Grains constitute a fundamental component of the global diet, providing essential nutrients, dietary fiber, and bioactive compounds. Among these, millet is recognized as a highly nutritious cereal belonging to the Poaceae family and is extensively cultivated in semi-arid and arid regions due to its remarkable tolerance to drought and harsh environmental conditions (Saleh et al., 2013). Millet is naturally gluten-free, making it an ideal dietary alternative for individuals with wheat intolerance or celiac-related disorders (Kumar et al., 2018). Pearl millet (Pennisetum glaucum) is the most widely cultivated millet species, accounting for nearly 40% of global production, followed by finger millet, foxtail millet, and proso millet (Satyavathi et al., 2024). Globally, India, Niger, China, and Nigeria are the leading millet producers, each harvesting from about 2 to over 11 million tons annually (Food and Agriculture Organization of the United Nations, 2023). Similarly, millet is cultivated in the Kingdom of Saudi Arabia on approximately 7,100 hectares, with a total production of about 13,600 tons reported in 2024 (General Authority for Statistics, 2024). Production is primarily concentrated in traditional rain-fed farming systems in the southwestern regions, particularly Asir and Jazan (Food and Agriculture Organization of the United Nations, 2022, 2024). These production characteristics may indicate opportunities for further development of millet cultivation, utilization, and related value-chain activities within the Kingdom.

Nutritionally, pearl millet is rich in macronutrients and essential minerals. It typically contains 67–72% carbohydrates, 8–12% dietary fiber, 13–14% protein, and 5–7% fat, along with 40–45 mg calcium, 6–9 mg iron, 3–4 mg zinc, 130–140 mg magnesium, and 280–300 mg phosphorus per 100 g of grain (Triki et al., 2025; Munshi and Dashora, 2024). Additionally, whole millet grains are rich in phenolic and flavonoid compounds, with concentrations varying depending on variety, growing conditions, and processing methods (Chandrasekara and Shahidi, 2011). Pearl millet contains phenolic compounds (250–1,200 μg/g DW) and flavonoids (4–250 μg/g DW), including quinic acid, p-coumaric acid, caffeic acid, catechin, epicatechin, and procyanidins, enhancing its antioxidant potential (Triki et al., 2025; Hassan et al., 2020). These bioactive compounds contribute to the antioxidant, antiviral, anticancer, and antiplatelet properties reported for millet (Olawoye et al., 2024; Shahidi and Chandrasekara, 2013). Millet also demonstrates a low glycemic index, making it beneficial for weight management and reducing the risk of metabolic diseases, including diabetes (Subaitha et al., 2024; Dias-Martins et al., 2018).

Although millet is relatively stable as a whole grain, its grains exhibits reduced shelf stability due to enzymatic activity—particularly lipase, lipoxygenase, peroxidase, and polyphenol oxidase—and susceptibility to lipid oxidation during storage (Goswami et al., 2020). Therefore, several pre-processing strategies, including mechanical, enzymatic, and thermal treatments, have been used to enhance millet grains quality, improve the extractability of bioactive compounds, and reduce antinutritional factors (Gowda et al., 2025; Saleh et al., 2013).

Previous studies have evaluated the effects of various processing methods, including germination, microwave treatment, cold plasma, fermentation, and thermal treatments, on millet phenolic content and functional properties (Choudhary et al., 2025; Pradeep and Sreerama, 2015; Chandrasekara et al., 2012). In search of advanced and green food processing strategies, low-frequency ultrasound (LFUS) has emerged as a promising technique due to its ability to enhance extraction efficiency, reduce treatment time and solvent usage, and induce structural modifications in starches and proteins through acoustic cavitation (Estivi et al., 2022; Balasubramaniam et al., 2019). Cavitation involves the formation, expansion, and collapse of microbubbles as ultrasound waves propagate through a medium, producing localized pressure and temperature changes that can disrupt cellular matrices and modify biopolymer structures (Zhu et al., 2025; Mounika et al., 2024; Suslick, 1990). Cavitation enhances swelling power, solubility, pasting viscosity, gelation, thermal stability, and retrogradation by disrupting starch granules and influencing molecular reorganization.

By disrupting molecular linkages, inducing partial unfolding of peptide chains, and altering their aggregation dynamics, ultrasound treatment enhances protein solubility, surface hydrophobicity, and functional attributes such as emulsification, foaming, and gel formation (Adam et al., 2025; Zhu et al., 2025). Millet is traditionally cultivated in southern Saudi Arabia, particularly in Jizan, where it is used in local bread and traditional dishes. Recently, millet has gained renewed attention status, and resilience to climate change, making it an important crop for achieving food security (Kumar et al., 2018). Given the nutritional importance and functional potential of millet, this study aimed to evaluate the impact of ultrasound treatment on the physicochemical characteristics, phenolic and flavonoid content, antioxidant activity, pasting behavior, and texture of millet grains.

