Variations in Element Levels Accumulated in Different Parts of Boletus edulis Collected from Central Yunnan Province, China

ICP-AES andmicrowave assisted digestion were applied to determine P,Mg, Ca, Zn, Na, Cu, Ba, Ni, V, Cd, Sr, Co, and Li in the caps and stipes of Boletus edulis collected from six spatially distant sites in Yunnan province, China. Fruiting bodies of King Bolete are abundant in P, Mg, Ca, Zn, Cu, and Na, followed by Ba, Cd, Ni, V, Li, Sr, and Co.


Introduction
Edible wild-grown mushrooms are traditionally consumed as delicacy in lots of countries and many are also used in traditional Chinese medicine [1][2][3][4].This would be due to the abundant sources of protein, carbohydrates, dietary fibre and certain vitamins, and minerals as well as bioactive components [5][6][7].Reports suggested that edible wild-grown mushrooms have many pharmacological effects such as antioxidant, antitumor, and hypoglycaemic effect and boosting the immune system [8,9].In Yunnan province, the main wild edible and medicinal fungi are Boletus, Tricholoma, Termitomyces, Aphyllophorales, and Tuber [10].
King Bolete (Boletus edulis Bull.Fr.) is famous for its nutrition, flavor, taste, appearances, and medicinal value worldwide [11].In China, they are mainly distributed in Yunnan, Sichuan, Fujian, Shanxi, and Guizhou province and usually grow up under the pine forest and broad-leaved forest [12].Some alkaloid substances such as adenine, choline, and putrescine are produced by King Bolete, which are one of the ingredients of traditional Chinese medicine-Shujin Pill [11].Besides, studies have indicated that inhibition rate of King Bolete extract for Sarcoma-180 is 100% and 90% for ehrlich ascites carcinoma [13,14].These functional characteristics are, as suggested by Qi et al., mainly due to the type and content of trace element but other active compounds seem also to take part [15].
Central Yunnan province is one of the most wild edible mushrooms resource-rich and largest production regions in China.The main species are Boletus, Leccinum, Xerocomus, Tricholoma matsutake, Termitomyces, and Thelephora ganbajun [10].Data published on element concentration of King Bolete did indicate the considerable variation between the sites, years, and reports [30,31].There is scarcity of data on minerals composition variation of King Bolete collected from China.In addition, due to the presence of hymenophore with generative spores in caps, distribution of elements is unevenly within the fruiting body of mushroom [32].It is necessary to ascertain elements variation of King Bolete in China through knowledge of the concentrations of many essential and toxic elements.The objective was to examine and evaluate the distribution disparity in elements concentration (P, Mg, Ca, Zn, Na, Cu, Ba, Ni, V, Cd, Sr, Co, and Li) of caps and stipes of King Bolete collected from central Yunnan province, China.

Materials and Methods
2.1.Mushrooms Sampling.King Bolete (Boletus edulis Bull.: Fr.) samples were collected during summer and autumn in 2011 from six spatially distant sites in central Yunnan province, China (Figure 1).The specific site and number of specimens used in this study are given in Table 1.Fresh fruiting bodies were cleaned up with a plastic knife from visible plant or substrate debris and next separated to two parts (cap and stipe).Each sample was washed with deionized water and dried in an electrically heated oven at 65 ∘ C to constant weight.Dried samples were pulverized with a muller and stored in sealed polyethylene bag in dry condition for analysis.

Reagents and Apparatus.
Deionized water and nitric acid solution were used to prepare all aqueous solutions and clean or soak the glassware.Nitric acid solution (HNO 3 65%) and hydrogen peroxide (H 2 O 2 30%) were used for digestion of samples in automatic microwave digestion system.The contents of the minerals in King Bolete were determined using inductively coupled plasma atomic emission spectrophotometer (ICP-9000, Shimadzu, Japan).
2.3.Analysis.0.5 g of dried and powdered sample was mixed with 4 mL HNO 3 (65%), 2 mL H 2 O 2 (30%), and 3 mL deionized water in polytetrafluoroethylene (PTFE) pressure vessels and digested in microwave digestion system.Ultimate digest was transferred to 25 mL colorimetric cylinder using deionized water for constant volume and subjected to instrumental analysis.Concentration of all elements in caps and stipes was determined using inductively coupled plasma atomic emission spectrophotometer and for blank solutions and certified reference material (GBW07605) as well.Discrepancies between certified values and concentrations quantified were all below 10%.

