Pleurotus geesteranus was cultivated on the substrates blended with different ratios of treated and untreated Camellia oleifera shells using cottonseed hull as the control substrate. The mycelial growth rate, yield, nutritional composition, ash and heavy metals of the Pleurotus geesteranus cultivated on these substrates were compared. The results suggest that the Camellia oleifera shell in substrate can accelerate the mycelial growth and increase the yield, nutrients and the contents of protein, ash, crude fiber and amino acid of Pleurotus geesteranus. It was found that the contents of tannin and saponin in Camellia oleifera shell affected the mycelial growth rate. The optimal C/N of the substrate for the growth of Pleurotus geesteranus was determined to be 27 ± 0.7. The C/N ratios higher than 30 reduced the protein, fat and soluble sugar contents of the cultivated Pleurotus geesteranus. The contents of heavy metals including Hg, As, Cd and Pb were found in Pleurotus geesteranus cultivated on the substrates containing Camellia oleifera shell complex.
Camellia oleifera is an important woody oil crop in China. It belongs to the genus Camellia in the family Theaceae. Camellia oleifera is widely distributed in the provinces of Hunan, Jiangxi and Guangxi in China with the cultivation area of ~55 million mu. The oil content of Camellia oleifera seed is as high as ~55%. Camellia seed oil is rich in unsaturated fatty acids, such as oleic acid and linoleic acid, and thus is known as the “Oriental Olive Oil” [
Pleurotus geesteranus, also known as pocket-sized oyster, belongs to domain Enkarya, phylum basidiomycetes, order Agaricales, genus Pleurotaceae. It is rich in nutrients, proteins, polysaccharides, vitamins, micronutrients and the 8 essential amino acids for the human body. The crispy and delicious taste of Pleurotus geesteranus makes it very popular in China [
Camellia oleifera shell was collected from Dongfanghong Forest Farm in Jinhua City, Zhejiang Province, China. Pleurotus geesteranus spawn and cottonseed hull were supplied by Wuhan SuiSuiFeng Agricultural Technology Development Co., Ltd., China. Rice bran, lime and gypsum were collected from the Fuyang District, Hangzhou, Zhejiang, China. Tannin and saponin-degrading bacteria, Bacillus amyloliquefaciens S301 (CGMCC No. 15834), Meyerozyma guilliermondii S302 (CGMCC No. 15835) and Aspergillus awamori T301 (CGMCC No. 15862) were screened by the Chinese Academy of Forestry Institute of Subtropical Forestry and stored at the China General Microbiological Culture Collection Center (CGMCC).
Composting of Camellia oleifera shell was conducted in the greenhouse of Chinese Academy of Forestry Institute of Subtropical Forestry, Fuyang District, Hangzhou, Zhejiang Province, China, from February to April 2018. Camellia oleifera shells were blended with 1% dry weight of brown sugar and 3% dry weight of the mixture of tannin and saponin-degrading bacteria. The C/N ratio of the blend was adjusted to 27 with urea and the moisture content was adjusted to 55% with water. The blend was stirred homogenously and piled up for composting for one month. The compost pile was turned every 5 days. The pile temperature rapidly increased to 58˚C on day 2 and reached as high as 65˚C in the 20-day high temperature phase (>55˚C) and started to decrease on day 30. The compost pile was sampled by a five-point sampling method [
The conventional cottonseed hull mushroom cultivation substrate was used as a control substrate. Cottonseed hull substrates were respectively blended with different proportions of Camellia oleifera shell to formulate 9 substrates as shown in
The ingredients of each substrate were weighed and well mixed. The moisture content of each substrate was adjusted to 55% - 60% and mixed homogeneously for further use. The substrates were respectively bagged into polypropylene plastic bags (17 cm × 33 cm × 0.5 cm). The numbers of bags of each substrate was recorded, and dry weight of each bag was calculated. The substrates in bags were autoclaved at 121˚C under 103.4 KPa for 2 h, cooled for 2 h, inoculated and cultured in a dark culture chamber at 20˚C - 23˚C under the humidity of 50% - 70%.
The collar and lid were removed after the mycelia covered the bag completely, and the bags were moved to a mushroom cultivation room with the temperature of 22˚C - 24˚C and the humidity of over 90%. The cultivation room was kept ventilated to avoid malformation of mushrooms caused by high concentrations of carbon dioxide. The Pleurotus geesteranus were harvest as the mushroom cap became 2 - 3 cm big.
