Rheological and physical properties of gelatin suspensions containing cellulose nanofibers for potential coatings.

Rheological and physical properties of edible coating formulations containing gelatin, cellulose nanofibers (CNFs), and glycerol are characterized. Measured properties are analyzed in order to optimize edible coating thickness. Results show that coating formulations density increases linearly with gelatin concentration in presence of CNFs. Surface tension decreases with either gelatin or CNF concentration increases. Power law model well described the rheological behavior of edible coating formulations since determination coefficient was high (R(2 )> 0.98) and standard error was low (SE < 0.0052). Formulations showed pseudoplastic (shear-thinning) flow behavior and no time-dependent features were observed. The flow behavior index was not significantly affected by any factor. Consistency coefficient increases with gelatin concentrations but it decreases with glycerol concentrations.

Mechanical properties of calcium alginate fibers produced with a microfluidic device.

Fibers are important microstructural elements in many foods. The main objective of this research was to produce calcium alginate fibers with uniform diameters (about 300 and 550 µm) using a microfluidic device (MFD) and to study the effect of concentration of sodium alginate [Alg] and calcium chloride [CaCl2] on their mechanical properties (MP). Moisture content (MO) and MP as maximum tensile stress (σmax), tensile strain at break (ΔL/L0) and apparent Young's modulus (E) of fibers were determined and a statistical model and surface responses were developed as a function of [Alg] and [CaCl2]. As [CaCl2] increased first a strengthening and then a weakening of fibers were observed. Furthermore, σmax increased with the addition of Ca(2+) and a maximum of σmax was obtained for a [CaCl2] around 1.4% (exceeding several times the stoichiometric requirements of the carboxylate groups of the polymer). Such behavior prompted a molecular explanation of what happens during gelation based on the "egg-box model" and this model is tried to complete. Moreover, fibers with [Alg] ≥1.8% showed high extensibility (ΔL/L0 around 100%) and low values of MO. High values of E (∼0.5 MPa) were obtained for [CaCl2] close to 1.4%. A greater understanding is needed of the interaction between cation-polysaccharide-water, taking into account [Alg] and [CaCl2] to predict the mechanical behavior of fibers. Calcium alginate fibers are important in food engineering as texture and microencapsulation agents.