Konjac / Glucomannan

by Mike September 25, 2011

Konjac It is a perennial plant, growing from a large corm up to 25 cm in diameter. The single leaf is up to 1.3 m across, bipinnate, and divided into numerous leaflets. The flowers are produced on a spathe enclosed by a dark purple spadix up to 55 cm long.

The corm of the konjac is often colloquially referred to as a yam, although it bears no marked relation to tubers of the family Dioscoreaceae.

Cultivation and use:

Konjac is grown in India, China, Japan and Korea for its large starchy corms, used to create a flour and jelly of the same name. It is also used as a vegan substitute for gelatin.

In Japanese cuisine, konjac (known as konnyaku) appears in dishes such as oden. It is typically mottled grey and firmer in consistency than most gelatins. It has very little taste; the common variety tastes vaguely like salt. It is valued more for its texture than flavor.

Ito konnyaku is a type of Japanese food consisting of konjac cut into noodle-like strips. It is usually sold in plastic bags with accompanying water. It is often used in sukiyaki and oden. The name literally means "thread-konjac."

Japanese konnyaku is made by mixing konjac flour with water and limewater. Hijiki is often added for the characteristic dark color and flavor. Without additives for color, konnyaku is pale white. It is then boiled and cooled to solidify. Konnyaku made in noodle form is called shirataki (see shirataki noodles) and used in foods such as sukiyaki and gyudon.

Konjac is consumed in parts of China's Sichuan province; the corm is called moyu (or Devil's Taro), and the jelly is called "konjac tofu" (moyu doufu) or "snow konjac" (xue moyu).

The dried corm of the konjac plant contains around 40% Glucomannan gum. This polysaccharide makes konjac jelly highly viscous.

Konjac has almost 0 calories but is very high in fiber. Thus, it is often used as a diet food. It can also be used for facial massage accessories which are currently popular in Korea.

The product Lipozene is made from the Konjac root.

Fruit jelly:

Konjac can also be made into a popular Asian fruit jelly snack, known variously in the United States as lychee cups (after a typical flavor and Nata de coco cube suspended in the gel) or konjac candy, usually served in bite-sized plastic cups.

Choking risk:

Perhaps due to several highly publicized deaths and near-deaths in the San Francisco Bay Area among children and elderly due to suffocation while eating konjac candy, there were U.S. Food and Drug Administration (FDA) product warnings in 2001 and subsequent recalls in the United States and Canada. Unlike gelatin and some other commonly used gelling agents, konjac fruit jelly does not melt readily in the mouth. Some products formed a gel strong enough such that only chewing, not tongue pressure or breathing pressure, could disintegrate the gel. product out with enough force to unintentionally lodge it in his trachea. Konjac fruit jelly was subsequently also banned in the European Union.

Some konjac jelly snacks are not of a size and consistency to pose any unusual choking risk but are nonetheless affected by the government bans. Some products that remain in Asian markets have an increased size, unusual shape, and more delicate consistency than the round plug-like gels that were associated with the choking incidents. The snacks usually have warning labels advising parents to make sure that their children chew the jelly thoroughly before swallowing. Japan's largest manufacturer of konjac snacks, MannanLife, has temporarily stopped production of the jellies after it was revealed that a 21-month-old Japanese boy had choked to death on a frozen MannanLife konjac jelly. As of 2008, seventeen people have died from choking on konjac since 1995.

Glucomannan is a water-soluble polysaccharide that is considered a dietary fiber. Glucomannan is a food additive used as an emulsifier and thickener. Products containing glucomannan, marketed under a variety of brand names, are also sold as nutritional supplements for constipation, obesity, high cholesterol, acne vulgaris and type 2 diabetes. Although there is some clinical support for potential health benefits, the U.S. Food and Drug Administration (FDA) has not approved any product containing Glucomannan for the treatment of these medical conditions. Several companies selling products containing Glucomannan have been disciplined by the U.S. Federal Trade Commission (FTC) for misleading or exaggerated claims pertaining to the health benefits of Glucomannan

Chemistry:

Glucomannan is mainly a straight-chain polymer, with a small amount of branching. The component sugars are β-(1→4)-linked D-mannose and D-glucose in a ratio of 1.6:1. The degree of branching is about 8% through β-(1→6)-glucosyl linkages.

Glucomannan with α-(1→6)-linked galactose units in side branches is called galactoglucomannan.

Natural sources:

Glucomannan comprises 40% by dry weight of the roots, or corm, of the konjac plant. It is also a hemicellulose that is present in large amounts in the wood of conifers and in smaller amounts in the wood of dicotyledons.

