Antimicrobial activity of hydroxytyrosol: a current controversy

Valorization of Olive Pomace Using Ultrasound-Assisted Extraction for Application in Active Packaging Films

Bioactive compounds that can be recovered by the solid wastes of the olive oil sector, such as polyphenols, are known for their significant antioxidant and antimicrobial activities with potential application in nutraceutical, cosmetic, and food industries. Given that industrial demands are growing, and the polyphenol market value is ever increasing, a systematic study on the recovery of natural antioxidant compounds from olive pomace using ultrasound-assisted extraction (UAE) was conducted. Single-factor parameters, i.e., the extraction solvent, time, and solid-to-liquid ratio, were investigated evaluating the total phenolic content (TPC) recovery and the antioxidant activity of the final extract. The acetone-water system (50% v/v, 20 min, 1:20 g mL-1) exhibited the highest total phenolic content recovery (168.8 ± 5.5 mg GAE per g of dry extract). The olive pomace extract (OPE) was further assessed for its antioxidant and antibacterial activities. In DPPH, ABTS, and CUPRAC, OPE exhibited an antioxidant capacity of 413.6 ± 1.9, 162.72 ± 3.36 and 384.9 ± 7.86 mg TE per g of dry extract, respectively. The antibacterial study showed that OPE attained a minimum inhibitory activity (MIC) of 2.5 mg mL-1 against E. coli and 10 mg mL-1 against B. subtilis. Hydroxytyrosol and tyrosol were identified as the major phenolic compounds of OPE. Furthermore, active chitosan-polyvinyl alcohol (CHT/PVA) films were prepared using different OPE loadings (0.01-0.1%, w/v). OPE-enriched films showed a dose-dependent antiradical scavenging activity reaching 85.7 ± 4.6% (ABTS) and inhibition growth up to 81% against B. subtilis compared to the control film. Increased UV light barrier ability was also observed for the films containing OPE. These results indicate that OPE is a valuable source of phenolic compounds with promising biological activities that can be exploited for developing multifunctional food packaging materials.

Polyphenol-Rich Extracts from Agroindustrial Waste and Byproducts: Results and Perspectives According to the Green Chemistry and Circular Economy

Polyphenols are natural secondary metabolites found in plants endowed with multiple biological activities (antioxidant, anti-inflammatory, antimicrobial, cardioprotective, and anticancer). In view of these properties, they find many applications and are used as active ingredients in nutraceutical, food, pharmaceutical, and cosmetic formulations. In accordance with green chemistry and circular economy strategies, they can also be recovered from agroindustrial waste and reused in various sectors, promoting sustainable processes. This review described structural characteristics, methods for extraction, biological properties, and applications of polyphenolic extracts obtained from two selected plant materials of the Mediterranean area as olive (Olea europaea L.) and pomegranate (Punica granatum L.) based on recent literature, highlighting future research perspectives.

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.

Preventing Microbial Growth in Game Meat by Applying Polyphenolic Extracts from Olive Mill Vegetation Water

We studied the efficacy of different formulations of polyphenol extracts (mainly containing hydroxytyrosol and tyrosol) from olive mill vegetation water on the microflora on the surfaces of game meat cuts with high or low initial bacterial loads. Meat with a high microbial load (>5 Log cfu/g; mean value = 6.83 ± 0.45 standard deviation) was immersed for 10 or 60 sec into 25% and 10% solutions of microencapsulated freeze-dried and non-encapsulated polyphenolic extracts. Aerobic colony, Enterobacteriaceae, Pseudomonas spp., and lactic acid bacteria counts were determined on treated samples compared to controls after 7 days of storage (in vacuum-packed conditions at +3 °C). Significant differences were registered only for aerobic colony count for a 10% liquid extract treatment (0.64 log reduction). In contrast, the dipping or immersion of game meat with low initial microbial loads (<5 Log cfu/g; mean value = 3.58 ± 0.72 standard deviation) in 10% solutions of the polyphenol extracts effectuated significant reductions in all bacteria counts (p < 0.002) at 7 and 14 days of storage for different extracts, independently from the application methods. The use of the extracts to inhibit bacterial growth in game meat should only be considered if a good hygienic baseline is guaranteed.

