Superheated Steam Turns Highland Barley Into a Gel With Slower-Digesting Starch

Highland barley, a hulless cereal cultivated for centuries on the Qinghai-Tibet Plateau, has long been prized as a staple food rich in dietary fiber and polyphenols. Yet despite its nutritional credentials, the grain has a stubborn processing problem: it lacks the gluten-forming proteins that give wheat dough its cohesion and elasticity, and its native lipids and enzymes undermine shelf life. A new study published in Food Chemistry: X suggests that a six-minute blast of superheated steam may solve both problems at once, reshaping the molecular architecture of the whole flour in ways that improve gel texture and, remarkably, slow down starch digestion.

The research, led by Haoran Wang and colleagues, compared superheated steam treatment at 140, 160, and 180 degrees Celsius against two conventional pretreatments, steaming and stir-frying, using kernels of the Zangqing 320 cultivar from Tibet. Before treatment, the kernels were tempered to 20 percent moisture and equilibrated for six hours, then exposed to the steam for just six minutes. Conventional steaming required thirty minutes, and stir-frying involved twelve hours of soaking followed by thirty minutes of roasting at 160 degrees Celsius. The treated kernels were milled into whole flour, and gels were prepared from a 15 percent flour suspension heated at 95 degrees Celsius and cooled overnight.

The centerpiece of the investigation was beta-glucan, the soluble fiber responsible for many of barley’s health benefits. Using high-performance size-exclusion chromatography coupled with multi-angle laser light scattering, the team measured the weight-average molecular weight of beta-glucan isolated from both flour and gel. Native flour beta-glucan came in at 1.61 by ten to the fifth grams per mole. Every thermal treatment raised that figure, but superheated steam did so most dramatically: at 180 degrees Celsius the molecular weight climbed to 2.23 by ten to the fifth, the highest of any treatment. This finding runs counter to several earlier studies in which roasting, microwave heating, and oven baking depolymerized barley beta-glucan. The authors attribute the difference to moisture conditions and heating intensity. Tempering the kernels before treatment appears to shield the fiber from thermal degradation, while the rapid heat transfer and short exposure time of superheated steam limit chain scission.

The structural consequences extended well beyond beta-glucan. Fourier transform infrared spectroscopy revealed that gels made from steam-treated flour at 160 and 180 degrees Celsius showed increased short-range order in starch, reflected in a higher ratio of absorbance at 1047 to 1022 wavenumbers. Interestingly, this contrasts with the team’s own previous work on isolated starch, where the harshest steam treatment disrupted crystalline order most severely. In the whole-flour gel matrix, the researchers conclude, amylose and amylopectin chains released during gelatinization apparently reassociate into more ordered local domains upon cooling. Protein conformation shifted in parallel: as steam temperature rose, alpha-helix and beta-turn contents increased while beta-sheet and random coil proportions declined, signaling a partial rearrangement of the protein network.

Microscopy told a visually striking story. Scanning electron micrographs of the native gel revealed large, irregular pores, whereas gels from kernels treated at 160 degrees Celsius displayed a markedly more uniform morphology with smaller apparent pores. Confocal laser scanning microscopy, with starch stained green and protein red, showed that the numerous large dark voids of the native gel nearly vanished after treatment, with 160 degrees Celsius producing the most homogeneous starch-protein distribution. Push the temperature to 180 degrees Celsius, however, and the benefit reverses: larger, more irregular voids reappear alongside pronounced protein aggregation, indicating that excessive treatment intensity introduces new heterogeneity into the matrix.

Water behavior tracked these structural changes closely. Low-field nuclear magnetic resonance resolved three water populations in the gels, corresponding to bound, immobilized, and free water, with free water dominating at more than 95 percent of the total. Treatment at 160 and 180 degrees Celsius significantly increased the bound-water fraction, and all treatments raised the immobilized fraction, indicating a shift toward water populations with lower mobility. The effect was stronger for superheated steam than for conventional steaming or stir-frying. The authors suggest that higher molecular weight beta-glucan can retain water through hydrogen bonding, contributing to this immobilization, although at 180 degrees Celsius the bound and immobilized fractions dipped slightly, possibly because severe treatment depolymerizes starch chains that would otherwise hold water.

