Elsevier

Food Chemistry

Volume 76, Issue 3, March 2002, Pages 293-298
Food Chemistry

Sterol and vitamin D2 contents in some wild and cultivated mushrooms

https://doi.org/10.1016/S0308-8146(01)00275-8Get rights and content

Abstract

The contents of vitamin D2 and sterols in some wild and cultivated mushrooms were determined, and the distribution of these compounds in different parts of the wild mushrooms was evaluated. In addition, the variation in vitamin D2 contents between individual fruiting bodies of wild mushrooms was studied. Vitamin D2 was determined using an HPLC method, including saponification and semipreparative normal-phase HPLC purification before analytical reversed-phase quantification with an internal standard. Sterol contents were analysed with gas chromatography using an internal standard method, including saponification before derivatizing sterols to trimethylsilyl ethers. Mass-spectral analyses were used to further confirm the identification of sterols. Vitamin D2 was almost totally absent in cultivated mushrooms, while some wild mushrooms contained high concentrations of this vitamin (4.7–194 μg/100 g dry weight). Ergosterol was the most abundant sterol found in mushrooms, and its contents were higher in cultivated mushrooms (602.1–678.6) than in wild mushrooms (296–489 mg/100 g dry weight). The contents of vitamin D2 and ergosterol varied greatly and moderately, respectively, between different parts of the mushrooms and were lowest in stipes. In addition, high variation in vitamin D2 contents between individual fruiting bodies was found.

Introduction

The origin of ergosterol and vitamin D2 (ergocalciferol) lies in the kingdom Fungi. Vitamin D2 is derived by photoirradiation from its precursor ergosterol. Ergosterol undergoes photolysis when exposed to UV light of wavelengths 280–320 nm to yield a variety of photoirradiation products, the principal ones being previtamin D2, tachysterol and lumisterol. The previtamin D2 undergoes spontaneous thermal rearrangement to vitamin D2 (Jones et al., 1985, Parrish, 1979, Singh, 1985). In the kingdoms Plantae and Animalia, ergosterol or vitamin D2 are almost absent. However, low levels of these compounds can be found in plants if they are contaminated with mould or yeast (Young & Games, 1993). Analytical methods to determine ergosterol in foods are based on either those detecting such contaminants in cereals and other foods or those examining the taxonomy or phylogenesis of fungi (Staffas, 2001, Weere and Gandhi, 1997, Young, 1995).

Vitamin D is an essential compound for humans. It can be produced in the skin by the action of sunlight or absorbed from the diet in the intestinal tract. The intake of vitamin D from food is especially emphasized in the northern (or southern) latitudes. Furthermore, some population groups, e.g. vegetarians, are at special risk of receiving insufficient levels of this vitamin from their diet (Lamberg-Allardt, Kärkkäinen, Seppänen, & Biström, 1993). Although vitamin D deficiency is classically associated with rickets and osteomalacia, milder deficiency states can, lead to osteoporosis (Eastell & Riggs, 1997).

In previous studies, we found that wild mushrooms are a rich natural vitamin D source (Mattila, Piironen, Uusi-Rauva, & Koivistoinen, 1994), which is also accepted by most vegetarians. In addition, at least from freeze-dried Chantarellus tubaeformis, the bioavailability of vitamin D2 was favourable (Outila, Mattila, Piironen, & Lamberg-Allardt, 1999). However, Mattila et al. (1994) studied only pooled samples, and more specific information on the distribution of vitamin D2 in different parts of the mushrooms and variation in individual mushrooms is needed.

More advanced fungi produce ergosterol as the principle sterol, differing from major plant sterols in having two double bonds in the sterol ring structure instead of one. Fungal and plant sterols are biosynthetized in similar reactions, but the sequence of postsqualene reactions and the stereochemistry of the major products differ. Most fungal sterols, e.g. ergosterol, contain 28 carbon atoms (Parks & Weete, 1991). Various minor sterols, present in fungi, have been identified, including fungisterol, ergosta-5,7-dienol, 24-methyl cholesterol and methylene cholesterol (Lyznik and Wojciechowski, 1981, Weere and Gandhi, 1997). The fungal sterols provide characteristic functions that are necessary for vegetative growth. Fungi can, however, accept different sterols in their membranes, but then they must adjust the membrane structure by modifying the phospholipid composition.

Plant sterols are recognized as having positive health effects, because they have been shown to decrease serum cholesterol levels and may also be beneficial in preventing colon cancer, as reviewed by Piironen, Lindsay, Miettinen, Toivo, and Lampi (2000). Fungal sterols may have similar functions to other plant sterols, there are however, few data on their nutritional effects.

The aim of the present study was to evaluate the vitamin D2 and sterol contents of wild and cultivated mushrooms and to learn more of their distribution in different parts of mushrooms and between individuals. Finally, the vitamin D2 and ergosterol contents in these edible mushrooms were compared, since vitamin D2 is biosynthetized from ergosterol.

Section snippets

Sampling

The sterol and vitamin D contents were determined from cultivated Pleurotus ostreatus, Agaricus bisporus/brown, A. bisporus/white and Lentinus edodes in summer 2000. These mushrooms were obtained from the major mushroom producers in Finland. The mushrooms (1.5 kg of each species) were cut into 1-cm3 cubes, mixed, packed into 300-ml plastic containers with 50–70 g in each, freeze-dried and stored at−18 °C. Before sterol analysis, the contents of the container were homogenized. The sample

General

Wild mushrooms, C. cibarius, C. tubaeformis, B. edulis and Lactarius trivialis, were chosen for subjects of investigation because all these mushrooms are popular in Finland, and they differ in their crop season and/or their morphology. In addition, more information on the vitamin D2 and ergosterol contents of the Chantarellus species was desired, because previous data suggested that they contain high levels of vitamin D2 (Mattila et al., 1994). We have previously reported the vitamin D2

Acknowledgments

The authors would like to thank Karoliina Könkö (M.Sc.) and Marjo Toivo for their skilful technical help.

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