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■The True Nature of the Umami of Kombu
When we chew a piece of Kombu or taste Kombu Dashi, we can feel the mild Umami sensation in our mouth. The main constituent of Umami in Kombu is glutamic acid (discovered by Dr. Kikunae Ikeda of Tokyo Imperial University in 1908). Glutamic acid is a type of amino acid that is particularly important among Umami constituents, and plays a major role in the tastiness of food.
■Kombu Dashi, a Fundamental Part of Japanese Cuisine
Kombu Dashi and Katsuobushi (bonito flakes) Dashi have been widely used to season Japanese cuisine for centuries, along with soy sauce. Kombu Dashi, in particular, is the most widely used Dashi by professional chefs at Ryotei (traditional Japanese restaurants), and is a vital component in delicate dishes that bring out the best in the ingredients. This is because Kombu Dashi has a rich Umami taste that brings out the flavor of other foodstuffs.
The Umami of food is divided into 1) glutamic acid, an Umami represented by Kombu, 2) inosinic acid, an Umami of meat and fish, and 3) guanylic acid, an Umami of Shiitake mushrooms. The reason why Kombu Dashi goes well with fish and meat is not only that vegetable Umami and animal Umami work well together and enhance each other's different Umami, but also because of the Synergistic Effect of Tastes.
■What is the Synergistic Effect of Tastes?
The synergistic effect of tastes means that the entire Umami becomes even stronger than when used alone, when glutamic acid is used in combination with the Umami of meat or Shiitake mushrooms.
This famous synergistic effect of tastes was discovered by Dr. Akira Kuninaka, a researcher at Yamasa Co. Ltd. In the culinary world, the Umami of Kombu, bonito flakes, and Shiitake mushrooms have been used together empirically, but their effectiveness has also been scientifically proven.
17 September 2021 posted
Makombu and Gagome Kelps Belong to the Same Genus!?
The scientific name for Makombu is Laminaria japonica, while the scientific name for Gagome is Kjellmaniella crassifolia. These are the brown algae that we first learned the scientific names when we were introduced to marine botany. In 2006, a group of Canadian researchers, using molecular phylogenetic methodology based on gene sequences, discovered that the two species are clustered. Canadian researchers also proposed that Makombu and Gagome belong to the same genus and should be placed in a new genus, Saccharina, rather than Laminaria or Kjellmaniella (Lane et al. 2006). It has been proposed that Makombu should be placed in Saccharina japonica and that Gagome should be placed in Saccharina sculpera (Lane et al. 2006). Gagomekombu as a Japanese name was proposed by Yotsukura (2007).
The framework of molecular phylogenetic methodology used there was reported in the 1990s by Carl Woese, an American evolutionary biologist (Woese 1987). Woese used molecular phylogenetic methodology to explain the evolution of microorganisms, especially bacteria, and proposed that cellular organisms should be divided into three domains: Bacteria, Archaea, and Eukarya. Many scientists now accept this molecular phylogenetic methodology, and it is even taught in high school biology textbooks in Japan. Since this methodology has the potential to provide objective classification criteria and can be applied to almost all cellular organisms, including marine organisms, new taxonomic groups are being discovered and modified using this methodology at an ever-increasing rate. Using molecular phylogenetic analysis, we now know that Makombu belong to the Diaphoretickes (a higher taxonomic group meaning "diverse") / SAR (Stramenopile alveolata lizaria) group / stramenopile within the eukaryotic domain, and also to the phylum Heterokontophyta (Heterokontophyta) / Phaeophyceae / Laminariales / Laminariacea / Saccharina.(http://shigen.nig.ac.jp/algae_tree/Eukarya.html)。
However, there is more to the story of the classification of Makombu and Gagome. An international team of researchers reanalyzed more nuclear, mitochondrial, and plastid genes than Lane et al. (2006), and re-proposed that Gagome could not be included in the genus Saccharina, but should be placed in its own genus, i.e., Kjellmaniella (Starko et al. 2019). One of the weaknesses of molecular phylogenetic analysis is that if the genes used in the analysis contain homoplasy, or if the data sets used in the analysis are different, the topology of phylogenetic tree may change and the phylogeny may be misidentified, and this point needs to be carefully considered. We hope that young researchers will challenge solving the phylogenetic classification of kelp and the other seaweeds to establish more reliable systematics. As this reason, we allow to use both Kjellmaniella crassifolia and Saccharina sculpera for the scientific names, and Gagome and Gagomekombu as the Japanese common names in this website.
