The application of hydroxytyrosol in low-fat foods

As a natural polyphenolic compound, hydroxytyrosol exhibits dual potential to replace synthetic preservatives and optimize sensory quality in low-fat food systems due to its antioxidant and antibacterial activities. The following analysis covers action mechanisms, application scenarios, and technical challenges:

I. Antiseptic and Antioxidant Mechanisms of Hydroxytyrosol: Foundation for Natural Substitution of Synthetic Preservatives

Molecular Basis of Antibacterial Activity

The catechol structure of hydroxytyrosol disrupts microbial cell membrane integrity, inhibiting the reproduction of bacteria (e.g., E. coli, Staphylococcus aureus) by suppressing respiratory chain enzyme activity and biofilm formation in fungi (e.g., yeast). Studies show its minimum inhibitory concentration (MIC) against Gram-negative bacteria is ~0.1–0.5 mg/mL, comparable to common synthetic preservatives (such as potassium sorbate), but with a milder mechanism that rarely induces microbial drug resistance.

Antioxidant Synergy

In low-fat foods, lipid oxidation is the primary cause of rancidity and flavor deterioration. Hydroxytyrosol delays lipid peroxidation by scavenging free radicals (e.g., DPPH・, ABTS+・), chelating metal ions (e.g., Fe²+, Cu²+), and inhibiting lipoxygenase activity. Compared with traditional synthetic antioxidants (such as BHT), its antioxidant capacity is more prominent in aqueous systems (ORAC value ~17,000 μmol/g) and meets the "clean label" demand.

II. Application in Low-Fat Dairy Products: Solving the Dual Contradiction of Flavor and Antisepsis

Sensory Optimization and Antiseptic Strategy for Low-Fat Yogurt

Technical Path for Preservative Substitution: Traditional low-fat yogurt (fat content <1.5%) tends to have a thin texture due to reduced fat and is more susceptible to contamination by non-lactic acid bacteria. Adding 0.05–0.1% hydroxytyrosol (which can be compounded with tea polyphenols) improves viscosity through hydrophobic interactions between phenolic substances and milk proteins, while inhibiting psychrophilic bacteria (e.g., Pseudomonas), extending shelf life to 21 days (7 days longer than the control group).

Flavor Regulation Mechanism: Hydroxytyrosol has a slight bitter taste, but it can be metabolized by lactic acid bacteria into phenolic acids (such as hydroxyphenylacetic acid) during fermentation, enhancing the mellow taste of yogurt and offsetting the "watery" sensation caused by low fat. Attention should be paid to controlling the addition amount, as excessive addition (>0.15%) may lead to prominent astringency.

Anti-Browning and Antibacterial Application in Low-Fat Cheese

Low-fat cheese is prone to deterioration due to enzymatic browning (tyrosinase action) and mold contamination (e.g., Penicillium) during storage. Hydroxytyrosol inhibits browning by chelating enzyme cofactors (Cu²+), while its lipophilic phenolic ring structure penetrates the mold cell membrane to suppress spore germination. Italian scholars added 0.08% hydroxytyrosol to low-fat Mozzarella cheese, reducing the mold detection rate by 80% during shelf life, with better maintenance of cheese stretchability and color (ΔE value) than the control group.

III. Application in Low-Fat Meat Products: Inhibiting Oxidative Rancidity and Improving Texture

Antisepsis and Flavor Retention in Low-Fat Sausages

Potential to Replace Nitrite: Nitrite in traditional meat products has both antiseptic and color-preserving effects, but low-fat sausages experience faster heme oxidation, prone to "fading" and rancidity due to reduced fat. Hydroxytyrosol (0.03–0.06%) forms stable complexes with myoglobin to delay oxidative discoloration, while inhibiting anaerobic bacteria such as Clostridium botulinum (MIC 0.3 mg/mL). Studies show that low-fat sausages added with hydroxytyrosol have a thiobarbituric acid reactive substances (TBARS) value <0.5 mg/kg after storage at 4°C for 14 days, significantly lower than the untreated group (1.2 mg/kg).

Synergistic Effect of Texture Improvement: Hydroxytyrosol crosslinks with sulfhydryl groups of muscle proteins to compensate for reduced elasticity caused by low fat. A Spanish meat products enterprise compounded 0.05% hydroxytyrosol with 0.1% inulin in low-fat turkey sausages, reducing product hardness by 15% and increasing elasticity by 20%, with a taste close to traditional high-fat products.

Anti-Off-Flavor and Freshness Preservation in Ready-to-Eat Low-Fat Surimi Products

After defatting, surimi is more prone to releasing off-flavor substances (such as trimethylamine) and faces increased risk of halophilic bacteria contamination. The phenolic hydroxyl groups of hydroxytyrosol form hydrogen bonds with off-flavor substances to mask unpleasant flavors, while its antibacterial activity inhibits spoilage bacteria such as Shewanella (MIC 0.2 mg/mL). Adding 0.07% hydroxytyrosol to low-fat fish balls, combined with vacuum packaging, extends the shelf life with volatile basic nitrogen (TVB-N) value <15 mg/100g to 10 days (5 days in the control group), and improves sensory scores (flavor, elasticity) by 1–2 points.

