The team’s choice of almond protein isolate was deliberate. Almonds already have a reputation in the plant-milk world for mild flavor and smooth texture, avoiding the beany off-notes and allergenic baggage that complicate soy. The isolate is roughly 97 percent protein, most of it the water-soluble globulin amandin, which makes up 65 to 70 percent of the total. Crucially, almond protein shares an isoelectric point with casein, in the pH 4.5 to 5.5 range, and retains about 70 to 80 percent solubility even at pH 4. That means it can undergo heat- and acid-driven structural changes at almost exactly the point where yogurt fermentation ends, mimicking the acid coagulation that builds dairy gels. The researchers hypothesized that varying the almond protein concentration within a xanthan gum-stabilized millet matrix would tune protein–polysaccharide interactions and dictate whether the final gel held together or fell apart.

The experimental design was straightforward but rigorous. Millet milk was prepared by soaking, blending, and filtering proso millet grains, then supplemented with almond protein isolate at 0, 0.5, 1, 1.5, and 2 percent weight per volume, alongside 0.5 percent xanthan gum, 3 percent inulin as a prebiotic, and 3 percent sucrose. After hydration, pasteurization at 90 degrees Celsius for 30 minutes, and inoculation with a vegan starter culture containing Streptococcus thermophilus, Lactobacillus delbrueckii subsp. bulgaricus, L. acidophilus, and Bifidobacterium animalis subsp. lactis, the mixtures were fermented to pH 4.6 and chilled. The resulting yogurts were then put through an unusually complete battery of tests: proximate composition, fermentation kinetics, electron microscopy, infrared spectroscopy, zeta potential, free sulfhydryl measurement, selective-solvent interaction analysis, colorimetry, water-holding capacity, texture profiling, rheology, and a trained sensory panel.

The compositional results alone tell a striking story. Millet milk starts with a meager 1.23 percent crude protein, and the unsupplemented control yogurt contained just 0.38 percent. Adding almond protein raised protein content in a concentration-dependent manner, reaching 2.23 percent at the 2 percent dose, roughly a six-fold increase over the control. Fat stayed below 0.5 percent across all formulations, comfortably meeting the European Union criterion for a fat-free claim. But the more consequential effects appeared during fermentation. Yogurts with 1 percent almond protein or more acidified faster and reached the pH 4.6 endpoint earlier than the control, and viable lactic acid bacteria counts climbed from 5.29 log CFU per gram in the control to 7.00 log CFU per gram at the highest dose. The likely explanation is nitrogen: the o-phthaldialdehyde assay showed that trichloroacetic acid-soluble amino groups rose significantly during fermentation, from 2.39 to 3.42 millimolar glycine equivalents in the 2 percent formulation, providing the peptides and free amino acids that fuel bacterial metabolism and acid production.

Microscopy revealed exactly why the control yogurt failed. Under focused ion beam scanning electron microscopy, the unsupplemented sample showed a fragmented, poorly connected structure of irregular particles that remained fluid and flowed when the cup was inverted. At 0.5, 1, and 1.5 percent almond protein, however, the gels formed compact, homogeneous networks with honeycomb-like pores, smooth cohesive surfaces, and the ability to hold their shape upside down. At 2 percent, the picture reversed: pores collapsed, fractures appeared, the surface turned rough and aggregated, and visible syneresis, or water separation, set in. The lesson is that gel quality is not a simple dose–response curve. Moderate protein supplementation builds a continuous network, while too much pushes the system past the point where electrostatic repulsion can keep protein molecules from clumping into a coarse, grainy mass.

