Ronca, Carolina Liana (2024) A New Functional Food Starting From By-Products of the Olive Industry. [Tesi di dottorato]

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Abstract

In the food industry, functional foods are becoming increasingly popular. This trend is due to the fact that, in addition to providing the essential nutrients required for the development, preservation and optimal functioning of the body, these foods also include ingredients with health-promoting properties, along the lines of traditional foods. These ingredients include compounds with anti-hypertensive, anti-hypercholesterolemic, hypoglycaemic, anti-inflammatory and antioxidant effects. Generally, these ingredients are obtained from plant matrices and are known as phytocomponents. Recent research has focused on polyphenolic compounds, which in addition to the aforementioned effects, have demonstrated antitumour, antimicrobial and protective action against cardiovascular and neurological degenerative processes. These polyphenolic compounds, mostly extracted from plants, fruits, vegetables, algae and also from their waste or by-products, can be incorporated into the formulation of functional foods, supplements or cosmetic products. Conversely, olive leaves (Olea Europaea L.) present a significant environmental and sectoral challenge. They represent a considerable proportion of the solid waste generated in olive cultivation (25 kg per tree per year) and by the olive industry (approximately 10% of the weight of the fruit) and are typically discarded or used in the production of animal feed. The European Union is the world's largest producer of olive by-products, with Spain, Italy, Greece and Portugal accounting for the majority of this production. In recent years, there has been a notable increase in interest in agri-food by- products, with the objective of exploiting this resource, which is rich in polyphenols and has thus far been underutilised. Olive leaves are a notable example of an abundant source of phenols, as widely reported in scientific literature. Nevertheless, this resource has not yet been fully exploited. In line with the circular economy action plan for the recovery and reuse of food industry waste, olive leaves have been recovered for the generation of food ingredients with high added value. The extensive geographical extension and diversity of the land dedicated to olive production may be reflected in both the composition and the antioxidant activity of the polyphenols present in the leaves. This research project involved the preparation and analysis of olive leaves extracts, both liquid and lyophilised. The methodology employed adhered to the most up-to-date protocols outlined in the relevant literature. The entire preparation process has been conducted with solvents, such as water and ethanol, that have been shown to be biodegradable, ecological, non-toxic, low cost, and respectful of the environment and human health. A sample of olive leaves was gathered from olive trees in Italy, Portugal and Spain, and their polyphenol profiles and antioxidant activities were analysed. It was found that in the varieties under investigation, there is a correlation between a high polyphenol content and high antioxidant capacity. Liquid olive leaf extracts have been freeze-dried and microencapsulated to improve the stability of the phytocomponents and to use them as an ingredient to be incorporated in food matrices. The freeze-drying process has not affected the major polyphenols (oleuropein and hydroxytyrosol), and the polyphenol content of the freeze-dried extract has remained stable during in vitro digestion tests. However, research in the literature has indicated that environmental factors (such as heat, light, humidity) and factors related to absorption and metabolism by the human body (such as pH, enzymes, microorganisms) can affect the bioavailability and bioaccessibility of these components. Additionally, other challenges associated with the use of these plant extracts include their organoleptic properties, which in most cases make their direct incorporation into food unfeasible. In order to enhance the bioavailability, stability and viability of antioxidant compounds in food matrices, the technique of microencapsulation has been employed. Among the materials currently available on the market for the development of microparticles, sodium alginate has emerged as one of the most extensively researched natural anionic polymers, which can be incorporated into a variety of food products, supplements or pharmaceutical preparations in combination with a range of other ingredients due to its low manufacturing cost and low toxicity, combined with its biocompatibility, biodegradability and ability to form gel-like matrices in the presence of calcium ions. This project demonstrates a promising microencapsulation rate of olive leaf polyphenolic compounds entrapped in sodium alginate, with approximately 98% of the polyphenols successfully micronencapsulated. The food chosen to be enriched with the polyphenols extracted from olive leaves was yoghurt, for which goat's milk was used, given its characteristics in terms of composition and nutritional properties. Further research should focus on the digestive processes and bioavailability of these fortified yoghurts, as well as the antioxidant activity and any potential beneficial effects on human health.

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