An Engineered Plant Metabolic Pathway Results in High Yields of Hydroxytyrosol Due to a Modified Whole-Cell Biocatalysis in Bioreactor

Hydroxytyrosol (HT) is a phenolic substance primarily present in olive leaves and olive oil. Numerous studies have shown its advantages for human health, making HT a potentially active natural component with significant added value. Determining strategies for its low-cost manufacturing by metabolic engineering in microbial factories is hence still of interest. The objective of our study was to assess and improve HT production in a one-liter bioreactor utilizing genetically modified Escherichia coli strains that had previously undergone fed-batch testing. Firstly, we compared the induction temperatures in small-scale whole-cell biocatalysis studies and then examined the optimal temperature in a large volume bioreactor. By lowering the induction temperature, we were able to double the yield of HT produced thereby, reaching 82% when utilizing tyrosine or L-DOPA as substrates. Hence, without the need to further modify our original strains, we were able to increase the HT yield.

A Novel Microbial Consortia Catalysis Strategy for the Production of Hydroxytyrosol from Tyrosine

Hydroxytyrosol, a valuable plant-derived phenolic compound, is increasingly produced from microbial fermentation. However, the promiscuity of the key enzyme HpaBC, the two-component flavin-dependent monooxygenase from Escherichia coli, often leads to low yields. To address this limitation, we developed a novel strategy utilizing microbial consortia catalysis for hydroxytyrosol production. We designed a biosynthetic pathway using tyrosine as the substrate and selected enzymes and overexpressing glutamate dehydrogenase GdhA to realize the cofactor cycling by coupling reactions catalyzed by the transaminase and the reductase. Additionally, the biosynthetic pathway was divided into two parts and performed by separate E. coli strains. Furthermore, we optimized the inoculation time, strain ratio, and pH to maximize the hydroxytyrosol yield. Glycerol and ascorbic acid were added to the co-culture, resulting in a 92% increase in hydroxytyrosol yield. Using this approach, the production of 9.2 mM hydroxytyrosol was achieved from 10 mM tyrosine. This study presents a practical approach for the microbial production of hydroxytyrosol that can be promoted to produce other value-added compounds.

Exploring Olive Pomace for Skincare Applications: A Review

The cosmetic industry is continuously searching for new active ingredients in an effort to attend to consumer demands which, in recent years, are focused on more natural and environmentally friendly products, obtained from sustainable resources. Nevertheless, they are required to provide cosmetologically appealing skincare products, ultimately with the purpose of improving skin appearance. The olive oil industry generates a large amount of liquid and semi-solid by-products such as olive pomace. Their phytotoxicity impairs safe disposal, so valorization strategies that promote by-product reuse are needed, which may include skincare products. Hydroxytyrosol is the main phenolic compound present in olive pomace and possesses biological effects that make it a desirable active compound for cosmetic formulations such as antioxidant and anti-aging activities as well as photoprotector, depigmenting, antimicrobial and anti-inflammatory actions. Other compounds present in olive pomace can also have functional properties and skin-related benefits. However, the application of this by-product can be a challenge in terms of formulation’s design, stability, and proven efficacy, so appropriate methodologies should be used to validate its incorporation and may include extraction and further encapsulation of bioactive compounds in order to achieve effective and aesthetic appealing skincare products.

Olive Leaf as a Source of Antibacterial Compounds Active against Antibiotic-Resistant Strains of Campylobacter jejuni and Campylobacter coli

Campylobacter spp. are the main cause of bacterial gastroenteritis worldwide, and broiler chicks are the main vector of transmission to humans. The high prevalence of Campylobacter in poultry meat and the increase of antibiotic resistant strains have raised the need to identify new antimicrobial agents. For this reason, the aim of the current study was to evaluate the antibacterial activity of two extracts of olive leaf against antibiotic-resistant Campylobacter strains (C. jejuni and C. coli) isolated from poultry food chain. The extracts of olive leaf (E1 and E2) were markedly different in their chemical compositions. While E1 was composed predominantly of highly hydrophilic compounds such as hydroxytyrosol and hydroxytyrosol glucosides (14,708 mg/100 g), E2 mainly contained moderately hydrophilic compounds, with oleuropein (20,471 mg/100 g) being prevalent. All Campylobacter strains exhibited similar antibiotic profiles, being resistant to ciprofloxacin and tetracycline. E1 showed strong antibacterial activity and reduced bacterial growth from 4.12 to 8.14 log CFU/mL, depending on the strain. Hydroxytyrosol was the main compound responsible, causing the inhibition of growth of Campylobacter strains at low concentrations (0.1-0.25 mg/mL). E2 demonstrated a lower antibacterial effect than E1, reducing growth from 0.52 to 2.49 log CFU/mL. The results of this study suggest that the optimization of the composition of olive-leaf extracts can provide improved treatment results against Campylobacter strains.