Results and Discussion
Data on the parameters determined for caps and stipes of King Bolete are presented in Table 2.The element concentrations vary significantly not only among the collection sites but also within morphological parts of a particular fruiting body.Samples of King Bolete collected from different sites show rich content in P, Mg, Ca, Zn, Cu, and Na which accumulate both in cap and in stipe, followed by Ba, Cd, Ni, V, Li, Co, and Sr.Meanwhile, prominent differences in the concentrations of these elements are also found in the caps and in the stipes of King Bolete.Qc/s value is a quotient between the minerals concentrations in caps and stipes, which is used to express the elements distribution within the fruiting body of the mushrooms.Significant differences have been suggested in loads of accumulated elements between caps and stipes, and some were caused by the site or year of mushroom collection [30,31,33].In this study, multivariate Qc/s values are obtained between the elements and collection sites (Table 2).Minerals such as P, Mg, Zn, and Cu prefer to accumulate in the cap of King Bolete collected of all sites in this study.Except for the prevailing elements P, Mg, Zn, Ca, and Cu, Qc/s values for other elements in King Bolete collected from BE5 are <1.Consequently, these different distributions of elements between caps and stipes are mainly related to different bedrock soil geochemistry and ability to accumulate various elements.
3.1.Essential Elements: P, Mg, Ca, Zn, Na, Cu, Ni, and Co. P is the essential element that nearly participates in all physiological chemical reactions such as forming the bones, teeth, and nucleic acid, maintaining balance of ATP metabolism, and regulating acid-base balance.Rich concentrations are found in King Bolete and with the range of 4356-9013 mg kg −1 and 2150-3891 mg kg −1 dm for cap and stipe, respectively.So contents in caps are higher than in stipes, and Qc/s values vary between 1.62 and 2.57 (Table 2).King Bolete collected from mountain area of Liaoning province in China with 4995 mg kg −1 dm agreed with this study [11].P value in fruiting body (cap and stipe) and Qc/s of King Bolete is insufficient.
Ca is the activator of more than 200 kinds of enzymes in the human body, which can make each organ function well.Na concentration values distribution in King Bolete varies depending on the sites (Table 2).Qc/s values for Ca vary between 0.67 and 2.74, and contents of stipes for BE4 (0.67) exceed that of caps, and opposite feature could be observed for BE3 (2.74) and BE5 (2.35), while they are similar for BE1 (1.01), BE2 (1.06), and BE6 (0.98).
Zinc contents were reported at between 28 and 140 mg kg −1 dm for edible wild-grown mushrooms collected from China [7].Meanwhile, higher concentration was also reported showing its physiological importance to mushroom.The examples are as follows: 190 mg kg −1 dm (cap) [34], 240 mg kg −1 dm (cap) [35], and 580 mg kg −1 dm (whole fruiting body) [30].As shown in Table 2, stipes of King Bolete are half or even less than caps in essential Zn, and value of Qc/s for Zn in this study is 1.54-3.4,which extremely agrees with literature data previously reported [16].Nevertheless, a higher value (Qc/s = 4.6) was reported in fruiting body of King Bolete collected from Xichang in Sichuan province, China [36].
Na content for caps is between 2.9 and 100 mg kg −1 dm and for stipes between 19.6 and 148 mg kg −1 dm.Higher values were determined in cultivated and some preserved mushrooms and content was 860, 1000, and 16000-25000 mg kg −1 dm for Agaricus bisporus (whole), Lentinula edodes, and Agaricus bisporus (preserved), respectively [37][38][39].Na is present higher in concentrations in stipes than in caps, except for samples collected from BE2 (Yulu, Nanhua) with the value of 1.28 (Table 2).Published data in stipes of King Bolete are about twice more abundant in Na than the caps [16].Report also suggested the similar Qc/s value (0.45) for sodium in parasol mushroom Macrolepiota procera [40].
