Introduction

Katsuyoshi Nishinari

I.1 Why/How/What Do We Eat?

What do we expect from food? Food supplies energy and nutrition. We eat food when we feel hungry. This has been known to be controlled by the feeding center and satiety center in the hypothalamus in the brain. Since the discovery of leptin, a hormone regulating food intake, the understanding of the mechanism of food intake has greatly advanced. Now, the mechanism of food intake is being studied further, and it is thought that the central nervous system in addition to hypothalamus is governing the food intake.

Food has such a physiological function, but also has psychological or cultural aspects that have not been understood completely by physiology. The mechanism that explains why people lose their appetite in dejection caused by events such as the death of beloved persons, a broken heart, or being scolded has not been identified.

Food has a special function to unite people by conviviality. This function plays important roles to strengthen family ties in daily life, but was also used by feudal kings and aristocrats to tame or govern subordinates. People like to eat special foods on the occasion or the turning point in their lives such as birthday, marriage, and funeral. Selection of foods depend on the preference, which is influenced by culture and economic status.

Food processing/cookery has assured the safety by sterilization and removal of harmful ingredients, storage, and transportation, as well as improving the palatability. Texture has been known to be the most important attribute determining the palatability, and has recently attracted more and more attention in relation to the safe delivery of food into digestive organs without causing choking or aspiration (i.e. the wrong transport of masticated foods or liquids bolus into the airway instead of to the esophagus then stomach). In addition to these urgent problems, the interaction between the food and oral organs governed by brain function has attracted much attention, although these are not yet well understood. Thin liquids are known to be swallowed faster than thick liquids. Firm foods are masticated more strongly and the number of chews is greater than for soft foods. Are firmer foods chewed slower or faster than soft foods? Or is the chewing speed independent of firmness? It may depend not only on the firmness but also on aroma and taste (Nishinari and Fang 2018).

Society for Mastication Science and Health Promotion was founded by Kinziro Kubota in Japan in 1990. The collaboration among dentists, food scientists, and related disciplines is thought to be important. People tend to prefer softer processed foods that do not need mastication. As a result, the jaw is degenerated and the space for teeth to grow is becoming insufficient, and thus the problem of snaggleteeth/irregular teeth can become serious.

The growth of the dental industry in developed countries indicates that people do not want to be deprived of the gratifying sensations that arise from eating their food. From the nutritional standpoint, it is possible to have a completely adequate diet in the form of fluid foods that require no mastication. However, few people are content to live on such a diet. It clearly shows that people want to continue to enjoy the textural sensations that arise from masticating their food (Bourne 2002). Bourne raises the following reasons for masticating food: gratification, comminution, mix with saliva, temperature adjustment, released flavor, and increased surface area. The link between reduced mastication ability and hippocampal neuron loss has been suggested, which might indicate that chewing plays a role in fending off dementia.

Saito examined the number of chewing using restored menus in each era in Japanese history. According to his examination, the restored menu for Himiko, queen of Yamatai in the third century, was found to need 3990 chews taking 51?minutes, 1366 chews and 31?minutes for Murasaki Shikibu (the author of Tale of Genji in the tenth to eleventh century), 2654 chews and 29?minutes for Minamoto Yoritomo (the first warrior Shogunate) in the end of twelfth century, 1465 chews and 22 minutes for Tokugawa Ieyasu (who established Edo Bakufu Shogunate in 1603) while only 620 chews and 11?minutes for a common menu in the present.

The decreasing tendency of the number of chews is a reflection of the decrease in the intake of tough/firm/hard foods. Many reports have been published that eating slowly with much mastication reduces the likelihood of obesity. Will this gradual change of food texture from firm to soft continue? Although the invention of softening of firm foods by enzymatic action that retains food appearance is good news for persons with difficulty in mastication, the decrease in chewing cycles sometimes results in fast eating, overeating, and obesity for normal persons. Bolhuis et al. (2014) and Forde et al. (2016) reported that smaller bite (amount of food ingested in the mouth) sizes and more chewing increased oro-sensory exposure time and slowed the eating rate, thus providing a stronger satiety response per energy consumed.

While many studies have reported that the expected satiation increased with increasing thickness/hardness for liquid/solid foods, and texture is more important determinant for expected satiation and thus for the selected portion size of food, other factors such as the means of consumption (e.g. using straw or spoon), affecting the eating rate, could not be neglected. It is also expected that a creamy flavor will cause a higher satiation than fruity flavor, but this remains inconclusive (Hogenkamp et al. 2011). Texture and flavor are the two most important determinants of food consumption in addition to the cost, and their respective roles and interaction should be studied further.

I.2 Terms for Texture/Taste/Aroma Related to Diverse Foods/Recipes

Is there a relationship between the two representing systems of written language, alphabets (phonetics) and ideograms, and the universality/diversity problem?

Ancient Egyptians used hieroglyphics representing shapes of all the things around them, and ancient Chinese used also hieroglyphic characters engraved on bones and tortoise shells. Origins of letters seem to be not so different. It can be imagined that ancient people devised these tools for communication by representing the shape faithfully and then simplified these shapes. However they came to their language, people of world now speak more than 7000 languages (although not all of these have a written equivalent, and many of these are spoken only by a small number of people). In an attempt to improve communication, Polish doctor L. L. Zamenhof invented what he hoped could be a universal language, Esperanto, although it has not gained many users/speakers.

While most languages have evolved into alphabets that represent only sounds (i.e. phonetics, without specific meaning), Chinese-based languages have kept the enormous number of hieroglyphic characters. However, the characters were simplified in the twentieth century in mainland China and Singapore; Japan and Taiwan retain the traditional Chinese characters.

The number of Chinese characters was thought to be about 50?000, but the publication of the largest Chinese character dictionary Zhonghua Zihai (simplified Chinese: ????) compiled in 1994 listed 85?568 different characters. It is thus difficult to determine the exact number of Chinese characters. I had a lucky experience to be nourished by a Chinese family during my stay in the United Kingdom and was given different dish every day for more than six months. I enjoyed different dish every day for 180?days! This family knew so many recipes! Is this diversity of dishes related to the enormous number of Chinese characters?

Japan is known to have the largest number of texture terms - about 500. In his visits to Japan, Bourne was impressed by the textural diversity of Japanese foods (Bourne 2002). The great number of texture terms represents the deep attachment to texture difference of foods. The high ratio of the Japanese texture terms is onomatopoetic (Nishinari et al. 2008; Hayakawa 2015). Onomatopoetic representation of the texture is similar to the hieroglyphic representation of things. Only a slight difference of the appearance, shape, size, color, sound, etc. requires a different term in onomatopoeia, just as in the enormous number of characters in Egyptian or Chinese hieroglyphic representation. There has been no systematic published study on the relation between the actual sound one hears during mastication and the onomatopoeic word chosen to represent the sound. Is it determined by anatomic structural difference of organs in the oral cavity or in the cultural difference originated in one's personal environmental background, historical, geographical, or education? It is well known that the onomatopoeic words for birds and other animals are different in English, French, and other languages, and therefore, these cultural differences partly account for differences in the onomatopoeia. Whether physiological difference or cultural differences are more important has not been studied, as far as the author is aware.

I.3 Universality and Diversity

For most physicists, it is valuable to understand a phenomenon by a simple equation symbolized by a Newton's law of motion. Although all the events in the universe seem to be very complicated, we can understand the essence of the event by extracting the most important core of the event. Thus,...