IV. Application in Low-Fat Baked Goods: Delaying Oil Oxidation and Optimizing Texture

Antioxidant and Moisturizing Strategy for Low-Fat Cakes

Low-fat cakes have accelerated starch aging and reduced emulsion stability due to reduced oil. Hydroxytyrosol (0.02–0.04%) improves quality through the following mechanisms:

Antioxidation: Inhibits oxidation of unsaturated fatty acids (such as linoleic acid) in flour, keeping the acid value of cakes <1.5 mg KOH/g after 7 days of storage (2.8 mg KOH/g in the control group);

Moisturizing and Anti-Aging: The hydroxyl groups of phenolic substances form hydrogen bonds with water molecules, maintaining cake water activity (Aw) at 0.85–0.90, delaying starch recrystallization, and keeping the texture softer. A French baking brand added 0.03% hydroxytyrosol to low-fat sponge cakes, and blind tests showed no significant difference in consumer acceptance compared with high-fat cakes.

Prevention of Oil Rancidity and Brittleness Retention in Low-Fat Biscuits

Low-fat biscuits rely on oil to form a crisp structure, and defatting easily leads to softness due to insufficient starch gelatinization. Hydroxytyrosol (0.01–0.03%) compounded with emulsifiers (such as monoglycerides) forms stable lipid-phenolic complexes in dough, replacing partial oil functions. Studies show that low-fat biscuits added with 0.02% hydroxytyrosol have a breaking strength equivalent to the high-fat group (>30 N), and after storage at 30°C for 4 weeks, the peroxide value (PV) is <10 meq/kg, far lower than the untreated group (25 meq/kg).

V. Technical Challenges and Solutions in Application

Limitations of Water Solubility and Stability

Hydroxytyrosol has good water solubility (solubility ~5 g/L at 25°C), but it is easily oxidized and polymerized in acidic foods (such as juices with pH <3.5), causing color darkening.

Solution: Cyclodextrin embedding (β-CD:hydroxytyrosol = 10:1) improves its photostability and antioxidant efficiency. After embedding, the retention rate in acidic beverages stored for 3 months exceeds 85%.

Balance of Sensory Thresholds

The bitter taste threshold of hydroxytyrosol is about 0.08% (mass fraction), and excessive addition will affect food palatability.

Solution: Enzymatic modification (such as catalysis by glucosyltransferase) to generate hydroxytyrosol glycosides reduces bitterness by 70% while retaining over 60% of antibacterial activity (e.g., MIC against E. coli increases from 0.5 mg/mL to 0.8 mg/mL).

Cost and Large-Scale Production Issues

Currently, natural hydroxytyrosol is mainly extracted from olive pomace, with a high cost (~2,000 CNY/kg), limiting its application in low-price low-fat foods.

Alternative Plan: Using genetically engineered yeast (such as Saccharomyces cerevisiae) to express tyrosine hydroxylase, producing hydroxytyrosol by fermentation, with the cost reduced to below 500 CNY/kg. An Italian biotech company has achieved pilot production in a 500 L fermentation tank.

VI. Industry Trends and Regulatory Compliance

Clean Label and Functional Claims

The EU has approved hydroxytyrosol as a nutritional claim component with antioxidant function (daily intake ≥5 mg), and the US FDA classifies it as GRAS (Generally Recognized As Safe). Adding hydroxytyrosol to low-fat foods can simultaneously meet consumer demands for "no synthetic preservatives" and "rich in antioxidants". For example, a Spanish brand launched low-fat olive paste replacing sodium benzoate with hydroxytyrosol (0.05%), increasing its market share in the European organic food market by 12%.

Synergy with Other Natural Additives

Hydroxytyrosol compounded with organic acids (such as lactic acid) and plant essential oils (such as thymol) can enhance antiseptic effects through "multi-site antibacterial". For example, compounding 0.04% hydroxytyrosol + 0.1% lactic acid in low-fat salad dressing increases the inhibitory effect on Salmonella by 3 times compared with single use, and the sensory score (color, flavor) is 1.5 points higher than the potassium sorbate group.

Hydroxytyrosol provides a natural solution for replacing synthetic preservatives in low-fat foods through multiple functions of "antiseptic-antioxidant-sensory optimization". Its application requires adjusting dosage forms and doses according to food matrix characteristics (such as pH and water activity), and overcoming stability and taste challenges through embedding, enzyme modification, and other technologies. With the cost reduction of biosynthesis technology, hydroxytyrosol is expected to become a key functional factor for "clean label" upgrading in the low-fat food sector, promoting the development of functional low-fat foods towards safer and higher quality.