Nutritional and Bioactive Compounds: Evaluation of Pleurotus pulmonarius (Fries) Quel. Fruit Bodies Grown on Different Wood Logs in Abia State, Nigeria
Received date: Febraury 28, 2017; Accepted date: April 05, 2017; Published date: April 07, 2017
Citation: Nwoko MC, Onyeizu UR, Okwulehie IC, Ukoima HN (2017) Nutritional and Bioactive Compounds: Evaluation of Pleurotus pulmonarius (Fries) Quel. Fruit Bodies Grown on Different Wood Logs in Abia State, Nigeria. J Bioremediat Biodegrad 8:393. doi: 10.4172/2155-6199.1000393
Copyright: © 2017 Nwoko MC, et al. This is an open-a ccess article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
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This study was conducted to determine the nutritional and bioactive compounds composition of Pleurotus pulmonarius fruit bodies cultivated on tree logs of Dacryodes edulis, Mangifera indica and Treculia africana. Pure mycelium culture of P. pulmonarius was aseptically bulked in sorghum grains. Logs were cut into average length of 18 cm with inoculation holes of 3 cm × 15 mm diameter; using high speed drill (HSD) of 5 drill bit and allowed to decompose for 8 months. During mushroom cultivation, logs were soaked in tap water for 24 hrs and pasteurized at 80°C in an improvised metallic drum (IMD) for 1 hour; using cooking gas as heat source and allowed to cool overnight. 10 g of grain based spawn was inserted into 2/3 of each hole by way of inoculation and sealed with sterile polybag for mycelium incubation. Polybags were cut open after spawn run following primordial initiation. Fruit bodies were harvested at maturity, sundried ground and packed in airtight container prior to further analysis. Data was analysed using Analysis of Variance (ANOVA) and mean separation by Duncan Multiple Range Test (DMRT) while levels of significance were determined at 5%. Results indicate that P. pulmonarius fruit bodies harvested from various tree logs were significantly different p<0.05 in their nutritional and bioactive compounds composition. Fruit body samples were rich in protein, carbohydrates, Na, K, and Ca. It was also observed that fruit bodies contained significant amount of Alkaloids, Tannins and Saponins; and could be useful in drug synthesis. Therefore adopting this technique in oyster mushroom cultivation would lead to more jobs creation and food security; but this must be done with careful regulations to avoid indiscriminate falling of trees.
Pleurotus pulmonarius; Logs; Nutrients; Bioactive; Fruit bodies
Mushrooms are unique biota which assemble their food by degrading enzymes and decompose the complex food materials present in the biomass where they grow . Oyster mushrooms can be grown on various substrates due to its strong enzymatic features. Different substrates are used in each region depending on their availability . Wheat straw, sawdust and other agricultural by-products resulting after processing of waste paper, Hazelnut and Tilia have been used in Oyster mushroom cultivation ; maize, corn, rice, elephant grass , sugarcane , coffee  have been examined as alternative substrates for its cultivation. These substrate materials are usually by products from industries, households, agriculture etc., and are usually considered as wastes . However, these wastes are actually resources in the wrong place at a particular time and mushroom cultivation can harness them for its own benefit .
Kadiri and Aizai  showed that Lentinus subnudus could be cultivated on wood logs of tropical trees. According to Hyunjong and Seung , hard woods such as poplar, willow, beech, elm and alder are the most commonly used tree species in oyster mushroom cultivation. He noted that unlike shiitake, Oyster mushrooms do not grow well on Oak tree logs. Hyunjong and Seung  reported that since mushroom feed primarily on sapwood, any tree trunk selected for inoculation must have a larger sap wood area. The lighter or outermost wood of a log is the sapwood and the darker or inner wood is the heartwood.
The desirability of a food product does not necessarily bear any correlation to its nutritional values instead, its appearance, taste and aroma, sometimes can stimulate one’s appetite . Mushroom has been used as a food and medicine by different civilizations since immemorial time, due to its delicious taste and dietetic qualities [11,12]. Mushrooms are also known for their medicinal properties; they are low in calories and are ideal food for diabetic and heart patients. Mushroom has qualities like lowering the blood cholesterol level, warding against cancer and invigorating hair growth. Tewari  reported that the fresh mushroom contains about 85-90% moisture, 3% protein, 4% carbohydrates, 0.3- 0.4% fats and 1% minerals and vitamins. Pleurotus species are good source of protein, vitamins and minerals [8,14]. Mushroom protein is intermediate between that of animals and vegetables, but superior to most other foods, including milk and contains all the essential amino acids required by man [15-17]. Mushrooms contain appreciable quantities of crude fibres although little information exists on the total dietary fibre (TDF) content of mushrooms. Okwulehie et al.  reported high crude protein and carbohydrate contents in P. ostreatus cultivated on different substrates.
