Effect of pH and salts on microstructure and viscoelastic properties of lemon peel acid insoluble fiber suspensions upon high pressure homogenization. (September 2018) - Willemsen, Katleen L.D.D.
Abstract: In the present paper the effect of pH and salts on microstructural and viscoelastic properties of lemon peel acid insoluble fiber residue (AR) suspensions upon mild and intense shearing was investigated. To this aim, AR suspensions were adjusted to a pH of 2.5 (as is), 4.5, 5.5, 7 or 10 prior to or after high pressure homogenization (HPH) at 20 MPa (high shearing), with or without blending (low shearing). Furthermore, the effect of salts was investigated by addition of NaCl or CaCl2 to the AR suspensions upon blending and HPH. Microstructural characterization of the AR suspensions, was performed through microscopic visualization and determination of the particle size distribution by laser diffraction, whereas viscoelastic properties were determined by rheological analysis. Regardless of the pH conditions, blending prior to HPH was essential to obtain optimally functionalized AR suspensions. Furthermore, the effect of the sequence of blending and pH adjustment was negligible, whereas pH adjustment played a crucial role prior to HPH. In particular, increasing the pH above its intrinsic condition (pH 2.5) assisted the functionalization of AR suspensions by HPH, improving its viscoelastic properties. Contrarily, high salt concentrations negatively influenced the functionalization of AR suspensions. This effect of pH and salts was attributed to changes in electrostatic forces between AR fibers due to the presence of negative charged residual pectin polymers, favoring fiber separation (upon HPH) and increasing its hydration potential. On the other hand, high salt concentrations will shield AR fiber charges, thereby reducing the viscoelastic properties of the fiber suspensions. Graphical abstract: Image 1 Highlights: HPH at 20 MPa is sufficient to thicken lemon peel AR suspensions. Blending prior to HPH results in optimal texturizing properties of AR suspensions. pH and addition of salts are crucial to optimize the effects of HPH. Electrostatic interactions favor the separation of AR fibers upon HPH. Extensive salt addition negatively influences the texture of AR suspensions.