Hazelnut and Linseed Improve Lamb Meat Oxidative Stability

30

Red meat is known for its rich nutritional profile, including high-quality proteins, essential amino acids, and vital nutrients like vitamin B12 and iron. However, its association with health risks such as cardiovascular diseases and colorectal cancer has raised concerns.

One major factor behind these risks is lipid oxidation, a chemical process where fats in meat react with oxygen, heat, or metal ions like iron, leading to the formation of harmful compounds. During cooking or digestion, polyunsaturated fatty acids (PUFAs)—healthy fats found in meat—undergo oxidation, producing unstable molecules called lipid hydroperoxides.

These compounds break down further into advanced lipoxidation end-products (ALEs), such as malondialdehyde (MDA) and 4-hydroxynonenal (HNE), which are toxic and linked to DNA damage, inflammation, and chronic diseases. To address these challenges, researchers have focused on modifying animal diets to enhance the antioxidant capacity of meat.

Antioxidants are molecules that neutralize free radicals (unstable atoms that damage cells) and slow oxidation. A groundbreaking 2025 study published in Food Chemistry explored how adding hazelnut skins (a food industry byproduct) and extruded linseed (rich in omega-3 fatty acids) to lamb feed reduces harmful oxidation during cooking and digestion.

Implementation of the Experiment

The research team from Italian universities conducted a controlled experiment involving 40 male lambs of the Valle del Belice × Comisana breed. The lambs, aged 60 days, were divided into four groups and fed different diets for 60 days.

The first group received a standard maize-barley diet (control), while the others had portions of maize replaced with linseed (8%), hazelnut skins (15%), or a combination of both (7.5% hazelnut skins + 4% linseed).

  After the feeding period, the lambs were slaughtered, and samples from the Longissimus thoracis et lumborum muscle—a key cut of meat along the spine—were collected for analysis. The meat samples underwent cooking and in vitro digestion, a laboratory process that mimics human stomach and intestinal conditions to study how food breaks down. Key measurements included:

• Lipid Hydroperoxides: Measured using the FOX assay, a chemical test that detects peroxide compounds by reacting with ferrous ions.

• Thiobarbituric Acid-Reactive Substances (TBA-RS): A method to quantify MDA, a toxic ALE, by measuring its reaction with thiobarbituric acid.

• Phenolic Compounds and Metabolites: Identified using high-resolution mass spectrometry (UHPLC-ESI-Q Exactive Orbitrap), a precise technique to analyze complex molecules.

• Tocopherols (Vitamin E): Quantified in raw meat and feed using ultra-high-performance liquid chromatography (UHPLC).

Key Findings on Lipid Oxidation and Antioxidant Enhancement

The study revealed significant differences in oxidation markers and antioxidant content between the control and supplemented diets. For instance, raw meat from lambs fed hazelnut skins (H diet) contained 409.07 mg/100g of total phenolic compounds, compared to 306.33 mg/100g in the control group.

Phenolic compounds are plant-derived antioxidants that neutralize free radicals. Among these, hydroxybenzoic acids—a class of phenolics with strong antioxidant properties—were particularly abundant in the H diet, with one isomer reaching 14.02 mg/100g, nearly seven times higher than the control.

Flavanols, another critical antioxidant group found in hazelnut skins (e.g., procyanidins), were 100.60 mg/100g in the H diet, more than double the control group’s 40.77 mg/100g. Flavanols work by donating electrons to stabilize free radicals, preventing them from damaging fats in meat.

Tocopherols, a form of vitamin E, showed similar trends. The H diet provided 43.2 mg/kg of α-tocopherol and 57.8 mg/kg of γ-tocopherol, far exceeding the control diet’s 6.43 mg/kg and 15.7 mg/kg, respectively. Tocopherols are fat-soluble antioxidants that protect cell membranes from oxidative damage by interrupting the chain reaction of lipid peroxidation.

When assessing oxidation during cooking, meat from the control group showed a doubling of lipid hydroperoxides (from 8.50 ± 4.04 μmol H₂O₂/100g in raw meat to 17.2 ± 3.21 μmol H₂O₂/100g after cooking). However, diets supplemented with hazelnut skins, linseed, or both consistently produced lower levels of TBA-RS—a marker for toxic ALEs.