Phenols recovered from olive mill wastewater as natural booster to fortify blood orange juice

In the present study, a tangential membrane filtration system was applied to recover phenols from olive mill wastewater. The obtained concentrates were characterised for physico-chemical traits, antioxidant activity and antimicrobial effects. Results indicated that the highest concentration of hydroxytyrosol (7203.7 mg/L) was detected in the concentrate obtained by reverse osmosis, which also showed the highest antioxidant and antimicrobial activity. Moreover, the same concentrate was added, at different ratio, up to 4:250 v/v, into a commercial blood orange juice. The fortified juice with the addition of the concentrate, up to 2:250 v/v ratio, did not show off-flavour and off-odour compared to the control. Furthermore, after 60 days of refrigerated storage, the fortified juice exhibited a hydroxytyrosol content still complying with the daily intake recommended by EFSA health claim. The obtained results can be industrially useful in producing orange juice added with a natural antioxidant concentrate as a 'clean label' ingredient.

Modern vision of the Mediterranean diet

The Mediterranean diet is the most well-known and researched dietary pattern worldwide. It is characterized by the consumption of a wide variety of foods, such as extra-virgin olive oil (EVOO), legumes, cereals, nuts, fruits, vegetables, dairy products, fish, and wine. Many of these foods provide several phytonutrients, among which polyphenols and vitamins play an important role. Data from several studies have strongly established that nutrition is a key factor in promoting a healthy lifestyle and preventing many chronic diseases. In particular, a large number of studies have established the protective effects of the Mediterranean diet against several chronic diseases, among which are diabetes, cardiovascular diseases, cancer, aging disorders, and against overall mortality. Animal and human translational studies have revealed the biological mechanisms regulating the beneficial effects of the traditional Mediterranean diet. Indeed, several studies demonstrated that this nutritional pattern has lipid-lowering, anticancer, antimicrobial, and anti-oxidative effects. Moreover, the Mediterranean diet is considered environmentally sustainable. In this review, we describe the composition of the Mediterranean diet, assess its beneficial effects, and analyze their epigenomic, genomic, metagenomic, and transcriptomic aspects. In the future it will be important to continue exploring the molecular mechanisms through which the Mediterranean diet exerts its protective effects and to standardize its components and serving sizes to understand more precisely its effects on human health.

Production of biologically active hydroxytyrosol rich extract via catalytic conversion of tyrosol

An effective and economical process was established to produce hydroxytyrosol, a naturally occurring orthodiphenolic antioxidant molecule found in olive oil from its monophenolic precursor tyrosol. The approach proposed in the present work presents an environment-friendly method based on wet hydrogen peroxide catalytic oxidation with montmorillonite KSF as an inexpensive and environmentally benign solid acid at room temperature. The influence of the principal operating parameters including concentration of tyrosol, H₂O₂, and catalyst used were studied. The antioxidant activity was realized by the 2,2-diphenyl-1-picrylhydrazyl (DPPH) method. High antioxidant activity was detected according to the high hydroxytyrosol production (IC₅₀ = 0.7 μg mL⁻¹). The bactericidal and fungicidal properties of hydroxytyrosol rich extract were investigated using the NCCLS broth dilution and EN 1276 standard methods. Positive bactericidal and fungicidal effects of concentrations ranging between 1–0.5 g L⁻¹ and 4–2 g L⁻¹ were obtained.

An effective and economical process was established to produce hydroxytyrosol, a natural antioxidant molecule.

