The application of hydroxytyrosol in functional foods

As the core functional component in olive oil, hydroxytyrosol demonstrates diverse application potentials in functional food development due to its unique antioxidant, anti-inflammatory, and cytoprotective activities. From natural olive oil matrices to dosage form innovations of high-purity supplements, its formula development must balance activity retention, bioavailability enhancement, and product stability. The following analysis covers application scenarios, technical challenges, and innovative strategies:

I. Functional Enhancement of Olive Oil Matrix: From Traditional Edible Oil to Functional Carrier

1. Optimization of Natural Content and Category Innovation

Variety and Process Regulation: Hydroxytyrosol content in olive oil is typically 5–50 mg/kg, closely related to olive varieties (e.g., Coratina, Arbequina), fruit maturity, and pressing processes. Cold-pressed extra virgin olive oil retains over 80% hydroxytyrosol due to no high-temperature treatment, while refined olive oil loses over 50% due to deacidification and decolorization processes. By screening high-polyphenol olive varieties (e.g., Greek "Koroneiki") and adopting low-temperature pressing + inert gas protection technology, hydroxytyrosol content in finished products can be increased to over 100 mg/kg, developing functional categories of "high-polyphenol olive oil".

Composite Functional Formulation: Blending olive oil with other antioxidant components (e.g., vitamin E, rosemary extract) enhances stability through synergistic effects. For example, adding 0.1% tea polyphenols reduces hydroxytyrosol degradation rate from 30% to 12% after storage at 60°C for 3 months, while endowing products with superimposed effects of "antioxidation + anti-inflammation".

2. Application Scenarios in Food Matrices

Bakery Food Improvement: Adding 5%–10% high-polyphenol olive oil to bread and biscuit formulas, hydroxytyrosol extends product shelf life by inhibiting lipoxygenase activity (acid value increase rate reduced by 40%). Meanwhile, its phenolic compounds undergo Maillard reactions with flour proteins, improving the color and flavor of baked goods.

Functional Oil Beverages: Microencapsulating olive oil to prepare oil-in-water (O/W) emulsions, forming a stable system by compounding dietary fiber (e.g., inulin) and emulsifiers (e.g., lecithin). For example, hydroxytyrosol microcapsule powder prepared by high-pressure homogenization (150 MPa) + spray drying technology has an encapsulation rate of over 90%, which can be directly added to fruit juices or plant-based beverages to achieve "water-soluble transformation of oil functional components".

II. High-Purity Hydroxytyrosol Supplements: From Active Ingredients to Dosage Form Innovation

1. Breakthroughs in Extraction and Purification Technologies

Green Extraction Processes: Traditional solvent extraction (methanol/water system) carries risks of solvent residues, while supercritical CO₂ extraction (35°C, 20 MPa) combined with molecular distillation technology enables efficient separation of hydroxytyrosol with purity over 98% and no organic solvent residues. Additionally, using olive leaf waste (e.g., leaf residue after juicing) through enzymatic hydrolysis (cellulase + pectinase) + macroporous adsorption resin purification reduces hydroxytyrosol extraction costs by 30%, promoting sustainable production of supplement raw materials.

2. Strategies for Improving Bioavailability of Oral Preparations

Nano Drug Delivery System Design: Poor water solubility (0.1 g/L) and significant first-pass effect (oral bioavailability only 10%–15%) of hydroxytyrosol limit its absorption efficiency. Preparing solid dispersions (e.g., hydroxytyrosol-PVP K30 coprecipitates) increases its dissolution rate by 5 times; or using liposome encapsulation (phospholipid-cholesterol molar ratio 3:1), when particle size is controlled at 100–200 nm, the intestinal lymphatic absorption pathway increases, and bioavailability is enhanced to over 30%.

pH-Sensitive Drug Release System: Given that hydroxytyrosol is easily degraded in the gastric acid environment (40% loss within 2 hours at pH 1.2), enteric coating technology (e.g., Eudragit L100-55) can be used to make the preparation disintegrate and release in the intestinal pH 6.8–7.4 environment, with activity retention over 90%. Clinical studies show that the plasma Cmax (peak concentration) of 100 mg enteric-coated hydroxytyrosol supplements is 2.3 times higher than that of ordinary capsules.

3. Diversification of Dosage Forms and Functional Positioning

Sports Nutrition Foods: For endurance athletes, develop energy gels containing 500 mg hydroxytyrosol. Its antioxidant properties can reduce exercise-induced muscle oxidative damage (serum creatine kinase levels reduced by 25%), and compounding with carbohydrates can enhance glycogen storage and improve exercise performance.

