Bioactive and Antioxidant Differences in Sliced and Crushed Garlic

Garlic has been a beloved ingredient in kitchens and traditional medicine for thousands of years. Its sharp aroma and bold flavor make it a culinary staple, while its potential health benefits—ranging from boosting immunity to fighting infections—have earned it a place in natural remedies.

Modern science continues to uncover how garlic’s preparation and storage impact its nutritional value, and a groundbreaking 2025 study published in Applied Food Research offers clear answers. By analyzing how slicing, crushing, and drying affect garlic’s key compounds, this research provides practical insights for everyday cooking.

Why Garlic Preparation Impacts Nutritional Benefits

Garlic’s health benefits stem from sulfur-containing compounds like allicin, which forms when garlic is chopped, crushed, or sliced. Allicin is a volatile organosulfur compound celebrated for its antimicrobial, antioxidant, and anti-inflammatory properties.  However, it is highly unstable and breaks down quickly when exposed to heat, air, or time.

Alongside allicin, garlic contains pyruvic acid, a byproduct of enzymatic reactions that contributes to its pungent flavor, and phenolic compounds, a class of antioxidants that protect cells from oxidative damage.  These compounds degrade under certain conditions, making preparation and storage critical for preserving garlic’s nutritional value. The study by Rababah et al. compared three forms of garlic:

• fresh sliced,
• fresh crushed
• dried slices.

Each form was stored at two temperatures—4°C (refrigeration) and 20°C (room temperature)—for periods ranging from 10 minutes to 2 days. Using advanced laboratory techniques, the researchers measured changes in allicin, pyruvic acid, phenolic compounds, and antioxidant activity.

Additionally, sensory tests with 40 participants revealed how these changes translate to flavor and aroma in dishes like hummus. Together, these findings offer a roadmap for using garlic in ways that balance health benefits and taste.

How Garlic Processing Methods Were Tested Scientifically

The research team began by preparing fresh garlic into uniform slices and crushed paste. A portion of the sliced garlic was dried in an oven at 60°C for 24 hours to simulate commercial dehydration. Each form of garlic—sliced, crushed, and dried—was stored under 13 different conditions, combining time and temperature.

To measure key compounds, the team used precise methods. Allicin, the primary bioactive compound in garlic, was quantified using high-performance liquid chromatography (HPLC), a technique that separates and identifies chemicals in a mixture based on their interaction with a solvent and a stationary phase.

 Pyruvic acid, a marker of garlic’s pungency, was measured using a colorimetric assay involving a chemical reaction with dinitrophenylhydrazine, which changes color based on pyruvic acid concentration. Total phenolic content, which reflects antioxidant potential, was assessed using the Folin-Ciocalteu method, where phenols react with a reagent to produce a blue color whose intensity correlates with phenol levels.

Antioxidant activity was tested by evaluating how well garlic extracts neutralized free radicals using the DPPH (2,2-diphenyl-1-picrylhydrazyl) assay, a common method to measure a substance’s ability to scavenge harmful oxidative molecules.

For the sensory evaluation, 40 participants sampled hummus infused with garlic from each treatment. They rated the dishes on a scale of 1 to 9 for flavor, aroma, pungency, and appearance. This human element bridged the gap between lab data and real-world culinary experiences.

Key Findings on Garlic’s Allicin and Antioxidant Levels

1. Allicin Stability: The study revealed striking differences in allicin levels based on preparation and storage. Fresh crushed garlic had the highest allicin content, peaking at 32.14 mg/g after 10 minutes at room temperature (20°C).

In contrast, fresh sliced garlic reached a maximum of 17.51 mg/g under the same conditions, while dried garlic slices retained only 6.68 mg/g immediately after drying.  Over time, allicin degraded rapidly, especially at room temperature.

For example, crushed garlic stored for 2 days at 20°C retained just 0.60 mg/g of allicin—a 98% loss.

Refrigeration slowed this decline but did not stop it; crushed garlic kept at 4°C for 1 day retained 7.88 mg/g, compared to 4.80 mg/g at 20°C. The reason for these differences lies in how garlic is processed. Crushing ruptures more garlic cells than slicing, activating the enzyme allinase, which converts the precursor alliin into allicin.

Drying, however, exposes garlic to heat, which destroys both the enzyme and the compounds needed for allicin formation. These findings highlight the importance of using fresh garlic and minimizing storage time.

2. Pyruvic Acid and Flavor Intensity: Pyruvic acid, responsible for garlic’s sharp taste, followed a similar pattern. Fresh crushed garlic had the highest levels, reaching 30.77 µmol/g after 10 minutes at 4°C. Sliced garlic followed closely, while dried garlic lagged far behind, with levels as low as 10.12 µmol/g after 2 days at 20°C.