The world production of oyster mushroom is estimated to be 875,000 tons in 1997 . China was responsible for 87% of world supply, oyster mushroom is the easiest to produce and least expensive to grow. Most of the world’s supply of oyster mushrooms today comes from commercial mushroom growers . For small-scale cultivation with limited budget, oyster mushroom is the clear choice for gaining entry into the mushroom industry . This work aims to determine the nutritional and bioactive compounds composition of P. pulmonarius cultivated on tree wood logs.
Source of culture
Pure culture of P. pulmonarius (Fries) Quel. Was obtained from the laboratory of the department of plant science and biotechnology, Michael Okpara University of Agriculture, Umudike, Abia State, Nigeria.
Spawn of P. pulmonarius was produced using sorghum grains. Grains were washed in tap water and soaked overnight. They were then boiled in water in the ratio of 1:1 (sorghum grain: water) using cooking gas for 1520 mins and drained of excess water. Completely drained sorghum grains were mixed with 4% (w/w) CaCo3 and 2 % (w/w) CaSO4 to optimize pH and prevent clumping of grains respectively as described by Muhammad et al. . Grains were later stuffed into 35 cl Lucozade bottles tightly plugged with cotton wool and sterilized in an autoclave at 121°C for 30 mins. After sterilization, the bottles were allowed to cool, before they were inoculated with actively growing mycelium of P. pulmonarius by grain-to-grain transfer and incubated in the dark (at 27 ± 2°C) for 10-15 days until the grains were fully colonized by mycelium .
Preparation of wood logs (substrates)
Average trees size of T. africana, M. indica and D. edulis were fell during the Hammattern season (winter) according to the recommendations of Oei . Trees were cut into logs of 18 cm using Electric wood saw (EWS); Model: Elect. 1710, Japan. Care was taken to ensure that the barks of the logs were not peeled off as instructed by Hyunjong and Seung .
Holes of depth 3 cm by 15 mm diameter were made hexagonally on each log with high speed drills (HSD) of 5 drill bit in respect to log size. Average number of holes per log was determined by the formula, according to Stamets , Nwoko .
Where: NH=Number of holes,
DL=Diameter of log (cm),
LL=Length of Log (cm),
Logs were laid in open field for 8-9months in alternating rains and sun to allow for decomposition. Dry weight of logs (g/kg) were determined before they were soaked in water for 24 hr. Logs were pasteurized at 80°C in an improvised metallic drum (IMD) for 1 hr using cooking gas as a local heat source and allowed to cool overnight, as recommended by Canford , Nwoko et al. .
Log inoculation was done by inserting about 10 g grain spawn of P. pulmonarius into 2/3 of the holes and subsequently sealing the logs with transparent polybags to avoid contaminants. Mycelium recovery and colonization were clearly visible after 24 hrs; when fully colonized polythene bags were cut open to allow for fruiting . Before pinhead initiation, white mycelium was visibly noticed on the cut ends of the logs. Light intensity and humidity of the air were increased to about 400 lux and 75% respectively. To achieve these, logs were watered at least morning and evening and t cropping room of the mushroom house was flooded with water. Temperature was maintained at 27 ± 2°C [20,25]. Pinheads of P. pulmonarus were first noticed in D. edulis logs followed by T. africana and then M. indica logs after 9, 10 and 12 days of inoculation respectively. Mushrooms were harvested as soon as the fruit-bodies were fully matured .
Proximate analysis was carried out on each of the 3 mushroom samples. Nutrients like carbohydrates, protein, fat ash, moisture and crude fiber contents were determined by using the methods outlined in the AOAC . Protein determination was carried out using the Kjedahl method . Fat determination was carried out using a Soxhlet apparatus . Also, determination of fiber content was done according to the enzymatic gravimetric method .
Determination of minerals
Mineral compositions of dried mushroom samples were determined by wet-ashing method. The solutions of ash obtained from the samples were dissolved in a drop of trioxonitrate (V) acid made up to 50 ml with deionized water and analyzed for Calcium (Ca) and Magnesium (Mg) using vanadate ethyldiamine-tetra acetic acid (EDTA) complexometric titration method according to MFA . Sodium (Na) and Potassium (K) were estimated using flame photometer while Phosphorus (P) was determined using UV-visible spectrometer after making Ammonium vanado-molybdate at 436 nm according to the established procedures of Perkin Elmer .
Determination of percentage of bioactive compounds
Percentage Alkaloids were determined by the methods of AOAC  and Maxwell et al. . Percentage Flavonoids, Saponins and Tannins were also determined by the procedures according to Cloupai- Abyazini, Peng and Kobayashi  while percentage Phenols were estimated by the method of Harborn .
The data obtained were statistically analyzed using Analysis of Variance (ANOVA) mean separation and tests of significance were carried out by Duncan Multiple Range Test (DMRT) at p<0.05 .
Results and discussion of the work on the nutritional and bioactive compounds evaluation of P. pulmonarius fruit bodies grown on different wood logs are presented below.