FoM Editorial
References
四ツ倉典滋（2007）日本産寒海性コンブ科植物の学名について. 藻類 55: 167-172 (in Japanese).
Lane et al. (2006) Corrigendum [J. Phycol. 42, 493-512. (2006)]. J. Phycology 42:962.
Woese (1987) Bacterial evolution. Microbiol. Rev. 51, 221–271.
17 September 2021 posted
Utilization of Kombu
Kombu is one of the principal fishery products of Hokkaido, with its production amounting to around 90% of the national total. Although kombu is produced in Hokkaido, it is mainly consumed as a foodstuff in western Japan and in the Tohoku district in northern Honshu. Because rice, which was used as a form of tribute in Japan until the Edo period (ca. 400 years ago), was not cultivated in Hokkaido, dried kelp with high preservative property became a tribute and a strategic export product in place of rice for the feudal domain of Matsumae. There may be a relation between the facts that kombu became a food to eat in western Japan and it became a foodstuff to extract (make dashi, means soup stock) in Hokkaido.
The most notable constituents in kombu are glutamic and aspartic acids, which are amino acid-based umami compounds in the kombu extract dashi. These umami compounds have a different taste from inosinic acid, which is a nucleic acid-based umami compound derived from fish and meat. In addition, kombu is rich in minerals and dietary fiber. Effects of dietary fiber comes from fucoidan and alginic acid, which give kombu its sticky quality. Apart from its nutritional aspects, fucoidan has been reported to show anti-cancer, antioxidant, anti-coagulation and thrombogenic, immunomodulatory, antiviral, and anti-inflammatory properties. Furthermore, its positive effects on metabolic syndrome improvement, gastrointestinal tract protection, angiogenesis and bone health have been revealed (Wang et al. 2019). In addition, research has recently begun to chemically modify fucoidan and alginate for uses in new value-added applications (Fernando et al. 2019).
Characteristics of Kombu harvested at the coasts of Hokkaido (referred from Ippan Syadan Houjinn Hokkaido Suisanbutsu Kensa Kyokai 2021)
1) Scientific name, 2) Japanese common name, 3) Production area, 4) Characteristics, and 5) Application
1) Saccharina japonica, 2) Makombu, 3) Matsumae-Hakodate-Muroran, 4) good dashi (soup stock), good taste, 5) dashi, salted kombu, processed kombu food.
1) Saccharina sculpera, 2) Gagomekombu, 3) Matsumae-Hakodate-Muroran, 4) high viscosity, rich in fucoidan, 5) shredded kombu, matumaezuke.
1) Saccharina angustata, 2) Mitsuishikombu, Hidakakombu, 3) Hidaka Subprefecture, 4) narrow leaf part, can be boiled quickly, 5) dashi, tsukudani.
1) Saccharina longissima, 2) Nagakombu, Saomaekombu, 3) Kushiro-Nemuro, 4) over 10 m long, 5) kombu roll, tsukudani, seaweed salad.
1) Saccharina coriacea, 2) Atsubakombu, Gaggarakombu, 3) Kushiro-Nemuro, 4) thick leafy part, 5) kombu roll, salted kombu.
1) Arthrothamnus bifidus, 2) Nekoashikombu, 3) Kushiro-Nemuro, 4) stem and root parts look like cat foot, rich in mannitol and viscous constituent, 5) shredded kombu.
1) Saccharina japonica var. diabolica, 2) Rausukombu, 3) Shiretoko Peninsula, 4) broad and soft leaf parts, good flavor and soup stock, 5) dashi, tsukudani, kombu tea.
1) Saccharina japonica var. ochotensis, 2) Rishirikombu, 3) Rishiri and Rebun Isles, Northern area of Japan and Okhotsk Sea coasts, 4) slightly hard texture, dashi with clear and good taste, 5) dashi, shredded kombu.
1) Saccharina cichorioides, 2) Chijimikombu, 3) Soya Subprefecture, 4) sawtooth-like leaf part, 5) processed kombu food.
