Food hardness affects bolus size, swallowing

By Sarah Guy, medwireNews Reporter

The smaller the particles in a food bolus (chewed food), the harder the food is likely to be, report researchers in the Archives of Oral Biology.

The finding could have implications for disadvantaged populations such as the elderly, infants, patients with dysphagia, and those recovering from operations, for whom swallowing boluses can be a challenging and hazardous task.

The correlation between bolus particle size and food hardness can be explained by a power-law relationship, remark Jianshe Chen (University of Leeds, UK) and colleagues who add that even for the same food material, bolus particle size has a wide range depending on the individual who is chewing.

"A good understanding of the underpinning physical and physiological principles of bolus formation and swallowing is needed for both healthcare services and [the] food manufacturing industry. Without such knowledge, food provision to disadvantaged consumers will inevitably continue to be a practice of trial and error," writes the team.

Ten healthy individuals participated in the research, chewing seven food samples of varying mechanical strength and removing the bolus just before swallowing for Chen and co-authors to analyze.

The food samples were: weak jelly (Jell-O), strong jelly, canned peach slices in juice, cottage cheese, salted peanuts, and cashew nuts. The strength (hardness) of the food was measured by puncture test, with weak jelly having the smallest breaking force (0.11 N) and salted peanuts having the largest force (24.00 N).

Bolus particle size varied hugely, report Chen et al, with the smallest at 0.045 mm² (equivalent to 0.24 mm diameter if spherical) for peanut bolus, to 3.280 mm² (equivalent to 2.10 mm if spherical) for peach bolus.

Indeed, peach boluses contained the widest range of particle size among all the food samples, potentially because of the fruit's "highly oriented fibrous microstructure, leading to the formation of many elongated particles," note the authors.

The researchers conclude that the role of food hardness in bolus particle size can be explained by the flow and behavior of the bolus during swallowing. For example, the flow has to be "properly adjusted by either reducing particle size of increasing saliva contribution, so that the required pressure for bolus flow can be matched by one's capability in creating such a pressure," writes the team.

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