Upcycling Onion Peel in Pasta with a Focus on Nutritional, Thermal, and Storage Properties

60

In recent years, the food industry has increasingly turned to natural and sustainable ingredients to meet growing consumer demand for healthier, eco-friendly products.

A groundbreaking study published in Food Chemistry Advances (2025) offers a compelling solution by transforming onion peel waste—a common agricultural byproduct—into a functional ingredient for pasta.

This research not only tackles the global challenge of food waste but also enhances the nutritional value, visual appeal, and shelf life of pasta, a staple food consumed worldwide.

The Need for Natural Additives in Modern Food Production

Pasta, traditionally made from durum wheat semolina (a coarse flour from hard wheat), is prized for its affordability, versatility, and long shelf life.

However, conventional pasta lacks significant amounts of bioactive compounds—nutrients like antioxidants and flavonoids that offer health benefits beyond basic nutrition, such as reducing inflammation or preventing chronic diseases.

Over the years, researchers have experimented with adding plant-based ingredients such as chia flour, moringa leaves, and legume flours to improve its nutritional profile.

The COVID-19 pandemic further accelerated consumer preference for natural additives over synthetic ones, driven by concerns about the long-term health risks of artificial preservatives, colors, and stabilizers.

This shift in consumer behavior has led scientists to explore unconventional sources of natural additives. Onion peels, often discarded as waste during food processing, emerged as a promising candidate.

Rich in antioxidants , flavonoids, and anthocyanins , onion peels offer both nutritional and functional benefits.

Globally, onion processing generates millions of tons of waste annually, much of which ends up in landfills, contributing to environmental pollution.

By repurposing this waste into a food ingredient, the study addresses two pressing issues: reducing agricultural waste and creating healthier, more sustainable food options.

Transforming Onion Peel Waste into Nutritious Pasta Ingredients

The research team, led by S. Abinaya and colleagues, adopted a meticulous approach to convert onion peels into a functional pasta ingredient.

First, dried onion peels were ground into a fine powder using a laboratory mill. This powder was then mixed with ethanol and subjected to ultrasonic extraction (a process using high-frequency sound waves to break down plant cells and release compounds), which enhances the efficiency of pigment and bioactive compound extraction.

The resulting mixture was filtered, concentrated under vacuum to remove moisture, and stored as a thick paste. Next, the team incorporated this paste into pasta dough at concentrations ranging from 0% (control) to 8%, replacing semolina proportionally.

The dough was mixed, extruded (pressed through a mold to shape the pasta), dried, and packaged for analysis. To evaluate the impact of onion peel extract, the researchers conducted a series of tests, including:

• nutritional profiling (measuring protein, fat, fiber, etc.),
• phytochemical analysis (identifying plant-based nutrients like phenols and flavonoids),
• color measurement,
• cooking quality assessments,
• structural examinations using advanced techniques like scanning electron microscopy (SEM) (a high-resolution imaging method to study surface textures) and X-ray diffraction (XRD) (a technique to analyze the crystalline structure of materials).

Sensory panels involving 54 participants assessed the pasta’s taste, texture, and appearance, while storage studies tested its stability under harsh conditions (45°C and 90% humidity) for 60 days.

Boosting Pasta Nutrition with Onion Peel Bioactive Compounds

One of the most striking findings was the dramatic improvement in the pasta’s nutritional profile. As the concentration of onion peel extract increased, so did its content of beneficial compounds.

For instance, total phenolic content—a measure of antioxidant capacity calculated as milligrams of gallic acid equivalent (GAE) per 100 grams—rose from 59.05 mg GAE/100g in control pasta to 280.01 mg GAE/100g in pasta with 8% extract, representing a 374% increase.

Similarly, total flavonoids (measured as milligrams of quercetin equivalent (QE) per 100 grams), known for their anti-inflammatory properties, surged from 30.09 mg QE/100g to 250.48 mg QE/100g, a 732% jump.

Antioxidant activity, measured using the DPPH assay (a lab method to evaluate a substance’s ability to neutralize free radicals), nearly tripled from 16.10% to 44.82%.

These figures highlight the extract’s potential to transform ordinary pasta into a functional food (foods with added health benefits) capable of combating oxidative stress and chronic diseases.

In addition to phytochemicals, the pasta’s dietary fiber (indigestible plant material that promotes gut health) content saw significant gains.

At 8% extract concentration, fiber levels reached 7.11%, up from 2.18% in the control.

This increase is particularly beneficial for digestive health and blood sugar management. However, the study noted a slight decline in protein content (from 12.34% to 11.31%) due to the replacement of semolina with the extract, which is low in protein. Despite this trade-off, the overall nutritional benefits far outweigh the minor reduction in protein.

How Onion Peel Pigments Enhance Pasta Color Naturally

The incorporation of onion peel extract also transformed the pasta’s appearance. The extract’s anthocyanins—natural pigments responsible for red and purple hues in plants—imparted a rich, reddish-brown color to the pasta.

Using a Hunter Lab Colorimeter (a device that quantifies color in terms of lightness, redness, and yellowness), researchers quantified these changes.

In raw pasta, lightness (L*) decreased from 72.3 to 58.1 as extract concentration increased, while redness (a*) rose from 2.1 to 12.5. Yellowness (b*), on the other hand, declined from 28.4 to 18.9, shifting the color toward deeper, earthier tones. When cooked, some color loss occurred due to anthocyanins leaching into boiling water.

