2022 Volume 227 Issue 3 Pages 242-252
Nori (laver) is mainly made from the cultivated thallus of the red algae Pyropia yezoensis, and mostly is processed into dried sheets for consumption. It is a familiar food for us in Japan and is one of the indispensable foodstuffs in our daily diet. The origin of nori cultivation is believed to date back to the Edo period with subsequent development and improved cultivation technology in conjunction with the clarification of the life history of the algae resulting in peak domestic production of dried nori exceeding 10 billion sheets. Factors such as the shortening of the cultivation season, occurrence of diseases, and color fading of nori thallus have led to a gradual decline in nori production, and recent production has dropped to around 6 billion sheets per year. Saga Prefecture faces the Ariake Sea, the largest seaweed production area in Japan, and has been the largest producer of dried nori in Japan for 19 consecutive years in terms of both number of sheets and production value. However, the stagnation of nori consumption and the occurrence of low-quality and off-colored nori have become a concern in this prefecture.
This paper focuses on porphyran, a polysaccharide unique to red algae such as nori, and eicosapentaenoic acid (EPA), a representative functional lipid, as characteristic components in nori.
Carbohydrates are the main components, accounting for about half of the dry weight of seaweed, and most of the carbohydrates in nori are porphyran. Porphyran is a unique component of red algae and is a sulfated, viscous polysaccharide. Nori has a high lipid content (about 4% of dry weight) among edible seaweeds and is unique in that more than half of its component fatty acids are EPA. EPA and docosahexaenoic acid are typical n-3 polyunsaturated fatty acids and are found in abundance in fish. However, from the viewpoint of prevention of lifestyle-related diseases and metabolic syndrome, it has been pointed out that their intake in the population of developed countries is insufficient. Currently, the main source of these polyunsaturated fatty acids is fish, but algae are also attracting attention as an alternative source.
This paper describes (1) analytical methods for polysaccharides including porphyran contained in nori developed by the authors and its application, and the relationship between polysaccharides and quality of nori, and (2) how to make effective utilization of EPA in nori by changes in the structures of EPA-containing lipids and porphyran by fermentation of nori with koji.