Cu is an essential element, and a large variation of values is noted; they ranged, respectively, between 17-884 and 8.6-703 mg kg −1 dm for caps and stipes (Table 2).Cu in this study is more abundant in caps than stipes of King Bolete, and Qc/s value varies between 1.26 and 1.98.Higher Qc/s value of 2.8 was obtained for King Bolete collected from Pbocka Dale in Poland [34].In addition, Cu contents in caps of Leccinum mushrooms from Poland were half or even less than in stipes [41].
Published data on Ni and Co in caps and stipes of King Bolete is few and relatively insufficient.Ni content of King Bolete at six sites varied between 2.1 and 63.7 mg kg −1 dm in caps and between 1.1 and 42.9 mg kg −1 dm in stipes.The mean Co concentrations were 0.4-8.4 and 0.5-6.4mg kg −1 for caps and stipes, respectively.Published data on Co contents were usually below or around 0.5 mg/kg DM, which were lower than the results in this study [42].Contents in caps are somewhat higher than those in stipes except sample collected from BE5; that is, Qc/s value is 1.02-2.26and 1.1-1.6 for Ni and Co, respectively.
3.2.Ba, V, Cd, Sr, and Li.As shown in Table 2, Ba, V, Cd, Sr, and Li contents in samples from BE6 are obviously higher than those from other regions, which is most probably depending on the geological bedrock in this site.Arithmetic mean of Qc/s for these elements is 1.03-3.53;nevertheless, for certain site (BE5) the Qc/s value is <1.
Ba content is in the range of 4.8-66.7 and 2.7-65.5 for caps and stipes, respectively, and these values are particularly higher than the reference data previously reported, which were 0.2-1.5 mg kg −1 dm for caps and 0.36-1.4mg kg −1 dm for stipes [30,31,33,34].
Reports on V contents on King Bolete were very few, and literature data were 0.02-0.09mg kg −1 dm in caps, 0.03 mg kg −1 dm in stipes, and 1.27 mg kg −1 dm in whole fruiting body [27,31].King Bolete in this study contains V at elevated concentrations; for caps it is 1.2-27.3mg kg −1 dm and for stipes at 0.5 to 15.8 mg kg −1 dm, Qc/s value is 0.1-2.79.
Cd is toxic metallic element is found in edible mushrooms and can leach out of fruiting bodies during boiling.Tolerance limit is 2 g/g dm for cultivated mushroom, and no such tolerances exist for edible wild-grown fungi [43].Apart from the highest value (24.8 mg kg −1 dm) of cap from EB6, other values are relatively low, which is consistent with the results of earlier studies [16].
King Bolete contains Sr at 0.9-11.5 mg kg −1 dm in caps and at 0.9-9.9mg kg −1 dm in stipes, which is higher value than for samples from Poland.Most of the sites surveyed caps, when compared to stipes containing higher content of Sr, and opposite feature was found in earlier reports [30,31,33,34].
The lithium salt, Li 2 CO 3 , is considered as a therapeutic for neurodisorders.Li is a trace element in fungi, and content is relatively low [16].Li content of King Bolete from Italy was between 0.04 and 0.9 mg kg −1 dm [44].Higher results are determined in present study: mean value of Li is from 0.3 to 5.9 mg kg −1 dm in caps and from 0.2 to 4.3 mg kg −1 dm in stipes.

Conclusion
King Bolete collected from central Yunnan province contained high content of elements such as P, Mg, Ca, Zn, Na, and Cu, next for Ba, Ni, V, Cd, and Sr, and the least for Co and Li.Distribution of elements in different parts of King Bolete was unevenly, mainly depending on the hymenophore in the caps.In addition, spatial variations of Qc/s value were noted for King Bolete from different sites, which seem to be due to variations in local soil substrate geochemistry.Our results indicated that there is a close relationship between element concentrations and hymenophore in cap and bedrock soil geochemistry.

Figure 1 :
Figure 1: Localization of the sampling sites (dot) of Boletus edulis in central Yunnan, China.

Table 1 :
Locations and numbers of Boletus edulis samples collected from central Yunnan in 2011.

Table 2 :
Elements content of Boletus edulis collected from central part of Yunnan province in 2011 (mg/kg dm, mean, SD, range).
Qc/s is the ratio of the element concentration in cap to stipe.