Olive-Leaf Extracts Modulate Inflammation and Oxidative Stress Associated with Human H. pylori Infection

Helicobacter pylori (H. pylori) is one of the major human pathogens and the main cause of pathological damages that can progress from chronic gastritis to gastric cancer. During the colonization of gastric mucosa, this bacterium provokes a strong inflammatory response and subsequent oxidative process, which are associated with tissue damage. Therefore, the objective of this research was to evaluate the ability of two olive-leaf extracts (E1 and E2) to modulate the inflammatory response and oxidative stress in H. pylori-infected human gastric AGS cells. The obtained results showed that both extracts significantly decreased interleukin-8 (IL-8) secretion and reactive oxygen species (ROS) production in human gastric AGS cells. Both extracts also showed antibacterial activity against different H. pylori strains. HPLC-PAD-MS characterization demonstrated that extract E1 was mainly composed of highly hydrophilic compounds, such as hydroxytyrosol (HT) and its glucosides, and it was the most effective extract as an antibacterial agent. In contrast, extract E2 was composed mostly of moderately hydrophilic compounds, such as oleuropein (OLE), and it was more effective than extract E1 as an anti-inflammatory agent. Both extracts exhibited similar potential to decrease ROS production. These results show the importance of standardizing the extract composition according to the bioactive properties that should be potentiated.

Chemical Composition and Antimicrobial Activity of a New Olive Pomace Functional Ingredient

Olive pomace, an olive oil processing byproduct, can be upcycled and meet the current demand for natural and sustainable food ingredients. In this work, a patented process was used to obtain a functional ingredient from different olive pomaces. The nutritional, chemical and antioxidant profiles, as well as the antimicrobial activity against S. aureus, E. coli and C. albicans, were investigated for the first time. The amount of phenolics ranged between 3.1 and 3.8 g gallic acid eq./100 g in all samples and flavonoids between 2.0 and 3.2 g catechin eq/100 g. No significant differences were found regarding the antioxidant activity. The total fat varied between 5 and 11%, α-tocopherol being the major vitamer and oleic acid the main fatty acid. The protein and ash contents were 1–4% and 10–17%, respectively. The functional ingredient with a higher hydroxytyrosol content (220 mg/100 g) also presented the best minimal inhibitory concentration against the tested bacteria. No activity against C. albicans was verified. This new functional ingredient presents the potential to be used as a natural preservative or as a nutritional profile enhancer. Moreover, it can be an advantageous ingredient in food products, since it comprises specific lipid and hydrophilic bioactive compounds usually not present in other plant extracts.

Valorisation of Olea europaea L. Olive Leaves through the Evaluation of Their Extracts: Antioxidant and Antimicrobial Activity

Olea europaea L. leaves constitute a source of bioactive compounds with recognized benefits for both human health and technological purposes. In the present work, different extracts from olive leaves were obtained by the application of two extraction methods, Soxhlet and microwave-assisted extraction (MAE), and six solvents (distilled water, ethanolic and glycerol mixtures solvents). MAE was applied under 40, 60 and 80 °C for 3, 6.5 and 10 min. The effect of the extraction method, solvent and treatment factors (the latter in MAE) on the total phenol content (TPC), the antioxidant activity (AA) and the phenolic profile of the extracts were all evaluated. The extracts showed high values of TPC (up to 76.1 mg GAE/g DW) and AA (up to 78 mg TE/g DW), with oleuropein being the most predominant compound in all extracts. The Soxhlet extraction method exhibited better yields in TPC than in MAE, although both methods presented comparable AA values. The water MAE extract presented the strongest antimicrobial activity against five foodborne pathogens, with minimum inhibitory concentration (MIC) values ranging from 2.5 to 60 mg/mL. MAE water extract is proposed to be exploited in the food and nutraceutical industry in the frame of a sustainable economy.

XRD and ATR-FTIR techniques for integrity assessment of gamma radiation sterilized cortical bone pretreated by antioxidants

Terminal sterilization of bone allograft by gamma radiation is required to reduce the risk of infection. Free radical scavengers could be utilized to minimize the deteriorating effects of gamma radiation on bone allograft mechanical properties. The objective of this research is to assess the changes in structural and chemical composition induced by hydroxytyrosol (HT) and alpha lipoic acid (ALA) free radical scavengers in gamma sterilized cortical bone. Bovine femurs specimens were soaked in different concentrations of HT and ALA for 7 and 3 days respectively before irradiation with 35 KGy gamma radiation. The attenuated total reflection-Fourier transform infrared spectroscopy and the X-ray diffraction techniques were utilized to analyze the changes in chemical composition induced by irradiation in the presence of free radical scavengers. A significant increase in the proportion of amide I and amide II to phosphate was noticed in the irradiated group, while in the pretreated groups with ALA and HT this effect was minimized. In addition, gamma radiation reduced the mature to immature cross links while ALA and HT alleviated this reduction. No significant changes were noticed in the mineral crystallinity or crystal size. Bone chemical structure has been changed due to gamma irradiation and these changes are mainly relevant to amide I, amide II proportions and collagen crosslinks. The deteriorating effects of gamma sterilization dose (35 kGy) on chemical structure of bone allograft can be alleviated by using (HT) and (ALA) free radical scavengers before irradiation.

