A mini-review of chemical composition and nutritional value of edible wild-grown mushroom from China

Food Chemistry 151 (2014) 279–285

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Review

A mini-review of chemical composition and nutritional value of edible wild-grown mushroom from China Xue-Mei Wang a,1, Ji Zhang b,1, Li-Hua Wu b, Yan-Li Zhao b, Tao Li c, Jie-Qing Li a, Yuan-Zhong Wang b,⇑, Hong-Gao Liu a,⇑ a b c

College of Agronomy and Biotechnology, Yunnan Agricultural University, 650201 Kunming, China Institute of Medicinal Plants, Yunnan Academy of Agricultural Sciences, 650200 Kunming, China College of Resources and Environment, Yuxi Normal University, 653100 Yuxi, China

a r t i c l e

i n f o

Article history: Received 28 August 2013 Received in revised form 25 September 2013 Accepted 12 November 2013 Available online 20 November 2013 Keywords: Fungi Bioactive compounds Sensory active compounds Mushrooms Proximate composition

a b s t r a c t In China, many species of edible wild-grown mushrooms are appreciated as food and also found use in traditional Chinese medicine. In this mini-review, for the first time, is summarized and discussed data available on chemical components of nutritional significance for wild-grown mushrooms collected from China. We aimed to update and discuss the latest data published on ash, fat, carbohydrates, fibre, proteins, essential amino acids and nonessential amino acids, some essential (P, K, Na, Ca, Mg, Fe, Mn, Zn, Cu) and toxic elements (As, Hg, Cd, Pb), vitamins (thiamine, riboflavin, niacin, tocopherol, vitamin D), flavour and taste compounds, antioxidants and also on less studied organic compounds (lectin, adustin, ribonuclease and nicotine) contents of wild-grown mushrooms. Ó 2013 Elsevier Ltd. All rights reserved.

Contents 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11.

Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Dry matter, proximate composition and energy value Carbohydrate and fibre . . . . . . . . . . . . . . . . . . . . . . . . . Proteins and amino acids. . . . . . . . . . . . . . . . . . . . . . . . Lipids. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Ash and mineral constituents . . . . . . . . . . . . . . . . . . . . Vitamins . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Flavour and taste compounds . . . . . . . . . . . . . . . . . . . . Antioxidants . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Various constituents. . . . . . . . . . . . . . . . . . . . . . . . . . . . Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

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1. Introduction

⇑ Corresponding authors. Tel.: +86 871 65033575; fax: +86 871 65033441. E-mail addresses: [email protected] (Y.-Z. Wang), [email protected] (H.-G. Liu). 1 These two authors cotributed equally to this work. 0308-8146/$ - see front matter Ó 2013 Elsevier Ltd. All rights reserved. http://dx.doi.org/10.1016/j.foodchem.2013.11.062

The majority of mushrooms widely collected in China are the macrofungi forming basidiomycetes, and only a few are of the ascomycete group (Zhang et al., 2006). For some regions of China, the rate of mushroom consumption is relatively high, e.g., up to 20–24 kg fresh product per capita annually, which is a