Texture analysis translated these molecular shifts into measurable mechanical differences. Springiness, the ability of a gel to recover after compression, responded most strongly to treatment: every thermal pretreatment increased it significantly, and the 160-degree steam sample achieved the highest value at 2.73 millimeters, up from 2.18 millimeters in the native gel. That peak springiness coincided with the most uniform pore structure and the lowest water mobility, painting a coherent picture of a gel whose architecture resists deformation and rebounds efficiently. Hardness, cohesiveness, and gumminess, by contrast, changed little across treatments, and only stir-frying produced a hardness significantly different from the control.

Rheology added nuance to the texture story. During temperature sweeps, all treated samples showed higher storage and loss moduli than the native gel, with the 140-degree sample exhibiting the strongest small-deformation viscoelastic response. In frequency sweeps, all gels behaved as elastic-dominant materials, with the storage modulus exceeding the loss modulus and the loss factor remaining below one across the tested range. The apparent tension between the highest springiness at 160 degrees and the highest modulus at 140 degrees reflects the different deformation regimes of the two measurements: the modulus was recorded at 1 percent strain within the linear viscoelastic region, while springiness measures recovery after 30 percent compression. Different regimes, the authors note, probe different aspects of the same heterogeneous network.

Perhaps the most consequential result concerns digestion. In vitro hydrolysis with pepsin, pancreatic alpha-amylase, and amyloglucosidase showed that superheated steam treatment reduced both rapidly and slowly digestible starch while boosting resistant starch, with the effect strengthening as temperature rose. At 180 degrees Celsius, resistant starch reached 15.87 percent, up from 8.78 percent in the native gel, while the estimated maximum digestibility fell from 93.40 percent to 87.59 percent. A logarithm-of-slope analysis split digestion into fast and slow phases and showed that treatment mainly suppressed hydrolysis during the first thirty minutes, consistent with the drop in rapidly digestible starch. Stir-frying, by contrast, barely moved the needle, leaving resistant starch essentially unchanged.

The authors propose that three concurrent changes explain the slowed digestion: greater starch short-range order, which produces compact hydrogen-bonded structures with reduced enzyme accessibility; elevated beta-glucan molecular weight, which increases viscosity and hinders enzyme diffusion; and protein aggregation, which adds a further physical barrier. Notably, the whole-flour gel digested more slowly than the isolated starch examined in the team’s earlier work, underscoring that non-starch components matter enormously in real foods. The practical upshot is a kind of dial: processors seeking better gel uniformity and elastic recovery could choose steam at 160 degrees Celsius, while those prioritizing slower starch digestion might opt for 180 degrees. For a gluten-free grain struggling to enter modern staple foods, a six-minute steam treatment that simultaneously improves texture and nutritional profile is a compelling proposition, and one that could reshape how ancient plateau cereals reach contemporary tables.

Subject of Research: Effect of superheated steam treatment on beta-glucan, gel structure, and starch digestibility in highland barley whole flour

Article Title: Effect of superheated steam treatment on endogenous β-glucan and gel properties of highland barley whole flour: Changes in gel structure and starch digestibility

Article References: Wang, H., Ma, T., Wang, L., Wang, L., Li, Y., & Qiu, J. (2026). Effect of superheated steam treatment on endogenous β-glucan and gel properties of highland barley whole flour: Changes in gel structure and starch digestibility. Food Chemistry: X, 39, Article 104557. https://doi.org/10.1016/j.fochx.2026.104557

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104557

Keywords: highland barley, superheated steam, beta-glucan, starch digestibility, resistant starch, gel properties, food processing, whole flour, rheology, molecular weight, Qinghai-Tibet Plateau, functional foods