Encapsulação por extrusão através da gelificação iônica do extrato aquoso de folhas de estévia (Stevia rebaudiana Bertoni) com alginato de sódio: caracterização física e impacto na composição fenólica

Tese (doutorado) - Universidade Federal de Santa Catarina, Centro de Ciências Agrárias, Programa de Pós-Graduação em Ciência dos Alimentos, Florianópolis, 2017.

Access type:openAccess
Publication Date:2017
Main Author: Arriola, Nathalia Darminia Aceval
Advisor: Amboni, Renata Dias de Mello Castanho
Document type: Doctoral thesis
Online Access:https://repositorio.ufsc.br/handle/123456789/189156
English abstract:Abstract : The aim of this work was the design and characterisation of alginatebeads as delivery/carrier system of the crude aqueous Stevia rebaudianaBertoni leaves (stevia) extract for future applications as functionalingredients. Initially, a fractional factorial design was carried out aimingat the optimization of aqueous parameters (extraction temperature,extraction time, solvent volume and leaves particle size) to maximizethe total phenolic compounds content (TPC) extracted from dry leavesof stevia. According to the optimal extraction conditions, an aqueousextract was obtained with 20 mL deionised water at 90 ° C for 10minutes, employing 1 g of dry leaves with a particle size of 30 mesh(0.6 mm). The extracts obtained under the optimum conditions weresubjected to the ionic encapsulation process through the drippingextrusion method (25 ± 2 °C) with sodium alginate at 1% (w/v). Firstly,the effect of the overnight storage (4 ± 2 ° C) of freshly prepared beads(stored in the presence or absence of aqueous stevia extract) in thephenolic composition of the encapsulated extract was evaluated.Hydrogel (wet) and lyophilised beads were compared for both theevaluated conditions. The specific objectives included: evaluation of theinfluence exerted by the storage conditions of the wet beads, after thecrosslinking process and prior to lyophilisation, in relation toencapsulation efficiency (EE) of encapsulated TPC; characterisation ofonly the wet and lyophilised beads that presented the highest EE valuesaccording to their size, microstructure and fluorescence emission; studythe influence of the wet and lyophilised matrixes on the diffusiveproperties of total phenolic aqueous release; and finally to evaluate thepotential of sodium alginate in preserving the stability of theencapsulated TPC and their antioxidant capacities during 30 days ofstorage (4 ± 2 ° C). The wet beads that were stored in the presence of theextract showed a significant increase of 20% in the EE values comparedto the beads stored without extract, indicating the importance of thediffusive process of the extract to the capsule even after alginatecrosslinking. Although lyophilisation significantly affected the size andmorphology of the beads, the TPC of the two groups of capsules was notaltered, resulting in a suitable drying method in the preservation of theencapsulated TPC. The water-release kinetics of the encapsulated TPCshowed a similar trend in both the capsule types, releasing 50% of theTPC during the first 10 minutes. Encapsulation of the aqueous leafextract of stevia with sodium alginate proved to be an efficientalternative in the encapsulation and preservation of its TPC as well as itsantioxidant activity during 30 days of storage. Subsequently,considering the efficient protective effect of alginates on the stability ofphenolic compounds present in stevia extracts, a second phase carriedout during a sandwich doctorate study at Newcastle University (UK), wesought to explore the encapsulation of stevia extracts throughassociations of alginates with different molecular characteristics. Thus,the objective was to formulate and characterise two alginate blends asencapsulating agents of stevia extracts, evaluating three formulations foreach blend. It was sought to maximize the efficiency of the phenolicentrapment during the encapsulation, using the aqueous extract of steviain the crosslinking solution. To achieve this goal, two differentcrosslinking solutions were tested: calcium chloride dissolved in steviaaqueous extracts and aqueous solutions of calcium chloride. In addition,specific objectives included: evaluating the effects of the blends andcrosslinking solutions on the overall performance of the encapsulationprocess, including EE, size, morphology; as well as evaluating themolecular interactions between the coating material and theencapsulated active compounds through the infrared analysis of Fouriertransform (FT-IR). In addition, the profile of phenolic compounds in thestevia extract before and after encapsulation was obtained through thestrategy of untargeted metabolomic analysis using ultra-highperformanceliquid chromatography coupled to high resolution massspectrometry with quadrupole analyzers in flight time and ionisation byelectrospray (UHPLC-ESI / QTOF-MS). Regardless of the types ofblends and crosslinking solutions, all formulations evaluated showedhigh EE (> 60%) of TPC. For both the alginate blends, a very high EEvalue (> 95%) was obtained for the beads formed in the crosslinkingsolution containing the extract. The high EE obtained showed that whenusing the stevia extract in the crosslinking solution, losses of compoundsby diffusion were efficiently avoided. In addition, there was nosignificant change in characteristic peaks observed between the samplesformulated in the FT-IR analysis, suggesting that there was nosignificant interaction between the encapsulated stevia extract and thepolymers blends employed. Additionally, it was observed that theoverall characteristics of the alginate capsules (morphology, size,phenolic profile) evaluated under the experimental conditions were alsodependent on the crosslinking conditions. Consistent similarities ofmatching beads across blends were observed throughout thecharacterisation analysis, including similarities in size, morphology andphenolic class distribution (p > 0.05). Thus, not only the alginate blends,but also the crosslinking conditions significantly affected the phenolicprofile and beads characteristics. The metabolomic analysis resulted inthe identification of a total of 479 free and encapsulated phenoliccompounds. Thus, this study represents the first work published in theliterature to date involving the encapsulation of the aqueous leaf extractof stevia with alginates focusing on the preservation of its phenolicconstituents and their bioactive properties. This study is pioneer inhighlighting the detailed phenolic profile of free and encapsulatedaqueous leaf extract of stevia in alginate blends. These results willcontribute to understanding the chemical and structural changes as wellas the interactions between the encapsulating material and the functionalactive ingredients during encapsulation processes that seek thedevelopment of effective carrier systems for functional ingredients.