Olive oil and its principal bioactive compound: Hydroxytyrosol – A review of the recent literature

Design of immobilized biocatalyst and optimal conditions for tyrosol β-galactoside production

Tyrosol β-galactoside (TG) is a phenylethanoid glycoside with proven neuroprotective properties. This work deals with its biocatalytic production from tyrosol and lactose using Aspergillus oryzae β-galactosidase in immobilized form. Six commercial carriers were examined to find the optimal biocatalyst. Besides standard biocatalyst performance characteristics, adsorption of the hydrophobic substrate on immobilization carrier matrices was also investigated. The adsorption of tyrosol was significant, but it did not have adverse effects on TG production. On the contrary, TG yield was improved for some biocatalysts. A biocatalyst prepared by covalent binding of β-galactosidase on an epoxy-activated carrier was used for detailed investigation of the effect of reaction conditions on glycoside production. Temperature had a surprisingly weak effect on the overall process rate. A lactose concentration of 0.83 M was found to be optimal to enhance TG formation. The impact of tyrosol concentration was rather complex. This substrate caused inhibition of all reactions. Its concentration had a strong effect on the hydrolysis of lactose and all products. Higher tyrosol concentrations, 30-40 g/L, were favorable as pseudo-equilibrium concentrations of TG and galactooligosaccharide were reached. Repeated batch results revealed excellent operational stability of the biocatalyst.

Transrutinosylation of tyrosol by flower buds of Sophora japonica

Dried flower buds of Japanese sophora (Sophora japonica) comprising rutinosidase activity were tested in rutinosylation of tyrosol via transglycosylation process from rutin. Optimal conditions for transrutinosylation of tyrosol were 49 mM rutin and 290 mM tyrosol, giving maximum conversion up to 66.4% and 24% yield of isolated and purified rutinoside. The rutinosylation proceeded exclusively on the primary hydroxyl of tyrosol, thus forming rhamnosylated derivative of salidroside. This strict regioselectivity differentiates the sophora biocatalyst from microbial rutinosidases.

The biological activities of the spiderworts (Tradescantia)

Widely used throughout the world as traditional medicine for treating a variety of diseases ranging from cancer to microbial infections, members of the Tradescantia genus show promise as sources of desirable bioactive compounds. The bioactivity of several noteworthy species has been well-documented in scientific literature, but with nearly seventy-five species, there remains much to explore in this genus. This review aims to discuss all the bioactivity-related studies of Tradescantia plants and the compounds discovered, including their anticancer, antimicrobial, antioxidant, and antidiabetic activities. Gaps in knowledge will also be identified for future research opportunities.

Delivery Systems for Hydroxytyrosol Supplementation: State of the Art

This review aims to highlight the benefits and limitations of the main colloid-based available delivery systems for hydroxytyrosol. Hydroxytyrosol is a phenolic compound with clear biological activities for human wellness. Olive fruits, leaves and extra-virgin oil are the main food sources of hydroxytyrosol. Moreover, olive oil mill wastewaters are considered a potential source to obtain hydroxytyrosol to use in the food industry. However, recovered hydroxytyrosol needs adequate formulations and delivery systems to increase its chemical stability and bioavailability. Therefore, the application of hydroxytyrosol delivery systems in food sector is still a fascinating challenge. Principal delivery systems are based on the use of colloids, polymers able to perform gelling, thickening and stabilizing functions in various industrial sectors, including food manufacturing. Here, we review the recipes for the available hydroxytyrosol systems and their relative production methods, as well as aspects relative to system characteristics and hydroxytyrosol effectiveness.

An integrated approach to improve plant protection against olive anthracnose caused by the Colletotrichum acutatum species complex

The olive tree (Olea europaea L.) is the most important oil-producing crop of the Mediterranean basin. However, although plant protection measures are regularly applied, disease outbreaks represent an obstacle towards the further development of the sector. Therefore, there is an urge for the improvement of plant protection strategies based on information acquired by the implementation of advanced methodologies. Recently, heavy fungal infections of olive fruits have been recorded in major olive-producing areas of Greece causing devastating yield losses. Thus, initially, we have undertaken the task to identify their causal agent(s) and assess their pathogenicity and sensitivity to fungicides. The disease was identified as the olive anthracnose, and although Colletotrichum gloeosporioides and Colletotrichum acutatum species complexes are the two major causes, the obtained results confirmed that in Southern Greece the latter is the main causal agent. The obtained isolates were grouped into eight morphotypes based on their phenotypes, which differ in their sensitivities to fungicides and pathogenicity. The triazoles difenoconazole and tebuconazole were more toxic than the strobilurins being tested. Furthermore, a GC/EI/MS metabolomics model was developed for the robust chemotaxonomy of the isolates and the dissection of differences between their endo-metabolomes, which could explain the obtained phenotypes. The corresponding metabolites-biomarkers for the discrimination between morphotypes were discovered, with the most important ones being the amino acids L-tyrosine, L-phenylalanine, and L-proline, the disaccharide α,α-trehalose, and the phytotoxic pathogenesis-related metabolite hydroxyphenylacetate. These metabolites play important roles in fungal metabolism, pathogenesis, and stress responses. The study adds critical information that could be further exploited to combat olive anthracnose through its monitoring and the design of improved, customized plant protection strategies. Also, results suggest the necessity for the comprehensive mapping of the C. acutatum species complex morphotypes in order to avoid issues such as the development of fungicide-resistant genotypes.

