Pea pod peel is a lignocellulosic treasure chest. On a fresh-weight basis it accounts for nearly 30 percent of the total pod, and its composition is approximately 69 percent cellulose, 22 percent hemicellulose, 5 percent carbohydrates and 4 percent lignin. That makeup makes it a natural candidate for dietary fiber recovery, a field dominated until now by better-studied agricultural by-products such as citrus peel, apple pomace, wheat bran and sugar beet pulp. Pea pod peel, despite its abundance, has been investigated to a far lesser extent for fiber recovery, and because the chemical composition of lignocellulosic biomass varies with plant origin, results from other wastes cannot be directly transferred to it. A systematic study of this specific material was therefore needed.

Dietary fibers are the non-digestible carbohydrate polymers that resist enzymatic breakdown in the human gastrointestinal tract, and they fall into two physiologically distinct families. Insoluble dietary fiber, built from structural polysaccharides such as cellulose, lignin and portions of hemicellulose, adds fecal bulk and improves intestinal motility, while soluble dietary fiber, which includes functional polysaccharides such as pectins, β-glucans, inulin and galactomannans, helps regulate blood glucose, lowers cholesterol and increases gut viscosity, supporting cardiometabolic health. Because market demand for both fractions keeps climbing in the functional food and nutraceutical sectors, food scientists are hunting for cheap, sustainable raw materials, and pea pod peel fits the bill.

The researchers compared three extraction routes: conventional alkaline extraction, microwave-assisted alkaline extraction and ultrasound-assisted alkaline extraction. In the conventional method, ten grams of pea pod peel powder were treated with about 400 milliliters of 1.2 mol/L sodium hydroxide at 40 °C for two hours in a water bath with continuous mixing, then centrifuged for 15 minutes at 5000 g to separate the insoluble residue from the soluble supernatant. The microwave approach used the same alkaline chemistry but replaced the long water-bath treatment with a brief exposure to 450 W of microwave energy, varying the solid-to-solvent ratio from 0.025 to 0.1 g/mL and the treatment time from 3 to 6 minutes. The ultrasound route swept the ultrasonic power from 150 to 300 W, used the same range of solid-to-solvent ratios, and varied times from 3 to 12 minutes. All experiments were performed in triplicate, and the design space for each technique was first mapped by single-factor screening experiments.

To squeeze the maximum fiber recovery out of each technology, the team turned to response surface methodology. For microwave extraction, 13 experimental runs optimized two variables at fixed power; for ultrasound, 20 runs optimized power, solid-to-solvent ratio and time simultaneously. Quadratic regression models captured how each factor and their interactions shaped total, soluble and insoluble fiber yields. The models were statistically significant, with R² values as high as 0.9983 for the ultrasound responses, and non-significant lack-of-fit tests confirmed their adequacy. Validation runs showed prediction errors as small as 0.01 to 0.34 percent between predicted and measured yields, a remarkable agreement demonstrating how reliably the models describe extraction behavior across the studied parameter space.

The results delivered a clear winner. Conventional alkaline extraction, optimized at a solid-to-solvent ratio of 0.033 g/mL, recovered 84.40 percent total dietary fiber, comprising 23.35 percent soluble and 61.07 percent insoluble fiber. Microwave-assisted extraction at 0.0625 g/mL and 4.5 minutes raised the total to 88.90 percent, with 26.67 percent soluble and 62.23 percent insoluble fiber. But ultrasound-assisted extraction dominated, achieving 95.69 percent total dietary fiber, 28.71 percent soluble fiber and 66.98 percent insoluble fiber at 225 W, 0.0625 g/mL and 7.5 minutes. The mechanism behind this superiority is cavitation: collapsing ultrasonic bubbles generate shock waves and microjets that tear open cell walls, boost solvent penetration and accelerate mass transfer. Pushing the power beyond 225 W or extending sonication past 7.5 minutes actually reduced yields, because excessive cavitation fragments fiber molecules into pieces too small to recover, a reminder that in extraction, more energy is not always better.