Camellia shell | Cellulose | Hemicellulose | Lignin | Ash | TOC | TN | C/N | TK | Tannin | Saponin |
---|---|---|---|---|---|---|---|---|---|---|
Untreated | 18.62 | 49.34 | 29.71 | 2.57 | 48.6 | 0.42 | 116 | 0.85 | 2.26 | 4.86 |
Treated | 20.87 | 22.16 | 44.94 | 5.03 | 43.6 | 1.21 | 36 | 0.80 | 0.81 | 0.78 |
Cottonseed hull | 24.85 | 34.55 | 31.68 | 2.41 | 56.0 | 2.03 | 27.6 | 0.18 | - | - |
Note: -, not detected.
Formula | Cottonseed hull | Camellia oleifera shell | Rice bran | Lime | Gypsum | C/N |
---|---|---|---|---|---|---|
A1 | 73 | 5 | 20 | 1 | 1 | 26.82 |
A2 | 68 | 10 | 20 | 1 | 1 | 27.79 |
A3 | 58 | 20 | 20 | 1 | 1 | 30.06 |
A4 | 48 | 30 | 20 | 1 | 1 | 32.74 |
B1 | 73 | 5 | 20 | 1 | 1 | 26.15 |
B2 | 68 | 10 | 20 | 1 | 1 | 26.40 |
B3 | 58 | 20 | 20 | 1 | 1 | 26.88 |
B4 | 48 | 30 | 20 | 1 | 1 | 27.52 |
CK | 78 | 0 | 20 | 1 | 1 | 25.94 |
Note: A1-A4 with untreated Camellia oleifera shell; B1-B4 with treated Camellia oleifera shell; CK, regular cottonseed hull formula.
For each substrate, 10 bags were randomly selected. The lengths of mycelia were measured every 5 days and the mycelial growth rate at every measurement was calculated. The last measurement was conducted as the mycelia completely covered the bag. The average mycelial growth rate of each substrate was calculated and analyzed [
Biological efficiency (%) = yield per bag (g)/dry weight per bag (g) × 100% [
Fresh Pleurotus geesteranus were harvested and the residues of stipe were removed. The mushroom was dried at 60˚C to the constant weight and crushed for further use. The contents of protein, ash, fat, crude fiber and amino acids were measured by the protocols of GB5009.5-2016, GB 5009.4-2016, GB 5009.6-2016, GB/T 5009.10-2003 and GB 5009.124-2016. The contents of heavy metals including Hg Cd As and Pb were measured by the protocol of GB 5009.268-2016. The soluble sugar content was determined by the anthrone colorimetric method. Each measurement was repeated three times and the mean value was reported.
All data were processed and analyzed using EXCEL.
and B1-B4 containing Camellia oleifera shells are higher than that of the control group CK. On the substrates A1-A4, the mycelial growth rate decreased with the increase of the amount of untreated Camellia oleifera shell, the increase of tannin and saponin contents and the increase of C/N, e.g. followed the order of A1 > A2 > A3 > A4 > CK. In contrast, the mycelial growth rate increased with the increase of the amount of treated Camellia oleifera shell, following the order of B4 > B3 > B2 > B1 > CK. The mycelial growth rates on the substrates B1-B4 are higher than those on the substrates A1-A4. These results suggest that Camellia oleifera shell can promote the mycelial growth. The mycelial growth rate of Pleurotus geesteranus is correlated to the contents of tannin and saponin in the Camellia oleifera shell (
Formula | Yield (g/bag) | Biological Efficiency (%) |
---|---|---|
CK | 180.7 | 46.94 |
A1 | 202.85 | 52.69 |
A2 | 252.45 | 65.57 |
A3 | 226.51 | 58.83 |
A4 | 249.46 | 64.79 |
B1 | 298.27 | 77.47 |
B2 | 239.35 | 62.17 |
B3 | 270 | 70.13 |
B4 | 253.85 | 65.94 |
Each bag contains 385 g dry weight of substrate.
substrate A2. The yield and biological efficiency decreased as the content of treated Camellia oleifera shell increased to 30%, but both of them were higher than those obtained on the control substrate CK and the substrates containing untreated Camellia oleifera shell. These results suggest that a certain amount of Camellia oleifera shell in the cultivation substrate can effectively increase the yield and biological efficiency of Pleurotus geesteranus.