Phenolic Compounds Obtained from Olea europaea By-Products and their Use to Improve the Quality and Shelf Life of Meat and Meat Products-A Review

Consumers are interested in consuming clean label foods. Replacing synthetic additives with natural alternatives (especially sources rich in polyphenols) is a valid solution to produce and also preserve foods, especially meat and meat products. Olea europaea leaves and olive pomace and wastewater contain polyphenols that can be explored in this context. In this review, we summarize the main aspects related to the phenolic composition, extraction conditions, antimicrobial potential, and antioxidant activity (in vitro and in vivo) of Olea europaea leaves, olive pomace and wastewater as well as their applications in the production of meat and meat products. This review found evidence that extracts and isolated polyphenols from the Olea europaea tree and olive processing by-products can be explored as natural antioxidant and antimicrobial additives to improve the preservation of meat and meat products. The polyphenols found in these residues (especially oleuropein, hydroxytyrosol and tyrosol) increased the redox state in the main meat-producing animals and, consequently, the oxidative stability of fresh meat obtained from these animals. Moreover, the extracts and isolated polyphenols also improved the shelf life of fresh meat and meat products (as additive and as active component in film) by delaying the growth of microorganisms and the progression of oxidative reactions during storage. The accumulated evidence supports further investigation as a natural additive to improve the preservation of reformulated muscle products and in the production of edible and sustainable films and coatings for fresh meat and meat products.

Molecular Action of Hydroxytyrosol in Wound Healing: An In Vitro Evidence-Based Review

Hydroxytyrosol (HT) is an essential molecule isolated from the phenolic fraction of olive (Olea europaea). HT has been implicated for its health-stimulating effect mainly due to its antioxidative capacity. The current review summarises and discusses the available evidence, related to HT activities in wound healing enhancement. The literature search of related articles published within the year 2010 to 2020 was conducted using Medline via Ebscohost, Scopus, and Google Scholar databases. Studies were limited to in vitro research regarding the role of HT in wound closure, including anti-inflammation, antimicrobial, antioxidative, and its direct effect to the cells involved in wound healing. The literature search revealed 7136 potentially relevant records were obtained from the database search. Through the screening process, 13 relevant in vitro studies investigating the role of HT in wound repair were included. The included studies reported a proangiogenic, antioxidative, antiaging, anti-inflammatory and antimicrobial effect of HT. The current in vitro evidence-based review highlights the cellular and molecular action of HT in influencing positive outcomes toward wound healing. Based on this evidence, HT is a highly recommended bioactive compound to be used as a pharmaceutical product for wound care applications.

Role of Antioxidant Molecules and Polymers in Prevention of Bacterial Growth and Biofilm Formation

Background:

Antioxidants are multifaceted molecules playing a crucial role in several cellular functions. There is by now a well-established knowledge about their involvement in numerous processes associated with aging, including vascular damage, neurodegenerative diseases and cancer. An emerging area of application has been lately identified for these compounds in relation to the recent findings indicating their ability to affect biofilm formation by some microbial pathogens, including Staphylococcus aureus, Streptococcus mutans, and Pseudomonas aeruginosa.

Methods:

A structured search of bibliographic databases for peer-reviewed research literature was performed using a focused review question. The quality of retrieved papers was appraised using standard tools.

Results:

One hundred sixty-five papers extracted from pubmed database and published in the last fifteen years were included in this review focused on the assessment of the antimicrobial and antibiofilm activity of antioxidant compounds, including vitamins, flavonoids, non-flavonoid polyphenols, and antioxidant polymers. Mechanisms of action of some important antioxidant compounds, especially for vitamin C and phenolic acids, were identified.

