Pollution and Effects on Community Health

Abstract

Effect of agro-wastes on Pleurotus ostreatus nutrient and mineral composition was investigated using four substrates; bread fruit (Treculia africana), sterilized sawdust, non- sterilized sawdust and cassava peel. Mushroom grown on bread fruit substrate recorded significantly (p ≤ 0.05) the highest moisture content (14.68 %), followed by non-sterilized sawdust (13.97 %) comparable with cassava peel (13.95 %) and sterilized sawdust with least moisture content (13.54 %). Bread fruit substrate recorded the highest ash level (7.94 %) which was comparable with sterilized cassava peel (7.88 %) followed by non-sterilized sawdust (7.75 %) and sterilized sawdust (6.93 %). Also, bread fruit substrate recorded the highest protein content (22.43 %) followed by sterilized cassava peel (21.13 %), non-sterilized sawdust (20.11 %) and sterilized sawdust (19.15 %). The sterilized sawdust recorded the highest fat (3.82 %) comparable to cassava peel (3.75 %), followed by bread fruit substrate (3.40 %) and non-sterilized sawdust (3.34 %). Cassava peel had the highest Vitamin B1 content (2.11 mg/100 g), followed by non-sterilized sawdust (1.64 mg/100 g), breadfruit (1.28 mg/100g) and sterilized sawdust (1.03 mg/100 g). Sterilized sawdust recorded the highest Vitamin C (0.89 mg/100g) comparable (p ≤ 0.05) with cassava peel (0.87 mg/100 g) and there was no significant (p ≤ 0.05) difference in the Vitamin C content of breadfruit substrate (0.76 mg/100 g) and non-sterilized sawdust (0.70 mg/100 g). Non-sterilized sawdust significantly (p ≤ 0.05) recorded the highest Iron (Fe) content (8.28 mg/100 g), followed by breadfruit substrate (7.20 mg/100 g) comparable with cassava peel (7.16 mg/100 g) and sterilized sawdust (6.17 mg/100 g). Breadfruit substrate had the highest calcium (Ca) content (24.72 mg/100 g), followed by cassava peel (24.48 mg/100 g) that was comparable with sterilized sawdust (24.44 mg/100 g) and then non-sterilized sawdust (24.27 mg/100 g). Breadfruit substrate in addition gave the highest magnesium (Mg) content (21.69 mg/100 g) followed by sterilized sawdust (21.56 mg/100 g), non-sterilized sawdust (20.20 mg/100 g) and sterilized cassava peel that had the least magnesium (Mg) content (19.76 mg/100 g). In general, the highest nutrient and mineral composition were recorded in breadfruit substrate (moisture, ash, crude protein, Ca and Mg), sterilized sawdust (fat), cassava peel (Vitamin B1), sterilized sawdust (Vitamin C), and non-sterilized sawdust (Fe).

Introduction

Mushrooms are the world’s greatest untapped resources and delicacy of future (Wani et al., 2010) with high nutritional value that promote good human health (Oyetayo, 2006; Kinge et al., 2014). Moisture, protein, fibre, ash, crude fat and carbohydrate have been found in Pleurotus genus (Sharmila et al., 2015; Duru et al., 2019). Studies by Liasu et al., (2015) implicated sodium, calcium, magnesium, potassium and manganese in Pleurotus which was supported by the findings of Jonathan et al., (2013) alongside iron, zinc and copper. They contain vitamin C and B complex, and folic acid, which is blood building vitamin that relieves anaemia as well as other essential nutrients needed in the body (Buigut, 2002; Caglarimak, 2007; Jiskani, 2001; Odero, 2009). Their protein content varies from 4 - 44 % based on the species (Oei, 2003). Apart from the nutritional value, many mushrooms have multi-functional properties and contain pharmacologically active compounds with therapeutic properties such as anticancer, anticoagulant, induction of cytokine production, anti-radiation, anti-allergic, anti-diabetic, anti-cholesterol, anti-tumor, anti-inflammatory, antimicrobial and antioxidant effects  for prevention and treatment of different ailments (Wani et al., 2010; Chang and Wasser, 2017; Akinyele et al., 2011; Zhou et al., 2012; De Silva et al., 2013; Wasser, 2011; Macrae et al, 2009).Some mushrooms serve as a natural source of biologically active compounds with fungicidal, herbicidal and insecticidal properties since the synthetic form is toxic to both human health and environment (Naraian et al., 2009). Some others possess bactericidal, nematicidal, and antiphytoviral activities (Stamets, 2005).