1) Saccharina japonica var. religiosa, 2) Hosomekombu, 3) Japan Sea coast, 4) narrow, thick and hard leaf part, high viscosity, 5) shredded kombu, matumaezuke.
KURIHARA Hideyuki・Faculty of Fisheries Sciences, Hokkaido University・Associate Professor
References
一般社団法人北海道水産物検査協会, 2021 (http://www.h-skk.or.jp/) (in Japanese)
17 September 2021 posted
Two Generations
The life of kelp species is sustained by repeating the filamentous microscopic generation (gametophyte) (see Figure for Two Generations) and the leafy macroscopic generation (sporophyte) that we utilize. The change from gametophyte to sporophyte takes place through fertilization of a sperm produced in the male gametophyte with an egg produced in the female gametophyte. The fertilized egg undergoes repeated somatic cell division and grows into the large kelp (sporophyte) that we see today. On the other hand, the generational change from sporophyte to gametophyte is completed when the sporophyte matures and undergoes meiosis (division of the cell nucleus in which the number of chromosomes is reduced by half), and the zoospore, which are germ cells, germinate and become gametophytes (Kanda 1936). Gametophytes grow in higher water temperatures than sporophytes, while sporophytes grow in lower water temperatures and in a high nutrient environment brought about by cold currents such as the Oyashio Current. It is interesting to note that the optimal growth water temperature at the time of generational change (when both generations mature) is close to the optimal growth water temperature of the next generation. This seems to correspond well to the seasonal changes we see in kelp, where the kelp grows larger in the cold winter and dies back from the tip in the summer (also called Suegare or Sakigare in Japanese). Sporophytes grow by dividing the cells between the thallus and stipe and pushing up the old parts (cell groups). The pushed-up old parts supply nutrients to the newly formed parts. Under high water temperatures and low nutrient conditions in summer, the old parts of the plant die off by consuming themselves and supplying nutrients to the new parts (Mizuta et al. 1994). The sporophytes that survive the senescence and die-off and retain the meristem at the base of the thallus start to grow again as second-year individuals. The sporophytes that survive for multiple years mature each year and release zoospores that lead to the gametophyte generation. These zoospores and the male and female gametophytes that develop from them are not only the target of seedling collection and terrestrial seed production in kelp cultivation, but are also the life stages for seedling conservation and hybridization.
MIZUTA Hiroyuki・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Two Generations: Preserved kelp gametophytes and their cell masses in a petri dish (top) and magnified images of male and female gametophytes (bottom)
References
17 September 2021 posted
Generational Change to the Microscopic Generation
The maturation of the macroscopic generation (sporophytes) of the kelp we use is not only important as a phenomenon that affects the wild bioresources of the next generation, but also the mature thalli are used as mother plants for seed production in kelp aquaculture. Mature sporophytes produce reproductive organs called sori, which are raised on the surface of the thallus (see Figure for Generational Change to the Microscopic Generation). In a specialized case, Wakame seaweed, a member of the kelp family, produces leaves on its stipe that are specialized for maturation called mekabu (sporophylls), and on these sporophylls, sori are produced. These sori are made up of epidermal cells that divide and elongate to form zoosporangia, cells called paraphyses that protect the zoosporangia, and a mucilage cap above the pharaphyses. In the case of Makombu, a single zoosporangium produces 32 zoospores, which eventually differentiate into male and female gametophytes (Abe 1939). They are pear-shaped (about 11 µm long × 6 µm short), have no cell wall, and have two flagella. They swim to the bottom and migrate to a new generation (gametophytes). They are released mainly during the night and start swimming at a speed of about 160 µm/s. The swimming speed decreases with time. As time passes, the swimming speed decreases and eventually stops with the longest swimmers lasting about a day. When swimming at its maximum speed, it moves about 57 cm per hour. Depending on the timing and location of their release, they may be strongly affected by the flow of seawater, which may lead to an expansion of their growth area. In addition, these zoospores are chemotactic, which means that they move in response to chemical substances and swim around in search of a place where nutrients can be sufficiently supplied in the future, albeit within a narrow area on the substrate (Fukuhara et al. 2002).