Conclusion:

The findings of this review confirm the potential benefits of the use of natural antioxidants as antimicrobial/antibiofilm compounds. Generally, gram-positive bacteria were found to be more sensitive to antioxidants than gram-negatives. Antioxidant polymeric systems have also been developed mainly derived from functionalization of polysaccharides with antioxidant molecules. The application of such systems in clinics may permit to overcome some issues related to the systemic delivery of antioxidants, such as poor absorption, loss of bioactivity, and limited half-life. However, investigations focused on the study of antibiofilm activity of antioxidant polymers are still very limited in number and therefore they are strongly encouraged in order to lay the foundations for application of antioxidant polymers in treatment of biofilm-based infections.

Healthspan Enhancement by Olive Polyphenols in C. elegans Wild Type and Parkinson's Models

Parkinson's disease (PD) is the second most prevalent late-age onset neurodegenerative disorder, affecting 1% of the population after the age of about 60 years old and 4% of those over 80 years old, causing motor impairments and cognitive dysfunction. Increasing evidence indicates that Mediterranean diet (MD) exerts beneficial effects in maintaining health, especially during ageing and by the prevention of neurodegenerative disorders. In this regard, olive oil and its biophenolic constituents like hydroxytyrosol (HT) have received growing attention in the past years. Thus, in the current study we test the health-promoting effects of two hydroxytyrosol preparations, pure HT and Hidrox® (HD), which is hydroxytyrosol in its "natural" environment, in the established invertebrate model organism Caenorhabditis elegans. HD exposure led to much stronger beneficial locomotion effects in wild type worms compared to HT in the same concentration. Consistent to this finding, in OW13 worms, a PD-model characterized by α-synuclein expression in muscles, HD exhibited a significant higher effect on α-synuclein accumulation and swim performance than HT, an effect partly confirmed also in swim assays with the UA44 strain, which features α-synuclein expression in DA-neurons. Interestingly, beneficial effects of HD and HT treatment with similar strength were detected in the lifespan and autofluorescence of wild-type nematodes, in the neuronal health of UA44 worms as well as in the locomotion of rotenone-induced PD-model. Thus, the hypothesis that HD features higher healthspan-promoting abilities than HT was at least partly confirmed. Our study demonstrates that HD polyphenolic extract treatment has the potential to partly prevent or even treat ageing-related neurodegenerative diseases and ageing itself. Future investigations including mammalian models and human clinical trials are needed to uncover the full potential of these olive compounds.

Antibacterial Activity of Three Extra Virgin Olive Oils of the Campania Region, Southern Italy, Related to Their Polyphenol Content and Composition

Production of extra virgin olive oil (EVOO) represents an important element for the economy of Southern Italy. Therefore, EVOO is recognized as a food with noticeable biological effects. Our study aimed to evaluate the antimicrobial activity exhibited by the polyphenolic extracts of EVOOs, obtained from three varieties of Olea europea L. (Ruvea antica, Ravece, and Ogliarola) cultivated in the village of Montella, Avellino, Southern Italy. The study evaluated the inhibiting effect of the extracts against some Gram-positive and Gram-negative bacteria. Statistical analysis, used to relate values of antimicrobial activity to total polyphenols and phenolic composition, revealed a different behavior among the three EVOO polyphenol extracts. The method applied could be useful to predict the influence of singular metabolites on the antimicrobial activity.

Chemical, physical and biotechnological approaches to the production of the potent antioxidant hydroxytyrosol

Hydroxytyrosol (HT) is a polyphenol of interest to the food, feed, supplements and pharmaceutical sectors. It is one of the strongest known natural antioxidants and has been shown to confer other benefits such as anti-inflammatory and anti-carcinogenic properties, and it has the potential to act as a cardio- and neuroprotectant. It is known to be one of the compounds responsible for the health benefits of the Mediterranean diet. In nature, HT is found in the olive plant (Olea europaea) as part of the secoiridoid compound oleuropein, in its leaves, fruit, oil and oil production waste products. HT can be extracted from these olive sources, but it can also be produced by chemical synthesis or through the use of microorganisms. This review looks at the production of HT using plant extraction, chemical synthesis and biotechnological approaches.

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.