Mushrooms depend on substrates which are usually lignocellulosic materials that form nutritional source and the substratum that facilitates growth and fruiting (Chang and Miles, 2004; Markson et al., 2012). Substrate is a very important element in mushroom production since the chemical and nutritional content of the substrate correlated with the yield and quality of oyster mushroom (Hoa et al., 2015; Aziz, et al., 2013). Substrates utilized in the production of mushroom have effect on the chemical, functional and sensorial characteristics of mushrooms (Pardo-Gimenez et al., 2018). The use of some selected agro-wastes bread fruit (Treculia Africana), sterilized sawdust, non- sterilized sawdust and cassava peel) in mushroom production and their effect on the nutrient, mineral and vitamin composition of P.ostreatus is presented in this report.

Materials And Methods

The spawn of P. ostreatus was obtained from the Department of Biological Sciences, Federal University of Technology (FUTO) Owerri, Imo State, Nigeria. Gmelina arborea sawdust was collected from Ahiaeke timber market, Breadfruit (Treculia Africana) from Isigate market and cassava peels from Umuariaga, all in Abia State, Nigeria. The study was carried out in the Department of Plant Health Management Laboratory, Michael Okpara University of Agriculture Umudike Umuahia, Abia State, Nigeria.

The breadfruit (Treculia Africana) tree substrate and cassava peel were crushed into pieces and prepared according to modified method of Adenipekun and Fasidi, (2003). Each substrate was measured (200 g) in replicates using a weighing balance and used as substrates. The substrates were sterilized using a drum containing stacks of sticks and water up to the level of the sticks and covered with fresh plantain leaves in order to generate enough heat. The substrates were subjected to heating up to 100oCthen steam-sterilized for 2hours after monitoring the temperature with a thermometer and allowed overnight to cool while still in the drum. White sterile transparent buckets that served as experimental units were perforated using a sterile cork borer (5mm diameter) and 200 g of each of the sterilized substrates were separately placed into each of the perforated buckets and were inoculated with the spawn of the fungus. Grain based spawn of P. ostreatus (30 g) was aseptically inoculated into each of the treatments. The spawn was sprinkled on the substrates and covered properly then watered every two days to maintain a high relative humidity of between 75-80%. The three replicates of each treatment in the sterile buckets were maintained at 30 ± 2°C. The four organic substrates used in the study were; sterilized Gmelina arborea sawdust, unsterilized Gmelina arborea sawdust, breadfruit (Treculia africana), cassava peels.

The proximate analysis of the mushroom was prepared by drying the fruit bodies in an oven at 104°C for four hours. The dried samples were broken into smaller pieces before grinding into fine powder using a Thomas Willey milling machine (Okwulehie and Odunze, 2004b). The dried and powdered samples were dispensed into air-tight bottles and used for analysis. Moisture content of the mushroom was determined by the gravimetric method (Konuk et al., 2006). Measured weight of each sample (5g) was placed in a weighed moisture can. The cans with the samples were dried in the oven at 1050C for 3hrs in the first instance. It was cooled in desiccators and reweighed. The drying, cooling and reweighing continued until constant weights were obtained. The incineration gravimetric method was used (AOAC, 2003). A sample of mushroom (5g) was put in a previous weighed porcelain crucible. The sample in crucible was put in a muffle furnace set at 5500Cand allowed to burn for 2-3 hours (until the sample became a grey ash). The sample in crucible was carefully removed from the furnace and cooled in a desiccator and reweighed. By difference the weight of ash was obtained and expressed in percentage using the formula: The protein content was determined using the Kjedahl method by A.O.A.C (2003). Each sample (0.2g) was digested and made up of 50ml in a flask and 10ml of the digested sample was distilled with 0.2 M sulphuric acid to determine the total nitrogen. The spectrophotometric method (AOAC, 2003) was used in the determination of vitamin content of the mushroom.

