscosity tended to inhibit foam formation. Additionally, more larger protein aggregates were observed with prolonging of storage period under a scanning electron microscope. This investigation reveals the change mechanisms of egg white properties during different storage periods and provides guidance for the processing of egg products. [ABSTRACT FROM AUTHOR]

The effects of ultrasonic treatment (180 W, 25 min) on the foaming and physicochemical properties of egg white from shell egg stored for seven periods (0, 15, 30, 45, 60, 75 and 90 d) were investigated in this study. The foaming ability significantly increased after ultrasound treatment and the highest foaming ability (99.13%) was achieved at 60 d compared to untreated egg white (29.75%). This improvement was ascribed to the increased free sulfhydryl content and surface hydrophobicity, indicating that egg white protein became easier to adsorb at the air-water interface and its structure was more flexible. However, a reduction in the foaming stability of ultrasound-treated egg white resulted from the lower absolute zeta potential. Moreover, decreasing particle size and broadening protein size distribution were obtained after ultrasonic processing. Using scanning electron microscopy, small aggregates were observed on the surface of the untreated sample after storage, while the ultrasound-treated sample had large numbers of irregular and unevenly distributed pores with different sizes. These results provide important evidence of the protein properties induced by ultrasound modification during storage, and further expand the ultrasound application in the food storage industry. • The highest foaming ability (99.13%) was achieved at 60 d by ultrasound modification. • Surface hydrophobicity and sulfhydryl content increased by ultrasound treatment. • Ultrasound decreased the absolute zeta potential of cold stored egg white. • Ultrasound decreased particle size and broadened size distribution of egg white. • Scanning electron microscopy showed irregular and unevenly distributed pore structure after ultrasound. [ABSTRACT FROM AUTHOR]

The foaming property of egg white (EW) is essential in food processing. In this study, we investigated the effect of ultrasound combined with adding different concentrations (0, 0.4, 0.5, 0.6, 0.7, and 0.8 %, m/v) of flaxseed gum (FG) on EW foaming. The results showed that the cooperation of ultrasound treatment and FG significantly improved the foaming stability. Regarding details, FG reduced the sulfhydryl content and surface hydrophobicity of EW proteins while increasing the average particle size and PDI value. Despite the ultrasound treatment, FG significantly improved the foaming stability from 62.83% to 99.82% (p < 0.05). Based on the analysis of ξ-potential, surface tension, rheology, etc., FG improved the EW microenvironment, which is conducive to foaming stability. As a new type of polysaccharide, FG combined with ultrasound can significantly improve the foaming properties. This research could solve the problem of reduced foaming stability of EW treated by ultrasound alone, making promising applications in the food industry. [Display omitted] • Ultrasound combined with flaxseed gum improved the foaming of egg white. • Flaxseed gum overcame the problem that ultrasound reducing the foaming stability. • Flaxseed gum formed a viscoelastic interfacial film to increase surface tension. • Egg white protein's structure was more compact and increased foaming stability. [ABSTRACT FROM AUTHOR]