The protein edible fungus is considered as the “plant meat” and is well recognized as a very good source of protein worldwide. The protein content of edible fungi can be up to 15% - 60% [
substrate greater than 30 significantly decrease the protein contents of the cultivated Pleurotus geesteranus.
The ash content reflects the mineral content of an edible fungus. The higher the ash content is, the richer the mineral elements in the edible fungus. In general, the mineral content in edible fungi is 3% - 12% with the average value of 7%, among which K, P, Na, Ca and Mg account for 56% - 80% of the total mineral content. These minerals can regulate body fluids and maintain normal metabolism of cells [
geesteranus is affected by the ash content of its substrate. The ash content of Pleurotus geesteranus cultivated on the substrate containing untreated Camellia oleifera shell is low and ash content of Pleurotus geesteranus cultivated on substrate containing treated Camellia oleifera shell is high, which was 7% higher than the average ash content of edible fungi.
The fat contents of edible fungi are generally below 10% [
The soluble sugar contents of the Pleurotus geesteranus cultivated on the substrates containing no Camellia oleifera shell, untreated Camellia oleifera shell and treated Camellia oleifera shell are significantly different (
Crude fiber is mainly composed of insoluble dietary fibers including cellulose, hemicellulose and lignin. As shown in
Edible fungi contain 17 - 18 of the 20 essential amino acids, and almost all 8 amino acids required by the human body, especially lysine, methionine and threonine which are lacking in cereals [
CK | A1 | A2 | A3 | A4 | B1 | B2 | B3 | B4 | |
---|---|---|---|---|---|---|---|---|---|
Aspartic acid (Asp)# | 1.10 | 1.68 | 1.92 | 2.06 | 1.65 | 2.18 | 1.83 | 1.78 | 1.78 |
Threonine (Thr)* | 0.52 | 0.89 | 1.02 | 1.08 | 0.89 | 1.22 | 1 | 0.98 | 0.96 |
Serine (Ser) | 0.60 | 0.92 | 1.06 | 1.13 | 0.93 | 1.28 | 1.05 | 1.02 | 0.99 |
Glutamic acid (Glu)# | 4.16 | 3.7 | 4.22 | 4.42 | 4.19 | 5.82 | 4.56 | 4.56 | 4.42 |
Glycine (Gly) | 0.19 | 0.82 | 0.93 | 0.99 | 0.84 | 1.16 | 0.92 | 0.88 | 0.87 |
Alanine (Ala) | 1.30 | 1.11 | 1.25 | 1.34 | 1.19 | 1.65 | 1.38 | 1.36 | 1.3 |
Valine (Val)* | 0.68 | 1.78 | 1.98 | 2.08 | 1.91 | 2.39 | 2.02 | 2.06 | 1.99 |
Cystine (Cys) | 0.14 | 0.13 | 0.15 | 0.13 | 0.11 | 0.14 | 0.13 | 0.14 | 0.14 |
Methionine (Met)* | 0.11 | 0.31 | 0.35 | 0.35 | 0.27 | 0.36 | 0.3 | 0.28 | 0.29 |
Isoleucine (Ile)* | 0.4 | 0.77 | 0.89 | 0.93 | 0.79 | 1.04 | 0.86 | 0.84 | 0.85 |
Leucine (Leu)* | 0.78 | 1.31 | 1.5 | 1.6 | 1.36 | 1.74 | 1.46 | 1.43 | 1.46 |
Tyrosine (Tyr) | 0.50 | 0.56 | 0.72 | 0.63 | 0.55 | 0.76 | 0.63 | 0.59 | 0.64 |
Phenylalanine (Phe)* | 0.89 | 0.81 | 0.94 | 1.01 | 0.86 | 0.95 | 0.93 | 0.9 | 0.91 |
Lysine (Lys)* | 0.84 | 1.07 | 1.34 | 1.34 | 1.11 | 1.46 | 1.19 | 1.09 | 1.13 |
Histidine (His) | 0.18 | 0.27 | 0.32 | 0.36 | 0.34 | 0.45 | 0.37 | 0.3 | 0.3 |
Arginine (Arg) | 0.65 | 0.85 | 0.97 | 1.07 | 0.8 | 1.11 | 0.91 | 0.88 | 0.89 |
Proline (Pro) | 0.32 | 0.81 | 0.94 | 1.01 | 0.84 | 1.13 | 0.92 | 0.94 | 0.92 |
Total amino acids (T) | 13.35 | 17.79 | 20.5 | 21.53 | 18.63 | 24.84 | 20.46 | 20.03 | 19.84 |
Total essential amino acids (E) | 4.22 | 6.94 | 8.02 | 8.39 | 7.19 | 9.16 | 7.76 | 7.58 | 7.59 |
Total non-essential amino acids (N) | 9.13 | 10.85 | 12.48 | 13.14 | 11.44 | 15.68 | 12.7 | 12.45 | 12.25 |
Total umami amino acids (W) | 5.26 | 5.38 | 6.14 | 6.48 | 5.84 | 8 | 6.39 | 6.34 | 6.2 |
E/N (%) | 46.19 | 63.96 | 64.26 | 63.85 | 62.85 | 58.42 | 61.10 | 60.88 | 61.96 |
E/T (%) | 31.60 | 39.01 | 39.12 | 38.97 | 38.59 | 36.88 | 37.84 | 37.84 | 38.26 |
*essential amino acid; #umami amino acid.