The mushroom sample (5 g) was homogenized with 50 ml of ethanoic sodium hydroxide and filtered into 100 ml flask. 10 ml of the filtrate was pipette and colour developed by addition of potassium dichlorate and then read at 360 nm wavelength of spectrometer. A standard thiamine solution was prepared and diluted and 10 ml of the solution was analyzed. The processed sample (20 g) was homogenized in 100 ml of EDTA/TCA extraction solution and filtered. The filtrate was passed through a packed cotton wool containing activated charcoal to remove the colour. The volume of the filtrate was adjusted to 100 ml by washing with more of the extracting solution. 20 ml of the filtrate was measured into a conical flask and 10mlpotassium iodide added followed by 5 ml of starch solution (indicator) and the mixture titrated against 0.01 ml CuSO4 solution. The vitamin C content a also determined Calcium and magnesium content of the digested sample were determined by complex iometric titration. (10ml) of the sample solution was dispensed into separate conical flasks, pinches of the masking agent like potassium cyanide, potassium ferrocyanide, hydroxyl hydrochloride) were measured into content of each flask 20ml of ammonia buffer was added to one, the flasks to raise the pH to 10.0 while 10ml of NaOH solution was added to the buffer to raise the pH to 12.0. The flask at pH to 10.0 (for calcium and magnesium) a pinch of erichrome dark black indicator was added and titrated against 0.02 EDTA solution the other flask at pH 12.0 (for calcium alone) solochrome dark blue indicator was added and titrated against 0.02N EDTA solution at PH  12. Calcium complexes with EDTA while at ph 10. Both calcium and magnesium form complexes with EDTA. A reagent blank was titrated as a control. The calcium and magnesium content of the sample were calculated using the standard that 1ml of 1N EDTA has an equivalence of 24mg magnesium and 20.04mg calcium respectively.

The determinations of iron in the dry samples were done following the wet digestion extraction methods. The powdered samples were sieved and 0.2 g of each put into a 25 ml round bottomed flask. The samples were digested using 5 ml nitric acid (HNO3) and 2 ml perchloric acid (HClO4). The solution was filtered after adding 15 ml of distilled water into a 50 volumetric flask and the volumes made up to mark with more distilled water. The minerals in the digested samples were then determined by atomic absorption spectrophotometer following the development of colour with ammonium molybdate.

The experiment was laid out in a Completely Randomized Design (CRD) and treatments were replicated three times. The data collected were analyzed using Analysis of Variance (ANOVA) while the different means were separated using Least Significant Difference (LSD) at 5% level of probability.

RESULTS AND DISCUSSION

Result of the effect of substrate on the nutrient content of the mushroom (Table 1) showed that mushroom harvested from sterilized bread fruit substrate had significantly (p ≤ 0.05) the highest moisture content (14.68 %), followed by non-sterilized sawdust (13.97 %) and sterilized cassava peel (13.95 %) which were comparable and then sterilized sawdust that gave the least moisture content (13.54 %). Sterilized bread fruit substrate alsosignificantly (p ≤ 0.05) recorded the highest ash level (7.94 %) which was comparable with sterilized cassava peel (7.88%) followed by non-sterilized sawdust (7.75 %) and sterilized sawdust that recorded the least ash content (6.93 %). Mushroom grown in sterilized bread fruit substrate significantly (p ≤ 0.05) recorded the highest protein content (22.43 %) followed by sterilized cassava peel substrate (21.13 %), non-sterilized sawdust substrate (20.11 %) and sterilized sawdust (19.15 %).The sterilized sawdust recorded the highest fat (3.82 %) which was not significantly (p ≤ 0.05) different with sterilized cassava peel (3.75 %),followed by sterilized bread fruit substrate (3.40 %) and non-sterilized sawdust that had the least fat content(3.34 %).

Table 1: Effect of substrates on nutrient composition of Pleurotus ostreatus

Nutrient content (%)

The result in Table 2showed that mushroom harvested from the test substrates contained Vitamin B1, Vitamin C, Iron (Fe), Magnesium (Mg) and Calcium (Ca) though to varying degrees. Sterilized cassava peel recorded significantly recorded the highest Vitamin B1 content (2.11 mg/100 g), followed by non-sterilized sawdust (1.64 mg/100 g), sterilized breadfruit substrate (1.28 mg/100g) whereas sterilized sawdust gave the lowest Vitamin B1 content (1.03 mg/100 g). Sterilized sawdust recorded the highest Vitamin C (0.89 mg/100g) which was comparable (p ≤ 0.05) with cassava peel (0.87 mg/100 g) and there was no significant (p ≤ 0.05) difference in the Vitamin C content of mushroom from breadfruit substrate (0.76 mg/100 g) and non-sterilized sawdust that gave the lowest (0.70 mg/100 g). Non-sterilized sawdust significantly (p ≤ 0.05) recorded the highest Iron (Fe) content (8.28 mg/100 g), followed by breadfruit substrate (7.20 mg/100 g) which was comparable with cassava peel (7.16 mg/100 g) and then sterilized sawdust that gave the least (6.17 mg/100 g). Sterilized breadfruit substrate significantly (p ≤ 0.05) recorded the highest Calcium (Ca) content (24.72 mg/100 g), followed by cassava peel (24.48 mg/100 g) that was comparable with sterilized sawdust (24.44 mg/100 g) whereas non-sterilized sawdust gave the least Calcium (Ca) content (24.27 mg/100 g). Sterilized breadfruit substrate gave the highest Magnesium (Mg) content (21.69 mg/100 g) and this was significant followed by sterilized sawdust (21.56 mg/100 g), non-sterilized sawdust (20.20 mg/100 g) and sterilized cassava peels which gave the least Magnesium (Mg) content (19.76 mg/100 g).

