The key to the innovation lies in the unusual composition of pineapple stem starch, abbreviated PSS by the researchers. Earlier work by the same group had shown that starch drawn from pineapple stems contains roughly 30 percent amylose, a linear starch molecule, which is substantially higher than commercial rice, corn, or cassava starches. That high amylose content translates into unusually large fractions of slowly digestible starch and resistant starch, the latter being a carbohydrate that escapes digestion in the small intestine and behaves, physiologically, much like dietary fiber. Resistant starch has attracted considerable attention in nutrition research because it moderates blood glucose responses after meals and may help protect against obesity, type 2 diabetes, and other chronic metabolic conditions. Unlike chemically modified resistant starches, PSS delivers these properties in its native form, requiring no industrial alteration before use.

Turning the stems into a food-grade ingredient began on a pineapple farm in Kanchanaburi, Thailand, where the team collected twenty kilograms of stems from mature Smooth Cayenne plants after harvest. Using a wet-milling process, the stems were washed, peeled, ground with water, and passed through a series of progressively finer mesh screens to strip away fibrous material. Centrifugation, repeated washing, and overnight drying at 45 degrees Celsius yielded just over one kilogram of fine white starch powder, a yield of about 10.7 percent based on the peeled stem weight. Because PSS had never before been used in a baked product, the researchers subjected it to a battery of safety tests before any biscuit dough was mixed.

Those safety results were reassuring on every front. Atomic absorption spectrophotometry detected no lead and no cadmium in the extracted starch, indicating that the growing environment and processing conditions were clean. Microbiological testing found Escherichia coli levels below three MPN per gram, while Salmonella and Staphylococcus aureus were entirely absent from the sample quantities tested, satisfying Thai food safety standards. The starch also arrived with a moisture content just under ten percent and a water activity of 0.27, far below the 0.6 threshold at which microbes can grow, meaning the powder is inherently stable in storage. The authors note one limitation: antinutritional compounds were not directly quantified, though prior literature suggests pineapple by-products carry only negligible levels, and the extensive aqueous washing during extraction likely removes any water-soluble antinutrients.

With a safe ingredient in hand, the team formulated biscuits in which rice flour was replaced by PSS at 25, 50, 75, and 100 percent by weight. Because neither rice flour nor PSS contains gluten, the recipe relied on soy protein isolate and carboxymethyl cellulose to provide structure, while butter was swapped for shortening rice bran oil and sugar for calorie-free monk fruit sweetener, moves designed to cut saturated fat and eliminate added sugar simultaneously. The physical consequences of substitution were striking. As PSS levels rose, dough became softer and stickier, with hardness falling from about 312 newtons in the all-rice control to 195 newtons in the all-PSS version. That softer, weaker dough expanded more freely during baking, producing biscuits that were wider, longer, and up to forty percent thicker than the control. Finished biscuit hardness dropped in parallel, from 8.41 newtons to 4.75 newtons, a trend the authors attribute both to the loss of gluten-forming protein and to the water-binding capacity of resistant starch. Surface color, remarkably, barely changed across all formulations, with lightness and yellowness values remaining statistically indistinguishable.

The nutritional payoff emerged from in vitro digestion experiments, in which ground biscuits were exposed to pepsin, pancreatin, and amyloglucosidase under conditions simulating the human digestive tract. After two hours of enzymatic attack, the all-rice control biscuits had released 88.3 percent of their starch as glucose, while the 100 percent PSS biscuits released only 36.6 percent. The starch fractions told the same story: rapidly digestible starch plummeted from 59.6 percent in the control to just 6.25 percent in the all-PSS biscuit, while resistant starch climbed from 11.7 percent to 63.4 percent. From these hydrolysis curves, the researchers calculated a hydrolysis index relative to white bread and then an estimated glycemic index, or eGI. The control biscuits scored 85.13, firmly in the high-glycemic category, whereas the 100 percent PSS biscuits scored 52.32, crossing into the low-glycemic range defined as an eGI at or below 55. Formulations at 50 and 75 percent substitution landed in the medium range, between 60 and 67.

Digestibility, however, means little if nobody wants to eat the result. Thirty untrained panelists, recruited under an approved ethics protocol from the Mahidol University community, rated each biscuit on a nine-point hedonic scale covering appearance, color, flavor, texture, and overall acceptability. Somewhat counterintuitively, the all-rice control fared worst, earning the lowest scores for appearance, flavor, texture, and overall liking, likely because its dense, hard structure left an oily surface. Preference rose steadily as PSS increased, peaking with the 75 percent substitution formulation, which scored 6.83 overall, between slight and moderate liking, and won the top marks for appearance, flavor, and texture. Only at full substitution did scores dip again, as the near-total absence of protein left the biscuits soft and crumbly. Crucially, every formulation scored above the acceptability threshold of five, and the winning 25:75 rice-to-PSS blend combined the best sensory profile with a medium eGI of 60.04.