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substantially higher figure than for people from many other countries (Zhang et al., 2010). Edible wild-grown mushrooms are collected at all continents worldwide because they are traditionally recognised as valued sources of nutrients (Kalacˇ, 2013; Nnorom et al., 2013; Zheng, Suwandi, Fuller, Doromla, & Ng, 2012). Apart from flavour and taste, the fruiting bodies of mushrooms are considered sources of organic nutrients such as digestible proteins, carbohydrates, fibre and certain vitamins, as well as minerals and antioxidants (Nnorom et al., 2012; Pereira, Barros, Martins, & Ferreira, 2012; Szubstarska, Jarzyn´ska, & Falandysz, 2012). In China, Yunnan province, with an area of 390,000 km2 and elevation of 76.4–6740 m, is a specific region abundant in wild-grown mushrooms and over 880 species are identified as edible, which accounts for 80% of the edible species identified in China and around 40% in the world (Wu, Luo, Liu, & Gui, 2010). China also exports edible wild-grown mushrooms. For example, in 2010 and 2011 the export rate of Yunnan was 105,000 and 135,000 tonnes, respectively (Zhang and Yang, 2013). Tricholoma matsutake is the most valuable wild-grown mushroom in China and the export rate of this species from Yunnan accounts for more than 80% of the total export from China (Wu et al., 2010). Mushrooms can be cooked in several ways and this can have an impact on the nutrients and other compounds in the meal (Falandysz and Borovicˇka, 2013). China has its own traditional method of cooking called ‘‘urgent fire stir fry’’. Using this traditional way of cooking, it is possible to preserve vitamin B2 and a collection of minerals completely (Zhou and Yin, 2008). This is as sliced fresh mushrooms are cooked using a wok (a Chinese pan) with boiling vegetable oil and some additional ingredients (green onion, ginger, garlic, pepper, salt, mono-sodium glutamate, soy, etc.) for about 5 min. In this way, there is no loss of any constituent of a mushroom meal. China also employs other ways to cook mushrooms (frying, baking, boiling etc.), but they used relatively infrequently, while sliced Tricholoma matsutake is even eaten raw. The number of reports on nutrients and antinutrients (As, Hg, Cd, Pb etc.) of uncooked mushrooms has grown recently (Akata, Ergonul, & Kalyoncu, 2012; Gucia et al., 2012; Liu, Li, & Tang, 2012; Zhang, Yang, & Ma, 2011; Zhang et al. 2013; Falandysz, Kawano, S´wieczkowski, Brzostowski, & Dadej, 2003; Falandysz, Jarzyn´ska et al., 2012; Falandysz, Widzicka et al.,2012; Guo et al., 2012). Nevertheless, due to a large number of species growing worldwide and various cooking methods and recipes, our knowledge on the nutrient composition and value of mushrooms is still limited (Falandysz and Borovicˇka, 2013). Another difficult problem is the quality of analytical data published on the chemical composition of mushrooms, a good example being a discussion on the quality of data published on mushroom mineral constituents (Falandysz, 2012, 2013; Jarzyn´ska and Falandysz, 2011a).

2. Dry matter, proximate composition and energy value Dry matter content of fresh mushrooms is relatively low, i.e. around 10%, and is mainly composed of carbohydrates, proteins, fibre and minerals (Table 1). When considering the chemical composition of mushrooms, it is worthwhile to keep in mind that water content is the parameter that is to some degree, variable for ‘‘fresh’’ mushroom. This is because changing weather conditions can to some degree influence the moisture content of collected fruiting bodies (mushrooms). Fruiting bodies, after collection, also lose moisture easily due to evaporation. There is a consensus that the moisture content of fresh fruiting bodies is 90%, and data published on the chemical composition of mushrooms needs to be normalised to dry matter contents (Chudzyn´ski and Falandysz, 2008). Accordingly, proximate composition of mushrooms also varies within and among species, and fruiting body maturity can also play a role. This is well illustrated by large sets of data available recently on certain minerals in the flesh of several species of edible mushrooms (Chudzyn´ski, Jarzyn´ska, Stefan´ska, & Falandysz, 2011; Falandysz, Mazur et al., 2012; Li, Wang, Zhang, Zhao, & Liu, 2011; Melgar, Alonso, & García, 2009; Aloupi, Koutrotsios, Koulousaris, & Kalogeropoulos, 2012). Environmental factors can have an impact on the abundance of certain compounds in mushrooms, but the reason(s) for the variations in the composition of mushroom species collected from background areas remains unclear (Falan_ dysz and Bielawski, 2007; Jarzyn´ska, Chojnacka, Dryzałowska, Nnorom, & Falandysz, 2012). Another source of variation in the composition and nutritional value of mushrooms is time variation as noted for certain mineral elements in a few species (Brzostowski, Jarzynska, Kojta, Wydmanska, & Falandysz, 2011; Gucia, Jarzyn´ska, Kojta, & Falandysz, 2012). As such certain types of variations impact the nutritional value of mushrooms and as such, more research on different constituents of edible mushrooms is desirable. The species listed in Table 1 are mushrooms that are high in carbohydrates, crude protein and fibre and comparatively less abundant in minerals and crude fat. In a report by Liu and co-workers (2012), energy values of five wild-grown species of mushrooms varied between 15164 kJ kg1 dm for Catathelasma ventricosum and 17366 kJ kg1 dm for Clitocybe maxima.

