Effect of salivary fluid characteristics on the physical features of in vitro bread bolus: From the absence of saliva to artificially simulated hypersalivation.

Saliva facilitates food oral processing, bolus formation, swallowing, and sensory perception, in addition to contributing to oral health and phonation. Ageing, health affections, and polymedication are among many causes altering salivary production, modifying the mastication process, the food impregnation ratio, and in turn altering the characteristics of the bolus, swallowing, and digestion. In this in vitro work, using the AM2 masticator apparatus, which replicates the mechanical actions taking place while chewing solid foods and produces realistic food bolus in various oral conditions, we investigated the effect of salivary fluid characteristics, i.e., composition, quantity (from absence to hypersalivation), temperature, and enzymatic action, on the physical characteristics (i.e., particle size distribution (PSD), bolus mass, salivary fluid content) of in vitro boluses of Traditional French baguette. A ready-to-swallow bolus of baguette displayed on average a d50 value (median particle size by mass) of 4.1 ± 0.4 mm, with saliva fluid constituting âˆ¼ 35 % of the final bolus mass. The absence of saliva in mouth led to a deficient oral processing, forming bread boluses constituted by extremely big particles (ca. 80 % of particles had a size > 7.1 mm) that likely cannot be swallowed safely. On the contrary, an excess of saliva favoured an excessive breaking down of bread, leading to bread boluses constituted by smaller particles than those formed under healthy salivary conditions (d50 decreased from 4.1 mm to 3.1 mm), having a higher salivary fluid content (+10 %). On the other hand, the salivary fluid temperature did not affect PSD, d50, bolus mass, or salivary fluid content of in vitro bread boluses, however, the addition of human salivary α-amylase did, favouring particle size reduction (d50 decreased to 2.6 mm). Therefore, beyond the correlation between bolus hydration by saliva and food properties such as hardness and moisture content, our findings indicate that the quantity of salivary fluid present in the oral cavity and the enzymatic activity of salivary α-amylase during bread mastication significantly influence both the particle size distribution and the fluid content of bread boluses, ultimately determining the physical properties of the bolus and, therefore, potentially impacting the subsequent swallowing process.

Dynamic wetting on a thin film of soluble polymer: effects of nonlinearities in the sorption isotherm.

The wetting dynamics of a solvent on a soluble substrate interestingly results from the rates of the solvent transfers into the substrate. When a supported film of a hydrosoluble polymer with thickness e is wet by a spreading droplet of water with instantaneous velocity U, the contact angle is measured to be inversely proportionate to the product of thickness and velocity, eU, over two decades. As for many hydrosoluble polymers, the polymer we used (a polysaccharide) has a strongly nonlinear sorption isotherm φ(a(w)), where φ is the volume fraction of water in the polymer and aw is the activity of water. For the first time, this nonlinearity is accounted for in the dynamics of water uptake by the substrate. Indeed, by measuring the water content in the polymer around the droplet φ at distances as small as 5 µm, we find that the hydration profile exhibits (i) a strongly distorted shape that results directly from the nonlinearities of the sorption isotherm and (ii) a cutoff length ξ below which the water content in the substrate varies very slowly. The nonlinearities in the sorption isotherm and the hydration at small distances from the line were not accounted for by Tay et al., Soft Matter 2011, 7, 6953. Here, we develop a comprehensive description of the hydration of the substrate ahead of the contact line that encompasses the two water transfers at stake: (i) the evaporation-condensation process by which water transfers into the substrate through the atmosphere by the condensation of the vapor phase, which is fed by the evaporation from the droplet itself, and (ii) the diffusion of liquid water along the polymer film. We find that the eU rescaling of the contact angle arises from the evaporation-condensation process at small distances. We demonstrate why it is not modified by the second process.

Benchmarking of a microgel-reinforced hydrogel-based aqueous lubricant against commercial saliva substitutes.

Xerostomia, the subjective sensation of 'dry mouth' affecting at least 1 in 10 adults, predominantly elders, increases life-threatening infections, adversely impacting nutritional status and quality of life. A patented, microgel-reinforced hydrogel-based aqueous lubricant, prepared using either dairy or plant-based proteins, has been demonstrated to offer substantially enhanced lubricity comparable to real human saliva in in vitro experiments. Herein, we present the benchmarking of in vitro lubrication performance of this aqueous lubricant, both in its dairy and vegan formulation against a range of widely available and employed commercial saliva substitutes, latter classified based on their shear rheology into "liquids", "viscous liquids" and "gels", and also had varying extensional properties. Strikingly, the fabricated dairy-based aqueous lubricant offers up to 41-99% more effective boundary lubrication against liquids and viscous liquids, irrespective of topography of the tested dry mouth-mimicking tribological surfaces. Such high lubricity of the fabricated lubricants might be attributed to their limited real-time desorption (7%) from a dry-mouth mimicking hydrophobic surface unlike the tested commercial products including gels (23-58% desorption). This comprehensive benchmarking study therefore paves the way for employing these microgel-based aqueous lubricant formulations as a novel topical platform for dry mouth therapy.

Effect of α-amylase and pH on the rheological properties of thickened liquids containing starch in in vitro conditions relevant to oral processing and swallowing.

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.

In vitro and sensory tests to design easy-to-swallow multi-particulate formulations.

Flexible dosing and ease of swallowing are key factors when designing oral drug delivery systems for paediatric and geriatric populations. Multi-particulate oral dosage forms can offer significant benefits over conventional capsules and tablets. This study proposes the use of an in vitro model to quantitatively investigate the swallowing dynamics in presence of multi-particulates. In vitro results were compared against sensory tests that considered the attributes of ease of swallowing and post-swallow residues. Water and hydrocolloids were considered as suspending vehicles, while the suspended phase consisted of cellulose pellets of two different average sizes. Both in vivo and in vitro tests reported easier swallow for smaller multi-particulates. Besides, water thin liquids appeared not optimal for complete oral clearance of the solids. The sensory study did not highlight significant differences between the levels of thickness of the hydrocolloids. Conversely, more discriminant results were obtained from in vitro tests, suggesting that a minimum critical viscosity is necessary to enable a smooth swallow, but increasing too much the carrier concentration affects swallowing negatively. These results highlight the important interplay of particle size and suspending vehicle rheology and the meaningful contribution that in vitro methods can provide to pre-screening multi-particulate oral drug delivery systems before sensory evaluation.