Refrigeration again proved beneficial, preserving pyruvic acid better than room temperature. For instance, crushed garlic stored at 4°C for 10 minutes retained 30.77 µmol/g, compared to 30.50 µmol/g at 20°C. Drying, however, reduced pyruvic acid by 64%, underscoring its negative impact on flavor.

3. Phenolic Compounds and Antioxidants: While crushed garlic excelled in allicin and pyruvic acid, sliced garlic retained more phenolic compounds and antioxidants. Fresh sliced garlic had 91.05 mg GAE/100g of total phenols (measured as gallic acid equivalents), nearly three times higher than crushed garlic (29.10 mg GAE/100g).

Antioxidant activity followed suit, with sliced garlic showing 53.89% radical scavenging activity compared to 34.65% in crushed garlic. Dried garlic performed poorly, with phenolic content and antioxidant activity dropping by over 80% and 63%, respectively.

The explanation lies in cellular damage. Crushing releases enzymes like polyphenol oxidase, which oxidize phenolic compounds, reducing their potency. Slicing causes less damage, preserving these antioxidants. Heat from drying further degrades these sensitive compounds, making fresh garlic the clear winner for nutritional value.

4. Sensory Evaluation: The sensory tests provided practical insights. Participants preferred hummus made with fresh crushed garlic stored for 10 minutes at 20°C, rating it highest for flavor, aroma, and overall appeal.

This treatment struck a balance between pungency and freshness. Dried garlic, despite its intense flavor, scored lower due to bitter, burnt notes. Hummus without garlic received neutral ratings, confirming that garlic enhances both taste and enjoyment.

The Chemistry Behind Garlic’s Health Compounds

Allicin’s Instability: Allicin’s instability is rooted in its chemistry. When garlic is crushed or sliced, the enzyme allinase converts alliin (a stable, odorless compound) into allicin.

However, allicin reacts quickly with oxygen and heat, breaking down into less beneficial compounds like diallyl disulfides and ajoenes. This explains why allicin levels peak shortly after preparation and decline rapidly. Refrigeration slows but does not stop this process, as enzymes remain active at low temperatures.

Phenolic Compounds and Oxidation: Phenolic compounds, such as flavonoids and phenolic acids, are vulnerable to oxidation. Crushing releases enzymes like polyphenol oxidase, which accelerates their degradation. Slicing minimizes this damage, preserving antioxidants. Heat from drying destroys both enzymes and phenolic compounds, making dried garlic nutritionally inferior.

Pyruvic Acid as a Pungency Marker: Pyruvic acid is a byproduct of the enzymatic breakdown of alliin into allicin. Its concentration correlates with garlic’s pungency and flavor intensity. Higher pyruvic acid levels indicate stronger flavor, but excessive pungency can overwhelm the palate, as seen in dried garlic samples.

Best Methods to Preserve Garlic Nutrients in Cooking

To apply these findings in your kitchen, consider the following:

1. Crush Garlic for Maximum Allicin: Use a garlic press to rupture more cells and activate allinase. Let the crushed garlic sit for 10 minutes at room temperature before cooking to allow allicin to form. Add it late in the cooking process to minimize heat exposure.

2. Slice Garlic for Antioxidants: When making salads, dressings, or cold dishes, thinly slice garlic to preserve phenolic compounds. Avoid crushing if antioxidants are your priority.

3. Avoid Drying: Fresh garlic retains significantly more nutrients than dried versions. If long-term storage is needed, freeze crushed garlic in olive oil instead of dehydrating it.

4. Refrigerate for Short-Term Storage: While refrigeration slows nutrient loss, use crushed or sliced garlic within a day for best results.

5. Balance Flavor and Nutrition: For dishes like hummus or sauces, combine fresh crushed garlic with acidic ingredients like lemon juice to stabilize allicin and enhance flavor.

Conclusion

The study by Rababah et al. confirms that garlic’s preparation is both an art and a science. Crushing maximizes allicin, slicing preserves antioxidants, and freshness is non-negotiable. Dried garlic, while convenient, loses up to 90% of its bioactive compounds, making it a poor substitute for fresh.

By aligning your cooking habits with these insights—crushing for health benefits, slicing for antioxidants, and avoiding prolonged storage—you can transform garlic into a targeted health booster and flavor enhancer. Whether you’re crafting a gourmet meal or seeking natural remedies, these strategies ensure you unlock garlic’s full potential.

• Source: https://cultivationag.com/bioactive-and-antioxidant-differences-in-sliced-and-crushed-garlic/