3. Carbohydrate and fibre Carbohydrates in foods provide energy and digestible carbohydrates found in mushrooms are such as mannitol (0.3–5.5% dm) (Vaz et al., 2011), glucose (0.5–3.6% dm) (Kim et al., 2009) and glycogen (1.0–1.6% dm) (Díez & Alvarez, 2001). Non-digestible carbohydrates form a large portion of the total carbohydrates of mushrooms, and major compounds are oligosaccharides and

Table 1 Proximate composition of some edible wild-grown mushrooms of China (mean values; % of dry matter). Species

Number of samples (n)

Carbohydrates

Crude fibre

Crude protein

Crude fat

Ash

References

B. aereus B. edulis B. speciosus C. aureus Lactarius deliciosus Lactarius hatsudake Lactarius volemus L. crocipodium Lentinula edodes R. virescens S. aspratus T. matsutake

1 1 1 1 1 1 1 1 1 1 1 3

34.0 30.6 28.6 61.5 25.0 38.2 15.0 12.8 30.2 13.4 64.6 36.7

17.0 15.3 21.0 5.2 36.3 31.8 40.0 37.9 39.4 32.8 5.1 29.1

26.9 28.7 28.1 14.1 20.2 15.3 17.6 29.3 17.1 28.3 12.0 14.3

2.1 4.1 2.9 4.0 2.5 1.0 6.7 1.0 1.9 1.5 2.8 5.0

8.5 9.2 7.6 9.2 7.5 7.3 13.3 5.8 4.3 11.9 10.4 8.9

Zhou and Yin (2008) Zhou and Yin (2008) Zhou and Yin (2008) Zhang and Chen (2012a) Yin and Zhou (2008) Yin and Zhou (2008) Yin and Zhou (2008) Zhou and Yin (2008) Zhu et al. (2007) Yin and Zhou (2008) Zhang and Chen (2011) Liu et al. (2010)

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non-starch polysaccharides such as chitin, b-glucans and mannans (Cheung, 2010). The carbohydrate content of mushrooms collected in China varies with species and ranges from 13% to 65% dm (Table 1). In a study by Liu and co-workers (2012), the carbohydrate content of C. maxima, C. ventricosum, Stropharia rugoso-annulata, Craterellus cornucopioides and Laccaria amethystina was between 57% and 65% dm. Carbohydrate content up to 70% dm was found in Agaricus campestris and Armillaria mellea (Wang and Zhang, 2010), while proportions as low as 13% were observed in Leccinum crocipodium and Russula virescens (Table 1). Crude fibre is a group of indigestible carbohydrates. It can improve the function of the alimentary tract and also lower blood glucose and cholesterol levels. The amount of soluble and insoluble fibre in certain Boleztus mushrooms is about 4–9% and 22–30% dm, respectively (Manzi, Marconi, Aguzzi, & Pizzoferrato, 2004). Some mushrooms were found to be low in crude fibre, e.g. for Craterellus aureus and Sarcodon aspratus values were 5% dm, while for many others, up to 40% dm was reported (Table 1).

(Sun, Lin, Wan, Liu, & Xu, 2012). L. crocipodium and Boletus speciosus showed similar EAA/TAA ratios with 0.31 and 0.43, respectively (Table 3). The ratio of essential amino acids (EAA) to non-essential amino acids (NEAA) is 0.53–0.70 for Russula and 0.45–0.77 for Boletus mushrooms (Yin & Zhou, 2008; Zhou & Yin, 2008). Those results meet well with the reference value of 0.6 recommended by FAO/ WHO (1973). Higher ratios were found for C. cornucopioides, S. ugoso-annulata, L. amethystina and C. ventricosum, i.e. 0.82, 0.96, 1.52 and 1.86, respectively (Liu et al., 2012). Alfalfa, due to the favourable composition of amino acids, is considered a plant of the highest nutritional value. The mushrooms Laccaria amethystina and C. ventricosum show amino acid composition similar to that of alfalfa. Aspartic and glutamic acid are monosodium glutamate-like (MSG-like) components, which give the most typical mushroom taste, umami taste or palatable taste (Tsai, Tsai, & Mau, 2008). The ratio of umami amino acids to total amino acids is relatively high and the mean value of 0.22 was detected by Sun and co-workers (2012). Values of this quotient for mushrooms in Table 3 vary between 0.21 and 0.32 dm.

