Kinetic study of hydroxytyrosol oxidation and its related compounds by Red Globe grape polyphenol oxidase

Enhancement of the biological activity of hydroxytyrosol through its oxidation by laccase from Trametes versicolor

The laccase-catalyzed oxidation of hydroxytyrosol (HT) towards the formation of its bioactive oligomer derivatives was investigated. The biocatalytic oligomerization was catalyzed by laccase from Trametes versicolor in aqueous or various water-miscible organic solvents and deep eutectic solvent (DES)-based media. Mass Spectroscopy and Nuclear Magnetic Resonance were used for the characterization of the products. The solvent system used significantly affects the degree of HT oligomerization. The use of 50 % v/v methanol favored the production of the HT dimer, while other organic solvents as well as DESs led to the formation of hydroxytyrosol trimer and other oligomers. In vitro studies showed that the HT dimer exhibits 3- to 4-fold enhanced antibacterial activity against Gram-positive and Gram-negative bacteria compared to the parent compound. Moreover, the ability of HT dimer to inhibit the activity of soybean lipoxygenase and Candida rugosa lipase was 1.5-fold higher than HT, while molecular docking supported these results. Furthermore, HT dimer showed reduced cytotoxicity against HEK293 cells and exhibited a strong ability to inhibit ROS formation. The enhanced bioactivity of HT dimer indicates that this compound could be considered for use in cosmetics, skin-care products, and nutraceuticals.

Olive Polyphenol Oxidase Gene Family

The phenolic compounds containing hydroxytyrosol are the minor components of virgin olive oil (VOO) with the greatest impact on its functional properties and health benefits. Olive breeding for improving the phenolic composition of VOO is strongly dependent on the identification of the key genes determining the biosynthesis of these compounds in the olive fruit and also their transformation during the oil extraction process. In this work, olive polyphenol oxidase (PPO) genes have been identified and fully characterized in order to evaluate their specific role in the metabolism of hydroxytyrosol-derived compounds by combining gene expression analysis and metabolomics data. Four PPO genes have been identified, synthesized, cloned and expressed in Escherichia coli, and the functional identity of the recombinant proteins has been verified using olive phenolic substrates. Among the characterized genes, two stand out: (i) OePPO2 with its diphenolase activity, which is very active in the oxidative degradation of phenols during oil extraction and also seems to be highly involved in the natural defense mechanism in response to biotic stress, and (ii) OePPO3, which codes for a tyrosinase protein, having diphenolase but also monophenolase activity, which catalyzes the hydroxylation of tyrosol to form hydroxytyrosol.

Biocatalytic Approaches for an Efficient and Sustainable Preparation of Polyphenols and Their Derivatives

Many sectors of industry, such as food, cosmetics, nutraceuticals, and pharmaceuticals, have increased their interest in polyphenols due to their beneficial properties. These molecules are widely found in Nature (plants) and can be obtained through direct extraction from vegetable matrices. Polyphenols introduced through the diet may be metabolized in the human body via different biotransformations leading to compounds having different bioactivities. In this context, enzyme-catalyzed reactions are the most suitable approach to produce modified polyphenols that not only can be studied for their bioactivity but also can be labeled as green, natural products. This review aims to give an overview of the potential of biocatalysis as a powerful tool for the modification of polyphenols to enhance their bioaccessibility, bioavailability, biological activity or modification of their physicochemical properties. The main polyphenol transformations occurring during their metabolism in the human body have been also presented.

Enzymatic oxidation of oleuropein and 3-hydroxytyrosol by laccase, peroxidase, and tyrosinase

The oxidation of oleuropein and 3-hydroxytyrosol by oxidases laccase, tyrosinase, and peroxidase has been studied. The use of a spectrophotometric method and another spectrophotometric chronometric method has made it possible to determine the kinetic parameters Vmax and KM for each enzyme. The highest binding affinity was shown by laccase. The antioxidant capacities of these two molecules have been characterized, finding a very similar primary antioxidant capacity between them. Docking studies revealed the optimal binding position, which was the same for the two molecules and was a catalytically active position. PRACTICAL APPLICATIONS: One of the biggest environmental problems in the food industry comes from olive oil mill wastewater with a quantity of approximately 30 million tons per year worldwide. In addition, olive pomace, the solid residue obtained from the olive oil production, is rich in hydroxytyrosol and oleuropein and the action of enzymatic oxidases can give rise to products in their reactions that can lead to polymerization. This polymerization can have beneficial effects because it can increase the antioxidant capacity with potential application on new functional foods or as feed ingredients. Tyrosinase, peroxidase, and laccase are the enzymes degrading these important polyphenols. The application of a spectrophotometric method for laccase and a chronometric method, for tyrosinase and peroxidase, allowed us to obtain the kinetic information of their reactions on hydroxytyrosol and oleuropein. The kinetic information obtained could advance in the understanding of the mechanism of these important industrial enzymes.

