Seaweeds, mushrooms and tofu

In this lesson seaweeds and mushrooms will be presented. Even if quite unusual for our gastronomic traditions, we invite you to discover them, both for health and taste. Seaweed, or marine plants and algae, are plant-like organisms that grow in the ocean, rivers and lakes. The edible seaweed, also known as sea vegetables, has been used in traditional medicine and diets in different places, above all in Asia but also in some Western countries such as Scotland, Ireland and Iceland. In Japan seaweed is traditionally used as feedstock in the production of various foods and the average annual consumption per person is about 1.4 kg (dry weight). There are over 10,000 species of seaweed.

They are often categorized according to their cell structures, pigments, uses and where they are grown. The 3 most common varieties are red algae (nori and dulse), brown algae (wacame, kelp, kombu) and green algae (spirulina). Seaweed could be consumed raw in salads, steamed or can be used to prepare sushi or soups. Spirulina algae are less frequently consumed and are a good source of dietary proteins, iron and B vitamins. Now, let’s have a look to the three most common seaweeds

in Japanese cuisine: nori, kombu kelp and wakame. Nori seaweed is available in paper-thin dark green sheets and is the most frequently consumed seaweed worldwide; it is mainly used for wrapping sushi, for onigiri rice balls, for snacks and chips and as a garnish for noodles, rice balls and soups. When chopped into small pieces, nori could be mixed with sesame seeds, chili pepper, salt or sugar as a seasoning powder. Nori seaweed is shredded and dried and then pressed into thin layers. Kombu kelp is a dark green seaweed with thick leather-like texture. There are more than 10 species of kombu kelp, each of which has specific tastes and flavors.

In Japan, kombu, for its high glutamate content, is mostly used for “dashi”, the Japanese soup stock used as a base for many foods and as a flavor enhancer. Kombu seaweed is usually sold in a dried form, eaten raw in sashimi or pickled in vinegar. Wakame, grown in Japan for centuries in cool and Arctic waters, is commonly used in soups like miso soup and salads, such as the Goma Wakame, with roasted seasoning seeds, soy sauce and vinegar dressing. Finally, Mozuku is a seaweed typical of the Okinawa Islands, which are Japan’s largest producers of mozuku, accounting for over 90% of the national production. The harvest season is from March to May.

Mozuku has a slimy and viscous texture and can be used fresh, dried or salted, for soups, salads, sauces and many other recipes. Mozuku is a natural source of a fucoidan, a natural sulfated polysaccharide, which has many potential properties on health, although at present more human-based studies are necessary. What are the nutritional properties of seaweed? Seaweed is rich in antioxidants like carotenoids and polyphenols, in particular brown algae are rich in beta-carotene, fucoxanthin and violaxanthin. The algae get from the sea a great amount of minerals, both macro minerals and trace elements, in particular iodine. Finally, seaweeds provide a good source of healthy omega-3 fatty acids. You should combine the different types of seaweed to get the maximum health benefits.

There are, however, some potential concerns relative to seaweed consumption. Because of the high sodium and iodine content, people with hypertension and thyroid diseases should eat seaweed with moderation. Now let’s move to Japanese mushrooms. Mushrooms, called “Kinoko”, are extensively used in the Japanese cuisine. The most used varieties are Shiitake mushrooms. They are available fresh, and are widely used grilled, deep fried or dried, which need to be rehydrated and are usually used boiled. The liquid deriving from the rehydration is widely used to make dashi. Maitake mushroom (Grifola frondosa) grows in clusters at the base of tree (particularly oaks) and is native to the northeastern part of Japan and North America.

The reishi mushroom (Ganoderma lucidum), widespread in Japan, China and North America, can be present in six different colors. The red variety is the most commonly used. Let’s have a look to the nutritional properties of mushrooms. Mushrooms are the only plants providing a natural source of vitamin D, i.e. ergosterol, that converts to vitamin D2 when exposed to ultraviolet light. Mushrooms are good sources of antioxidant. Maitake mushrooms have a particularly high content in ascorbic acid, tocopherols phenolic compounds and carotenoids. Mushrooms contain polysaccharides, including beta-glucans and triterpenes, with antioxidant, antiproliferative, immunomodulating, antiviral and antibacterial effects. Shiitake contain lentinan, a particular beta glucan, with immunostimulant properties, at least in animal-based studies, since results in humans are at present controversial.

Few studies on humans have shown that the regular consumption of shiitake might improve immunity and reduce inflammation, but further studies with larger samples are needed in order to confirm these properties. All seaweed and mushrooms have a strong umami taste, the fifth taste, which is usually described as a rich savory flavor. The darker the mushroom, the more umami it contains – and longer cooking methods intensify the mushroom flavor. Glutamate and guanylate are the substances which are responsible for the umami taste in vegetable food. Large amounts of glutamate can be found in seaweed and in mushrooms, while guanylate could be found especially in dried mushrooms. Tofu is another very common food in the Japanese cuisine, deriving from soy.

Tofu is an important source of proteins in China, Japan and, in general, in Southeast Asia, even if nowadays it is widely consumed all over the world. Tofu derives from soy milk, after heating it and adding a coagulant. The mixture will clot and then, after filtering the liquid, you can press it to the desired density. Tofu may be flavoured or seasoned with spices. It may be grilled, fried, simmered, steamed or eaten fresh and served with toppings, such as tapioca or sweet syrups. Tofu provides a small amount of kilocalories, fats and carbohydrates (no cholesterol) and is a good source of proteins. Conversely, cheese (the animal alternative), for example feta, the traditional Greek cheese, provides more calories, saturated fats and obviously cholesterol.

We can conclude that a moderate consumption of seaweed and mushrooms is advisable for their nutritional properties. Further studies are needed to improve our knowledge about these foods.