Table 2: Effect of substrate on Vitamin and Mineral contents of Pleurotus ostreatus

Discussion

The agro-wastes supported the growth of P. ostreatus with high nutritional and mineral values that could promote good human health (Oyetayo, 2006; Kinge et al., 2014). The highest nutrient and mineral composition of P. ostreatus were recorded in breadfruit substrate (moisture, ash, crude protein, Ca and Mg), sterilized sawdust (fat), cassava peel (Vitamin B1), sterilized sawdust (Vitamin C), and non-sterilized sawdust (Fe). Moisture, protein, fibre, ash, crude fat and carbohydrate have been found in P. ostreatus by Duru et al., (2019) and Chirinang and Intarapichet, (2009) supported by findings of Sharmila et al., (2015). Similar findings were reported for Pleuritic genus (Sharmila et al., 2015; Duru et al., 2019) and P. florida produced with wheat, rice, sugarcane, maize and sorghum substrates (Iqbal et al., (2016). Familoni et al., (2018) reported lower moisture content and higher values of other parameters assessed in this study for Pleurotus species cultivated on different substrates. Adebola et al., (2018) reported lower proximate values for P. ostreatus cultivated on different sterilized sawdust substrates. The values obtained on sterilized sawdust in for P. ostreatus which could be due to the substrate supplements with wheat bran and lime. this study were lower than those reported by Ahmed et al., (2016) Nwoko et al., (2017) reported higher values of protein and lower values for other parameters in this study whereas Oyetayo and Ariyo, (2013) reported lower values for moisture, ash, and lipid for P. ostreatus. Though the protein content of P. pulmonarius reported by Islam et al., (2017) was higher than those found in this study, the values compared favorably with the value of crude protein (16.90-26.82%) reported by Oliveira et al., (2007) who studied the chemical composition of Pleurotus pulmonarius grown on some substrates. The differences in the protein content of the mushrooms in relation to the substrates may be attributed to the type and level of nitrogen available in the substrates used for production. The parameters assayed in this study cannot be overlooked in the day-to-day activities of man as they support in the provision of energy, amino acid and reduction of cholesterol (Campos-Vega et al.,2010; Marten et al., (2017).

The substrates had significant effect on calcium, iron, magnesium, Vit. C and Vit. B1 contents of P. ostreatus. Mushroom from breadfruit substrate was better than other substrates in terms of calcium and magnesium indicating high content of these minerals in the agro-residue. Liasu et al., (2015) implicated sodium, calcium, magnesium, potassium and manganese in Pleurotus which was supported by Jonathan et al., (2013) in addition to iron, zinc and copper. The mineral composition of the mushroom in this study was in line with those reported by Adebayo et al., (2014) for P. ostreatus but higher than values reported by Ahmed et al., (2016) for several species of Pleurotus including P.ostreatus. Lower mineral values have been recorded for mushrooms cultivated on various agro-wastes, P. ostreatus (Oyetayo and Ariyo, 2013), P. florida (Iqbal et al.,2016) and P. pulmonarius (Nwoko et al., 2017; Jonathan et al., 2013). The study of Duru et al., (2019) implicated higher contents of calcium for P. ostreatus. These minerals that are assayed in this study are therefore important as they have been found to support the physiological, biochemical and metabolic processes in human (Piska et al., 2017; Idu and Onyibe, (2007).

Acknowledgment

We sincerely appreciate the support by the Executive Director of the National Root Crops Research Institute, Umudike, Abia State and the efforts of staff of the Plant Pathology Unit of the Institute as well as the assistance by the technical staff of the College of Crop and Soil Sciences of the Michael Okpara University of Agriculture, Umudike, Abia State Nigeria.

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