Table 1 shows the proximate composition of P. pulmonarius as affected by different log substrates. The results of the moisture, ash, fat, fibre, protein, carbohydrate, dry matter and free nitrogen contents of P. pulmonarius fruit bodies cultivated on the D. edulis, M. indica and T. africana are significantly different p<0.05. This shows that the mushroom is highly nutritious when grown on these logs. This also indicates the major reason why oyster mushrooms grow naturally on already degrading logs in the wild and sometimes, around homes [8,20].
Values are means of 3 replicates and values bearing the same letter are not significantly different (P>0.05). MC: Moisture Content, CHO: Carbohydrate, DM: Dry Matter
Table 1: Effect of log substrates on proximate composition (%) of P. pulmonariusfruit bodies.
The relative high percentage of dry matter, carbohydrate and protein in the mushroom fruit bodies cultivated on the log substrates conforms to the work of Marlow and Ukaima et al. . The high protein contents of the P. pulmonarius fruit bodies cultivated on the various logs confirms the assertion by several workers that mushroom protein is intermediate between that of animals and vegetables, but superior to most other foods, including milk and contains all the nine essential amino acids required by man [15-17]. Low fat content of the mushroom shows that the mushroom could be good for people with cardiac problems. This is in line with the reports of Okhuoya and Okigbo , Okwulehie and Odunze , who maintained that mushrooms generally contain lowoil and fat, and because of the low content of oil and fat in mushrooms, they are recommended as good supplements for patients with cardiac problems.
Table 2 represents the results of minerals compositions of P.pulmonarius grown on various logs. The results showed that the mushroom samples were significantly p<0.05 rich in Sodium, Potassium, Magnesium, Calcium and Phosphorus. Potassium and Phosphorus contents were higher than other minerals analyzed and also higher in mushrooms harvested from D. edulis logs. In this study, Sodium was found to be the lowest among other minerals analyzed in the mushroom across all log substrates. The low Sodium content in mushrooms makes them ideal for persons with certain types of heart and kidney ailments .
Values are means of 3 replicates and means bearing the same letter are not significantly different (P>0.05).
Table 2: Mineral constituents (mg/100g) of P. pulmonariusfruit bodiesas affected by different log substrates.
The rich minerals contents in P. pulmonarius fruit bodies grown on the logs as observed in this study could be because the mushroom effectively utilized the high amount of nutrients present in the sapwood as reported by Hyunjong and Seung . These mineral values are higher than those reported by Ogbo and Okhuoya ; Okwulehie et al. , Okoi and Iboh . D. edulis gave the highest constituents of all the mineral nutrients analysed while M. indica gave the lowest. The observed appreciable quantities of various mineral elements analysed in the three mushroom samples indicates that these logs contain the corresponding nutrients in a relative amount since the nutritional composition of mushrooms depends on the substrate where they were grown .
Bioactive constituents of P. pulmonarius as affected by different log substrates are shown in Table 3. Results show that Alkaloids, flavonoides phenols, tannins and saponins were significantly different p<0.05 at different quantities. Alkaloids were found in higher quantity than other bioactive compounds analysed. Alkaloids have powerful effect in animal physiology and are important in pharmaceutical industries for drug manufacturing . Rambeli and Menini  reported that alkaloids are stimulants and acts by prolonging the action of several hormones. Flavonoids, phenols, tannins and saponins concentrations in P. pulmonarius fruit bodies cultivated on the different trees logs were higher than those reported by Okwulehie et al. . Flavonoids act as anti-carcinogens, anti-bactarials , saponins and are implicated in the prevention of parasitic fungal diseases  while tannins have been used as anti-tumor agents and perform a wide range of anti-infective actions . The high concentrations of these important bioactive compounds in the fruit bodies of P. pulmonarius with respect to their various log substrates indicate that the trees may also contain the compounds in high amount. This also shows that these mushroom samples may be considered useful in the production of certain pharmaceutical chemicals . The high concentrations of these compounds may also contribute to their taste, aroma and flavour,thereby increasing their nutritional, medicinal and food value.
Values are means of 3 replicates and means bearing the same letter are not significant at (P>0.05).
Table 3: Effect of wood logs on bioactive compounds composition (%) of P.pulmonarius fruit bodies.
Pleurotus pulmonarius fruit bodies were successfully cultivated on the logs of D. edulis, M. indica and T. africana. Nutritional and bioactive compounds analysis of fruit bodies from different log substrates showed that they were rich in nutrients and could be of high pharmaceutical importance. Therefore, efforts should be made to determine the composition of other nutrients such as vitamins and amino acids of P. pulmonarius with respect to the same log substrates. Commercialization of log technique of mushroom cultivation should also be encouraged since log does not easily get spent and can be repeatedly used for a long period of time. Wherever log cultivation of oyster mushroom is practiced, afforestation should be encouraged to avoid indiscriminate logging, which can lead to desertification.