Varietal Effect on the Concentration and Anti-Inflammatory Activity of Hydroxytyrosol in French Olive Oils

Numerous studies have been carried out on the bioactive properties of hydroxytyrosol (HT) in olive oils (OOs), although there are few reports comparing anti-inflammatory activity among different olive varieties or regions of production. The purpose of this study was to investigate the in vitro inflammatory action of HT in extracts of four OO varieties in the Languedoc region of the French Mediterranean. Factors other than cultivar were eliminated, which enabled unambiguous varietal differences to be identified. Purified extracts of OO were obtained using an optimized solid-phase extraction procedure by which only polar compounds were recovered. High performance liquid chromatography-photodiode array detection-tandem mass spectrometry was used to identify and quantify HT and oleacein in the extracts. The total polyphenol concentration ranged from 93.00 mg gallic acid equivalent/kg OO for Picholine to 27 mg gallic acid equivalent for Verdale OOs. The concentrations of HT in Picholine, Olivère, and Lucques varieties were 25.3, 18.8 and 12.1 mg/kg, respectively, whereas the concentration of HT in Verdale OOs was less, 1 mg/kg. The in vitro anti-inflammatory response of purified OO extracts, evaluated by the inhibition of nitric oxide release in lipopolysaccharide-induced interferon-γ activated J774.A1 macrophages, strongly correlated with total polyphenol content (R² > 0.995). The effect increased asymptotically between the equivalent of 2 and 37 mg of OO, reaching, at the maximum tested concentration, 90%, 75%, 62%, and 30% activity for Picholine, Olivière, Lucques, and Verdale, respectively. The results presented here clearly show that, by comparison with authentic standards, the activity of HT in OO extracts was enhanced in a concentration-dependent manner, varying from 3-fold at the highest extract concentration to over 6.5-fold at the lowest extract concentration. Therefore, the anti-inflammatory activity of OOs should be rationalized on the basis of whole extracts rather than solely on the concentration of HT or other bioactive compounds in OO.

Composition and Antibacterial Activity of Aronia melanocarpa (Michx.) Elliot, Cornus mas L. and Chaenomeles superba Lindl. Leaf Extracts

The purpose of this study was to investigate the composition of leaf extracts from Aronia melanocarpa, Chaenomeles superba, and Cornus mas, and their antimicrobial activity against typical spoilage-causing and pathogenic bacteria found in meat and meat products. The highest total phenolic content (TPC) was detected in C. superba extract, followed by C. mas and A. melanocarpa extracts. The antioxidant capacity of the extracts was measured by DPPH and ABTS assays. The lowest IC₅₀ values were found for C. superba extract, followed by C. mas and A. melanocarpa extracts. LC-MS and HPLC analysis revealed that A. melanocarpa and C. superba extracts contained hydroxycinnamic acid derivatives and flavonoids (mainly flavonols). Hydroxycinnamic acid derivatives were detected in the C. mas extract, as well as flavonols, ellagitannins, and iridoids. The antibacterial activity of the plant extracts was tested against Gram-negative bacteria (Moraxella osloensis, Pseudomonas fragi, Acinetobacter baumanii, Escherichia coli, Enterobacter aerogenes, Salmonella enterica) and Gram-positive bacteria (Enterococcus faecium, Staphylococcus aureus, Brochothrix thermosphacta, Lactobacillus sakei, Listeria monocytogenes) using the microculture method. The extracts acted as bacteriostatic agents, decreasing the growth rate (µ_max) and extending the lag phase (t_lag). C. mas showed most potent antibacterial activity, as confirmed by principal component analysis (PCA).

Efficient extraction and sensitive LC-MS quantification of hydroxytyrosol in wine, oil and plasma

Hydroxytyrosol (HT) possesses significant biological activity. However, the methodologies for its quantification always suffered from low sensitivity, intricate treatment and high sample consumption. Here, we presented the very first attempt for specific extraction of HT through cis-diol recognition mechanism. By using easily prepared zirconia as dispersive solid phase extraction medium, HT from small amount of wine (10 μL), oil (20 mg) and plasma (100 μL) was efficiently purified within ten minutes. Coupled with LC-MS/MS analysis, the method limit of detection (LOD) could reach 1 ng/mL in wine, 0.5 μg/kg in oil and 0.1 ng/mL in plasma. Profited by this superior method, HT analysis was successfully performed in diverse wine and oil products as well as human plasma samples after intake of extra virgin olive oil. In addition, we further confirmed the endogenous HT was undetectable from routine human plasma even after upgrading the detection sensitivity through post isonicotinoyl chloride derivatization.