substrate directly affect the amino acid content of the cultivated Pleurotus geesteranus. According to WHO/FAO, it is required that E/T is about 40% and E/N is above 60% in the ideal protein. Except for formula B1 and control group, the ratio of essential amino acids in the cultivated Pleurotus geesteranus under the other formulas is close to the standard of ideal protein.
The GB 7096-2003 “Hygienic standard for edible fungi” requires the total arsenic (As) ≤ 1.0 mg/kg, total mercury (Hg) ≤ 0.2 mg/kg and total lead (Pb) ≤ 2.0 mg/kg in edible fungi. As shown in
Hg | As | Cd | Pb | |
---|---|---|---|---|
A1 | 0.014 | 0.499 | 0.092 | 0.035 |
A2 | 0.017 | 0.496 | 0.091 | 0.033 |
A3 | 0.020 | 0.551 | 0.106 | 0.022 |
A4 | 0.019 | 1.00 | 0.092 | 0.19 |
B1 | 0.018 | 0.617 | 0.075 | 0.019 |
B2 | 0.020 | 0.569 | 0.052 | 0.010 |
B3 | 0.021 | 0.65 | 0.027 | 0.047 |
B4 | 0.017 | 0.78 | 0.022 | 0.033 |
CK | 0.013 | 0.152 | 0.440 | 0.042 |
the Pleurotus geesteranus cultivated on all substrates are within the limits defined in GB7096-2003. It is worth noting that the total As content of Pleurotus geesteranus of each group is higher than that of the substrate. It has been reported that edible fungi can strongly accumulate heavy metals. Inorganic As is highly toxic and organic As is less toxic or non-toxic. Therefore, it is suggested that the As limit should mainly refer to the inorganic As [
Partially substituting the conventional cottonseed hull substrate with treated Camellia oleifera shell can increase the mycelial growth rate, yield, biological efficiency, protein content, crude fiber content and amino acid content of the Pleurotus geesteranus. The tannin and saponin in Camellia oleifera shell are responsible for the increased mycelial growth rate. The suitable C/N of substrate for the cultivation of Pleurotus geesteranus was determined to be 27 ± 0.7. The C/N ratios greater than 30 can cause low contents of protein and soluble sugar in Pleurotus geesteranus. Camellia oleifera shell in cottonseed hull substrate can also reduce the fat content of Pleurotus geesteranus and affects its ash content. The total contents of Hg, Cd, Pb and As of the Pleurotus geesteranus cultivated on the substrates containing Camellia oleifera shells are within the limits defined by the national regulation.
This work was supported by the Provincial Department of Science and Technology of Zhejiang, China (Grant NO. 2017C02022).
The authors declare no conflicts of interest regarding the publication of this paper.
Zhang, J.P., Li, X.B., Ying, Y. and Yao, X.H. (2019) Effects of the Camellia oleifera Shell Substrate on the Yield and Nutritional Composition of Pleurotus geesteranus. Agricultural Sciences, 10, 1298-1311. https://doi.org/10.4236/as.2019.1010096