Olive leaves, one of the most abundant olive production by-products, have shown incredible potential for their characteristic bioactive compound composition, with unique compounds such as the polyphenol oleuropein. In order to evaluate the bioaccessibility of bioactive compounds present in an olive leaf extract, samples were submitted to an in vitro digestion process following INFOGEST protocol, and qualitative and quantitative characterization of the original extract and digestive samples at different times were carried out using HPLC-ESI-TOF-MS. The analyzed extract presented an abundance of phenolic compounds, such as secoiridoids, with oleuropein being the main identified compound. The in vitro digestion process showed an effect on the phenolic profile of the extract, with a lower recovery in the gastric phase and an increase at the beginning of the intestinal phase. Most of the studied compounds showed high bioaccessibility at the end of the digestion, with oleuropein, ligstroside, and quercetin-3-O-galactoside being among the ones with higher value. These findings show the potential for future use of olive leaf polyphenols. However, further research is needed in order to evaluate the absorption, delivery, and interaction of these compounds with the colon.

The olive oil industry generates by-products like olive leaves and pomace, which are rich in bioactive compounds, especially polyphenols. This study applied a circular economy approach to valorize these residues using green ultrasound-assisted extraction (UAE) with GRAS solvents. Key parameters (solvent composition, ultrasound amplitude, and specific energy) were optimized via Response Surface Methodology (RSM) to enhance polyphenol recovery and yield. Ethanol concentration proved to be the most influential factor. Optimal conditions for olive pomace were 100% ethanol, 46 μm amplitude, and 25 J∙mL⁻¹ specific energy, while olive leaves required 72% ethanol with similar ultrasound settings. Under these conditions, extracts were prepared and analyzed using HPLC-ESI-QTOF-MS and DPPH assays. The optimized UAE process achieved yields of 15–20% in less than 5 min and under mild conditions. Optimal extracts showed high oleuropein content (6 mg/g in leaves, 5 mg/g in pomace), lower hydroxytyrosol levels, and minimal oxidized derivatives, suggesting reduced degradation compared to conventional methods. These findings demonstrate UAE’s effectiveness in recovering valuable phenolics from olive by-products, supporting sustainable and efficient resource use.

Phenolic compounds have recently gained interest, as they have been related to improvements in health and disease prevention, such as inflammatory intestinal pathologies and obesity. However, their bioactivity may be limited by their instability or low concentration in food matrices and along the gastrointestinal tract once consumed. This has led to the study of technological processing with the aim of optimizing phenolic compounds’ biological properties. In this sense, different extraction systems have been applied to vegetable sources for the purpose of obtaining enriched phenolic extracts such as PLE, MAE, SFE, and UAE. In addition, many in vitro and in vivo studies evaluating the potential mechanisms of these compounds have also been published. This review includes a case study of the Hibiscus genera as an interesting source of phenolic compounds. The main goal of this work is to describe: (a) phenolic compound extraction by designs of experiments (DoEs) applied to conventional and advanced systems; (b) the influence of the extraction system on the phenolic composition and, consequently, on the bioactive properties of these extracts; and (c) bioaccessibility and bioactivity evaluation of Hibiscus phenolic extracts. The results have pointed out that the most used DoEs were based on response surface methodologies (RSM), mainly the Box–Behnken design (BBD) and central composite design (CCD). The chemical composition of the optimized enriched extracts showed an abundance of flavonoids, as well as anthocyanins and phenolic acids. In vitro and in vivo studies have highlighted their potent bioactivity, with particular emphasis on obesity and related disorders. This scientific evidence establishes the Hibiscus genera as an interesting source of phytochemicals with demonstrated bioactive potential for the development of functional foods. Nevertheless, future investigations are needed to evaluate the recovery of the phenolic compounds of the Hibiscus genera with remarkable bioaccessibility and bioactivity.

Phenolic compounds have become interesting bioactive antioxidant compounds with implications for obesity, cancer and inflammatory gastrointestinal pathologies. As the influence of digestion and gut microbiota on antioxidant behavior is yet to be completely elucidated, and due to limitations associated to in vivo studies, dynamic in vitro gastrointestinal models have been promoted. A systematic review was conducted of different databases (PubMed, Web of Science and Scopus) following PRISMA guidelines to assess different dynamic digestion models and assay protocols used for phenolic compound research regarding bioaccesibility and interaction with colonic microbiota. Of 284 records identified, those including dynamic multicompartmental digestion models for the study of phenolic compound bioaccesibility, bioactivity and the effects of microbiota were included, with 57 studies meeting the inclusion criteria. Different conditions and experimental configurations as well as administered doses, sample treatments and microbiological assays of dynamic digestion studies on polyphenols were recorded and compared to establish their relevance for the dynamic in vitro digestion of phenolic compounds. While similarities were observed in certain experimental areas, a high variability was found in others, such as administered doses. A description of considerations on the study of the digestion of phenolic compounds is proposed to enhance comparability in research.

Lyophilized plant-origin extracts are rich in highly potent antioxidant polyphenols. In order to incorporate them into food products, it is necessary to protect these phytochemicals from atmospheric factors such as heat, light, moisture, or pH, and to enhance their bioavailability due to their low solubility. To address these challenges, recent studies have focused on the development of encapsulation techniques for antioxidant compounds within polymeric structures. In this study, lyophilized olive leaf extracts were microencapsulated with the aim of overcoming the aforementioned challenges. The method used for the preparation of the studied microparticles involves external ionic gelation carried out within a water–oil (W/O) emulsion at room temperature. HPLC analysis demonstrates a high content of polyphenols, with 90% of the bioactive compounds encapsulated. Meanwhile, quantification by inductively coupled plasma optical emission spectroscopy (ICP-OES) reveals that the dried leaves, lyophilized extract, and microencapsulated form contain satisfactory levels of macro- and micro-minerals (calcium, potassium, sodium). The microencapsulation technique could be a novel strategy to harness the polyphenols and minerals of olive leaves, thus enriching food products and leveraging the antioxidant properties of the polyphenolic compounds found in the lyophilized extract.

The interest on the use of natural sources in the food industry has promoted the study of plants’ phenolic compounds as potential additives. However, the literature has been focusing on essential oils, with very few studies published regarding aqueous extracts, their phenolic composition, and bioactivity. A systematic review was conducted on different databases following PRISMA guidelines to evaluate the relevance of the phenolic content of different aromatic spices (oregano, rosemary, thyme, ginger, clove, and pepper), as related to their bioactivity and potential application as food additives. Although different extraction methods have been applied in the literature, the use of green approaches using ethanol and deep eutectic solvents has increased, leading to the development of products more apt for human consumption. The studied plants present an interesting phenolic profile, ranging from phenolic acids to flavonoids, establishing a correlation between their phenolic content and bioactivity. In this sense, results have proven to be very promising, presenting those extracts as having similar if not higher bioactivity than synthetic additives already in use, with associated health concerns. Nevertheless, the study of spices’ phenolic extracts is somehow limited to in vitro studies. Therefore, research in food matrices is needed for more understanding of factors interfering with their preservation activity.