Aging Health Intervention: Make hydroxytyrosol and Omega-3 fatty acids into soft capsules for the prevention of Alzheimer's disease. Animal experiments show that 10 mg/kg hydroxytyrosol + 200 mg/kg EPA/DHA daily can reduce Aβ plaque deposition in the brains of APP/PS1 transgenic mice by 35%, with mechanisms related to inhibiting excessive activation of microglia and promoting tau protein dephosphorylation.

III. Technical Challenges and Solutions in Functional Food Development

1. Stability Problems and Protection Strategies

Oxidative Degradation Control: The phenolic hydroxyl groups of hydroxytyrosol are easily catalyzed and oxidized by oxygen, light, and metal ions in the air, leading to product discoloration (browning) and activity decline. Solutions include: ① adding chelating agents (e.g., EDTA-2Na) to complex metal ions; ② using nitrogen-filled packaging + light-proof containers (e.g., brown glass bottles); ③ low-temperature storage (≤4°C) to reduce oxidase activity. For example, when adding 0.05% hydroxytyrosol to nut bar formulas, combining with 0.02% vitamin C and 0.01% citric acid can increase activity retention rate from 50% to 85% within a 6-month storage period.

2. Balance Between Taste and Function

Bitter Taste Masking Technology: High-concentration hydroxytyrosol (>0.1%) has obvious bitter and astringent taste, affecting food palatability. Amorphous complexes can be formed by β-cyclodextrin inclusion (inclusion ratio 1:5) to mask bitter substances; or lactic acid bacteria fermentation (e.g., Lactobacillus bulgaricus) can be used to metabolize phenolic substances, generating flavor esters, while retaining over 60% antioxidant activity. When applied in yogurt products, this technology can increase the hydroxytyrosol addition amount from 0.05% to 0.2%, and consumer acceptance scores from 3.2 (on a 5-point scale) to 4.1.

3. Regulation and Safety Threshold Control

Safety Assessment of Intake: According to EFSA (European Food Safety Authority) assessment, the upper limit of safe daily intake of hydroxytyrosol is 1.2 mg/kg body weight (approximately 84 mg/day for a 70 kg adult), and exceeding this dose may cause gastrointestinal discomfort (such as diarrhea). Functional food labels must clearly indicate "recommended daily intake ≤50 mg" and avoid simultaneous administration with other polyphenol supplements. In addition, safety verification for special populations (such as 90-day feeding experiments) is required for pregnant women, lactating women, and people with liver and kidney dysfunction.

IV. Future Trends: From Single Component to Systemic Functional Regulation

1. Precision Nutrition and Personalized Formulations

Develop customized hydroxytyrosol products based on individual gut microbiota differences. Studies have found that people with high abundance of Akkermansia in the intestine have higher metabolic efficiency for hydroxytyrosol (urinary phenolic acid metabolite concentration increases by 2 times), and supplement dosage adjustment can be guided through microbiota detection to achieve precise matching of "dose-effect".

2. Plant-Based Substitution and Sustainable Production

In addition to olives, explore other plant resources with high hydroxytyrosol content (such as olive leaves, hydrolysis products of amygdalin), and heterologously express hydroxytyrosol synthase (such as tyrosine decarboxylase + phenolic hydroxylase) through synthetic biology technology (such as engineered E. coli), realizing microbial fermentation production, reducing dependence on olive oil raw materials, and simultaneously reducing agricultural waste emissions.

3. Strengthening Clinical Evidence for Functional Claims

Currently, health claims of hydroxytyrosol in foods are mostly based on in vitro experiments, and more human clinical trials (such as RCT studies) are needed to verify its efficacy. For example, for people with metabolic syndrome, carry out a study on "the effect of 100 mg hydroxytyrosol intervention daily for 12 weeks on blood glucose and blood lipids", providing a higher level of evidence support for product functional claims.

Conclusion: Functional Food Development of Hydroxytyrosol Requires Balancing Activity, Stability, and Compliance

The application development of hydroxytyrosol has extended from natural components of olive oil to precisely designed functional preparations, but technical bottlenecks such as bioavailability, stability, and taste need to be broken through. In the future, combining nano-delivery, synthetic biology, and precision nutrition concepts, it is necessary to build a full-chain development system of "sustainable raw materials - efficient dosage forms - clear functions", promoting its transformation from a natural antioxidant to a functional factor with disease prevention functions, while strictly following regulatory requirements to ensure consumer safety and product market compliance.