The bolus then moves through the stomach mixing with gastric acid secretion to form chyme. During swallowing and on arrival into the proximal part of the stomach, limited mixing takes place but salivary amylase begins to digest the starch in the bolus. Boluses are irregular in shape in the mouth and they become elongated during their passage through the oesophagus thanks to their cohesiveness. Their shape is dynamic and continually changing on their journey through the mouth to the oesophagus and into the stomach. Other important factors include the mastication pattern and the duration and number of cycles of chewing, which can vary between subjects. These include factors such as bolus cohesion and elasticity. There are known criteria that a food bolus needs to meet before it can be swallowed. Research comparing the oral digestion of nuts and raw vegetables showed that vegetables, on average, resulted in larger particle size in the bolus compared to nuts. The texture and elasticity of food as well as the particle size of food in the mouth regulate the muscle force applied in chewing food, the volume of saliva secreted and the number of cycles of mastication, resulting in different final bolus properties. Food properties such as hardness, texture, initial moisture, and fat content will affect the bolus properties. Salivary amylase starts the hydrolysis of starch in the mouth, and the movements of the tongue mix food particles and assist the comminution and swallowing processes that play important roles in bolus formation within this first part of digestion. Mastication incorporates saliva to increase the lubrication and cohesiveness of the food particles. ĭigestion starts in the mouth, where the main goal is to reduce the size and increase the lubricity of the food particles before swallowing. It is then influenced by individual physiology, mastication patterns and saliva. Oral bolus properties are a function of the properties of the food consumed, including its structure, texture and composition. In particular, the properties of the bolus formed in the mouth can influence gastric behaviour, and thus, digestion kinetics and consequent physiological outcomes. These new in vivo data from undisturbed organ imaging can improve knowledge of the digestion process, which will, in turn, inform in vitro and in silico modelling of digestion, thus improving their in vitro/in vivo relevance.ĭigestion comprises a series of sequential processes, whereby each stage of digestion is influenced by the previous one. The cohesiveness as well as the meal composition seem to play a key role in the resulting boluses. The median number of boluses within the stomach was 282, 106 and 9 for Meal 1, Meal 2 and Meal 3 ( p < 0.0001) with an average volume of 0.47 mL, 2.4 mL and 13.6 mL, respectively ( p < 0.0001). Three groups of nine healthy participants were fed three different meals: chicken and roasted vegetables (Meal 1), bread and jam (Meal 2) and cheese and yogurt (Meal 3), and then, their stomach content was imaged. In this work, non-invasive magnetic resonance imaging (MRI) was used for the first time to measure boluses in the stomach a few minutes after swallowing. Knowledge of these parameters, however, is incomplete due to limitations of the techniques used. The number, size and surface properties of the boluses will affect their processing and emptying from the stomach. Oral processing of food results in the formation of food boluses, which are then swallowed and reach the stomach for further digestion.
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