Proximate analysis of that optimal biscuit revealed further advantages. Its dietary fiber content of 1.65 percent was double that of the control, a direct consequence of the resistant starch it carried, while total carbohydrate rose to about 61 percent. Protein fell from 10.9 to 8.3 percent, reflecting the low protein content of PSS relative to rice flour, though the added soy protein isolate and egg kept levels respectable. Fat, ash, and energy values were essentially unchanged, with both biscuits supplying roughly 520 kilocalories per 100 grams. The authors acknowledge that vitamins and minerals were not measured, leaving micronutrient profiling as a task for future work.

Shelf life proved equally encouraging. Samples of the control and the 75 percent PSS biscuit were sealed in foil and stored at 45 degrees Celsius for two months, an accelerated regime that, by Arrhenius estimates, models roughly eight months at room temperature. Lipid oxidation was tracked through peroxide values, which mark early-stage hydroperoxide formation, and TBARS measurements, which capture the secondary breakdown products responsible for rancid odors. Both biscuits oxidized slowly for the first twenty days and then accelerated, with the PSS biscuit oxidizing somewhat faster, plausibly because rice flour contributes antioxidant phenolics that PSS lacks. Even so, at day sixty the peroxide values of 7.17 and 10.50 milliequivalents per kilogram of fat and the TBARS values of 2.03 and 2.73 milligrams of malonaldehyde per kilogram all remained within accepted quality limits, a resilience the authors credit partly to the natural tocopherols, tocotrienols, and oryzanols in rice bran oil.

The study’s authors are careful to frame the findings as a beginning rather than an endpoint. Animal and human feeding trials will be needed to confirm that the low eGI measured in the laboratory translates into genuine glycemic benefits in people, and microbiological testing during storage should complement the chemical oxidation data in future shelf-life studies. Still, the core message is compelling: a starch recovered from stems that farmers throw away can replace most of the flour in a gluten-free biscuit, double its fiber, cut its glycemic index from high to low-to-medium, and win over a taste panel, all without chemical modification of the ingredient. If subsequent clinical work holds up, the humble pineapple stem may find itself promoted from farm waste to functional food, one biscuit at a time.

Subject of Research: Development of gluten-free biscuits using pineapple stem starch as a resistant starch source to reduce glycemic index

Article Title: Development of Gluten‐Free Biscuits From Rice Flour‐Pineapple Stem Starch Blends: Physicochemical Properties, In Vitro Starch Digestibility, Estimated Glycemic Index, Sensory Evaluation, and Storage Stability

Article References: Sriprablom, J., Phansuea, P., Sahasakul, Y., Disnil, S., Aursalung, A., Srisangwan, N., Keeratichamroen, A., Srisungwan, S., & Wongsagonsup, R. (2026). Development of Gluten‐Free Biscuits From Rice Flour‐Pineapple Stem Starch Blends: Physicochemical Properties, In Vitro Starch Digestibility, Estimated Glycemic Index, Sensory Evaluation, and Storage Stability. Food Science & Nutrition, 14(10), Article e72449. https://doi.org/10.1002/fsn3.72449

Image Credits: AI Generated

DOI: 10.1002/fsn3.72449

Keywords: pineapple stem starch, gluten-free biscuits, resistant starch, glycemic index, starch digestibility, food science, agricultural waste, rice flour, monk fruit sweetener, rice bran oil, sensory evaluation, storage stability

The research, led by Suho Choi and Chang Joo Lee of Wonkwang University with contributions from Taiyoung Kang of Chungnam National University, appears in the journal Food Science and Biotechnology. The team prepared rice–wheat composite noodle doughs containing six different levels of hydroxypropyl methylcellulose, or HPMC, a chemically modified cellulose that has been a quiet workhorse of the food industry for decades. The levels ranged from zero, the control formulation with no HPMC at all, up to 1.25 percent of the rice flour weight. Each formulation was then put through a battery of standardized tests covering how the flour behaved during heating, how the noodles looked, how they felt when chewed, how far they could stretch before snapping, and how much of their substance they surrendered to the cooking water.

HPMC belongs to a family of ingredients called hydrocolloids, long-chain carbohydrate polymers that dissolve or disperse in water and dramatically alter its flow and gel behavior. What makes HPMC special among them is a property known as thermogelation. Most gels in the kitchen, from gelatin desserts to pectin jams, set when they cool. HPMC does the opposite: it is soluble in cold water, and when the temperature climbs past a characteristic threshold, the polymer chains lose their hydration shells, aggregate with one another, and knit themselves into a three-dimensional network. This means that in a pot of boiling water, precisely the moment when an ordinary rice noodle is at its most vulnerable, HPMC is hardening into a reinforcing scaffold woven through the noodle matrix. The Korean team attributes the improvements they measured largely to this very mechanism.

One of the first things the researchers noticed was where HPMC did not act. In pasting tests, which track the viscosity of a flour slurry as it is heated and cooled, the additive had little effect on the behavior of the flour itself. Starch granules swelled and burst on essentially the same schedule whether HPMC was present or not. That might sound like a null result, but it is actually the most telling part of the study. It indicates that HPMC is not fundamentally changing the starch, the dominant component of the flour. Instead, it is acting on the continuous phase that surrounds the swollen granules, forming its own heat-induced network that binds the whole structure together. The noodle improves not because its starch behaves differently, but because it has acquired a second, independent skeleton.

