Definition of “Koku” Involved in Food Palatability

Abstract

It is well known that many factors—taste, aroma, tenderness, juiciness, viscosity, and so on—are involved in food palatability. In Japan, the term “koku” (referring to koku attributes) is used in eating and evaluating to be palatable foods such as curry, stew, ramen noodles, natural cheese, and so on. Thus, it has been thought to be one of the important factors enhancing food palatability. However, koku has not yet been defined, and there have been few research studies on the compounds that enhance koku (koku attributes).

This chapter introduces definitions of koku and koku attributes. Koku is the unique sensation caused by lots of stimulation in terms of taste, aroma, and texture, which is expressed as complexity in koku. This is the essence of koku attributes. Furthermore, when this sensation is spread out without changing its characteristic flavor in our whole oral cavity, and it lingers after swallowing, we can sense strong koku attributes such as mouthfulness and lingeringness. Therefore, koku is constituted by three elements: complexity, mouthfulness, and lingeringness (continuity). Complexity in the koku attributes of foods is produced by aging, fermentation, and heating, causing production of various compounds. Mouthfulness and lingeringness (continuity) have recently been explained as being caused by umami compounds and/or phytosterols in onions.

Recent sensory evaluation analyses have shown that the addition of umami compounds enhances the retronasal aroma sensation, resulting in enhancement of the flavor of foods (mouthfulness). Umami compounds have also been shown to cause an effect of lingeringness of the taste sensation. Furthermore, phytosterols in onion have been confirmed to contribute to a sensation of lingeringness of the aroma—a koku attribute. Headspace gas chromatography analyses have shown that β-sitosterol binds with methyl propyl disulfide and hexanal. The addition of 0.02% β-sitosterol to consommé soup enhances the mouthfulness and lingeringness of the aroma sensation. On the basis of these findings, umami compounds and phytosterols are thought to be candidates for enhancement of koku attributes in palatable foods.