The solid-to-solvent ratio told a similar story of a sweet spot. Yields climbed as the ratio rose from 0.025 to 0.0625 g/mL, then fell at 0.1 g/mL, because thicker slurries impede both microwave energy transmission and ultrasonic wave propagation. Microwave time peaked at 4.5 minutes, after which thermal degradation of polysaccharide chains set in. The authors note that these energy-assisted methods work by fundamentally different mechanisms: microwaves heat the material volumetrically and build internal pressure that ruptures cells, while ultrasound applies mechanical shear that disintegrates the fiber matrix. Both improve mass transfer, but ultrasound does so with fewer thermal side effects, which appears to protect the fiber’s molecular integrity while opening up its structure. Each method also carries known limitations: conventional alkaline treatment demands long times and large chemical inputs and can break down fiber structure under harsh alkaline conditions, microwaves can cause non-uniform heating and localized overheating, and overly intense sonication can depolymerize fibers and alter their functionality.

Characterization revealed how deeply extraction technology rewrites fiber architecture. Particle size analysis showed that ultrasound produced the finest powders, with mean diameters of 136.28 μm for soluble fiber and 233.18 μm for insoluble fiber, the smallest among all treatments. Scanning electron microscopy made the difference visible. Alkaline-treated fibers displayed compact, smooth, low-porosity surfaces, whereas ultrasound-treated fibers were rough, cracked, porous and fibrillated, a consequence of cavitation-driven erosion. Microwave-treated fibers showed a looser, sponge-like honeycomb texture produced by internal superheating. X-ray diffraction found the same crystal phases in all samples, confirming that no new chemical phases formed, but the degree of crystallinity dropped significantly after assisted extraction, with ultrasound-extracted soluble and insoluble fibers showing the lowest values at 15.24 and 22.27 percent. A more amorphous structure means more accessible binding sites for water and oil, which is precisely what the functional tests confirmed.

Those functional gains are the study’s most commercially significant finding. Ultrasound-extracted insoluble fiber held 4.8 g of water per gram, 2.7 g of oil per gram and swelled to 7.0 mL/g, while the soluble fraction held 3.2 g of water, 1.5 g of oil and swelled to 4.0 mL/g, all the highest values among the three methods. Fourier transform infrared spectroscopy confirmed that despite this structural remodeling, the chemistry survived intact: characteristic O-H, C-H and C-O stretching bands, including lignin-associated aromatic signals, were all preserved, indicating that the polysaccharide backbones of cellulose, hemicellulose and pectic components remained undamaged. Thermogravimetric analysis added another advantage: ultrasound-extracted fibers were the most thermally robust, with the highest thermal resistance at 270 °C, meaning these ingredients could withstand baking and other high-temperature food processes without collapsing.

Together, the data sketch a coherent structure-function story. Ultrasound cavitation reduces particle size, roughens surfaces, loosens crystalline order and exposes hydrophilic and hydrophobic binding sites, all of which translate into superior hydration, oil binding and swelling, the very properties food technologists prize when formulating high-fiber breads, beverages and meat alternatives. The technique also cuts extraction time from two hours to 7.5 minutes, a dramatic process intensification that could reduce energy and solvent costs at scale. The authors caution that the work remains at laboratory scale: energy consumption, economic feasibility, pilot-scale performance and real-food application, including effects on texture, shelf life and consumer acceptance, still need to be demonstrated. Future studies should also probe health-relevant functions such as glucose adsorption, bile acid binding, fermentability and prebiotic potential.

Even so, the message is striking. A waste stream generated at a scale of millions of tons a year, currently treated as a disposal problem, can be converted into a dietary fiber ingredient that outperforms conventionally processed material on nearly every functional metric, using nothing more exotic than sound waves and dilute alkali. As food manufacturers race to meet consumer demand for fiber-enriched products and regulators push for greener processing, ultrasound-assisted extraction of pea pod peel offers a rare win-win: less waste in the landfill, more functionality on the plate, and a sustainable, cost-effective route to value-added ingredients grown from one of the world’s most widely cultivated and freeze-tolerant legume crops.

Subject of Research: Green extraction of dietary fiber from pea pod peel waste using ultrasound and microwave assisted alkaline methods

Article Title: Optimization and characterization of microwave and ultrasound assisted alkaline extracted pea pod peel dietary fiber

Article References: Sharma, P., & Kumar, P. (2026). Optimization and characterization of microwave and ultrasound assisted alkaline extracted pea pod peel dietary fiber. Discover Industrial Chemistry and Materials, 1(1), Article 19. https://doi.org/10.1007/s44508-026-00020-z

Image Credits: AI Generated

DOI: 10.1007/s44508-026-00020-z

Keywords: pea pod peel, dietary fiber, ultrasound-assisted extraction, microwave-assisted extraction, response surface methodology, soluble dietary fiber, insoluble dietary fiber, food waste valorization, green extraction, functional properties, agro-industrial byproducts, thermal stability