The visible consequences of that hidden skeleton were striking. Noodles made with the composite flour alone measured a lightness value of 38.29 on the standard color scale, a dull, somewhat gray reading that plagues many rice-blended products. Adding just 0.25 percent HPMC lifted that figure to 42.28, a brightness gain that matters enormously in a market where consumers judge noodles by eye before they ever lift them with chopsticks. The authors link this to the way the HPMC network restrains structural changes during heating and cooking, producing a smoother, more uniform surface that scatters light more evenly. Color, often treated as a cosmetic afterthought in food engineering, here serves as a window into the internal architecture of the strand.

Texture told an even clearer story. Adhesiveness, the sticky tendency that makes rice noodles cling to teeth, fingers, and each other, plummeted from 0.81 joules in the control noodles to just 0.22 joules with HPMC incorporation, roughly a quarter of the original stickiness. At the same time the noodles became stronger and more supple. Tensile strength, the force needed to pull a cooked strand apart, nearly quadrupled, rising from 0.11 to 0.39 newtons. And the noodles became dramatically more extensible: the maximum elongation, the distance a strand could be stretched before breaking, peaked at 36.12 millimeters in the formulation containing 1.00 percent HPMC. A noodle that stretches farther before snapping is a noodle that survives factory processing, packaging, transport, and the final violent tumble of a strainer without disintegrating.

The cooking tests completed the picture. Water absorption during boiling decreased with HPMC, meaning the noodles took on less excess water and therefore retained a firmer, more distinct structure rather than bloating into softness. More significantly, the turbidity of the cooking water dropped. Cloudy noodle water is essentially dissolved and leached starch escaping from the strands, a visible sign of structural failure and the first step toward a gummy, clumped finished dish. Clearer cooking water means less starch leaching, which the researchers read as direct evidence of improved cooking stability. Once again the thermogelation mechanism provides the explanation: as the strands enter the boiling water, the HPMC network sets up around the gelatinizing starch and physically walls it in, keeping granules where they belong inside the noodle.

Perhaps the most practically important finding is the dose–response shape. More HPMC was not always better. The formulation with 1.00 percent HPMC delivered the best overall balance of textural and cooking properties, while pushing to 1.25 percent did not improve the picture further. This kind of optimum is common in hydrocolloid science: beyond a certain concentration, polymer networks can become too rigid or compete with the starch matrix for water, and benefits plateau or reverse. For food manufacturers, identifying the sweet spot is what turns laboratory chemistry into a workable recipe. The result suggests that a single percentage-point addition of an ingredient that is already approved, inexpensive, and routinely handled in industrial bakeries and batters could upgrade a blended noodle across the board.

The broader context gives the work its urgency. Rice production in Korea and across much of Asia routinely exceeds demand for table rice, and milling industries are under steady pressure to find higher-value uses for the surplus. Replacing part of the wheat flour in noodles, one of the most consumed staple foods on the continent, is an obvious outlet, and previous studies have explored everything from heat-moisture treatments of the rice flour to protein isolates and microbial transglutaminase enzymes. Each approach adds cost, processing steps, or its own complications. HPMC stands out for its simplicity: it is mixed in with the dry ingredients, hydrates in the dough water, and then activates on its own at cooking temperature. The authors also note the ingredient’s established track record as a water barrier in other applications, such as keeping microwave-reheated battered foods crisp, which hints that its protective behavior extends beyond the noodle pot.

For consumers, the upshot is refreshingly tangible. The noodles described in this study are brighter, less sticky, stronger, more stretchable, and less prone to dissolving into their cooking water, all from an additive that carries no flavor of its own and performs its work silently, at exactly the moment it is needed, in the heat of the boil. The research was supported by the Korea Institute of Planning and Evaluation for Technology in Food, Agriculture and Forestry through its High Value-added Food Technology Development Program, a reflection of the national push to convert surplus rice into products people actually want to buy. It remains to be seen whether the same thermogelating scaffold can rescue more extreme formulations, such as fully gluten-free noodles where no wheat network exists at all, but as a demonstration of how a molecular trick of polymer physics can fix a very old problem in one of the world’s oldest foods, the study sets a clear and appetizing benchmark.

Subject of Research: Effect of hydroxypropyl methylcellulose on the physicochemical and cooking properties of rice–wheat composite noodles

Article Title: Improvement of noodle quality by HPMC incorporation in rice–wheat composite flour

Article References: Choi, S., Kang, T., Jeong, G. A., & Lee, C. J. (2026). Improvement of noodle quality by HPMC incorporation in rice–wheat composite flour. Food Science and Biotechnology. https://doi.org/10.1007/s10068-026-02314-6

Image Credits: AI Generated

DOI: 10.1007/s10068-026-02314-6

Keywords: HPMC, rice–wheat composite noodles, hydrocolloids, thermogelation, noodle texture, cooking quality, starch leaching, tensile strength, rice flour, food science, gluten reduction, Wonkwang University