Ripening Rewrites Banana Peel Fiber: Green Stage Wins for Function, Yellow Stage for Gut Bacteria

Every year, the global banana industry throws away tens of millions of tons of peel, most of which rots in landfills and releases greenhouse gases while a potentially valuable ingredient disappears into the waste stream. A new study published in Food Chemistry: X suggests that this discarded material, and specifically the thick white inner layer of the peel known as the albedo, could be transformed into a tailored dietary fiber ingredient whose properties depend on one surprisingly simple variable: how ripe the fruit was when the peel was collected. The research, led by Sarinya Sangkasanya and colleagues at Rajamangala University of Technology Thanyaburi in Thailand, is among the first to track how ripening reshapes the molecular and microscopic architecture of fiber purified exclusively from banana albedo, and it points toward a strategy in which food manufacturers could select fibers with deliberately different functional profiles from the same fruit.

The team worked with Hom Thong bananas (Musa acuminata, AAA group), a cultivar widely consumed across Southeast Asia whose peel contains a comparatively thick, spongy albedo layer rich in complex carbohydrates. Rather than using harsh chemical solvents, the researchers purified the fiber enzymatically, a greener approach that operates under moderate conditions and causes less structural damage. The protocol was a carefully sequenced three-enzyme cascade: alpha-amylase at 80 degrees Celsius to break down starch, glucoamylase at 60 degrees Celsius to mop up the resulting sugars, and neutral protease at 50 degrees Celsius to strip away proteins. After washing with warm water and ethanol and drying to below ten percent moisture, what remained was an enzymatically purified dietary fiber, or EPDF, essentially the cell-wall skeleton of the albedo, stripped of everything the human small intestine could digest on its own.

The enzymatic treatment proved dramatically effective. The raw albedo contained 27.43 percent total dietary fiber on a dry weight basis, a figure held down by intracellular proteins, resistant starches, and other digestible carbohydrates that dilute the fiber measurement. After enzymatic purification, total dietary fiber jumped 2.09-fold to 57.13 percent, with insoluble fiber rising 2.20-fold from 22.69 to 50.01 percent and soluble fiber increasing 1.53-fold from 4.67 to 7.12 percent. The authors attribute this selectivity to the enzymes’ ability to dismantle the non-fiber matrix and release the structural polysaccharides, cellulose, hemicellulose, and pectin, that constitute the fiber proper. Compared with traditional acid or alkaline extraction, the enzymatic route achieved higher purity while preserving the structural integrity of the fiber, an attribute that matters because the physical architecture of a fiber largely determines how it behaves in food and in the gut.

With the purification method validated, the researchers turned to their central question: does ripening change the fiber itself? They classified bananas into three stages using peel color coordinates and soluble solids content: mature green, yellow-green, and fully yellow, then extracted fiber from each. The answer was emphatically yes. Total dietary fiber fell significantly from 58.15 percent in the mature green stage to 48.66 percent at yellow-green and 46.94 percent when fully yellow, driven almost entirely by a decline in insoluble fiber from 55.19 to 43.55 percent. Meanwhile, soluble fiber crept upward from 2.96 to 3.39 percent, raising the soluble-to-insoluble ratio from 0.054 to 0.078. Crude fiber dropped even more steeply, from 9.22 to 4.82 percent. These shifts mirror the endogenous enzymatic storm of ripening: xylanase activity rises and hemicellulose degrades, while pectin methylesterase and polygalacturonase solubilize insoluble pectic polysaccharides, converting rigid cell-wall material into softer, more fermentable forms.

Microscopy made this molecular story visible. Under the scanning electron microscope, fiber from mature green bananas displayed a rough, heterogeneous surface studded with pores, folds, and micro-fissures, an open architecture consistent with its high insoluble fiber content. The yellow-green sample occupied an intermediate state, more aggregated and compact but still rough, while fiber from fully yellow bananas showed a dense, smooth, nearly continuous surface with few visible openings. As the fruit’s own cell-wall enzymes remodel the polysaccharide network, the extracted fiber loses the porous, fibrous topology that makes the green-stage material so interactive with water and oil. Fourier-transform infrared spectroscopy added molecular detail: all samples retained the characteristic lignocellulosic framework, but the fully yellow spectra showed changes in the carbohydrate fingerprint region and in pectic ester and carboxylate bands, consistent with hydrolytic modification of hemicellulose and pectin rather than wholesale breakdown.