Potential health risk:

A health advisory was released by Health Canada stating the following: "natural health products containing the ingredient Glucomannan in tablet, capsule or powder form, which are currently on the Canadian market, have a potential for harm if taken without at least 8 ounces of water or other fluid. The risk to Canadians includes choking and/or blockage of the throat, esophagus or intestine, according to international adverse reaction case reports. It is also important to note that these products should NOT be taken immediately before going to bed."

Potential health benefits:

Constipation:

Glucomannan is a soluble fiber, and as such, has been investigated for the treatment of constipation. Glucomannan may relieve constipation by decreasing fecal transit time. In the treatment of chronic constipation, Glucomannan significantly improved symptoms of constipation while being well-tolerated and free of relevant side effects.

Cholesterol and other lipids:

Glucomannan has demonstrated statistically significant improvements in the total cholesterol of obese patients. In healthy men, 4 weeks of taking 3.9 grams of Glucomannan decreased total cholesterol, low-density lipoprotein, triglycerides, and systolic blood pressure; notably, triglycerides dropped by 23%. Glucomannan has also been tested in children with high cholesterol in conjunction with a diet. Interestingly, greater decreases in total cholesterol and low-density lipoprotein were observed in female children when compared to male children. When used in conjunction with chitosan, Glucomannan decreases serum cholesterol possibly by increasing steroid excretion via the feces.

Type 2 diabetes:

Glucomannan may be useful as a therapeutic adjunct for type 2 diabetes. It has been shown to improve the lipid profile and alleviate the fasting blood glucose levels of type 2 diabetics.

Weight Loss:

In one study involving 200 obese subjects, Glucomannan or a placebo were given for 16 weeks. They found that Glucomannan & fiber group lost 4.52 kg on average compared to 0.79 of control group. The Glucomannan group also had increased satiety compared to control group. LDL cholesterol was significantly reduced as well during the 16 week period. The study also reported that the treatments were well tolerated, and did not report any side effects.

A 8 week double blind trial involved 20 obese patients. A placebo or a Glucomannan fiber supplement of 1 gram was given to the subjects one hour before each meal. No changes were made to the diet or exercise habits of the patients. The study found that over the 8 week period, cholesterol levels were significantly reduced, and the Glucomannan group had an average weight loss of 5.5 lbs.

Commercial use:

As a food additive, Glucomannan is used as an emulsifier and thickener. It has E number E425(ii).

Dietary supplements:

Glucomannan is an ingredient in a variety of dietary supplement  products marketed via television advertisements claiming to aid in weight loss. According to the FTC, there are no clinical data supporting many of the claimsand several companies have been determined by the FTC or the FDA to have, at some time, violated the Federal Food, Drug, and Cosmetic Act including Vitacost, PediaLean, Herbal Worldwide Holding,  BioTrim, and others. The company Obesity Research Institute, the marketer of FiberThin, Zylotrim, Propolene and Lipozene, settled FTC charges that their misleading weight-loss claims violated federal laws by agreeing to pay $1.5 million in consumer redress.

Shirataki noodles:

Shirataki are very low carbohydrate, low calorie, thin, translucent, gelatinous traditional Japanese noodles made from devil's tongue yam (elephant yam or the konjac yam). The word "shirataki" means "white waterfall" describing the appearance of these noodles. Largely composed of water and Glucomannan, a water-soluble dietary fiber, they have little flavor of their own.

Shirataki noodles can be found both in dry and soft "wet" forms in Asian markets and some supermarkets. When wet, they are purchased pre-packaged in liquid. They normally have a shelf life of up to one year. Some brands may require rinsing or par-boiling as the water they are packaged in has an odor that may be unpleasant to those not accustomed to it.

Alternatively, the noodles can be drained and dry roasted. This gets rid of the aku (bitterness). It also makes the noodles have a more pasta like consistency. Dry roasting is done by placing noodles in a non-stick skillet on high for a minute or until you hear a slight squeaking noise when moving them around. After that they are ready to be added to soup stock or have a sauce added to them.

There are two types of shirataki noodles sold in the United States. Traditional shirataki noodles have zero net carbohydrates, no food energy, and no gluten, and they are useful for those on low-carbohydrate diets. Tofu-based shirataki-style noodles are becoming increasingly popular in U.S. supermarkets and health food stores. They have a much shorter shelf life and require refrigeration even before opening. Tofu-based noodles contain a minimal amount of carbohydrate.

Source:

The Glucomannan noodles come from the root of an Asian plant called konjac (full name amorphophallus konjac). It has been nicknamed elephant yam, and also called konjaku, konnyaku, or the konnyaku potato.

Other names:

Shirataki also goes by the names "ito konnyaku," yam noodles, and devil's tongue noodles.