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

Superheated steam is not a new idea. It is produced by heating ordinary steam above its saturation point, so that instead of condensing into droplets when it touches a cooler surface, it remains a dry, high-energy gas. That distinction matters enormously in food processing. Saturated steam delivers moisture along with heat, which can leave surfaces wet and hospitable to microbes. Superheated steam, by contrast, transfers intense heat while simultaneously dehydrating the surface, and it does so in an environment nearly devoid of oxygen. For oxygen-sensitive foods, that combination is potentially ideal: rapid microbial kill, suppressed oxidation, and no added water. Until now, however, most applications have focused on drying and on decontaminating low-moisture foods such as spices, nuts, and food-processing equipment, leaving a significant gap in understanding how the technology treats delicate, high-moisture, ready-to-eat produce.

The research team, led by Jingyu Gao and colleagues including Boran Yang and Xin Wen, sourced Fuji apples from Yantai in Shandong Province and cut them into uniform pieces roughly one centimeter thick. The pieces were briefly dipped in a dilute sodium chloride solution to limit browning during preparation, then subjected to one of five steam treatments: conventional saturated steam at 100 degrees Celsius, or superheated steam at 150, 200, 250, or 300 degrees Celsius, each for exactly ten seconds. The treated samples were sealed in sterile bags and stored at 4 degrees Celsius, with detailed measurements taken on days one, three, five, seven, and nine. The parameters tracked ranged from the routine, such as microbial counts, color, and firmness, to the sophisticated, including enzyme activities, oxidative stress markers, total phenolics, and a full gas chromatography-mass spectrometry analysis of volatile aroma compounds.

The microbial results were unambiguous. Bacteria, molds, and yeasts all multiplied over time in every group, but the hotter the superheated steam, the slower the growth. After nine days, samples treated at 300 degrees Celsius carried the lowest total bacterial count of any group, at 4.61 log colony-forming units per gram, and the counts in the 200, 250, and 300 degree groups were reduced by roughly one log unit compared with the saturated steam control. The effect on molds and yeasts was even more dramatic: reductions of up to 2.85 log units relative to the control. The authors attribute this to the greater sensible heat carried by higher-temperature steam, which damages microbial proteins and membranes within the brief exposure window, combined with the dry, non-condensing environment that denies microbes the surface moisture they need to thrive.

Enzyme activity told a more nuanced story. Polyphenol oxidase and peroxidase are the two principal enzymes behind enzymatic browning in cut apples, and controlling them is central to preserving visual appeal. Peroxidase responded predictably: treatments at 200 degrees Celsius and above kept its activity significantly lower than the control throughout storage, with the hottest treatment producing the strongest and most sustained inhibition. Polyphenol oxidase, however, behaved in a strikingly non-linear way. At 250 degrees Celsius, its activity actually rose above that of the control, apparently because intermediate temperatures partially disrupt the plastid membranes that sequester the enzyme from its substrates, releasing it into an active state. At 300 degrees Celsius, the extreme heat denatured the released enzyme outright, restoring strong inhibition. This dual effect, the authors note, underscores the importance of carefully optimizing superheated steam conditions rather than assuming that more heat is always better.

Curiously, these enzyme shifts did not translate into visible color differences. Lightness values, total color difference, and the browning index all evolved gradually during storage, and while the steam-treated groups consistently showed numerically lower browning indices than the control, the differences never reached statistical significance. The authors point out that browning development in fresh-cut produce is not always tightly correlated with enzyme activity, and that the enzyme changes induced by a ten-second treatment may simply have been too modest to alter the overall color trajectory. Weight loss was similarly unaffected, and firmness remained stable across all groups during storage, although after nine days the steam-treated samples were slightly softer than the control, hinting that even brief high-temperature exposure can nudge cell wall structures toward degradation.

Where the study delivers its most commercially relevant surprise is in aroma chemistry. Using headspace solid-phase microextraction coupled with gas chromatography-mass spectrometry, the team identified 41 volatile compounds, dominated by esters, the chemicals responsible for the fruity, sweet character of apples. Esters, alcohols, and aldehydes together accounted for more than 99 percent of the total volatile content. After nine days, every superheated steam group retained more total volatiles than the saturated steam control, and the 150 degree treatment consistently preserved the highest levels throughout storage. The relative proportion of esters in the treated samples exceeded 49.5 percent by day nine, compared with just 40 percent in the control, whose volatile profile had shifted toward aldehydes associated with green, grassy notes. In other words, the conventional steam treatment left the apples smelling less like ripe apples and more like cut grass.

To translate chemistry into perception, the researchers calculated odor activity values, which weigh each compound’s concentration against its sensory threshold. Ten aroma-active compounds emerged, led by ethyl 2-methylbutyrate, 2-methylbutyl acetate, and hexanal. Every superheated steam group maintained higher total odor activity values than the control across storage, and the 150 degree group peaked at 1217.35 on day three, nearly double the control’s value. The 300 degree group, despite its superior antimicrobial performance, retained fewer aroma compounds than its milder counterparts, suggesting that excessive heat accelerates the thermal degradation of volatile molecules. The authors caution that these conclusions rest on instrumental analysis alone and that formal sensory panels will be needed to confirm what consumers would actually perceive.

Weighing all the evidence, the team identified the 250 degree Celsius, ten-second treatment as the best overall compromise. It delivered effective microbial control and sustained peroxidase inhibition, kept superoxide anion formation rates relatively low, and avoided the excessive aroma losses seen at 300 degrees, even though polyphenol oxidase activity remained elevated. The authors acknowledge the limitations of their single fixed exposure time and call for future work on temperature-time combinations, sensory validation, and pilot-scale trials addressing treatment uniformity, throughput, and energy consumption. Still, the study makes a compelling case that superheated steam deserves a place in the fresh-cut conversation. In an industry long reliant on antibrowning dips and modified atmosphere packaging, a chemical-free, oxygen-free, ten-second heat pulse that simultaneously tames microbes and protects the fruit’s signature fragrance is a proposition worth taking seriously.

Subject of Research: Effects of short-time superheated steam treatment on quality and aroma-active volatiles in fresh-cut Fuji apples during refrigerated storage

Article Title: Beyond microbial control: Effects of short-time superheated steam on storage quality and aroma-active volatiles in fresh-cut Fuji apples

Article References: Gao, J., Wei, S., Li, M., Ni, Y., Yang, B., & Wen, X. (2026). Beyond microbial control: Effects of short-time superheated steam on storage quality and aroma-active volatiles in fresh-cut Fuji apples. Food Chemistry: X, 39, Article 104527. https://doi.org/10.1016/j.fochx.2026.104527

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104527

Keywords: superheated steam, fresh-cut apples, Fuji apples, food preservation, aroma volatiles, polyphenol oxidase, peroxidase, microbial inactivation, enzymatic browning, odor activity value, gas chromatography-mass spectrometry, refrigerated storage