4. Proteins and amino acids The nutritional value of mushrooms is primarily related to their protein content. Mushroom protein is considered to have higher nutritional quality than that of plant proteins (FAO, 1991). The protein content of mushroom is not only dependent on environmental factors and stage of fruiting body maturity, but also on species (Colak, Faiz, & Sesli, 2009). Due to the high proportion of non-protein nitrogen compounds, especially indigestible chitin, we used the conversion factor of 4.39 to calculate protein content. Mushrooms usually contain proteins of 12.0–29.3% dm (Table 1). However, some authors reported a higher protein content for Cantharellus cibarius and Lepista nuda with 54 and 59% dm, respectively (Barros, Venturini, Baptista, Estevinho, & Ferreira, 2008). The amino acid composition is close to or better than that of soy proteins, and even for some species of mushrooms the composition can be analogous to that of hen’s egg (Yin & Zhou, 2008). Essential amino acids that cannot be synthesized by humans can be supplied with mushrooms. Hence, the ratio of essential amino acids (EAA) to total amino acids (TAA) gives an idea on the nutritional quality of proteins in foods. Data on essential (Lys, Thr, Val, Ile, Leu, Met,Try, Phe) and nonessential (Arg, Ala, Tyr, Gly, Ser, Pro, His, Asp, Glu, Cys) amino acids for several species of mushrooms are given in Tables 2 and 3. A large set of data on amino acids content and composition was recently published for 41 species of mushrooms from Yunnan. In that study, Dictyophora indusiata was low with 8000 mg kg1 fresh weight and Tuber indicum was higher with 32,000 mg kg1 fresh weight in amino acids, and the ratio of EAA/TAA was 0.27–0.51

5. Lipids Crude fat content of mushrooms is usually low, and was from 1.0% to 6.7% for certain species collected in China (Table 1). Linoleic and linolenic acid are essential fatty acids for humans, which must be obtained from food. Linoleic acid is obtained from omega-6 fatty acids and linolenic acids come from omega-3 fatty acids. Data published on the fatty acid composition of mushrooms from China are rather fragmentary. The value (% of total fatty acids) for stearic, palmitic, linoleic and oleic acid in Tricholoma matsutake was 2%, 9%, 27% and 58%, respectively (Liu, Wang, Zhou, Guo, & Hu, 2010). Ratio of unsaturated to saturated (UFA/SFA) fatty acids is an important measure to judge stand or fall of fatty acid in mushrooms (Zhang & Ran, 2005). In the study by Liu and co-workers (2012), the UFA/SFA ratio ranged from 4.3 to 12.7 for five wild-grown species, while a lower value of 0.7–4.5 was observed for cultivated mushrooms (Zhang & Ran, 2005). 6. Ash and mineral constituents Ash content of edible fruiting bodies is actually the least studied parameter or considered an insignificant constituent for assessment of the quality of mushroom flesh. More attention is given to individual chemical elements and especially to their multi-elemental composition (Falandysz et al., 2007; Falandysz, Kunito, Kubota, Bielawski et al., 2008; Falandysz, Kunito, Kubota, Gucia

Table 2 Essential amino acid composition in edible wild-grown mushrooms of China (mean values; mg kg1 of dry matter). Species

Number of samples (n)

Lys

Thr

Val

Ile

Leu

Met

Try

Phe

EAA

References

B. aereus B. eduli B. speciosus Cortinarius rufo-olivaceus C. aureus L. delieiosus L. hatsudake Lactarius hygrophroides L. volemus L. crocipodium R. virescens S. aspratus Collybia albuminosa

1 1 1 1 1 1 1 1 1 1 1 1 1

1040 990 1200 16200 4441 960 750 21348 500 1580 850 4602 13651

1670 2110 2120 13900 9230 930 890 10227 820 1750 1350 8479 19889

2560 2750 3730 36800 6794 1300 1040 12284 990 2840 1310 4787 12748

3100 2030 4190 8300 5054 1350 1620 9787 1490 1080 1360 4187 10231

2350 2470 3500 10700 7014 2240 2480 13563 2060 1930 1660 5780 19048

440 750 690 10400 2813 360 320 6676 160 580 890 1476 5900

– –

1290 1700 1860 9200 4240 880 800 4561 750 1240 1440 3913 10704

12450 12800 18120 105500 39586 8350 8190 90774 6920 11000 9260 33224 92170

Zhou and Yin (2008) Zhou and Yin (2008) Zhou and Yin (2008) Zhang et al. (2011) Zhang and Chen (2012a) Yin and Zhou (2008) Yin and Zhou (2008) Li and Wang (2006) Yin and Zhou (2008) Zhou and Yin (2008) Yin and Zhou (2008) Zhang and Chen (2011) Zhang and Chen (2012b)

830 – – 330 290 12328 150 – 400 – –

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Table 3 Nonessential amino acid composition in edible wild-grown mushrooms of China (mean values; mg kg1 of dry matter). Species

Number of samples (n)

Arg

Ala

Tyr

Gly

Ser

Pro

His

Asp

Glu

Cys

EAA/TAA

References

B. aereus B. eduli B. speciosus C. rufo-olivaceus. C. aureus L. delieiosus L. hatsudake L. hygrophroides L. volemus L. crocipodium R. virescens S. aspratus C. albuminosa