The present study demonstrates that ultrasound at 40 kHz significantly influences the physicochemical, functional, and structural properties of millet grains, with effects strongly dependent on both treatment duration and temperature. These observations align with the established principles of acoustic cavitation, in which the formation, growth, and collapse of microbubbles generate intense, localized shear forces and transient thermal effects that can alter biopolymers (Suslick, 1990). The increase in lightness (L*) and total color difference (ΔE) following ultrasound treatment may be attributed to cavitation-induced microstructural changes at the grains surface, resulting in increased light reflectance. Similar improvements in brightness have been reported in ultrasound-treated cereal matrices, where cavitation produces surface erosion and pigment redistribution (Estivi et al., 2022; Choudhary et al., 2025). The shift in a* toward negative values and fluctuations in b* suggest partial oxidation or structural modification of natural pigments, consistent with sonochemical effects described in cereal grains (Kutlu et al., 2022). Guo et al. (2021) stated that color parameters L*, a* and b* were significantly changed in white yak meat because of ultrasonic treatments.

Regarding the TPC and TFC, the significant increase in TPC, particularly at 20 and 60 min and at elevated temperatures, indicates enhanced extraction of bound phenolics due to disruption of the cell wall matrix, a phenomenon widely documented in ultrasound-assisted extraction (Chandrasekara and Shahidi, 2011). It has been reported that ultrasonic pretreatment is positively affected on the TPC. Balasubramaniam et al. (2019) stated that ultrasonic energy promotes the release of pound phenolic compounds, hence cause an increment in the TPC in finger millet. Similarly, Meena et al. (2023) found that the TPC in ultrasonic-treated white finger millet is grater that control one.

Cavitation improves solvent penetration and breaks ester and glycosidic linkages, facilitating the release of phenolic compounds (Balasubramaniam et al., 2019). Conversely, the decline in TFC at longer sonication times suggests that flavonoids, especially those with more labile structures, may undergo degradation under prolonged exposure to thermal and mechanical stresses. Similar sensitivity of flavonoids to ultrasonic and thermal processing has been reported in cereal and pulse grains (Pradeep and Sreerama, 2015).

The variable responses across antioxidant assays (ABTS, FRAP, DPPH) reflect differences in their mechanisms and chemical specificity. The improvement in antioxidant activity at 40–60 °C may be due to increased solubility and the release of antioxidant-active phenolics (Dias-Martins et al., 2018). The temporary reduction in DPPH scavenging at early sonication stages may be linked to the formation of intermediate radicals during bubble collapse, as suggested in sonochemical oxidation pathways (Suslick, 1990). Recovery of antioxidant activity at 60 min aligns with findings that prolonged ultrasound can generate lower-molecular-weight phenolic derivatives with increased reactivity (Chandrasekara and Shahidi, 2011).

The impact of ultrasonic treatments of millet grains under different temperature and time on the rheological properties (pasting properties and texture profile) revealed substantial reductions in peak, breakdown, and setback viscosities suggest weakening of starch granule integrity under ultrasound exposure. Similar trends have been reported in sonicated cereal starches, where cavitation disrupts granular morphology, breaks amylopectin branches, and decreases crystallinity (Balasubramaniam et al., 2019). Lower setback values indicate reduced retrogradation potential, which may improve storage stability of millet-based products—a desirable trait in gluten-free formulations.

Increasing temperature, on the other hand, enhanced gelatinization and increased viscosity, consistent with the thermally driven swelling of starch granules observed in previous millet studies (Goswami et al., 2020). The reductions in hardness, cohesiveness, and springiness following ultrasound treatment reflect structural loosening of the starch–protein matrix. Cavitation likely disrupts intermolecular hydrogen bonds and partially depolymerizes starch chains, producing softer gels—a behavior consistent with ultrasound-treated millet (Zhu et al., 2025; Mounika et al., 2024). However, the increase in hardness and cohesiveness at higher temperatures (40–60 °C) suggests thermal strengthening of gelatinized starch, which counterbalances cavitation effects. Similar thermal–mechanical interactions have been reported in studies on heat-assisted ultrasound processing.

In general, the results demonstrate that ultrasound processing can be strategically tuned to enhance the functional quality of millet grains. The combination of moderate temperatures (40–60 °C) and short-to-moderate sonication times (20–60 min) proved optimal for maximizing phenolic release, improving antioxidant activity, and achieving desirable pasting and textural properties. These findings align with the broader body of literature identifying ultrasound as a sustainable, energy-efficient, and highly versatile non-thermal technology suitable for improving the functionality of cereal-based products (Estivi et al., 2022; Balasubramaniam et al., 2019).

Ultrasonic emerged as an effective green technology for modifying and enhancing the physicochemical and functional properties of millet grains. The treatment significantly improved color attributes increased phenolic extractability, enhanced antioxidant activity, and reduced starch retrogradation—traits that collectively support superior processing behavior and product stability. The best results were obtained at 20 min and 40–60 °C, demonstrating that moderate temperature, combined with controlled sonication intensity, produces the most favorable balance between structural modification and preservation of bioactive compounds. These findings highlight ultrasound as a promising approach for developing high-quality millet-derived food products, particularly within the expanding gluten-free and health-oriented food sectors, offering a more reliable and useful method of processing millet-based foods. However, future research should explore ultrasound-assisted modification of composite grains, optimize using advanced modeling tools, and assess scale-up feasibility in industrial systems.