Exponent

The pasted samples produced in Section 3.5 were first transferred to the molds and stored at 4 °C for three days. TA XT2i (Stable Micro System, Surrey, UK) was applied to analyze the texture profile and was equipped with a P/50 cylindrical probe. The testing parameters were as follows: Pre-test speed of 1.0 mm·s⁻¹, test speed of 1.0 mm·s⁻¹, post-test speed of 1.0 mm·s⁻¹, trigger force of 5 g, compression depth of 50%. Hardness, springiness, cohesiveness, chewiness, and resilience were recorded and calculated by Exponent (Version 4.0; Stable Micro Systems, Surrey, UK).

The evaluation of the mucoadhesive properties of the Ch/P fibers was carried out by a texture analyser (Stable Micro Systems, Surrey, UK) with a 50 N load cell equipped with a mucoadhesive test ring.
Fresh pig mucosal tissue was rinsed with phosphate-buffered saline (PBS) at pH 6.8, cut into pieces of 2.5 × 2.5 cm and placed in the mucoadhesion test ring. The mucoadhesion test ring/pig mucosal tissue were equilibrated at 37 °C in PBS, pH 6.8. Ch/P fibers collected on aluminium foil were pasted on a probe (1 cm diameter) using carbon pads prior the test. The assay consisted of placing fibers in contact with the mucosal tissue with 20 g of force for 1 min, and then withdrawn. To calculate the work of adhesion necessary to separate Ch/P fibers from the mucosal tissue the area under the curve of force versus the distance obtained from the software (Exponent, Stable Micro Systems, Surrey, UK) of the texture analyzer was determined. Teflon films of 1 cm in diameter were used as control samples. All the samples were tested three times.

The viscosity, susceptibility to syneresis, and texture analysis of yogurts were estimated at the refrigerated storage time of 1 and 28 days. The viscosity was measured on a cup at 4°C with a viscometer (DV‐II, Brookfield, Middleboro, MA, USA). The spindle used (spindle no. 3 at 30 rpm) in 150 g of yogurt was allowed to rotate for 1 min.
Syneresis of yogurt was determined by centrifuging 20 g of samples at 5000 × g for 5 min at 4°C and weighing the supernatant. Percent syneresis was calculated as: Syneresis (%) = weight of supernatant (g)/weight of sample (g) × 100%.
The texture analysis was determined by a TAXT Texture Analyzer (Stable Micro System) with a backward extrusion test. The cylindrical probe diameter of 36 mm was used for the purpose. Pretest speed, test speed, posttest speed, trigger force, and distance were 1.0 mm/s, 1.0 mm/s, 2.0 mm/s, 10.0 g, and 10.0 mm, respectively, as described by Du et al. (2021 (link)). The diameter of beaker for holding the sample was large enough to minimize the probe side wall effects. The firmness (N), consistency (N × s; total positive area), cohesiveness (N; maximum adhesive force), and viscosity index (N × s; total negative area) were calculated using texture Exponent software (Exponent, version 6.11.16.0, Stable Micro Systems).

The bioadhesion experiment was carried out using a tensile stress tester (TA.XT plus, Stable Micro System, Godalming, Waverley, UK) for the 3D-printed films (n = 3). Porcine ears were obtained from a local slaughterhouse (Ouro do Sul, Harmonia, Brazil) and their skin used as substrate. Porcine ear samples were cleaned by removing the hair and adipose tissue. They were stored at −20 °C in aluminium foil and used within 3 months. On the day of the experiments, skin tissue was maintained under room conditions for at least 30 min prior to the experiments. A fixed volume (20 μL) of ultrapure water was pipetted onto the tissue to standardise hydration, and excess water was removed with absorbent paper. Skin pieces were fixed to the equipment probe with double-sided adhesive tape, whereas the formulations were fixed on the equipment’s platform with the aid of an instant adhesive. The equipment promoted the contact of the skin piece with the film for 3 min with a force of 290 mN. The probe with the skin was then removed from the surface of the film at a constant speed of 0.10 mm·s⁻¹ until total displacement [26 (link)]. The debonding distance (mm) and the work (mN·mm) necessary to detach the skin (peaks of force (mN) x displacement (mm)) from the 3D-printed films were calculated by the software (Exponent, Stable Micro Systems, Godalming, Waverley, UK).

The maximum elongation at break and tensile strength were evaluated by the Texture Analyzer (TA.XT plus, Stable Micro Systems Ltd., Surrey, UK) (Hurler et al., 2012 ) and calculated with software (Exponent, Stable Micro Systems, Ltd., Surrey, UK). CbFG was casted on a polyester film, and oven-dried at 40 °C for 30 min until the CbFG-film was formed completely. The dimensions (width × length) of each film were 20 mm × 60 mm and the thickness was 50 μm. The distance between the supports was set at 40 mm, and the crosshead speed was fixed at 1 mm/min. The tensile strength and maximum elongation at break were calculated for the film, which was cut in two directions longitudinally.

A texture profile analysis (TPA) of the formulations was carried out with a TA-XT texture analyzer (Stable Micro Systems Ltd., Surrey, UK) to determine the mechanical properties. Cream samples measuring 10 g were placed in a beaker and left at room temperature (25 °C) for 24 h before the test, avoiding the introduction of air bubbles. The analytical polycarbonate probe (10 mm diameter) was compressed twice in the interiors of the samples, with a test speed of 2 mm/s⁻¹, a depth of 5 mm, and a delay period of 15 s between the first and second compressions [33 (link)]. The analyses were performed 10 times for each sample at 25 °C. Based on force vs. time graphs, hardness (force required to attain a given deformation), compressibility (work required to deform the product during the first compression of the probe), cohesiveness (ability to restructure the formulation after removing from the vial), and elasticity (deformation rate after applying a force) of the samples were calculated using the software Exponent (Stable Micro Systems Ltd., Surrey, UK).