Supercritical Fluid Extraction of “Koku” Enhancing Compounds from Fish and Fishery by-Products

Abstract

The potential of supercritical carbon dioxide (SC-CO 2 ) extraction of "koku" enhancing compounds from dried herring fillet ("Migaki-nishin" in Japanese) and sturgeon liver was explored. "Koku" enhancing compounds from a water-soluble extract and a mixed water miscible SC-CO 2 extract were isolated and evaluated for their effects on sensory perception. Results showed that only select compounds were found in the mixed water miscible SC-CO 2 extract compared to the complicated composition of the water-soluble extract. A notable feature was that the mixed water miscible SC-CO 2 extract contained "koku" enhancing compounds, e.g., nicotinamide, glycerol and creatine. This study revealed for the first time that these compounds were extracted by SC-CO 2 extraction and that nicotinamide enhances "koku". We also extracted "koku" enhancing compounds from sturgeon liver using the SC-CO 2 extraction technique. Instrumental analysis revealed that the sturgeon liver contained relatively large amounts of nicotinamide and glycerol. Thus, it is suggested that this technique might be applicable to the extraction of select compounds from fish and fishery by-products.Keywords: "koku", supercritical carbon dioxide (SC-CO 2 ), nicotinamide, glycerol, creatine, sensory evaluation IntroductionDried herring (Clupea pallasii) fillet, called "Migaki-nishin" in Japanese, is a traditional popular food item in Japan due to its remarkable flavor-enhancing properties. It is widely used as an ingredient in savory dishes, including noodles. In particular, the addition of dried herring fillet to noodle soup enhances flavor characteristics such as mouthfulness and continuity. The flavor characteristic that encompasses the sensation of mouthfulness and taste continuity is known as "koku" in Japanese. It has been reported that the addition of a dialyzed water-soluble fraction (MW 1000 _ 5000 Da) of "Migaki-nishin" to Japanese noodle soup enhanced "koku" (Shah et al., 2010). Furthermore, it was reported that pyrazines and some peptides, generated together in certain foods during the process of boiling or aging for extended periods, M. Shibata et al. 1200 form "koku" (Ogasawara, 2003). It is also known that some γ-glutamyl peptides such as glutathione enhance "koku" (Ueda et al., 1997;Kawajiri, 1999;Dunkel et al., 2007;Toelstede et al., 2009).The flavor of fish and shellfish principally originates from extractive components (Konosu and Yamaguchi, 1982). In general, most flavor components of foods are water-soluble, and include nucleotides, amino acids, peptides, organic acids and bases, and inorganic ions. Conventionally, flavor components from foods are recovered by the water extraction method. However, this method has a number of drawbacks, such as low selectivity, high energy costs, and the possible loss of volatile compounds during water removal. On the other hand, the high solubility and mass transfer rate makes extraction with a supercritical fluid very attractive.Additionally, supercritical fluid extraction has better transport properties t...