Printability of Nixtamalized Corn Dough during Screw-Based Three-Dimensional Food Printing.

This study aimed to analyze the printability of corn-based dough during screw-based three-dimensional (3D) food printing (3DFP) by relating its rheological and mechanical properties to its screw-based 3DFP performance, with the objective of providing insights into the utilization of corn-based dough to produce 3D-printed foods. Screw-based 3DFP was performed using seven corn-based doughs with different nixtamalized corn flour (NCF) and water contents. Afterward, their rheological and mechanical properties were analyzed and associated with their screw-based 3DFP performance. The results showed that stable printability was obtained within a specific range of NCF content in the dough (30-32.5 wt%). Below this range, the 3D-printed foods flattened, while above it, the extrudability of the dough was affected. The printability of the dough was influenced by different rheological and mechanical properties, depending on the stage of the screw-based 3DFP process. During the extrusion stage, the loss tangent at nozzle strain, yield stress, apparent viscosity, and adhesiveness mainly affected the extrudability of the dough. In contrast, the loss tangent at minimum strain, elastic modulus, Young's modulus, and hardness influenced the self-supporting stage. Therefore, it is important to find a balance between all of these properties, where stable extrudability and self-supporting of the 3D structure are achieved.

Effect of mechanical properties on in vitro dynamic digestion of starch contained in hydrogels.

BACKGROUND: This study evaluates the effect of mechanical properties on the in vitro dynamic gastrointestinal digestion of hydrogels containing starch (HCSs) as a model for studying the nutrient digestibility of solid foods. It provides a useful theoretical basis for the processing of specific foods. RESULT: Four types of HCSs with two levels of fracture stress (17.4-20.9 kPa and 55.5-57.6 kPa) and two levels of fracture strain (25.4-28.5% and 53.7-57.4%) were prepared. For these HCSs, the degree of gastric disintegration of hydrogels reduced significantly when fracture strain exceeded 30% (P < 0.05). The gastric emptying of HCS particles was also affected by mechanical properties. For example, even at the same level of fracture stress (ca. 20 kPa), the dry solids retention ratio decreased markedly from 0.90 to 0.43 with a decrease in fracture strain from 53.7% to 25.4% (P < 0.05). For the starch hydrolysis of HCSs after gastric digestion, more than 70% of starch in the particles of all types of HCSs emptied did not undergo digestion. The starch hydrolysis of HCSs during small intestinal digestion was also influenced by their mechanical properties. Fracture strains of HCSs, rather than their fracture stress, affected starch digestibility in hydrogels. CONCLUSION: The gastric disintegration, the gastric emptying, and the starch hydrolysis of HCSs are suppressed when fracture strain exceeded 30%. Even with the amount of nutritional components contained in hydrogels being the same, the in vitro gastrointestinal digestion behavior of HCSs depends on their mechanical properties. This behavior has the potential to be used in the design of processed foods with controlled bioaccessibility. © 2023 Society of Chemical Industry.

PIV and CFD studies on analyzing intragastric flow phenomena induced by peristalsis using a human gastric flow simulator.

This study quantitatively analyzed the flow phenomena in model gastric contents induced by peristalsis using a human gastric flow simulator (GFS). Major functions of the GFS include gastric peristalsis simulation by controlled deformation of rubber walls and direct observation of inner flow through parallel transparent windows. For liquid gastric contents (water and starch syrup solutions), retropulsive flow against the direction of peristalsis was observed using both particle image velocimetry (PIV) and computational fluid dynamics (CFD). The maximum flow velocity was obtained in the region occluded by peristalsis. The maximum value was 9 mm s(-1) when the standard value of peristalsis speed in healthy adults (UACW = 2.5 mm s(-1)) was applied. The intragastric flow-field was laminar with the maximum Reynolds number (Re = 125). The viscosity of liquid gastric contents hardly affected the maximum flow velocity in the applied range of this study (1 to 100 mPa s). These PIV results agreed well with the CFD results. The maximum shear rate in the liquid gastric contents was below 20 s(-1) at UACW = 2.5 mm s(-1). We also measured the flow-field in solid-liquid gastric contents containing model solid food particles (plastic beads). The direction of velocity vectors was influenced by the presence of the model solid food particle surface. The maximum flow velocity near the model solid food particles ranged from 8 to 10 mm s(-1) at UACW = 2.5 mm s(-1). The maximum shear rate around the model solid food particles was low, with a value of up to 20 s(-1).