Ramondo, Alessia (2023) Development of biopolymer-based nanoparticles for use in food formulation. [Tesi di dottorato]

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Abstract

Agricultural activities (crop and livestock production) and agro-industrial activities, such as fruit and vegetable processing, olive and oilseed processing, generate significant amounts of organic waste and by-products of excellent quality, since they are initially composed of parts of the same material that, in the case of agricultural products, are removed during harvesting or industrial processing. Agricultural residues mainly include all plant parts that are not the main product and are intended for human or animal consumption, such as stems, leaves, cobs, stalks, branches, twigs and wood. Moreover, food agro-industrial by-products derive from the processing of vegetables and fruits or their preparations for food consumption. The increase in oilseed production to meet the demand for organic vegetable oil is inevitable and leads to an increase in agricultural and industrial by-products with high valorization potential. After extracting the oil from oilseeds, the by-product is a defatted flour. The oil is used in human nutrition and in the production of biodiesel. The defatted flour, which consists mainly of proteins and carbohydrates, has a high nutritional value. Therefore, it is important to advance its valorization to ensure better global sustainability of the oilseed biodiesel industry. Extraction, concentration and isolation of protein fractions from defatted flours is essential for product upgrading. Proteins represent a group of food ingredients that find wide application in the food industry as texturized, concentrated, isolated or hydrolyzed proteins, especially from plant sources. The extracts obtained are called protein concentrates or isolates, depending on their protein concentration in dry matter. They are protein concentrates or isolates when their concentration reaches 65% or 90%, respectively. Protein-polysaccharide interactions play an important structural role in biological systems (e.g., in maintaining cellular integrity and cell division) and in controlling the macroscopic properties of foods (e.g., flowability, stability, texture, and mouthfeel). They can also be used to control the functionality of proteins in foods by altering the surface chemistry of proteins and their aggregation behaviour. Controlling the interactions between plant proteins and polysaccharides can lead to the development of new complex electrostatic structures that can confer unique functionalities. This in turn may expand the variety of applications for which they are suitable. While coacervation research is not new, most work has focused on studying the interactions of polysaccharides with animal proteins. Plant proteins have attracted tremendous attention from both consumers and industry in the last decade due to the increasing focus on the safety of animal-based foods, religious and cultural-based diets, and lower costs than animal protein. However, the solubility of plant-based protein products is generally lower than that of proteins from animal sources. Therefore, several strategies have been explored to improve their performance in food systems. One approach is to engineer their interactions with polysaccharides to create new surface features and structures. Considering these assumptions, the presented research would allow the introduction of an innovative technology based mainly on the mechanism of interaction between proteins and polysaccharides in an aqueous environment, with low environmental impact and economically viable. The aim of this PhD was to produce bio-nanoparticles from proteins extracted from defatted pumpkin seed flour to be used as stabilizers in high internal phase emulsions and to study their application as substitutes for fats in creams from fillings. The first case study involved the extraction and characterization of Pumpkin Seeds Proteins Isolate (PsPI) which were treated with High Intensity Ultrasounds (HIUS) to improve their solubility and solvation charge. In particular, the effect of HUIS treatment time on the solubility, zeta potential, and mean hydrodynamic radius of PsPI was determined. In fact, the aim of this study was to investigate the effect of high-intensity ultrasound (HIUS) treatment times on suspensions of PsPI as a function of pH (from 2.5 to 10.5) by evaluating particle size, zeta potential, and emulsion and foam properties. Aqueous PsPI suspensions with different pH values were sonicated at 150 W (pulse duration 0.5 s) for 5, 10, and 20 min. Overall, the results showed that prolonged treatment with HIUS promoted the formation of molecular aggregates. In fact, a 5-min treatment with HIUS was sufficient to achieve a significant increase in foam formation and emulsification capacity compared to the untreated control, especially in the pH range of 2.5-6.5. The use of HIUS was proved to be an excellent time-dependent treatment method to improve the physicochemical properties of PsPI, and therefore the 5-min HIUS treatment was chosen as the pretreatment for the next case study. In the second case study, the electrostatic and intermolecular interactions during the structure formation between pumpkin protein isolate (PsPI) and low molecular weight chitosan (Ch) were investigated to reveal their complex coacervation mechanisms. To this end, the formation of the complex as a function of pH (2.5-10.5) and protein to polysaccharide ratio (PsPI:Ch, R = 1:1-120:1 w/w) was evaluated by dynamic light scattering (DLS) analysis, ζ-potentiometry, and coacervate yield. The highest coacervation, which occurred at 8:1 ratio and an electrically neutral pH of 7.795, was characterized by the highest yield (94%) and the smallest particle size (664 nm). The morphological features of the lyophilized PsPI-Ch coacervates determined by scanning electron microscopy (SEM) provided further insight into the associative processes during complex coacervation. In addition, molecular interactions between PsPI and Ch were confirmed by Fourier Transform Infrared Spectroscopy (FTIR), which revealed mainly electrostatic interactions. In the third case study, the ability of pumpkin seed protein isolate (PsPI) and chitosan (Ch) to prepare Pickering emulsions and the stability of the resulting emulsions were investigated. The results showed that the coacervates were able to stabilize the O/W emulsions and that the separated particles had a maximum oil content of 81% at pH 5.5. The emulsifying ability of the PsPI-Ch coacervates was strictly dependent on their concentrations, with emulsions with High Internal Phase Pecking (HIPE) forming only at stabilizer concentrations of 1.5% (w/v) and higher. The HIPEs showed excellent stability to pH changes from 2.0 to 10.0, heating to 100°C, and centrifugation, but collapsed easily upon freezing and thawing; higher stabilizer concentration resulted in better stability. This study demonstrated the applicability of PsPI-Ch coacervates in the food industry as HIPE stabilizers. The final case study aimed to develop a sweet filling cream with stabilized fat by using a Pickering emulsion with a high internal phase stabilized by pumpkin chitosan-protein complex (PsPI-Ch), with the thick layer covering the oil droplets forming a physical barrier to prevent oil from leaking from the structure. The cream consisted of starch, sugar, water, and oil as it is in the control cream, which was substituted by the emulsion as the fat source for the emulsion cream. The physicochemical parameters of the two formulations were evaluated. The viscoelastic properties were evaluated through oscillatory dynamic tests to determine the elastic modulus G' and the viscous modulus G".and dynamically to estimate the apparent viscosity (η), whereas the Turbiscan tower was used to determine the physical stability. The results obtained show that the control cream is more structured and requires larger shear stresses to flow than the emulsion cream, having lower elastic modulus values than the latter. In addition, both creams exhibit medium-strength, gel-like, pseudoplastic behaviour and a slight frequency dependence, but the emulsion cream exhibits significantly higher zero shear viscosity values than the control cream. As for physical stability, expressed as Delta Back Scattering (∆BS) and Turbisca Stability Index (TSI), the emulsion cream shows significantly lower ∆BS and TSI values after 21 days and, most importantly, reaches a plateau in contrast to the control cream, which continues to show strong migration phenomena within the structure. The greater stability is due both to the smaller particle size and the higher viscosity of the whole structure and to the chitosan contained in the Pickering emulsion, which improves the quality of the food.

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