The molecular explanation lies in the balance of intermolecular forces. Selective buffer experiments showed that electrostatic interactions were the dominant force in most almond-supplemented yogurts, rising from 0.17 milligrams per milliliter at 0.5 percent protein to 0.49 at 1.5 percent before falling back to 0.27 at 2 percent, where hydrogen bonding took over. Zeta potential measurements reinforced this interpretation: all formulations were negatively charged, consistent with the anionic xanthan gum, but the potential became less negative as protein increased, dropping sharply to minus 26.0 millivolts at 2 percent. That collapse in electrostatic repulsion coincided with the aggregation and structural failure seen under the microscope. Free sulfhydryl content did decline during fermentation, indicating some disulfide bonding, but the values were far below those reported for soy yogurt, reflecting almond protein’s limited cysteine content. Disulfide bridges helped, but the electrostatic glue between charged protein regions and anionic polysaccharides was the real architect of the gel.

Physical performance tracked the molecular story closely. Water-holding capacity, the single best indicator of physical stability in set yogurt, jumped from a dismal 17.65 percent in the control to 99.00 percent at 0.5 percent almond protein and 97.92 percent at 1 percent, then slid to 89.47 percent at 1.5 percent and crashed to 59.77 percent at 2 percent. Firmness in the back-extrusion test rose from 0.19 newtons to 21.46 newtons across the same range, and the consistency index climbed from 4.56 to 437.18 newton-seconds. Notably, the 0.5 and 1 percent formulations landed nearest the firmness and consistency values typical of dairy set yogurt, around 2 to 3 newtons and 50 to 60 newton-seconds, while the two highest doses produced gels far harder than anything a consumer would recognize as spoonable. Rheology confirmed the pattern: storage modulus exceeded loss modulus in every sample, confirming solid-like behavior, but the 2 percent gel reached moduli of 10,000 pascals, orders of magnitude above the 1 to 100 pascal range of conventional yogurt.

Perhaps the most counterintuitive finding came from the three-interval thixotropy test, which measures how well a gel rebuilds itself after being sheared apart. The 1 percent formulation showed a significantly higher recovery rate than the 1.5 and 2 percent samples, and the 2 percent gel recovered worst of all. Pearson correlation analysis made the point explicit: firmness and storage modulus were negatively correlated with structural recovery, meaning that stiffer gels bounced back more poorly after mechanical deformation. Strength, in other words, is not the same as resilience. A dense, rigid network built on excessive protein aggregation and hydrogen bonding cannot absorb stress the way a balanced, electrostatically stabilized, porous network can. For product developers, this decoupling of hardness from quality is a critical design principle: the goal is not the strongest gel but the most organized one.

The sensory panel of twenty trained tasters agreed. The millet yogurts outscored a commercial soy set yogurt on appearance, and the 0.5 and 1 percent formulations earned the highest texture scores, consistent with their yogurt-like firmness and rheology. Almond protein improved taste and flavor across the board, but the 1 percent sample achieved the highest overall acceptability at 4.85 on the nine-point hedonic scale, a judgment that weighed color, water retention, microstructural uniformity, texture, and flavor together. The authors conclude that heat-induced protein unfolding and fermentation-driven acidification enabled almond protein to mediate protein–polysaccharide interactions that convert a weakly gelling cereal matrix into a self-supporting, low-fat, soy-free set yogurt whose gelation pattern resembles conventional dairy yogurt. They caution that the detailed molecular events of aggregation were not directly observed and will require further characterization. Even so, the study offers a practical recipe for the next generation of plant-based yogurts: a climate-hardy grain, a mild tree nut protein, and a dose window narrow enough that precision, not abundance, makes the gel.

Subject of Research: Using almond protein isolate to modulate protein–polysaccharide gel networks and improve the physicochemical stability of millet-based set yogurt

Article Title: Modulating protein–polysaccharide gel networks via almond protein to improve physicochemical stability of millet-based set yogurt

Article References: Modulating protein–polysaccharide gel networks via almond protein to improve physicochemical stability of millet-based set yogurt. (n.d.). https://doi.org/10.1016/j.fochx.2026.104535

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104535

Keywords: plant-based yogurt, almond protein isolate, proso millet, protein–polysaccharide interactions, xanthan gum, gel network, water-holding capacity, rheology, lactic acid fermentation, food texture, syneresis, dairy alternatives