Olive Leaves Extract from Algerian Oleaster (Olea europaea var. sylvestris) on Microbiological Safety and Shelf-life Stability of Raw Halal Minced Beef during Display

Oleaster (wild olive tree) by-products represent a renewable and low-cost source of biopolyphenols. Leaf extracts (sylv.OLE) of Algerian oleaster, locally called a'hachad (Olea europaea subsp. europaea var. sylvestris), were applied at 1 and 5% (v/w) to raw Halal minced beef (HMB) in order to test its safety and shelf-life prolongation during retail/display. The total phenolic compound content in the extract was 198.7 ± 3.6 mg gallic acid equivalent. Ten compounds were identified in the sylv.OLE by High Performance Liquid Chromatography/Diode Array Detector (HPLC/DAD), of which oleuropein was the most abundant (43.25%). Samples treated with 5% sylv.OLE had significantly higher antimicrobial and antioxidant effects than those treated with 1% extract (p < 0.05). The addition of sylv.OLE reduced psychrotrophic counts as well as the level of pathogens (Salmonella enterica ser. Enteritidis and Shiga toxin-producing Escherichia coli O157:H7). A thiobarbituric acid reactive substance (TBARS) value of 2.42 ± 0.11 was reached throughout six days of retail/display in control samples, while the addition of 5% sylv.OLE reduced TBARS value by 58% (p < 0.05). The presence of sylv.OLE at the tested concentrations did not negatively influence the overall acceptability and bitterness of HMB.

Hydroxytyrosol (HT) Analogs Act as Potent Antifungals by Direct Disruption of the Fungal Cell Membrane

Fungal infections constitute an emerging threat and a prevalent health problem due to increasing number of immunocompromised people and pharmacological or other treatments aiming at viral infections, cancer or allergies. Currently used antifungals suffer from inefficiency, toxic side effects and developing drug-resistance. Additionally, over the last two decades no new classes of antifungals have been approved, emphasizing the urgent need for developing a novel generation of antifungals. Here, we investigate the antifungal activity of a series of chemically synthesized Hydroxytyrosol (HT) analogs. HT is one of the major phenolic compounds in olive oil, shown to possess radical-scavenging antioxidant, antiproliferative, proapoptotic and anti-inflammatory activities. No previous report has studied HT analogs as antifungals. We show that specific analogs have broad and strong antifungal activity, significantly stronger than the parent compound HT. Using Aspergillus nidulans as an in vivo cellular model system, we show that antifungal HT analogs have an unprecedented efficiency in fungal plasma membrane destruction. Importantly, antifungal HT analogs did not show toxicity in a mammalian cell line, whereas no resistance to HT analogs was obtained by standard mutagenesis. Our results open the way for the development of a novel, efficient and safer class of antifungals.

Modulation by hydroxytyrosol of oxidative stress and antitumor activities of paclitaxel in breast cancer

PURPOSE

The main objective of this study was to test the therapeutic potential of hydroxytyrosol and its combination with paclitaxel in breast cancer on oxidative stress status.

METHODS

Impact on proliferation rates of different chemotherapy administration patterns was assayed in MCF-7 and MDA-MB-231 breast cancer cell lines. Breast tumor-bearing rats were randomly assigned to Control, Hydroxytyrosol, Paclitaxel and Paclitaxel plus hydroxytyrosol groups, for 6 weeks. Tumor volume, cell proliferation and several systemic oxidative stress parameters were measured. Anti-proliferative activity in vitro experiments was correlated with in vivo experiments.

RESULTS

Combination group did significantly reduce tumor volume when compared with paclitaxel alone. Additionally, the combination improved the antioxidant status without compromising the antitumor activity of standard chemotherapy.

CONCLUSION

These findings reveal for the first time that hydroxytyrosol is an active partner in combined therapies with paclitaxel against breast cancer. Combination with hydroxytyrosol would also ensure a less oxidative impact of chemotherapeutic drugs that could potentially improve patient wellness.

Thermal Decomposition Behavior of Hydroxytyrosol (HT) in Nitrogen Atmosphere Based on TG-FTIR Methods

The thermal decomposition behavior of olive hydroxytyrosol (HT) was first studied using thermogravimetry (TG). Cracked chemical bond and evolved gas analysis during the thermal decomposition process of HT were also investigated using thermogravimetry coupled with infrared spectroscopy (TG-FTIR). Thermogravimetry-Differential thermogravimetry (TG-DTG) curves revealed that the thermal decomposition of HT began at 262.8 °C and ended at 409.7 °C with a main mass loss. It was demonstrated that a high heating rate (over 20 K·min⁻¹) restrained the thermal decomposition of HT, resulting in an obvious thermal hysteresis. Furthermore, a thermal decomposition kinetics investigation of HT indicated that the non-isothermal decomposition mechanism was one-dimensional diffusion (D1), integral form g(x) = x², and differential form f(x) = 1/(2x). The four combined approaches were employed to calculate the activation energy (E = 128.50 kJ·mol⁻¹) and Arrhenius preexponential factor (ln A = 24.39 min⁻¹). In addition, a tentative mechanism of HT thermal decomposition was further developed. The results provide a theoretical reference for the potential thermal stability of HT.

