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Title:Manothermosonication (MTS) and pH-shifting combined treatment for modifying the functional properties of plant proteins: protein-stabilized nanocarriers and protection of docosahexaenoic acid (DHA)
Author(s):Yildiz, Gulcin
Director of Research:Feng, Hao
Doctoral Committee Chair(s):Padua, Graciela
Doctoral Committee Member(s):Engeseth, Nicki; Andrade, Juan
Department / Program:Food Science & Human Nutrition
Discipline:Food Science & Human Nutrition
Degree Granting Institution:University of Illinois at Urbana-Champaign
Subject(s):Mano-thermo-sonication (MTS)
Soy-protein isolate (SPI)
Abstract:Plant proteins are low cost, non-toxic, natural, biocompatible, and biodegradable polymers. In recent years, plant proteins have drawn increasing attention from the food and pharmaceutical industries as an alternative to animal proteins due to increased consumer concerns over the safety of animal-derived products (e.g., prion diseases). Plant protein-based nanocarriers have been investigated for use as delivery systems to encapsulate, protect, and release bioactive components. Many studies have attempted to improve the functional properties of plant proteins as they are inherently less effective emulsifying agents compared to animal proteins, with various degrees of success. The goal of this study is to explore the use of mano-thermo-sonication (MTS), a new sonication method and its combination with pH-shifting to modify the functionality of soy and pea proteins for preparing nanocarriers to encapsulate and protect docosahexaenoic acid (DHA). In study one, a new physical and chemical combined treatment for protein modification, i.e. mano-thermo-sonication (MTS) with and without pH-shifting was developed. This method was tested using soy protein isolate (SPI) as a model protein. The soluble soy protein nano-aggregates produced by this method were used to make SPI-stabilized nanoemulsions. The effect of treatments (pH shifting, MTS, and high pressure homogenization) on the physicochemical (e.g., solubility, surface hydrophobicity, free sulfhydryl and disulfide bond (S-S) content, antioxidant capacity, and total phenols), interfacial (e.g., rheology), and emulsifying (e.g., droplet size, turbidity, emulsion stability, and emulsion activity indexes) properties of SPI nano-aggregates were evaluated for the development of SPI nanostructures. In study two, a plant protein and polysaccharide complex was developed to address the low solubility of plant protein in the vicinity of pI encountered for soy protein nano-structures developed in Study 1. Specifically, pea protein isolate (PPI) and soy protein isolate (SPI) nano-aggregates produced with pH 12-MTS were used to form complexes with modified starch, gum Arabic, or pectin. The physicochemical (e.g., solubility, surface hydrophobicity, free sulfhydryl, and disulfide bond (S-S) content), interfacial (e.g., rheology), and emulsifying (e.g., droplet size, turbidity, emulsion stability, and emulsion activity indexes) properties of the protein-polysaccharide complexes were examined to choose the best combination for producing the most stable wall material for the encapsulation. Overall, the PPI and modified starch complex was identified as the best combination due to its high solubility, hydrophobicity, and improved emulsifying properties. In study three, the effect of wall material and the presence of surfactant (Tween 20 and SDS) in emulsion formula on protection of DHA against oxidation was examined. A total of 4 wall materials including pea protein isolate (PPI), pea protein isolate - modified starch (PPI-MS) complex, Tween 20, and sodium dodecyl sulfate (SDS) were used for microemulsion preparation with canola oil containing DHA. The microemulsions were dried with a lab-scale freeze dryer. The freeze-dried powders were characterized with respect to physicochemical characteristics, oxidative stability, and release properties. The PPI-MS complex as a natural polymeric wall material exhibited similar or better encapsulation efficiency and desirable level of peroxide value (<5 meq/kg) compared to the synthetic surfactants (Tween 20 and SDS). In summary, the MTS and pH-shifting combined treatment provided a new and effective protein modification method that can be used to produce protein nano-aggregates with significantly improved functional properties. Especially, the PPI nano-structures produced by this new method exhibited good physicochemical and functional properties representing a promising alternative to animal-derived proteins. The PPI and modified starch nano-complex was shown to be a stable wall material that can be used to encapsulate DHA to fortify omega-3 fatty acids in food products and supplements.
Issue Date:2017-07-13
Rights Information:Copyright 2017 Gulcin Yildiz
Date Available in IDEALS:2018-03-02
Date Deposited:2017-08

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