Chemical Analysis Of Mushrooms Shows Their Nutritional Benefits

Using modern analytic tools, scientists at the University of Illinois at Urbana-Champaign found that the six mushroom varieties tested -- in raw and cooked forms and at various harvest times and maturity levels -- are rich in total dietary fibers, including those associated with cholesterol-lowering (chitin) and healthy hearts (beta-glutan).

The findings appear online in advance of regular publication by the Journal of Agricultural and Food Chemistry. The same researchers last year reported in the same journal the carbohydrate profile of selected plum and prune products. The findings will become part of the U.S. Department of Agriculture's National Nutrient Database.

"What we've reported in these papers are the complete carbohydrate profiles of these two lines of popular foods," said George C. Fahey Jr., a professor of nutritional sciences in the department of animal sciences at Illinois. "These profiles include the digestible carbohydrates, the starches and the fermentable fibers that reach the large bowel. This work was important to the two commodity organizations that funded this research, because they had little information on these components."

It was already known that mushrooms offer high-quality protein, vitamins, unsaturated fatty acids and fiber, but a precise carbohydrate breakdown had been elusive.

The mushrooms studied were white button, crimini and portabella, all of which represent different maturity levels of Agaricus bisporus, and maitake (Grifola frondosa), shiitake (Lentinus edodes) and enoki (Flammulina velutipes). The latter two mushrooms were analyzed only in their consumed cooked form.

"The maitakes and shiitakes tended to be very similar in their nutrient concentrations, and quite a bit different than the others," said Cheryl L. Dikeman, a doctoral student in Fahey's lab and lead author on both papers. "Portabellas were off on their own in terms of their contents of oligosaccharides, beta-glucans and chitin."

Chitin concentrations were 8 percent in raw, mature portabellas and 6 percent in raw, immature ones. When cooked, chitin content fell to 2.7 percent in both forms, but their levels of total dietary fibers went up significantly. Also showing the same pattern were raw enokis, which had a 7.7 percent chitin content; cooking also lowered it to 2.7 percent but total dietary fibers jumped from 29.3 percent in raw to 41.6 percent in cooked.

Raw, mature white buttons and cooked, mature shiitakes boasted chitin levels of 3 percent and 3.6 percent, respectively.

Raw, mature portabellas also had the highest level of beta-glucan (0.2 percent), while most of the other mushrooms had 0.1 percent. Enokis and maitakes had none. Relatively small amounts are required to provide cardiovascular benefits, Fahey said.

Cooking tended to increase starch, total dietary fibers and fat contents and to decrease chitin concentrations in all of the mushrooms. "Some nutrients went up after cooking, while some went down," Dikeman said. "Part of that you'd expect to happen as water is cooked out."

Also measured were oligosaccharide levels. These sugar molecules are only partially digestible, but the undigested components are considered prebiotics in that they elicit growth of healthful bacteria in the colon.

Raw, immature portabellas had a total oligosaccharide concentration of 5,272 micrograms per gram (ug/g). Also found to have more than 1,000 ug/g were raw, mature portabellas and cooked, immature crimini. None were detected in enokis, maitakes or shiitakes. Most of the total oligosaccharides were in the form of glucooligosaccharides, but fructooligosaccharides (FOS) accounted for the total concentrations in cooked, immature white buttons. FOS did not appear in other samples.

In other findings: White buttons had the highest levels of ash; starch was highest in maitakes and shiitakes; and crude protein and acid-hydrolyzed fats were highest in crimini, white buttons and maitakes.

For plums and prunes, which are known to be good sources of dietary fiber, the researchers analyzed individual carbohydrate components that are in the various forms used by consumers: powders, juices, purees and fruits. They also looked at the waste byproducts, including dried plum pits.

All of the prune/plum products were found to have high total concentrations of oligosaccharides and free sugars. High in total dietary fibers as a percentage of total dry-matter were generally the various powder and fruit products.

The research primarily involved the use of high-performance liquid chromatography, which was adapted by Laura L. Bauer, a research specialist in animal sciences and a co-author on both papers, to quantify chitin concentrations in each mushroom. A spectrophotometer was used to analyze beta-glucan levels and sort out uronic acids that are associated with total dietary fibers.

The information obtained in the two studies, Fahey said, will allow people to choose the mushrooms and forms of plums and prunes that provide the dietary punch they may be needing. It also should allow food scientists to search for optimum preparation strategies for using the various products.

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The Mushroom Council of Dublin, Calif., funded the mushroom study and provided the samples. The plum/prune study was done with samples and funding provided by the California Dried Plum Board. Elizabeth A. Flickinger, a former postdoctoral researcher in Fahey's lab, also was a co-author on the plum/prune study.