1 1 1 1 1 1 1 1 1 1 1 1 1

1700 3360 2050 12900 2240 1050 1660 12798 880 1750 950 6035 14060

3570 3570 3750 17800 360 1830 890 14288 1000 3980 1120 6563 18621

700 500 1060 9100 330 860 400 15576 350 650 1720 4567 14390

2230 3650 2510 10400 880 1150 1440 11970 820 4500 1270 5228 13413

1840 1280 2300 15600 14525 870 930 7998 720 2430 1430 10859 31064

780 2720 740 13000 6121 860 510 16354 240 450 1280 5014 11035

440 2080 510 10800 3674 660 320 8052 210 1010 720 2745 24213

3320 2860 3870 23000 11263 1630 1290 19783 1410 3490 2480 9043 25801

7610 4930 6850 65000 16401 3490 4440 27462 3550 6840 2280 15436 37235

– – – 16900 485 – – 584 – – – 175 3142

35.9% 33.9% 43.4% 35.2% 31.5% 40.2% 42.1% 40.2% 43.0% 30.5% 41.1% 33.4% 32.3%

Zhou and Yin (2008) Zhou and Yin (2008) Zhou and Yin (2008) Zhang et al. (2011) Zhang and Chen (2012a) Yin and Zhou (2008) Yin and Zhou (2008) Li and Wang (2006) Yin and Zhou (2008) Zhou and Yin (2008) Yin and Zhou (2008) Zhang and Chen (2011) Zhang and Chen (2012b)

et al., 2008), but this requires highly advanced laboratory infrastructure and instruments that are still very costly (Falandysz et al., 2001; Randa, Kucera, & Soukal, 2003). Moreover, ash content gives only a rough idea about the mineral content of fruiting bodies or its morphological part. Wild-grown mushrooms are able to accumulate in their fruiting bodies large amounts of both macro- and micro-elements that are essential to fungi and its consumers. Mushrooms can also be specifically enriched with toxic elements such as As, Hg, Cd and Pb. Potassium (K) and phosphorus (P) are two prevailing elements in fruiting bodies and are usually followed by Ca, Mg, Na and Fe (Falandysz & Borovicˇka, 2013; Okoro & Achuba, 2012). Data on phosphorus and eight metals most frequently determined in mushrooms from China are given for 10 species in Table 4. Potassium content was between 16,000 and 37,000 mg kg1 dm, phosphorus was between 4820 and 19,000 mg kg1 dm, and Ca, Mg and Na (Table 4). Iron (Fe) content in Thelehhora ganhajun was 1500 mg kg1 dm, which is particularly higher than in other mushrooms (Table 4). For elements such as Zn, Cu and Mn, a large variation of values was noted, i.e., they ranged from 20–140, 20–180 and

10–80 mg kg1 dm, respectively (Table 4). For Cu and Mn in 16 species from the Henan Funiu Mountains (central China), the content ranged from 13–105 and 10–197 mg kg1 dm, respectively, and these values are higher than those for cultivated species, which were 2–77 and 3–29 mg kg1 dm, respectively (Zhao & Han, 2011). Toxic As, Cd, Hg and Pb were recently determined in 12 species collected from various regions of Yunnan, and the maximum mean content was 0.5, 1.3, 0.6 and 1.8 mg kg1 dm, respectively (Huang, Chen, Zhao, & Zhang, 2010). The maximum mean values of these toxic elements are lower when compared to data for certain other mushrooms subjected for this review. For other species, maximum values of As, Hg, Cd and Pb were up to 1.5, 3.9, 92 and 11, respectively (Table 5). Because of the rather high content of As, Hg, Cd and Pb noted for some species collected from the wild in China, certainly more data is needed to confirm source reports. Mushrooms collected from urban and industrial areas polluted with toxic compounds (As, Hg, Cd and Pb) usually show highly elevated content of such constituents in flesh (Falandysz & Borovicˇka, 2013). In a sole report, nearly all mushrooms collected from the rural area near the Panzhihua city (Sichuan province) showed very

Table 4 Essential element content in edible wild-grown mushrooms of China (mean values; mg kg1 of dry matter). Species

Number of samples (n)

K

P

Ca

Mg

Na

Fe

Zn

Cu

Mn

References

C. ventricosum C. maxima C. aureus C. cornucopioides L. amethystea L. hygrophroides S. aspratus S. rugoso-annulata T. ganhajun T. matsutake