MIZUTA Hiroyuki・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Generational Change to the Microscopic Generation: Wakame sporophyll (upper left) and Makonbu sporophyte with sori formed (upper right). In the lower row, a view of the release of the zoospores (left) and an enlarged image of the zoospore with two flagella (right).
References
Abe, K. (1939): Mitosen im sporangium von Laminaria japonica Aresch. Sci. Rep. Tohoku. Imp. Univ. Biol., 8, 259-265.
17 September 2021 posted
Overcoming Injury
Kombu is a sessile and cannot move by itself. Therefore, it has various abilities to overcome stress. When it is bitten by herbivores such as a sea urchin or scraped by waves, the cells in the injured area produce excessive amounts of reactive oxygen species and necrosis, while at the same time acting as a shield to protect the cells inside. This phenomenon, called hypersensitive cell death, is also observed when pathogens enter the body, and plays a role in preventing the spread of infection and injury. In the vicinity of the necrotic cells, changes occur to minimize the effects of further injury by accumulating protective substances such as polyphenols in the cell walls and intercellular spaces. In addition, of the cells in the body that were playing a role in supporting the body and storing nutrients before the injury (cortical cells and medullary cells), the cells that survive the injury produce pigments and become epidermal cells that play a role in photosynthesis and defense (see Figure for Overcoming Injury). In this way, the cells of the sporophyte demonstrate the ability to change their roles according to the situation.
Substances that trigger defense responses due to pathogen infection and other factors are called elicitors. These elicitors include a variety of substances, such as kelp cell wall degradation products and substances of microbial origin. When the elicitor is exposed to the sporophyte, a transient and localized generation of reactive oxygen species is observed. This is called an oxidative burst. Sporophytes treated with the elicitor undergo an oxidative burst, and various defense responses are triggered in response. In particular, an enzyme called haloperoxidase controls the amount of reactive oxygen species, and the halogenated compounds produced in the process, especially iodine compounds, are known to have strong antibacterial effects. The reason why kelp is rich in iodine is because it is essential for its survival. These responses occur within seconds to minutes, suggesting that they are responding quickly (Shimizu et al. 2018). In addition to that brief response, secondary metabolism is active in the body, producing antibacterial and repellent substances, including polyphenols. Transient and localized generation of ROS is also seen in the reproductive organ of the sporophyte, the sorus. Sori are equipped with various defense mechanisms to protect their germ cells, the zoospores, and to ensure successful generation (Mizuta and Yasui 2010, 2011).
MIZUTA Hiroyuki・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Overcoming Injury: Visible (upper left) and fluorescent (upper right) images of the cut surface of the sporophyte of the Japanese kelp, in which reactive oxygen species (ROS) were detected using a fluorescent probe. In the bottom row, cells on the cut surface of the cultured explant become surface cells (bottom row).
References
17 September 2021 posted
Toward Sustainable Production
The kelp sporophyte grows large and eventually matures while overcoming stress with its various defense strategies. As it matures, reproductive organs called sori, which contain zoosporangia (organs producing zoospores), are produced on the surface of the thallus, but how large is the area of sori produced by one individual? There is an index called reproductive effort, which is expressed as the ratio of the area of sorus formation to the total surface area of the thallus. If this value is 100%, it means that the entire surface of the thallus produced is covered with sori. The values reported in the past for brown algae of the genera Saccharina and Laminaria range from 1 to 37%, except for some Western species of kelp, and many species have values under 50%. In other words, in nature, more than half of the thallus area dies and is lost without forming sori (Mizuta et al. 1999a).
In our laboratory, we prepared thallus fragments and discs from various parts of the kelp foliage, from the base to the tip, and cultured them. This means that the ability to form sori is present in the entire thallus. It has also been found that the thallus tissues of Wakame and Chigaiso, which produce blades specialized for sorus formation, are also capable of forming sori (Kumura et al. 2006).
So why is it that the reproductive efforts of many species of wild kelp do not reach 100%? The formation of sori is costly. In other words, kelps need to accumulate a certain amount of resources in order to form sori (Nimura et al. 2002). The kelp has a meristem at the base of the sporophyte, where it actively divides and elongates to push up the old parts. In the process, the body's resources are transported from the fringe to the midzone and from the tip to the base, with the tip and fringe acting as a source and the base as a sink. As a result, the apical tissue becomes resource-limited (it lacks the accumulation of resources necessary for maturation) by sending out more nutrients to the base than it can absorb from the seawater, and dies out without maturing, even though it has the capacity to mature itself. This is the reason for the low reproductive effort seen in natural kelp sporophytes.
