Ultrasound-Treated Egg White Powder Could Give Yogurt a Protein Boost Without Ruining the Ferment

Yogurt is one of the world’s most popular fermented foods, but anyone who has scooped a spoonful of watery whey from the top of a cup knows its structural weaknesses. Food scientists have long searched for natural, clean-label ingredients that can firm up the delicate casein gel without resorting to starches or gums. Now, a team of Chinese researchers has reported that egg white powder — if first treated with a combination of ultrasound and mild heat — can be stirred into yogurt milk in small amounts to build a denser, more elastic gel, while a clever sequencing technique reveals exactly how the live bacterial cultures respond to the new ingredient. The study, published in Food Chemistry: X, offers one of the most detailed looks yet at how a protein supplement changes not just the texture of yogurt but the transcriptional behavior of the microbes that make it.

The core challenge the researchers set out to solve is a molecular conflict of interest. Egg white is packed with high-quality proteins — ovalbumin, ovotransferrin, ovomucin and others — that gel, foam and emulsify beautifully, making it an attractive textural modifier for dairy products. But egg white also contains lysozyme, a potent antibacterial enzyme that cleaves the β-1,4 glycosidic bonds in bacterial cell wall peptidoglycan. That is excellent news for food preservation and terrible news for yogurt starters, which rely on Gram-positive lactic acid bacteria — Lactobacillus delbrueckii subsp. bulgaricus and Streptococcus thermophilus — to ferment lactose into lactic acid. Adding raw egg white to yogurt milk risks sabotaging the very organisms the fermentation depends on.

The team, led by Yunxiao Xie and Fang Geng, applied a pretreatment strategy they had developed in earlier work, abbreviated UHSD: liquid egg white is first blasted with 20 kHz ultrasound in pulsed mode for ten minutes while kept cold, then heated in a water bath at 72 °C for ten minutes, and only then spray-dried into a powder. The ultrasound cavitation and mechanical shear unfold protein aggregates, and the subsequent moderate heating promotes controlled aggregation and disulfide exchange between lysozyme and other egg white proteins. When the researchers measured apparent lysozyme activity using Micrococcus lysodeikticus cells as a substrate, the results were striking. Fresh egg white showed an apparent activity of 5660 U/mg. Conventional spray drying alone cut that by 54.6 percent, but the full ultrasound–heat–spray-drying sequence reduced it by 90.3 percent — a dramatic taming of the antibacterial enzyme while keeping the functional proteins largely intact.

With the pretreated powder in hand, the researchers formulated yogurts in which the powder partially replaced milk at 0, 1, 2 and 4 percent by mass, heat-treated the mixes at 72 °C for 30 minutes, inoculated them with a commercial two-strain starter, and fermented for ten hours. Every batch set into a stable gel with no visible whey separation, and all samples met the Chinese national standard minimum titratable acidity of 60 °T for fermented milk. Color measurements showed the supplemented yogurts became progressively lighter, with reduced red and yellow components — a subtle whitening effect that could be commercially appealing. Texture analysis, however, revealed a dose-dependent trade-off: hardness was unchanged at 1 and 2 percent addition but dropped significantly at 4 percent, and springiness peaked at the 1 percent level before falling at the highest dose.

The structural story behind those numbers emerged from microscopy and rheology. Scanning electron micrographs of freeze-dried yogurt showed that the control gel was relatively loose, with large pores, while the egg white-supplemented samples displayed progressively smaller gel particles and a more uniform, compact three-dimensional network — most pronounced at 4 percent. Rheological testing showed all samples were shear-thinning pseudoplastic fluids, but apparent viscosity shifted upward with increasing powder addition, and both the storage modulus G′ and loss modulus G″ rose across the frequency range, with G′ consistently exceeding G″, confirming elastic, weak-gel behavior throughout. In short, the egg white proteins were genuinely participating in the acid-induced casein network, cross-linking the gel and stiffening its response to deformation.

