Development of nanoencapsulated phenolic green extracts for functional food and nutraceutical: hibiscus sabdariffa as example

Abstract

The current report encompasses all the results found during the work carried out for the PhD Thesis entitled: “DEVELOPMENT OF NANOENCAPSULATED PHENOLIC GREEN EXTRACTS FOR FUNCTIONAL FOOD AND NUTRACEUTICAL: Hibiscus sabdariffa as example”. This Thesis provides data on the developmental timeline for nutraceutical or functional food. This work is divided into two main sections: Introduction and Experimental Summary. The Introduction section begins by presenting the state of art with regards to nutraceuticals and functional foods. The normal timeline involved in their development is presented, beginning with the search for natural sources of phenolic compounds, their subsequent extraction by green technologies and characterisation using analytical approaches, and finally their encapsulation and incorporation in a food matrix. Firstly, bioactive compounds and phenolic compounds are described and classified according to their chemical structure. Next, the types of green extraction technologies (e.g. microwave assisted extraction, pressurised liquid extraction and supercritical fluid extraction) used for phenolic compounds in plant matrices are reported. Following this, chromatographic analytical techniques used for separation, such as high performance liquid chromatography (HPLC), detection like UV-Vis and mass spectrometry (MS) for the identification and quantification of phenolic compounds are described. Details are then given on the micro and nano-encapsulation of these phenolic compounds and the role of this in ensuring their stability against environmental conditions. In this Thesis, lipid-based nanosystems are detailed, in addition to the main stability mechanisms of this encapsulation technique. Finally, the present Thesis reports the incorporation of encapsulated phenolic compounds in a food matrix. The Experimental Summary is split into three subsections. The first section (Section A) deals with the search of new sources of phenolic compounds. In this sense, Hibiscus sabdariffa is chosen due to its bioactive composition. The origin, distribution, biological effects, nutritional value and phenolic composition of this plant are also mentioned in this section. The second section (Section B) examines the optimization of extraction systems for producing extracts rich in phenolic compounds from Hibiscus sabdariffa, which can then subsequently undergo characterization. This section is divided into 3 chapters. In Chapter 1, a green extraction technology, namely microwave assisted extraction (MAE), is optimized using different solvent-water ratios, extraction times and temperatures, to obtain the best extraction condition capable of providing the highest phytochemical content. In this regard, all experimental green extracts were characterized by HPLC-MS. In Chapter 2, the optimization of green pressurised liquid extraction (PLE) employing different solvent-water ratios and temperatures to achieve a green extract with the highest phenolic compound content is described. Finally, in Chapter 3 the optimization of supercritical fluid extraction (SFE) to obtain the best extraction conditions for phenolic compounds is described. In this technique, different pressures, temperatures and co-solvent amounts were tested. Finally, the characterization of green extract using HPLC-MS is described. The third section, (Section C) is dedicated to micro- and nano- encapsulation of phenolic compounds from Hibiscus sabdariffa and their incorporation into a food matrix. This section is divided into five chapters in which Chapter 5 and 6 were written in collaboration with the Chemical Engineering Department, whilst Chapter 4, Chapter 7 and Chapter 8 were prepared in collaboration with the University of Coimbra (Portugal), following a 3-month pre-doctoral mobility fellowship named “Estancias breves FPU”. In Chapter 4, different lipid-based nanosystems are detailed for the entrapment of phenolic compounds. Thus, the main characteristics of emulsions and nanostructured lipid carriers (NLC) (whose techniques are employed in the current Thesis) are reported. In Chapter 5, the development of new functional oils containing antioxidants from Hibiscus sabdariffa green extract using the emulsion method is detailed. In addition the physical and oxidative stability of these emulsions were evaluated and is reported here. Particle size, coalescence rate, total phenolic content (TPC), antioxidant activity and chemical composition as measured by HPLC-MS are also analysed. Chapter 6 describes the incorporation of an anthocyanidin-rich commercial Hibiscus sabdariffa extract into the inner phase of a water/oil/water emulsion and the improvement of its physical stability through the reinforcement of both interfaces with whey protein concentrate - arabic gum complexes. In Chapter 7, the development of an optimum formulation of NLC to protect the phenolic compounds from Hibiscus sabdariffa, extracted by MAE and PLE, is described. These particles are characterised according to particle size, polydispersity index and zeta potential in the context of a stable system. In addition, a high encapsulation efficiency of quercetin and anthocyanins was obtained and is discussed. Finally, Chapter 8 reports the incorporation of Hibiscus sabdariffa-loaded nanoparticles into a diary beverage. Following evaluation of a study examining long-term stability, texture properties and in vitro release, it is demonstrated that these enriched milks form a stable suspension.