For example, redness (a*) dropped by approximately 15% after cooking.

Despite this, the pasta retained its visual appeal, with total color change (ΔE) (a metric quantifying overall color difference) increasing steadily with higher extract concentrations.

This natural coloring eliminates the need for synthetic dyes like Red 40, aligning with the growing demand for clean-label products (foods with simple, natural ingredients).

Improving Pasta Texture and Cooking Efficiency Naturally

The study revealed nuanced effects on cooking quality. Pasta with higher extract concentrations cooked slightly faster—7.01 minutes for control versus 6.33 minutes for 8% extract—likely due to fiber disrupting the gluten network (the protein structure that gives pasta its elasticity).

This disruption allows quicker water absorption. However, this structural change also increased gruel loss (the percentage of solids lost into cooking water), which rose from 4.55% in control pasta to 6.33% at 8% extract, though it remained within acceptable limits (<10%) for pasta quality.

Water absorption index (WAI) (a measure of how much water pasta retains) improved significantly, increasing by 35% in pasta with 8% extract, resulting in a softer, more tender bite.

Conversely, the water solubility index (WSI) (a measure of dissolved solids during cooking) also rose slightly, indicating minor starch leakage during cooking. These findings suggest that while onion peel extract enhances tenderness, careful formulation is needed to maintain structural integrity.

The Science Behind Onion Peel Pasta’s Improved Digestibility

Advanced imaging techniques provided deeper insights into how onion peel extract alters pasta’s structure. Scanning electron microscopy (SEM) revealed that control pasta had a smooth, continuous gluten-starch matrix.

In contrast, pasta with 8% extract showed a porous structure with exposed starch granules, explaining the higher gruel loss.

• X-ray diffraction (XRD) further confirmed structural changes, with crystallinity (the degree of ordered structure in starch) dropping from 37.85% in control pasta to 27.34% at 8% extract. T

his reduction indicates disrupted starch helices, which may improve digestibility. Differential scanning calorimetry (DSC), a technique that measures heat flow in materials, showed that gelatinization temperatures  increased from 62.65°C in control pasta to 82.71°C at 8% extract, suggesting enhanced heat stability.

Enthalpy (ΔH) (the energy required for gelatinization) decreased from 1.04 J/g to 0.58 J/g, implying less energy is needed to cook the pasta. These thermal properties make the product more efficient to prepare while retaining its nutritional benefits.

Consumer Preferences for Health-Focused Onion Peel Pasta

Sensory panels played a crucial role in determining consumer acceptability. Participants rated pasta with 4% extract highest for overall acceptability (8.4/9), praising its balanced color, mild flavor, and firm texture.

At 8% extract, however, scores dropped significantly (6.0/9) due to a stronger onion flavor and darker color. Texture scores also declined at higher concentrations, with some panelists noting a slightly crumbly mouthfeel.

These results underscore the importance of moderation—while 4% extract delivers optimal sensory appeal, higher concentrations cater to niche markets prioritizing health over taste.

Extending Shelf Life with Onion Peel-Enhanced Pasta

Storage studies demonstrated the pasta’s resilience under accelerated conditions (45°C, 90% humidity) over 60 days. Color changes were minimal, with lightness (L) decreasing by 5–7% and redness (a) increasing by 3–5%.

Cooking quality remained stable, with gruel loss increasing only marginally (e.g., from 6.33% to 6.52% at 8% extract). Water absorption and solubility indices saw negligible changes, confirming the product’s shelf stability.

These findings suggest that onion peel extract not only enhances nutrition but also contributes to longer shelf life, reducing food waste further.

Challenges and Practical Solutions

Despite its promise, the study identified challenges. At higher concentrations (6–8%), the pasta’s texture became crumbly, and its onion-like flavor intensified. To address this, the team proposed optimizing extrusion parameters, such as reducing screw speed, to preserve the gluten network.

Adding natural binding agents like egg white or plant gums could also improve texture. For flavor masking, herbs like oregano or sweeteners like honey might balance the bitterness.

Cost efficiency is another consideration. Ultrasonic extraction, while effective, is energy-intensive. The researchers suggested using solar drying for peel preparation or partnering with food processors to collect waste peels, reducing raw material costs.

Broader Implications for the Food Industry

This research has far-reaching implications. By repurposing onion peel waste, the food industry could reduce global agricultural waste by 15–20%, aligning with sustainability goals like the United Nations’ Sustainable Development Goals (SDGs).

The extract’s natural pigments offer a safe alternative to synthetic dyes, catering to clean-label trends (demand for transparent, simple ingredient lists). Nutritionally enhanced pasta could appeal to health-conscious consumers, particularly those managing diabetes or cardiovascular conditions.

Conclusion

The study exemplifies how innovation can turn waste into wealth. Onion peel extract transforms ordinary pasta into a nutrient-dense, visually appealing, and eco-friendly product. With 4% extract emerging as the optimal level for sensory acceptance, and higher concentrations suitable for niche markets, this research paves the way for a new generation of functional foods.

By addressing both environmental and health challenges, it sets a precedent for sustainable food systems where every meal contributes to planetary well-being. As consumers increasingly prioritize sustainability and nutrition, such breakthroughs will play a vital role in shaping the future of food.