Complex systems of low content lipid stabilized by interaction electrostatic between biopolymers with application ultrasonic or high pressure

Author(s)

Kivia Mislaine Albano

• Document type: Doctoral Thesis
• Institution: Universidade Estadual Paulista (Unesp)
• Defense date: 2017-08-25
• Advisor: Vânia Regina Nicoletti

Abstract

Systems based on colloidal particles of natural biopolymers are being increasingly used as encapsulation systems, for delivering active ingredients, or to modulate the sensory properties of food. Most of these applications involve a step of emulsification during processing. The hyper-aggregation of the lipid droplets with proteins and polysaccharide can be used to create highly viscous emulsions or gels similar to, but with lower oil content than conventional emulsions. This aggregation is induced by mixing a primary emulsion - with oil droplets stabilized by a protein - and a polysaccharide solution at a pH at which the biopolymers have opposite charges. The application of high intensity ultrasound with the aim of changing functional properties of biopolymers has been widely studied and, in addition, the use of ultrasound is one of methods that allow the preparation of emulsions with reduced droplet sizes. The zeta potential of pure proteins (whey protein concentrate, WPC, soy protein isolate, SPI) and pure polysaccharides (pectin and sodium alginate), was determined searching for the pH value at which the potential for electrostatic interactions are maximum, occuring at pH 3.5. The interaction between polysaccharideprotein pairs (WPC/Pectin, WPC/Alginate, SPI/Pectin e SPI/Alginate) was investigated at pH 3.5 as a function of the protein:polysaccharide ratio (1:1, 2:1, 3:1, 4:1 and 5:1), with and without ultrasound application. The systems were analyzed by turbidimetry, visual evaluation, optical microscopy, and rheological measurements under steady shear, with adjustment of rheological models, and under oscillatory shear, at 25 °C. After this evaluation, due to the physical characteristics presented systems with and without US application in the protein:polysaccharide ratios 1:1 (without strong phase separation) and 4:1 (with strong phase separation), were selected for FTIR analysis and emulsions preparation. Turbidity values indicated that the application of ultrasound decreased the size of complexes dispersed in the medium, generating a less turbid solution which, consequently, resulted in lower absorbance reading, except for the pair SPI:PEC. Visual assessment showed formation of complex coacervates that sedimented in the pairs containing alginate, indicating an strong electrostatic interaction between biopolymers. The pairs with pectin did not show sediment formation, but complexes were also formed, however soluble which could indicate miscibility of the biopolymers. The rheological models Law of Power, Sisko and Newton fitted well to the data (R2 > 0.9) according to the characteristics of the samples. The pairs WPC: ALG and SPI:ALG exhibited pseudoplastic behavior (n < 1), the consistency index (K) increased with the increase of the proportion of protein, and there was a slight thixotropy. However, the application of ultrasound reduced thixotropy of the pair SPI: ALG because reduced the size of the complexes by minimizing the effects of the applied strain rate. The rheology of the pairs WPC:PEC and SPI:PEC showed that pectin has a different behavior than alginate, presenting predominantly Newtonian behavior. In oscillatory shear tests, with alginate pairs G’ was greater than G’’ to all pairs along the frequency range applied, indicating a structured viscoelastic material. Optical microscopy confirmed the images obtained in the visual assessment and helps explaining more clearly the data obtained in the rheological tests. FTIR indicated the structural groups of amines, C-H stretch, amides I and II present in proteins, and hydroxyls, saccharide structure and carboxylic acids I and II found in polysaccharides. Rheological testing of sonicated emulsions in steady and oscillatory shear were also performed. Emulsions prepared with proteins and pectin, showed Newtonian behavior and were stable, with small droplets, and no phase separation, except for SPI, in which some proportions showed instability. Emulsions made with proteins and alginate exhibited pseudoplastic behavior and although with phase separation, the cream reimaned stable over 7 days. There was formation of larger droplets and creaming rate decreased with increasing oil content, tending to a stable emulsion in the proportion 1:1. The components influence on the emulsion instability was confirmed by the chemical composition analysis. Creams from emulsions with alginate showed G’ > G’’ across the frequency range applied, indicating a structured, viscoelastic system. Following work rheological analyzes were performed on the emulsions in function heating /cooling ramp which allowed to identify the temperature effect on the emulsions and the influence of the predominant biopolymer. The confocal microscopy allowed to identify the physical form and the droplets size distribution for each system that was proven by the droplet size analysis that showed small droplets for pectin systems and larger droplets in alginate systems. Finally, a two-stage high-pressure homogenizer was applied in 1:1 emulsions with alginate, which allowed the emulsions stabilization with significant reduction of droplets size distribution in relation to emulsions prepared with ultrasound, diagnosed by visual analysis, optical microscopy and droplet size analysis, in addition to the apparent viscosity reduction in both systems and the permanence of a structured material (G '> G') at applied frequency. It is concluded that the biopolymers and the homogenization processes used in the emulsions preparation had a strong influence on the emulsions stabilization. The stable emulsions obtained suggest their application as possible fat substitutes due to the lipids content low, as well as the creams are a alternative in the improvement of sensory attributes of food products and in the bioactive compounds microencapsulantion due to its presented rheological characteristics. (AU)

• FAPESP's process: 13/10842-9 - Complex systems of low content lipid stabilized by interaction electrostatic between biopolymers with application ultrasonic or high pressure
• Grantee: Kivia Mislaine Albano
• Support Opportunities: Scholarships in Brazil - Doctorate