Takashi Yamamoto
Kio University
Sugar plays an important role in making delicious food, as well as in various kinds of sweets leading to the joy of life. In the first half of my talk, I would like to introduce various kinds of sugar used in Japan and, in the second half, I will talk about qualitative and hedonic (sweet and palatable) aspects of the physiological functions of sugar.
Sugar was first brought to Japan from China in the mid-eighth century. As trade with the continent flourished from the fourteenth to seventeenth centuries, imports of sugar increased and its use was expanded as a sweetener for cooking. The practice of the tea ceremony spread among the upper classes during this period, and sweets made with sugar were developed to accompany the tea. The tradition of sweets that evolved along with the tea ceremony forms a culture of confectionery of which Japan can be proud. It was not until the eighteenth century, however, when sugar cane began to be cultivated in Japan and sugar became more readily available to the common people. Sugar can be classed into two categories: one is the group of sugars including molasses, represented by ‘wasanbonto’, and the other, excluding molasses, represented by ‘johakuto’, is Japan’s most popular sugar.
Sugar is a source of vitality and energy because glucose, a component of sugar (sucrose), is a kind of ‘fuel’ for human metabolism. Sugar taken into the mouth stimulates a specific taste receptor, T1R2/T1R3, in taste cells of the taste buds distributed on the tongue, soft palate, and pharynx. The message from taste cells is sent to the brain through taste nerves and sensed as sweet. Other taste receptors are responsible for other basic tastes, such as salty, sour, bitter and umami. Among the five basic tastes, sweetness has the most powerful action in activating the reward system of the brain and releasing brain substances, such as β-endorphin, benzodiazepine, cannabinoids, dopamine and orexin. These substances are related to liking, wanting and eating behaviours, indicating that sweet taste is so palatable that food intake is enhanced. Palatability is one of the factors that enhance food and fluid intake and contributes to over-consumption, resulting in a risk of obesity and diabetes.
(Presented in the 2016 Chulalongkorn Asian Heritage Forum: Sweet Culture and the Joy of Life, 17-18 August 2016, Mandarin Oriental Hotel, Bangkok, organized by Institute of Thai Studies and Indian Studies Center, Chulalongkorn University)