Ultrasound-enhanced black bean protein gels deliver vitamin B2 during digestion

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In the rapidly evolving field of food science, researchers are constantly exploring innovative ways to improve nutrient delivery systems.

A groundbreaking study published in Ultrasonics Sonochemistry (2025) introduces a novel protein gel made from black bean and whey proteins, enhanced by ultrasound technology, that effectively protects and delivers riboflavin (vitamin B2) during digestion.

The Challenge with Traditional Protein Gels

Protein gels are widely used to encapsulate nutrients, shielding them from harsh stomach acids and enabling controlled release in the intestines.

However, gels made from single proteins, such as soy or whey, often face limitations. For instance, some gels have weak structures that collapse under mechanical stress, while others struggle to retain water, causing nutrients to leak out prematurely.

Additionally, inefficient cross-linking between proteins can result in a loose network that fails to protect sensitive nutrients effectively.

To address these challenges, researchers have turned to combining plant and animal proteins, such as black bean and whey. While this approach shows promise, achieving synergy between the two proteins is not straightforward.

This study solves the problem by using transglutaminase (TGase), an enzyme that bonds proteins, and ultrasound, a technology that reshapes protein structures for better performance.

Together, these tools create a gel that is not only strong and water-resistant but also ideal for delivering nutrients like riboflavin.

How the Gel Was Made: Ingredients and Methodology

The study began by extracting black bean protein isolate (BBPI) from defatted black beans. This process involved soaking the beans, adjusting the pH to 8.0 with alkali, and then lowering it to 4.5 with acid to precipitate the protein.

The final product was freeze-dried to preserve its functionality. Next, the researchers combined BBPI with whey protein isolate (WPI) in a 4:6 ratio to create a protein mixture.

To enhance the gel’s properties, the protein mixture was treated with ultrasound at varying powers (0–480 W) for 10 minutes.

Ultrasound uses high-frequency soundwaves to physically disrupt protein structures, exposing reactive sites for cross-linking. After ultrasound pretreatment, transglutaminase (TGase) was added to the mixture.

This enzyme creates covalent bonds between proteins, strengthening the gel matrix. The mixture was then incubated at 45°C for 4 hours, heated to 85°C to deactivate the enzyme, and cooled to form the gel.

Finally, glucono-δ-lactone (GDL), a natural acidifier, was added to the protein solution. GDL slowly lowers the pH, triggering gel formation. The gel was refrigerated overnight to enhance its firmness and stability.

The Role of Ultrasound in Transforming Protein Gels

Ultrasound pretreatment emerged as a game-changer in this study. By applying high-frequency soundwaves, researchers reshaped protein structures in three key ways.

First, ultrasound broke down large protein aggregates into smaller, more uniform particles. For example, untreated BBPI-WPI mixtures had an average particle size of 386.01 nm, but ultrasound at 240 W reduced this to 278.73 nm.

Smaller particles increased the surface area available for cross-linking, enabling TGase to create a denser network. Second, ultrasound exposed reactive groups within the proteins.

For instance, it decreased free amino groups by 25% at 240 W, maximizing TGase efficiency.

It also increased surface hydrophobicity, a measure of how well proteins interact via water-repelling forces. Ultrasound-treated gels showed higher hydrophobicity, which contributed to their stability.

Additionally, ultrasound increased free sulfhydryl (-SH) groups, which formed disulfide bonds during gelation, enhancing the gel’s rigidity.

Third, ultrasound altered the protein’s secondary structure. Fourier transform infrared spectroscopy (FTIR) analysis revealed that ultrasound reduced rigid α-helix structures and increased flexible β-sheets, improving the gel’s elasticity.

Fluorescence intensity also increased, indicating that ultrasound exposed aromatic residues like tryptophan, further confirming structural changes.

Evaluating Gel Performance: Hardness, Water Retention, and Structure

The study rigorously tested the gel’s properties under different ultrasound conditions. One of the key metrics was hardness, which measures the gel’s resistance to deformation.

Gels treated at 360 W achieved the highest hardness (98.95 N), thanks to the formation of robust disulfide bonds. Another critical property was water-holding capacity (WHC), which indicates how well the gel retains water.

Ultrasound-treated gels showed significant improvements in WHC, with the best performance at 480 W (60.59%).

Scanning electron microscopy (SEM) images revealed that these gels had a uniform, dense network with tiny pores, effectively trapping water. The researchers also analyzed the intermolecular forces responsible for gel stability.

Disulfide bonds and hydrophobic interactions were the dominant forces, while ionic and hydrogen bonds played minor roles. Low-field nuclear magnetic resonance (LF-NMR) analysis further confirmed that ultrasound-treated gels retained water in fixed or bound states, minimizing leakage.

Protecting Riboflavin: A Test for Nutrient Delivery

Riboflavin, a vitamin essential for energy metabolism, degrades rapidly in acidic environments. The study tested how well the gel shielded riboflavin during simulated digestion.

Ultrasound-treated gels achieved an impressive 95% encapsulation efficiency (EE), meaning they trapped almost all the riboflavin within their dense network.

In simulated gastric fluid (stomach conditions), gels treated at 360 W released 52% less riboflavin than untreated gels. This resistance to pepsin erosion ensured that most of the riboflavin reached the intestines intact.

Once in simulated intestinal fluid, the gel degraded gradually, releasing 80–90% of the riboflavin within 2 hours.

This controlled release aligns with the intestine’s role in nutrient absorption, making the gel an effective delivery system.

Why This Gel Stands Out

The combination of black bean and whey proteins, enhanced by ultrasound and TGase, creates a gel that excels in nutrient protection and delivery.

For example, at 360 W, ultrasound exposed sulfur groups, enabling robust disulfide bonds that increased gel hardness. Additionally, using BBPI reduces reliance on animal proteins, making the gel more sustainable.

This gel’s versatility is another standout feature. It could be used to deliver probiotics, vitamins, or even drugs, adapting to multiple industries.

For instance, it could fortify yogurt or protein bars with heat-sensitive nutrients or serve as a slow-release system for medications targeting the intestines.

Implications for Food and Healthcare

The findings of this study have far-reaching implications. In the food industry, this gel could revolutionize functional foods by fortifying products like yogurt, protein bars, and beverages with heat-sensitive nutrients.

In healthcare, it could be used to develop slow-release gels for drugs targeting conditions like inflammatory bowel disease. Additionally, the gel’s ability to stabilize nutrients could help reduce food waste by extending product shelf life.

Challenges and Future Research

While the results are promising, scaling ultrasound technology for industrial use remains costly. Future studies could explore alternative technologies, such as high-pressure processing or pulsed electric fields, to achieve similar effects.

Researchers could also experiment with new protein blends, such as pea-casein or lentil-whey combinations, to further optimize gel properties. Finally, human trials are needed to validate riboflavin absorption and confirm the gel’s effectiveness in real-world applications.

Conclusion: A Leap Forward in Food Science

This study demonstrates how combining black bean and whey proteins—enhanced by ultrasound and TGase—creates a gel that excels in nutrient protection and delivery.

With hardness exceeding 98 N, water-holding capacity over 60%, and riboflavin release reduced by 52%, this innovation bridges the gap between plant-based sustainability and functional performance.

As researchers refine these methods, we edge closer to a future where food not only nourishes but also intelligently delivers what our bodies need.