3 3 1 3 3 1 1 3 1 3

27230 26430 20637 36620 25290 23456 27909 16320 24296 23520

4820 5390 19019 7130 5040 _ 17807 7290 7704 5040

1973 962 146 1255 2004 178 76 1371 741 410

1538 520 1050 978 1482 910 752 1135 815 –

349 1692 – 1185 361 1645 – 411 156 310

673 308 718 413 211 171 318 195 1556 369

88 127 24 61 59 102 117 102 58 140

38 52 25 43 36 184 22 29 22 87

9 33 38 27 35 31 34 59 50 83

Liu et al. (2012) Liu et al. (2012) Zhang and Chen (2012a) Liu et al. (2012) Liu et al. (2012) Li and Wang (2006) Zhang and Chen (2011) Liu et al. (2012) Wu et al. (2005) Liu et al. (2010)

Table 5 Toxic element content in edible wild-grown mushrooms of China (mean values; mg kg1 of dry matter). Species

Number of samples (n)

As

Hg

Cd

Pb

References

Agaricus silvaticus Agaricus subrufescens Boletus tomentipes Calvatia craniiformis C. cibarius Macrolepiota crustosa Russula albida Russula cyanoxantha Russula delica Russula virescens

5 5 11 5 5 5 5 5 5 5

1.2 0.9 0.1 0.9 0.5 1.5 1.2 1.0 0.7 0.4

3.8 3.9 0.04 2.2 0.3 2.2 3.9 0.5 1.0 1.0

51.9 2.5 0.2 9.1 0.9 91.8 3.0 1.3 1.1 0.4

9.3 4.4 2.6 10.8 4.6 7.4 9.6 2.1 1.9 2.0

Chen, Zhou, and Qiu (2009) Chen et al. (2009) Li, Wang et al. (201b1) Chen et al. (2009) Chen et al. (2009) Chen et al. (2009) Chen et al. (2009) Chen et al. (2009) Chen et al. (2009) Chen et al. (2009)

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high content of Zn, Ni, Cd and Cr, which exceeded statutory standards limit for mushrooms in China. This phenomenon was probably caused by the mining and heavy industrial production activities in Panzhihua (Zhang, Cao, & Xu, 2012). Silver (Ag) is known as a metallic element with no nutritional value, but is toxic due to its high affinity for proteins and thus accumulates in mushrooms (Falandysz and Borovicˇka, 2013). Till now, reports are not available on the Ag content and accumulation in mushrooms of China. Reports on trace elements like Cr, Ni, Li, Sr and Sb in mushrooms from China are few and relatively insufficient. Content of Cr, Co and Ni for some species ranged from 0.5–6.3, 0.3–2.3 and 1.8– 21.2 mg kg1 dm, respectively (Liu, Zhang et al., 2012 Zhang et al., 2012). Li, Sr and Sb were less than 0.1 mg kg1 dm in Russula virescens (Xu, Lin, Duan, Wan, & Sun, 2012). Nine rare-earth elements were determined in Tremellodon gelatinosum and contents were 0.01, 0.05, 0.17 and 0.34 mg kg1 dm for Eu, Th, La and Ce, respectively (Du, Zhang, He, & Sun, 2010). Se is required in the biosynthesis of important selenoenzymes and is fundamentally essential to humans (Jarzyn´ska and Falandysz, 2011b). Soil, sediment and water are the primary sources of selenium to fungi (Falandysz, 2008). The mean value of Se in mushrooms collected from Ankang city in China was 6.8 mg kg1 dm, and the maximum for Boletus (Xerocomus) chrysenteron (18.8 mg kg1 dm) which reached up to 70 times the content of Se in soil (Chen, Wang, & Lu, 2012). The Selenium content of certain Boletus mushrooms often exceeds 10 mg kg1 dm (Falandysz, 2008, 2013), and in Boletus aestivalis (reticulatus) from Portugal was at 48.5 mg kg1 dm and in Boletus. pinophilus at 19.9 mg kg1 dm (Costa-Silva, Marques, Matos, Barros, & Nunes, 2011). 7. Vitamins Mushrooms contain several primary vitamins including thiamine, riboflavin, niacin, tocopherol and vitamin D (Cheung, 2010; Kalacˇ, 2013). For several species, the content of thiamine, riboflavin, niacin and ascorbic was 0.02–1.6, 0.3–4.5, 1.2–6.6 and 1.3– 2.7 mg 100 g1 dm, respectively (Quan, Wang, Shi, & Zhang, 2007; Wu Wang, Guo, Li, & Yin, 2005; Xu, Lin, Duan, Wan, Bai et al., 2012; Yin and Zhou, 2008; Zhou and Yin, 2008; Zhu, Wang, & Xiong, 2007). Tocopherol and vitamin D2 was found at a range of 8.9–45 and 4.7–194 mg 100 g1 dm for mushrooms such as Boletus edulis, Boletus speciosus and T. ganhajun (Wu et al., 2005; Zhou and Yin, 2008). Cooking and industrial processing of mushroom was found to have pronounced effects on the amount of vitamins in the product. Vitamin B1 and B2 are lost during industrial processing (canning) of Boletus at a rate of 21–57% and 8–74%, respectively (Zhou and Yin, 2008). In another study, the loss rates of vitamin B1 by processing and canning reach up to 76–82% (Zhou and Yin, 2008), and 86–99% for vitamine B2 (Yin and Zhou, 2008). The Yunnan traditional cooking method ‘‘urgent fire stir fry’’ can retain vitamin B2 completely, which is worthy of promotion (Zhou and Yin, 2008).