The ability of all thallus parts of the sporophyte to form sori is now being utilized to induce maturation by controlling light, temperature, and nutrient conditions (Mizuta et al. 1999b; Kai et al. 2006). Sori can be induced on almost the entire surface of a 1-meter leaf fragment (see Figure for Toward Sustainable Production). Immature individuals collected from natural waters and mother plants used in aquaculture seedling production can be matured under controlled environmental conditions and then used for aquaculture seedling production and mother plants spreading in natural waters. In other words, it may be possible to maintain and improve productivity by helping the natural cycle by hand. We must continue to make the best use of the capabilities of the thallus part of kelp to aid the sustainable production and maintenance of seaweed beds.
MIZUTA Hiroyuki・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Toward Sustainable Production: Sporophyte discs of kelp species with maturation-induced sori (top row from left to right: Aname, and Gagome). In the middle and bottom rows are thallus discs with sori, enlarged images of sori, and sections of sori in Chigaiso and Wakame, respectively.
References
Kumura T., Yasui H. and Mizuta H. (2006) Nutrient requirement for zoospore formation in two Alariaceae plants, Undaria pinnatifida (Harvey) Suringar and Alaria crassifolia Kjellman (Phaeophyceae: Laminariales). Fisheries Science, 72, 860-869.
17 September 2021 posted
Taking Advantage of Totipotency
In land plants, the cells and tissues that make up the body have the ability to form a complete individual (totipotency), and this ability is actively used in cell and tissue cultures, which are widely used for basic research such as the analysis of physiological mechanisms, as well as for applied applications such as seedling production and breeding. On the other hand, it was revealed in the late 1970s that seaweeds, like land plants, possess totipotency, and it has been confirmed that kelp also possesses totipotency (Saga and Sakai 1984; Matsumura et al. 2000). On the other hand, the formation and proliferation mechanisms of seaweed callus (an amorphous cell mass formed when a part of the plant is cultured in a medium containing plant growth regulators, such as auxin and cytokinin). There are still many unanswered questions about the formation and proliferation mechanisms of kelp calli, as well as the control mechanisms of their differentiation into sporophytes. The same is true for many kelp species, and to solve these problems, research is being conducted to elucidate the mechanisms by which callus-like cells and protoplasts (cell contents without cell walls) are formed, proliferated, and re-differentiated.
Normally, tissue fragments are cut from the macroscopic generation (sporophyte) of kelp in order to harvest explants for tissue culture. At that time, the aforementioned defense response mechanism is activated, and reactive oxygen species (ROS) are generated by the action of NADPH oxidase in the cell membrane of the cell that senses the injury. This generation of reactive oxygen species greatly affects the growth of callus-like cells (see Figure for Taking Advantage of Totipotency) that occur at the tissue cleavage surface, resulting in different morphologies, such as filamentous and lumpy specimens. Normally, a calcium concentration of about 10 mM in seawater promotes the generation of ROS and the formation of filamentous cells. On the other hand, when the calcium concentration is lowered to 5 mM and the tissue is cultured, the amount of ROS generation decreases and the cells do not elongate, forming a clump-like cell population. The redifferentiation of callus-like cells into sporophyte cells is independent of the calcium concentration in seawater, suggesting that the differentiation of callus-like cells into foliated cells can be controlled by regulating calcium concentration (Kanamori et al. 2011). As basic research in this field progresses, we hope to establish efficient and productive tissue culture technology, which will lead to its practical use in seed production and breeding at production sites.
MIZUTA Hiroyuki・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Taking Advantage of Totipotency: Massive (upper left) and filamentous (upper right) callus-like cells and regenerated phloem (lower right) from a piece of Laminaria explant.