Yet a denser microstructure did not translate into proportionally better macroscopic performance. The 1 percent group achieved the highest water-holding capacity, significantly above all other groups, while the 4 percent group showed no advantage over the control, which held 64.3 percent of its water. The explanation lies in acidification. At 4 percent addition, the final pH rose by 2.3 percent relative to the control’s 4.38, and titratable acidity fell by 4.4 percent to 93.8 °T. Because yogurt gelation depends on acid gradually neutralizing the electrostatic repulsion between casein micelles as pH approaches their isoelectric point, a weaker fermentation slows and shallows that aggregation. The powder partially replaced milk, so the higher pH also reflects altered buffering and substrate availability — and the authors are careful to note that their design cannot separate the effect of added protein and solids from the specific contribution of the ultrasound–heat pretreatment itself, since a conventional spray-dried powder control was not included.

The most novel part of the study is its use of metatranscriptomics — sequencing the expressed RNA of the entire microbial community — to see how the starter cultures actually responded. From nine samples across the control, 1 percent and 4 percent groups, the team generated over 608 million raw reads, averaging roughly 7.77 gigabases per sample with Q30 quality scores above 95.7 percent. After removing ribosomal RNA, assembling transcripts de novo and annotating predicted proteins against the NR, KEGG, eggNOG and CAZy databases, they found that Bacillota transcripts dominated at over 98 percent in every group, with Streptococcus thermophilus and Lactobacillus delbrueckii as the core expressed species — exactly the signature of a healthy yogurt ferment. Ordination analyses showed the control clearly separated from both supplemented groups in transcriptional space.

The functional annotations told a coherent story. In the 4 percent group, transcript abundance assigned to glycolysis/gluconeogenesis, pyruvate metabolism and carbon metabolism all declined, consistent with the observed higher pH and lower acidity — the bacteria were transcribing fewer genes for lactose breakdown and lactic acid production. Carbohydrate-active enzyme genes showed the same pattern: glycoside hydrolase transcript abundance in the 4 percent group fell to about 48.7 percent of control levels, and glycosyltransferases to about 41.1 percent. Meanwhile, LEfSe analysis flagged lactic acid bacteria taxa such as Lactobacillaceae as differential in the 1 percent group, whereas the 4 percent group showed relatively higher representation of low-abundance, non-core taxa — possibly because the weakened acidification relaxed the selective pressure that normally suppresses non-yogurt microbes, and possibly because residual lysozyme, to which Gram-negative bacteria are more tolerant, subtly shifted the competitive balance. The authors stress that transcript abundance is not direct evidence of altered enzyme activity or metabolite concentrations, and that enzyme assays and metabolomics would be needed for confirmation.

The practical takeaway is a dose window rather than a free pass. At around 1 percent, the pretreated egg white powder delivered the best overall package: the highest springiness, the best water retention, a more compact gel network and a microbial community whose transcriptional profile remained firmly lactic-acid-bacteria dominated. At 4 percent, the same powder produced a visually denser network but softer texture, weaker acidification and a transcriptional drift toward non-core taxa. For an industry eager to boost protein content and improve texture with clean-label ingredients, that distinction matters enormously. The study also demonstrates the power of metatranscriptomics as a quality-control lens for fermented foods: instead of merely counting microbes, it reveals which metabolic programs are actively running, catching functional shifts that pH and texture measurements alone could only hint at. Future work with composition-matched controls will need to isolate what the ultrasound–heat pretreatment itself contributes, but the concept — defusing egg white’s antibacterial arsenal while enlisting its gelling proteins — now has both a physical and a molecular evidence base.

Subject of Research: Effects of ultrasound–heat pretreated egg white powder on yogurt quality, gel properties and microbial metatranscriptomic profiles

Article Title: Effects of ultrasound–heat pretreated egg white powder addition on the quality, gel properties, and metatranscriptomic profiles of yogurt

Article References: Xie, Y., Wang, X., Shui, Y., Hu, G., He, H., Wang, J., & Geng, F. (2026). Effects of ultrasound–heat pretreated egg white powder addition on the quality, gel properties, and metatranscriptomic profiles of yogurt. Food Chemistry: X, 39, Article 104550. https://doi.org/10.1016/j.fochx.2026.104550

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104550

Keywords: yogurt, egg white powder, ultrasound, lysozyme, gel properties, metatranscriptomics, lactic acid bacteria, food texture, spray drying, water-holding capacity, rheology, fermented dairy