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matsutake, with a unique earthy taste and sweetness (Cheng et al., 2012). GC–MS analysis indicated that there were 42 volatile aroma compounds in T. gelatinosum, mainly alkyl alcohols, alkenes and heterocyclic compounds (Du, Zhang, He, & Sun, 2010). The unique taste of mushroom is ascribed to free amino acids, 50 -nucleotides and soluble sugars. A total of 20 free amino acids and five 50 -nucleotides were identified in truffle (5 species). The umami amino acids and flavour 50 -nucleotides content in truffle was 1.5–7.1 and 0.6–1.2 mg g1 dm, respectively, which are both lower than that of mycelia after fermentation (Liu, Li, & Tang, 2012). During industrial processing, the flavour compounds of mushrooms changed due to various chemical reactions, especially the Maillard reaction. Cooking can have a large impact on the flavour of mushrooms and the flavour profile can depend on the method of cooking. For example, volatile compounds identified in boiled mushroom soup were higher than in autoclaved and microwaved mushroom soup. Levels of free amino acids and 50 -nucleotides in the microwaved mushroom soup were higher than in boiled and autoclaved mushroom soup (Li, Zhang et al., 2011). 9. Antioxidants There are a number of edible wild-grown mushrooms which have been reported to possess high antioxidant activities. A high correlation between antioxidant capacity and total phenolic content indicates that phenolic compounds could be the foremost contributors to the antioxidant activity of edible macro-fungi (Guo et al., 2012). Quercetin, catechin, p-coumaric acids, caffeic acid and gallic acid are the main phenolics. Quercetin was the major component in C. ventricosum (66.7 mg kg1 dm) and catechin was the major component in L. amethystea (34.4 mg kg1 dm) (Liu, Sun et al., 2012). Other phenolics such as gallic acid, homogentisic acid, forulic acid and p-hydroxybenzoic acid were found in edible fungi, and gallic acid (308 mg kg1 dm) and homogentisic acid (342 mg kg1 dm) are the main phenolics in Boletus edulis and Boletus regius (Guo et al., 2012). Ergothioneine, a water-soluble thiol compound, is an excellent antioxidant in vivo (Dubost, Ou, & Beelman, 2007). The amount of ergothioneine ranges from 48 to 2851 mg kg1 dm for 29 species mushrooms (Chen, Ho, Hsieh, Wang, & Mau, 2012). So, edible mushrooms from the wild seem abundant in ergothioneine and can improve the antioxidant capacity of meals. Effects of different drying methods on antioxidant activities of polysaccharides for Inonotus obliquus indicated that freeze drying is a good choice for the preparation of polysaccharides and could be used to produce antioxidants for the food industry (Ma, Chen, Zhu, & Wang, 2013). A study showed that NO fumigation might have a potential application for enhancing the bioactive compounds and improving the antioxidant activity in the mushroom. The data suggested that activation of the biosynthetic pathways lead to NO-induced phenolic and flavonoid accumulation (Dong, Zhang, Lu, Sun, & Xu, 2012). 10. Various constituents

8. Flavour and taste compounds Characteristic flavour substances of wild-grown mushrooms can be classified into nonvolatile (taste) and volatile components (smell). Various volatile compounds such as terpenes, aromatic alcohols, aldehydes, ketones, eight carbon compounds and their derivatives, are the major aroma compounds in mushrooms. Eight-carbon volatiles are produced by oxidation of free linoleic acid catalysed by lipoxygenase. In 1938, 1-octen-3-ol was identified for the first time as a major ‘‘mushroom-like flavour’’ in T.