Modulation of intestinal epithelium homeostasis by extra virgin olive oil phenolic compounds

Extra virgin olive oil polyphenols concentrate at the intestinal level and, by modulating the microbiota, oxidative status and inflammation, contribute to prevent the onset or delay the progression of inflammatory/degenerative diseases.

Hydroxytyrosol: Bioavailability, toxicity, and clinical applications

Many beneficial properties have been attributed to the Mediterranean diet. Over the years, researchers have attempted to learn which foods and which food components are responsible for good health. One of these components is hydroxytyrosol, an important phenolic compound present in olive oil. Hydroxytyrosol is a molecule of high interest to the pharmaceutical industry due to its anti-inflammatory and antimicrobial qualities its role against cardiovascular diseases and metabolic syndrome and for its neuroprotection, antitumour, and chemo modulation effects. The interest in this molecule has led to wide research on its biological activities, its beneficial effects in humans and how to synthetize new molecules from hydroxytyrosol. This review describes the vast range of information about hydroxytyrosol, focusing on its involvement in biological mechanisms and modulation effects on different pathologies. This review also serves to highlight the role of hydroxytyrosol as a nutraceutical and as a potential therapeutic agent.

Preparation, Characterization, and Antioxidant Activity Evaluation of Liposomes Containing Water-Soluble Hydroxytyrosol from Olive

Due to the multiple hydroxyl groups in its structure, hydroxytyrosol (HT) is very sensitive to air and light and has very strong instability and hydrophilicity that affect its biological activity. This study attempted to prepare liposomes containing water-soluble HT to improve the bioavailability and biocompatibility of the target drug. The preparation process factors (temperature, mass ratio of phospholipid (PL) and cholesterol (CH), Tween-80 volume, HT mass) were studied and response surface methodology (RSM) was applied to optimize the conditions. The results demonstrated that by using a temperature of 63 °C, mass ratio of PL and CH 4.5:1, HT mass 5 mg and Tween-80 volume of 6 mL, HT liposomes with an encapsulation efficiency (EE) of 45.08% were prepared. It was found that the particle sizes of the HT liposomes were well distributed in the range of 100–400 nm. Compared to free HT, prepared HT liposomes had better stability and a distinct slow release effect in vitro. Besides, HT liposomes presented better DPPH radical scavenging activity than free HT, which could be due to the fact that HT was encapsulated fully inside the liposomes. In addition, the encapsulation mechanism of HT was evaluated. In summary, the results indicated that HT liposome could enhance the antioxidant activity and was a promising formulation for prolonging the biological activity time of the target drug.

Antimicrobial activity of Olea europaea Linné extracts and their applicability as natural food preservative agents

The antimicrobial activity of phenolic compounds from Olea (O.) europaea Linné (L.) is part of the scientific discussion regarding the use of natural plant extracts as alternative food preservative agents. Although, the basic knowledge on the antimicrobial potential of certain molecules such as oleuropein, hydroxytyrosol or elenolic acid derivatives is given, there is still little information regarding their applicability for food preservation. This might be primarily due to the lack of information regarding the full antimicrobial spectrum of the compounds, their synergisms in natural or artificial combinations and their interaction with food ingredients. The present review accumulates available literature from the past 40 years, investigating the antimicrobial activity of O. europaea L. derived extracts and compounds in vitro and in food matrices, in order to evaluate their food applicability. In summary, defined extracts from olive fruit or leaves, containing the strongest antimicrobial compounds hydroxytyrosol, oleacein or oleacanthal in considerable concentrations, appear to be suitable for food preservation. Nonetheless there is still need for consequent research on the compounds activity in food matrices, their effect on the natural microbiota of certain foods and their influence on the sensorial properties of the targeted products.