Strategies to Broaden the Applications of Olive Biophenols Oleuropein and Hydroxytyrosol in Food Products

Oleuropein (OLE) and hydroxytyrosol (HT) are olive-derived phenols recognised as health-promoting agents with antioxidant, anti-inflammatory, cardioprotective, antifungal, antimicrobial, and antitumor activities, providing a wide range of applications as functional food ingredients. HT is Generally Recognised as Safe (GRAS) by the European Food Safety Authority (EFSA) and the Food and Drug Administration (FDA), whereas OLE is included in EFSA daily consumptions recommendations, albeit there is no official GRAS status for its pure form. Their application in food, however, may be hindered by challenges such as degradation caused by processing conditions and undesired sensorial properties (e.g., the astringency of OLE). Among the strategies to overcome such setbacks, the encapsulation in delivery systems and the covalent and non-covalent complexation are highlighted in this review. Additionally, the synthesis of OLE and HT derivatives are studied to improve their applicability. All in all, more research needs however to be carried out to investigate the impact of these approaches on the sensory properties of the final food product and its percussions at the gastrointestinal level, as well as on bioactivity. At last limitations of these approaches at a scale of the food industry must also be considered.

Application of Hydroxytyrosol in the Functional Foods Field: From Ingredient to Dietary Supplements

Hydroxytyrosol (HT) is an amphipathic functional phenol found in the olive tree, both in its leaves and fruits, in free or bound forms, as well as in olive oil and by-products of olive oil manufacture. The European Food Safety Authority recommends regular consumption of HT due to its several beneficial effects on human health, which are closely associated to its antioxidant activity. These reasons make HT an excellent candidate for application as a functional ingredient in the design of novel food products. Patents already exist for methodologies of extraction, purification, and application of HT in supplements and food products. The present review discusses the impact of HT incorporation on food properties and its effects on consumers, based on relevant data related to the use of HT as a functional ingredient, both as a pure compound or in the form of HT-rich extracts, in various food products, namely in edible oils, beverages, bakery products, as well animal-based foods such as meat, fishery and dairy products.

Catalytic and Structural Characterization of a Browning-Related Protein in Oriental Sweet Melon (Cucumis Melo var. Makuwa Makino)

Polyphenol oxidase (PPO) in plants plays an important role in browning reactions and may affect the quality of sweet melon products. In this study, a browning-related protein (BRP) with PPO activity was partially purified from oriental sweet melon (Cucumis melo var. makuwa Makino) by salt precipitation and column chromatography. The BRP possessed a high degree of identity with several chitinase proteins, particularly defense-related proteins, by MS identification. Pyrogallol was determined as the most appropriate substrate for BRP (K_m = 0.04278 M). BRP exhibited extreme resistance under alkaline and high temperature conditions when pyrogallol was used as substrate. Polyacrylamide gel electrophoresis (PAGE) analysis indicated that BRP was a homo-dimer of two subunits and had a molecular weight of 37 kDa. Structural analysis indicated that the α-helix was the dominant conformation of BRP. The active site of the protein might be buried deeply in the protein, and BRP might be monodispersed in an aqueous system.

The antioxidant hydroxytyrosol: biotechnological production challenges and opportunities

Hydroxytyrosol (HT) is a highly potent antioxidant originating in nature as a second metabolite of plants, most abundantly in olives (Olea europaea). In the last decade, numerous research studies showed the health benefits of antioxidants in general and those of HT in particular. As olive oil is a prime constituent of the health-promoting Mediterranean diet, HT has obtained recognition for its attributes, supported by a recent health claim of the European Food Safety Authority. HT is already used as a food supplement and in cosmetic products, but it has the potential to be used as a food additive and drug, based on its anticarcinogenic, anti-inflammatory, antiapoptotic and neuroprotective activity. Nevertheless, there is a large gap between the potential of HT and its current availability in the market due to its high price tag. In this review, the challenges of producing HT using biotechnological methods are described with an emphasis on the substrate source, the biocatalyst and the process parameters, in order to narrow the gap towards an efficient bio-based industrial process.

Determination of hydroxytyrosol and tyrosol by liquid chromatography for the quality control of cosmetic products based on olive extracts

An analytical method for the simultaneous determination of hydroxytyrosol and tyrosol in different types of olive extract raw materials and cosmetic cream samples has been developed. The determination was performed by liquid chromatography with UV spectrophotometric detection. Different chromatographic parameters, such as mobile phase pH and composition, oven temperature and different sample preparation variables were studied. The best chromatographic separation was obtained under the following conditions: C18 column set at 35°C and isocratic elution of a mixture ethanol: 1% acetic acid solution at pH 5 (5:95, v/v) as mobile phase pumped at 1 mL min(-1). The detection wavelength was set at 280 nm and the total run time required for the chromatographic analysis was 10 min, except for cosmetic cream samples where 20 min runtime was required (including a cleaning step). The method was satisfactorily applied to 23 samples including solid, water-soluble and fat-soluble olive extracts and cosmetic cream samples containing hydroxytyrosol and tyrosol. Good recoveries (95-107%) and repeatability (1.1-3.6%) were obtained, besides of limits of detection values below the μg mL(-1) level. These good analytical features, as well as its environmentally-friendly characteristics, make the presented method suitable to carry out both the control of the whole manufacture process of raw materials containing the target analytes and the quality control of the finished cosmetic products.