The Materials Science of Eating and Food Breakdown
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The Materials
Science of Eating and Food Breakdown Peter J. Lillford
Introduction Most of the process of eating is a learned skill. While an infant readily puts most things in its mouth, the ability to distinguish food from any other material has to be taught, and even then it is several years before the whole range of foods can be consumed efficiently. Yet by the time we are 5–10 years old, our mastery of the complex set of mechanical actions involving tongue, teeth, and swallowing is so complete that we do not consciously note what we are doing or how we do it. We know that this process of mastication must contain the physics of flow, failure, and fracture, but how are we to explore these phenomena qualitatively, let alone quantitatively? We begin simply by asking people to describe what they are doing and perceiving as they eat. After encountering some initial resistance, we find that most people are able to describe the process of eating, often related to a specific food type, with a degree of common language using words describing mechanics (tough, tender, crisp, soft), flow (thick, thin, juicy, creamy), and size and shape (flaky, fibrous, gritty, smooth). It is clear that all the neural signals from pressure sensors in the tongue and soft palate, together with the forces and displacements operated by the muscles, are being combined to produce a sensory response. Furthermore, if individuals are properly trained using standard food items, they can reliably discriminate and quantitatively score all these parameters with remarkable consistency.
tion and release, and finally, reassembly into a swallowable bolus and the clearance of material from the palate, teeth, and tongue. We are obviously recording the materials science of comminution of the food itself, together with a mixing process with saliva. Thus, food is recognized by its performance in the complex machinery of the mouth; furthermore, “texture perception” is the measurement of the whole process and is not derived from the simple properties of the intact specimen. If food is recognized by its breakdown response, its “quality” is determined by reference to the “best” example of the type stored in the memory. Although we will not further examine quality or preference, we will examine the materials science of food breakdown and what makes cake different from a biscuit or meat. We begin by qualitative observation of the breakdown pathway of obviously different foods. Figures 2–4 show the sequential breakdown of whole cooked beef, a cracker biscuit, and analogue chicken meat constructed from spun fibers. The results were obtained by the gruesome but simple procedure of spitting out the samples
after a set number of chews. Notice that a similar process of fracture, reassembly, and subsequent fragmentation occurs in the first two examples. Normally, swallowing is associated with the reassembly process. Notice that in the synthetic meat, this does not occur. Not surprisingly, the meat-like texture of these analogues was suboptimal for this assembly property,
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