X-ray diffraction revealed a subtler trend. All three fibers showed the broad diffraction features of cellulose I-type structures, indicating that the ordered cellulose domains survived ripening intact. Yet relative crystallinity climbed steadily from 14.8 percent in mature green fiber to 17.1 percent at yellow-green and 26.3 percent when fully yellow. The authors interpret this not as new crystalline cellulose forming, but as a proportional effect: as the amorphous pectic and hemicellulosic components surrounding the cellulose are progressively modified and solubilized during ripening, the remaining ordered domains make up a larger share of the diffracting material. The raw, unpurified albedo, by contrast, showed a much higher crystallinity of 48.6 percent, reflecting crystalline constituents such as native starch that the enzymatic purification removed.

These structural differences translated directly into function. Fiber from mature green bananas dominated every hydration and adsorption measure: water-holding capacity of 5.00 grams of water per gram of fiber, oil-holding capacity of 2.84 grams per gram, cholesterol adsorption of 8.46 milligrams per gram, and glucose adsorption of 38.53 milligrams per gram, all significantly higher than the later stages, which declined in step with the smoothing of the fiber surface. Principal component analysis confirmed the pattern, with the first two components explaining 99.05 percent of the variance and separating the three ripening stages along an axis loaded with the hydration and adsorption variables. Swelling capacity was the lone exception, holding steady at 4.30 to 4.47 milliliters per gram across all stages, likely because the lignin-rich framework, whose spectral signature persisted even in fully yellow samples, preserved enough structural integrity to swell similarly regardless of maturity.

The prebiotic results added an unexpected twist. In anaerobic fermentation assays, all three fibers supported robust growth of Lactobacillus plantarum and Lactobacillus casei while viable counts of E. coli fell relative to the unsupplemented control, and prebiotic activity scores of 0.60 to 0.70 were broadly comparable to commercial inulin. But the star performer was not the green-stage fiber with its superior hydration; it was the intermediate yellow-green fiber, which achieved the highest score of 0.70, the largest pH drop of 2.42 units, the greatest titratable acidity at 0.577 percent lactic acid equivalents, and the highest acetate production at 0.483 grams per liter, exceeding even the inulin control on those fermentation measures. The authors suggest that fermentability depends not on soluble fiber content alone but on the combination of composition and structure: the yellow-green fiber’s layered surface with visible micro-fissures may offer an ideal balance of accessibility and substrate, whereas the fully yellow fiber’s denser surface, despite its higher soluble fiber ratio, did not confer an additional fermentation advantage.

The practical upshot is a maturity-based valorization strategy for a waste stream that currently exceeds 57.6 million metric tons of peel annually. Fiber from mature green albedo, with its exceptional water and oil retention and glucose and cholesterol adsorption, is a natural candidate for bakery products and formulated foods where moisture control and texture matter. Yellow-green fiber, the fermentation champion, suits fermented dairy or plant-based formulations where prebiotic activity is the goal. Fully yellow fiber, with the highest soluble fiber proportion, fits beverages, soups, and sauces. All the powders showed low water activity of 0.22 to 0.23, well below the 0.60 threshold that inhibits microbial spoilage, supporting shelf stability. By matching the ripening stage of the raw material to the intended application, processors could convert a disposal problem into a portfolio of differentiated functional ingredients, an elegant example of the circular bioeconomy turning fruit that has passed its prime into something genuinely valuable.

Subject of Research: Effects of banana ripening stage on the structure, functionality, and prebiotic activity of enzymatically purified dietary fiber from banana peel albedo

Article Title: Macromolecular and microstructural evolution of enzymatically purified banana albedo dietary fiber during ripening: Targeted valorization for functional and prebiotic applications

Article References: Sangkasanya, S., Ramirez, J. J. B., Inocencio, C. D. G., & Naknaen, P. (2026). Macromolecular and microstructural evolution of enzymatically purified banana albedo dietary fiber during ripening: Targeted valorization for functional and prebiotic applications. Food Chemistry: X, Article 104624. https://doi.org/10.1016/j.fochx.2026.104624

Image Credits: AI Generated

DOI: 10.1016/j.fochx.2026.104624

Keywords: banana peel, dietary fiber, albedo, ripening, enzymatic extraction, prebiotic, gut microbiota, food waste valorization, water-holding capacity, glucose adsorption, Lactobacillus, circular bioeconomy