References
17 September 2021 posted
Biotechnology
Alginic acid is a linear polysaccharide consisting of two types of uronic acid, beta-D-mannuronic acid and alpha-L-guluronic acid, as its smallest constituent units. It is widely used in the fields of food, fiber, printing, fermentation, medical and dental materials, and cosmetics (Gacesa 1998). Most of the alginates are derived from common brown algae such as Laminaria, Fucus and Macrocystis (Chapman & Chapman 1980). For this reason, the coastal area of Hokkaido, where kombu and other large brown algae are widely distributed and kombu cultivation is actively promoted, is a treasure trove of alginic acid.
Hokkaido is the largest producer of kombu in Japan, and its cultivation is actively practised. However, in 1985 and 1998, an outbreak of a disease known as a spot disease occurred in cultivated kelp in Hokkaido, causing serious damage to the industry. A bacterium capable of degrading small pieces of kombu was isolated from the damaged kombu, and was found to be a new species of marine bacterium, which was named Pseudoalteromonas elyakovii (Sawabe et al. 2000). The strain belonging to this new species was also isolated from a mussel (Crenomytilus grayanus) collected in the waters around Vladivostok by Professor Ivanova's group at the Institute of Biochemistry of the Far East of the Russian Academy of Sciences (Ivanova et al. 1996), I recall that I visited to Vladivostok to negotiate for the joint publication of the new species.
In general, the main skeletons of the cell walls of brown algae such as kelp are cellulose and alginate molecules. Alginate is attached to the cellulose chains that make up the small fibers in a network, and these are cross-linked by glycoproteins to form a three-dimensional structure. It is also known that alginate is an intercellular viscous polysaccharide (Kloareg & Quatrano 1988). In order to clarify the pathogenic mechanism of spot disease, the alginate-degrading enzyme of strain H-4 was characterized, and a new extracellular enzyme with broad substrate specificity, which had never been reported at that time, capable of degrading both poly-mannuronate and poly-guluronate blocks in the alginate molecule was found (Sawabe et al. 1992, 1997b). Enzyme activity was higher in seawater conditions. Since H-4 has a simple and rational alginate-degrading strategy that uses alginate as its sole carbon source and can degrade this molecule very efficiently in seawater, the alginate-degrading mechanism of this bacterium may pose a disease threat to kelp.
We investigated the effective use of the H-4 alginate-degrading enzyme to dissolve the cell wall of living Makombu to obtain a large number of live cells, and succeeded in producing a large number of active Makombu protoplasts (cell wall-less cells) with sufficient cell membrane function. We also succeeded in producing a large number of protoplasts with high viability that retained sufficient cell membrane function (see photo) (Sawabe et al. 1993). In addition, we attempted to culture the obtained protoplasts and succeeded in regenerating them to an almost sporophyte state after 3-4 months for the first time (Sawabe & Ezura 1996; Sawabe et al. 1997a).
When I presented this research at an international conference on seaweed in Cologne, Germany, a French researcher who had been competing with me in research on protoplast regeneration in Makombu called out to me, "Congratulations!”, I still remember that. Unfortunately, however, the practical use of the Makombu protoplasts for mass cultivation has been halted due to the lack of interest in the field and the difficulty in obtaining the appropriate culture equipment. We hope that this research will have the opportunity to contribute to sustainable kelp production.
SAWABE Tomoo・Faculty of Fisheries Sciences, Hokkaido University・Professor
Figure for Biotechnology: Live protoplasts stained by red pigment (neutral red), of which membrane permeability was active.
References
Chapman V. J. and Chapman D. J. (1980) Algin and alginates, in “Seaweeds and their uses” ( eds. By V. J. Chapman and D. J. Chapman), Chapman and Hall, New York, pp. 194-278.
Gacesa P. (1998) Bacterial alginate biosynthesis -recent progress and future prospects. Microbiol., 144, 1133-1143 (1998).
Ivanova E. P., Mikhailov V. V., Kiprianova E. A., Levanova G. F., Garagulya A. D., Frolova G. M. and Svetashev V. I. (1996) Alteromonas elyakovii sp. nov. a new bacterium isolated from marine mollusks. Russian J. Mar. Biol., 22, 209-215.
Kloareg B. and Quatrano R. S. (1988) Structure of the cell walls of marine algae and ecophysiological functions of the matrix polysaccharides. Oceanogr. Mar. Biol. Annu Rev., 26, 259-315.
17 September 2021 posted
Donation & Research Collaboration
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