Numerous other beneficial components have been determined in a diverse range of edible wild-grown mushroom species. A lectin that was isolated from fresh fruiting bodies of B. edulis is a dimer made up of two 16.3 kDa subunits, which displays activities including mitogenic and HIV-1 reverse transcriptase inhibiting. As a result, it is possible for B. edulis lectin to be developed into a pharmaceutical with similar effects for cancer patients and AIDS patients (Zheng, Li, Ng, & Wang, 2007). A polypeptide designated as adustin was isolated from the wild-grown mushroom

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Bjerkandera adusta and also represents one of the very rare mushroom translation-inhibiting polypeptides (Ng and Wang, 2004). A ribonuclease (RNase) with a molecular mass of 29 kDa was isolated from fruiting bodies of the mushroom Boletus griseus, its N-terminal sequence exhibited some similarity to RNases from Irpex lacteus and Lentinus edodes (Wang and Ng, 2006). Nicotine is an alkaloid that is abundant in tobacco. However, nicotine was first accidentally extracted from mushroom samples with water under the action of microwave energy. According to the European Food Safety Authority (EFSA) statement, the temporary maximum residue levels (MRLs) of nicotine are 0.036 for fresh wild mushrooms and 1.17 mg kg1 for dried wild mushrooms (2.3 mg kg1 for dried ceps only) (Cavalieri, Bolzoni, & Bandini, 2010). The determined content of nicotine in some mushrooms from China was in the range of 0.024–0.054 mg kg1 fm, and for some species was higher than MRLs (Wang et al., 2011). 11. Conclusion The rich amount of proteins, carbohydrate, essential minerals and low energy levels make many wild-grown mushrooms a good food for the consumer, which can virtually be compared with meat, eggs and milk. Potential medicinal value is also high including boosting the immune system, controlling blood lipids, antitumor function and so on. In order to preserve the nutrients further, more complete and effective storage methods and culinary treatments are necessary. In view of the current situation, the research of these components is deficient. We ought to identify more poisonous wild-grown mushroom and clear the noxious substances through testing, to ensure the safety of consumer. Owing to the unique geographical conditions, wild-grown edible mushrooms in China are abundant and varied, especially in Yunnan province. There are numerous characteristics and even undiscovered species, which can provide abundant resources for the research of wild fungi. Acknowledgements This study has been supported by the National Natural Science Foundation of China (31260496, 31160409) and the Yunnan Provincial Natural Science Foundation (2011FB053, 2011FZ195). References Akata, I., Ergonul, B., & Kalyoncu, F. (2012). Chemical compositions and antioxidant activities of 16 wild edible mushroom species grown in Anatolia. International Journal of Pharmacology, 8, 134–138. Aloupi, M., Koutrotsios, G., Koulousaris, M., & Kalogeropoulos, N. (2012). Trace metal contents in wild edible mushrooms growing on serpentine and volcanic soils on the island of Lesvos, Greece. Ecotoxicology and Environmental Safety, 78, 184–194. Barros, L., Venturini, B. A., Baptista, P., Estevinho, L. M., & Ferreira, I. C. F. R. (2008). Chemical composition and biological properties of Portuguese wild mushrooms: A comprehensive study. Journal of Agricultural and Food Chemistry, 56, 3856–3862. Brzostowski, A., Jarzynska, G., Kojta, A. K., Wydmanska, D., & Falandysz, J. (2011). Variations in metal levels accumulated in Poison Pax (Paxillus involutus) mushroom collected at one site over four years. Journal of Environmental Science and Health, Part A, 46, 581–588. Cavalieri, C., Bolzoni, L., & Bandini, M. (2010). Nicotine determination in mushrooms by LC-MS/MS with preliminary studies on the impact of drying on nicotine formation. Learning, Media and Technology, 27, 473. Chen, S.-Y., Ho, K.-J., Hsieh, Y.-J., Wang, L.-T., & Mau, J.-L. (2012). Contents of lovastatin, c-aminobutyric acid and ergothioneine in mushroom fruiting bodies and mycelia. LWT-Food Science and Technology, 47, 274–278. Chen, F., Wang, H. D., & Lu, X. H. (2012). Se content in wild edible fungi from Ankang district and their Se enrichment capacity. Hubei Agricultural Sciences, 51, 1237–1239. Chen, X. H., Zhou, H. B., & Qiu, G. Z. (2009). Analysis of several heavy metals in wild edible mushrooms from regions of China. Bulletin of Environmental Contamination and Toxicology, 83, 280–285. Cheng, Y., Sun, J., Ye, X. Q., Lv, B. B., Chu, Y., & Chen, J. C. (2012). Advances on flavor substances of edible mushrooms. Science and Technology of Food Industry, 33, 412–414.

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