For centuries, olive leaves have been used both in traditional medicine for their health benefits and in the nutritional field for their excellent antioxidant properties. They have a high content of bioactive compounds, although two groups of substances stand out for their importance for human health: polyphenols and triterpenic acids (Medina et al., 2019).
These compounds have been shown to possess a wide range of beneficial properties, including antioxidant, anti-inflammatory, antimicrobial, antitumor, antihypertensive, and hypoglycemic effects, among others (Rufino-Palomares et al., 2022), making them a target of interest for the prevention and treatment of various pathologies.
In the project BIOLEAVES, led by Dr. Edward Medina of the Department of Food Biotechnology of the Instituto de la Grasa-CSIC of Seville, these Bioactive compounds present in olive leaves have been studied in depth, as well as their use in the preparation of healthy infusions.
In an initial study, the presence of bioactive compounds was analyzed in commercial samples of dried olive leaves, finding considerable variability among them. The main phenolic compound identified in olive leaves is the bitter substance oleuropein, which can constitute between 6% and 9% of the dry weight of the leaf, although other compounds emerge in smaller quantities such as hydroxytyrosol, tyrosol and caffeic acid, among others (Medina et al., 2019). On the other hand, even the triterpenic acids are very abundant, in particular oleanolic acid and maslinic acid (1,5-3%).
Furthermore, despite the high concentration of polyphenols in the leaves, Only a small fraction (about 20%) of these compounds is transferred to the water during the preparation of olive leaf infusions., with virtually no transfer of triterpenic acids. This work thus laid the foundation for further research aimed at better understanding the composition of olive leaves, as well as the factors that influence their degradation, with the aim of improving their quality and potential for human health.
Subsequently, a second study characterized eight Spanish olive leaf varieties: Aloreña, Cacereña, Empeltre, Hojiblanca, Manzanilla, Verdial, Gordal, and Morona (Ramirez et al., 2022). The most notable feature is the variability of these compounds depending on the cultivar and harvest season. For example, the leaves of the Manzanilla variety showed the highest concentration of oleuropein, while the leaves of the Gordal variety showed the highest content of triterpenic acids.
These findings not only provide a more complete view of the composition of olive leaves, but also open the way to new possibilities in terms of varietal selection and use of by-products in the olive oil industryThe study also explored the various enzymatic activities present in olive leaves: polyphenol oxidase, peroxidase, β-glucosidase, and esterase. These enzymes can influence the composition and concentration of bioactive compounds, implying a complex interplay between biological and chemical factors in the leaves.
Despite the promising potential of olive leaves, their incorporation into consumer products, particularly herbal teas, remains limited. Several challenges may arise, including the lack of standardized processing methods and variability in product quality.
Unlocking the Potential of Olive Leaves: Processing and Preparation
Il olive leaf dehydration process is crucial for preserve their bioactive compounds. During this drying phase, the leaves lose moisture and a concentration of bioactive compounds occurs present in them. However, it is essential to carefully monitor the process, since High temperatures can cause the degradation of phenolic compounds, negatively affecting the quality of the dried leaves.
To address these challenges, researchers have delved into the optimization of olive leaf processing, including theair drying forced air oven drying andinfrared drying (Ramirez et al., 2023). Research indicates that drying temperatures above 50°C lead to a decrease in phenol concentration. However, brief preliminary storage of the leaves at room temperature has been shown to mitigate the loss of phenols during the drying process. In this study, the most effective treatment was performed on leaves left at room temperature for 24 hours and then dried in the oven at 40°C for 15 hours, recovering 85% of the initial polyphenolsDehydration time can be halved when using infrared technology, assuming energy savings and a continuous system, although it does slightly increase phenol loss.
In addition to drying, the degree of grinding significantly influences the transfer of compounds and the color of the infusion. It has been observed that Finer grinds increase the release of bioactive compounds and give a more intense color. By perfecting the dehydration and grinding techniques, the researchers aim to produce dried olive leaves rich in phenolic compounds and triterpenic acids, offering consumers a tasty and nutritious infusion option.
Recently, a study was proposed to analyze the evolution of phenolic compounds in whole or crushed dried leaves during a year of storage. It was found that these compounds remained stable regardless of the format, therefore the leaves maintain their beneficial properties for the entire duration of storage. Furthermore, the influence of the infusion time and the temperature on the extraction of polyphenols, noting that, for the preparation of infusions, Optimal conditions of 100°C for 15 minutes maximize the extraction of phenolic compounds.
one of the disadvantages associated with olive leaf infusions is their bitter taste, related to thehigh concentration of the polyphenol oleuropein. Therefore, an evaluation of the acceptability of the infusions was conducted through a tasting conducted by a consumer panel. The sensory panel detected greater bitterness in the infusions containing higher levels of oleuropein, as expected, reaching a acceptability threshold of 144 mg/l. However, acceptability improved significantly when the infusions were sweetened, allowing higher concentrations of oleuropein, up to 212 mg/l, to be tolerated.
Thanks to all the results obtained by the BIOLEAVES project, we can conclude that Olive leaf infusions are set to have a significant impact on the beverage market, both used alone and in combination with other herbs. Furthermore, combined with future sensory evaluations, they will help better determine consumer preferences, paving the way for the development of high-quality olive leaf infusions.
The future of olive leaves
With growing awareness of the health benefits of natural products, interest in olive leaves and their applications is experiencing a significant resurgence. From healthy infusions to Dietary Supplements and personal care products, olive leaves offer a wide range of opportunities for innovation and the creation of products that promote health and well-being, extending their interest not only to the food industry, but also to the pharmaceutical and nutraceutical industries.
In short, the humble olive leaves are much more than a simple agricultural by-product. They represent a veritable treasure trove of bioactive compounds with great potential to improve our health and well-beingWith continued research and a focus on sustainability and quality, olive leaves can become a valuable ingredient in our collective quest for a healthier, more balanced lifestyle.
by Eduardo Medina Pradas, Eva María Ramírez Castro, Concepción Romero Barranco, Mercedes Brenes Álvarez and Manuel Brenes Balbuena,
Institute of Fat-CSIC
References
Medina, E.; Romero, C.; García, P.; Brenes, M. Characterization of bioactive compounds in commercial olive leaf extracts, olive leaves, and their infusions. Food & Function, 2019, 10, 4716.
Ramírez, E.M.; Brenes, M.; Romero, C.; Medina, E. Chemical and enzymatic characterization of leaves from Spanish table olive cultivars. Foods, 2022, 11, 3879.
Ramírez, E.M.; Brenes, M.; Romero, C.; Medina, E. Processing of olive leaves for infusion. Foods, 2023, 12, 591.
Rufino-Palomares, E.E.; Pérez-Jiménez, A.; García-Salguero, L.; Mokhtari, K.; Reyes-Zurita, F.J.; Peragón-Sánchez, J.; Lupiáñez, J.A. Nutraceutical role of polyphenols and triterpenes present in Olea europaea fruit and leaf extracts as antioxidants, anti-infectives, and anticancer agents for healthy growth. Molecules, 2022, 27, 2341.