Seeking for sensory differentiated olive oils? The urge to preserve old autochthonous olive cultivars

Mediterranean olive heritage richness is poorly characterized. Olive oils from minor cultivars of Northeast-Portugal (Lentisca, Madural, Rebolã, Redondal, Verdeal and Verdeal Transmontana) from centenarian trees were chemical and sensory characterized, aiming to identify autochthonous cultivars capable of producing differentiated olive oils. All oils, produced during two campaigns, were classified as extra virgin. Cv. Redondal showed the highest oxidative stability (OS), total phenols, vitamin E and C_18:1/C_18:2. Contrary, cv. Madural presented the lowest OS and C_18:1/C_18:2 ratios, supporting the importance of fatty acids on OS, while cv. Verdeal had the lowest total phenols and vitamin E contents. Sensory notes of tomato, apple, dry fruits, fresh herbs, tomato leaves and cabbage were predominant on the oils of most cultivars, whilst some attributes were more specific, such as banana and kiwi (Madural), cherry and apricot (cvs. Lentisca and Madural). The chemical and sensory diversity enabled the statistical discrimination of all cultivars and harvesting years.

Antidiabetic Effects of Hydroxytyrosol: In Vitro and In Vivo Evidence

Insulin resistance, a pathological condition characterized by defects in insulin action leads to the development of Type 2 diabetes mellitus (T2DM), a disease which is currently on the rise that pose an enormous economic burden to healthcare systems worldwide. The current treatment and prevention strategies are considerably lacking in number and efficacy and therefore new targeted therapies and preventative strategies are urgently needed. Plant-derived chemicals such as metformin, derived from the French lilac, have been used to treat/manage insulin resistance and T2DM. Other plant-derived chemicals which are not yet discovered, may have superior properties to prevent and manage T2DM and thus research into this area is highly justifiable. Hydroxytyrosol is a phenolic phytochemical found in olive leaves and olive oil reported to have antioxidant, anti-inflammatory, anticancer and antidiabetic properties. The present review summarizes the current in vitro and in vivo studies examining the antidiabetic properties of hydroxytyrosol and investigating the mechanisms of its action.

Characterization of Phenolic Compounds and Their Contribution to Sensory Properties of Olive Oil

Olive oil is not only known for its pungent, bitter, and fruity taste, but also for its health potential, which is often hypothesized to depend on its phenolic compounds. One hundred extra virgin olive oil samples (monocultivaric as well as blends of varieties) were assessed with regard to their sensory properties and phenolic compound composition. Nineteen phenolic compounds have been determined and correlated with sensory data. In all olive oil samples, oleocanthal and oleacein were the most abundant phenolic compounds, with average amounts of 77.9 mg/kg and 41.8 mg/kg, respectively. The highest correlation coefficient between a sensory descriptor and the phenolic compounds was found for the bitter taste sensation and the total phenolic content with r = 0.72 and in particular, for 3,4-DHPEA-EA, with r = 0.57. Intensity plots were assessed for the three main sensory descriptors fruitiness, bitterness, pungency, and for the quality factor harmony, which is associated with the degree of ripeness aroma of olive oil. Positive correlations for the aroma descriptors freshly cut grass, leaves, and nuts, and the phenolic compounds were especially observed for oleoside 11-methylester and vanillic acid. The present study provides a comprehensive database of phenolic compounds in olive oils from six different varieties and seven countries.

Hydroxytyrosol, Tyrosol and Derivatives and Their Potential Effects on Human Health

The Mediterranean diet and olive oil as its quintessential part are almost synonymous with a healthy way of eating and living nowadays. This kind of diet has been highly appreciated and is widely recognized for being associated with many favorable effects, such as reduced incidence of different chronic diseases and prolonged longevity. Although olive oil polyphenols present a minor fraction in the composition of olive oil, they seem to be of great importance when it comes to the health benefits, and interest in their biological and potential therapeutic effects is huge. There is a growing body of in vitro and in vivo studies, as well as intervention-based clinical trials, revealing new aspects of already known and many new, previously unknown activities and health effects of these compounds. This review summarizes recent findings regarding biological activities, metabolism and bioavailability of the major olive oil phenolic compounds—hydroxytyrosol, tyrosol, oleuropein, oleocanthal and oleacein—the most important being their antiatherogenic, cardioprotective, anticancer, neuroprotective and endocrine effects. The evidence presented in the review concludes that these phenolic compounds have great pharmacological potential, however, further studies are still required.