For example, raw meat from the H diet had 1.21 ± 0.08 μmol MDA/100g, a 40% reduction compared to the control’s 2.05 ± 0.12 μmol MDA/100g.

MDA is a well-studied ALE that forms DNA adducts, increasing cancer risk. The most striking results emerged during simulated digestion. In the gastric phase, lipid hydroperoxides in control meat spiked to 228.93 ± 5.92 μmol H₂O₂/100g, while the combination diet reduced this by 56% to 99.87 ± 4.15 μmol H₂O₂/100g.

By the intestinal phase, TBA-RS levels in control meat surged to 18.39 ± 1.29 μmol MDA/100g, but the HL diet lowered this by 23% to 14.11 ± 1.14 μmol MDA/100g. These findings highlight the synergistic effect of combining hazelnut skins and linseed, where their combined antioxidants provided stronger protection than either ingredient alone.

How Antioxidants in Lamb Feed Combat Harmful Oxidation

The study also identified specific antioxidant metabolites in meat. For example, 5-(hydroxy-methoxyphenyl)-γ-valerolactone, a breakdown product of hazelnut flavanols produced by gut microbiota, was 1.3 times higher in the H diet than in the control.

This metabolite inhibits oxidation by scavenging free radicals. Similarly, hydroxyphenyl-valeric acid (HPVA), a microbial metabolite derived from phenolic compounds, was twice as abundant in supplemented diets. HPVA is known to reduce inflammation and oxidative stress in cells.

Tocopherol metabolites like δ-CEHC (carboxyethyl-hydroxychroman) were 6.5 times higher in the H diet. CEHCs are end-products of vitamin E metabolism that retain antioxidant activity, further enhancing oxidative stability in meat. Additionally, endogenous antioxidants—naturally occurring compounds in meat—like carnosine and reduced glutathione increased significantly in supplemented diets.

Carnosine levels rose by 40% in the H and HL diets, while glutathione increased by 63% in the H diet. Carnosine is a dipeptide (a molecule made of two amino acids) that chelates metal ions like iron, preventing them from catalyzing oxidation. Glutathione, a tripeptide, neutralizes free radicals directly and recycles other antioxidants like vitamin E.

Health and Environmental Implications

From a health perspective, reducing lipid oxidation products like MDA is critical. These compounds form DNA adducts—abnormal bonds between DNA and chemicals—that interfere with genetic function and are linked to colon cancer. MDA also promotes atherosclerosis by oxidizing LDL cholesterol, making it more likely to accumulate in artery walls.

By lowering MDA levels, diets enriched with hazelnut skins and linseed could mitigate these risks. Furthermore, the higher vitamin E and peptide content in such meat enhances its nutritional value.

For example, α-tocopherol protects cell membranes, while carnosine has anti-aging properties and may reduce muscle fatigue.

Environmentally, repurposing hazelnut skins—a waste product from the food industry—reduces landfill use and methane emissions, a potent greenhouse gas. This approach aligns with circular economy principles, where waste materials are reused to create value.

For instance, hazelnut skins, which are typically discarded after nut processing, were transformed into a nutrient-rich feed ingredient. Replacing traditional crops like maize with linseed and hazelnut byproducts also lowers the carbon footprint of livestock farming by reducing the energy and resources needed for cultivation and transportation.

The Road Ahead And Conclusions

While the study’s results are promising, further research is needed. Human trials could confirm whether consuming antioxidant-enriched meat reduces plasma MDA levels or inflammation markers.  Long-term studies might explore cumulative benefits, such as reduced cancer incidence in populations consuming such meat. Additionally, similar strategies could be tested in poultry, pork, or beef production to assess broader applicability.

In conclusion, supplementing lamb diets with hazelnut skins and linseed represents a transformative approach to meat production. By reducing harmful oxidation products by up to 74%, these diets address health concerns while promoting sustainability.

For consumers, this means safer, nutrient-rich meat; for farmers, a cost-effective way to add value to agricultural waste. As the global demand for sustainable food grows, such innovations could redefine the future of meat production, making it healthier for people and the planet.