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Solid oral dosage forms (SODF) are the most popular oral drug delivery forms, but they can be difficult to swallow, especially for patients suffering from swallowing disorders. This study investigated the dynamics of different combinations of liquid carriers and SODF during the oral phase of swallowing using an in vitro model. The rheological properties of the carriers were characterized using shear and extensional rheometry, and their effect on bolus velocity, bolus shape, post‐swallow residues, and SODF position within the bolus was evaluated. The latter has been identified as a novel and promising variable to discriminate between alternative formulations. When swallowed with water, capsules and tablets did not impact significantly the velocity of the bolus, but they lagged behind the liquid bolus, suggesting that low viscosity Newtonian fluids are not efficient carriers for SODF. Increasing the viscosity of the carrier at high shear rates improved the ability of the liquid to transport the SODF but also increased the amount of post‐swallow residues. At equivalent shear viscosity, elastic and extensional properties of carriers influenced positively the position of the SODF in the bolus. Capsules and tablets were transported toward the front of these boluses, during the oral phase of swallowing, which is considered beneficial to avoid SODF sticking to the mucosa in the following stages of swallowing. Thin elastic liquids appear as an interesting option to promote safe swallowing of capsules and tablets. Clinical studies are, however, necessary to confirm this positive effect in healthy and dysphagic patients.

A model gel of whey protein isolate (WPI) was prepared by cold gelation with calcium. This system was modified by the addition of free cysteine residues (Cys) at different steps of the process. The WPI cold-set gels obtained were then subjected to heat treatment at 90°C. First, the effect of Cys addition on the heat-induced aggregation of WPI was studied through Atomic Force Microscopy (AFM) and infrared spectroscopy (ATR-FTIR), while Cys' effect on cold gelation was observed by AFM, Confocal Laser Scanning Microscopy (CLSM) and oscillatory rheology (amplitude sweeps). The impact of heating on the microstructure and the viscoelastic properties of the WPI cold-set gels were finally investigated through several techniques, including DSC, ATR-FTIR, CLSM, cryo-SEM, and rheological measurements (temperature sweeps). When added during the first step of cold gelation, Cys modified heat-induced aggregation of WPI, resulting in the formation of a denser gel network with a fractal dimension (Df) of 2.8. However, the addition of Cys during the second step of cold gelation led to the formation of highly branched clusters of WPI and a looser gel network was observed (Df = 2.4). In this regard, the use and limitations of oscillatory rheology and the “Kraus model” to determine the Df of WPI cold-set gels was discussed. The viscoelastic properties and the microstructure of the WPI cold-set gels were irreversibly modified by heating. Gels were stiffer, more brittle, and coarser after heat treatment. New disulfide bonds and calcium bridges formed, as well as H-bonded β-sheets, all contributing to the formation of the final gel network structure.

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Polyunsaturated fatty acids and α-tocopherol were encapsulated in powders by spray drying using maltodextrins DE 12 as wall material and different emulsifiers (Tween®20, acacia gum or β-glucans-rich extracts from Pleurotus ostreatus). The aim was to study the effects of the surfactants on: (a) the oil droplet size distribution and α-tocopherol stability during in vitro digestion, and (b) the oxidative stability during 15 days of accelerated storage. Acacia gum sample had the most stable particle size distribution up to the gastric phase, but showed a significant α-tocopherol degradation prior to the intestinal stage. On the contrary, β-glucan-samples displayed a bimodal distribution in the oral and gastric phases but retained α-tocopherol up to the beginning of the intestinal stage. At the end of intestinal stage, no α-tocopherol was found in the samples. The storage study showed that β-glucans improved the oxidative stability of the powders, which displayed 82% α-tocopherol retention after 5 days under accelerated conditions (60 °C), corresponding to 310 days at 20 °C, while acacia gum and Tween® 20 did not delay α-tocopherol degradation. Results highlight the potential antioxidant activity of β-glucans used as emulsifying agents during in vitro digestion and accelerated aging conditions.

The objective of this study was to investigate quantitatively the impact of saliva on the rheological properties of thickened drinks (IDDSI level 3) with different pH. Oral digestion was simulated and followed using a rheometer. An insalivation ratio measured from spitted boli, was used in the in vitro oral digestion experiments, comparing unstimulated human saliva to artificial saliva. The initial viscosity of thickened water samples (pH 5.3 and 7.4) was reduced by 80% after only 5 s of in vitro oral digestion. A similar viscosity decay was observed with the artificial saliva. This decrease in viscosity was attributed to the breakdown of the starch granule structure by α‐amylase and in a lesser extent to a dilution effect. In contrast, the rheological properties of thickened lemon drink (pH = 2.7) and thickened orange juice (pH = 4.0) were not influenced significantly by human salivary amylase. These results suggest that at these pHs, starch‐based thickened drinks can maintain their initial IDDSI level, despite a strong dilution with saliva, which could help in the management of dysphagia. Clinical trials should be performed to confirm this hypothesis. Only human salivary α‐amylase should be used to study products between pH 3 and 5 to imitate the structural and rheological breakdown happening before swallowing, while α‐amylase from Bacillus sp. could also be used outside this range. The method developed in this study can be used to quantify the impact of food oral processing and evaluate rheological properties relevant for swallowing in the presence of saliva.