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Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus citrinopileatus Singer: An Indigenous Mushroom in Kenya



Fredrick Musieba, Sheila Okoth, Richard K. Mibey, Stella Wanjiku and Knight Moraa
 
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ABSTRACT

There are many species of indigenous mushrooms in Kenya which form part of the traditional food system but whose nutritional and cultivation studies have not been completely determined and hence under utilized. The indigenous P. citrinopileatus was collected from Kakamega forest in Western Kenya, characterized and grown at the Kenya Industrial Research and Development Institute laboratories. The objective of this study was to evaluate indigenous P. citrinopileatus mushroom with the aim of qualifying and quantifying chemical information that might serve as a guide to exploit its potentials and benefits for human nutrition. The proximate composition (moisture, energy, fibre, crude fat, ash, minerals and protein) and amino acids contents (by high performance liquid chromatography) and vitamins of the indigenous P. citrinopileatus mushroom were determined. Proximate analysis of P. citrinopileatus revealed that it contained 22.10% protein, 1.32% crude lipid and 20.78% fibre. The mushroom was also found to contain variable amounts of minerals. The most predominant mineral found in the mushroom was Potassium with value of 2.28%. Copper, zinc and iron minerals were generally low with values from 0.0002, 0.0015 and 0.01%, respectively. Eight essential amino acids were detected namely Leucine>Valine> Threonine>Lysine>Phenylalanine>Isoleucine>Methionine>Tryptophan in decreasing order of abundance. Glutamic acid though non-essential was present in high proportion (3.07%). Vitamin B3 (Nicotinic acid), vitamin B5 (Pantothenic acid) and vitamin B2 (Riboflavin) were the most abundant vitamins in all samples analyzed. While vitamin B12 (Cyanocobalamin) and vitamin A (retinol) were the least with values of 0.3 and <10 μg/100 g, respectively. In conclusion, Pleurotus citrinopileatus mushroom can be an excellent source of micronutrients and antioxidants components.

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Fredrick Musieba, Sheila Okoth, Richard K. Mibey, Stella Wanjiku and Knight Moraa, 2013. Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus citrinopileatus Singer: An Indigenous Mushroom in Kenya. American Journal of Food Technology, 8: 200-206.

DOI: 10.3923/ajft.2013.200.206

URL: https://scialert.net/abstract/?doi=ajft.2013.200.206
 
Received: August 28, 2012; Accepted: March 06, 2013; Published: July 19, 2013



INTRODUCTION

Mushrooms are well-balanced food stuff and good sources of amino acids, minerals and vitamins (Kumari et al., 2011). They can be recommended for the countries suffering from insufficient nutrition (Kumari et al., 2011). The problem of malnutrition with ever-increasing ‘protein gap’ is quite obvious in Asian, African and many developing countries.

The traditional source of protein has not kept pace with the population growth. There is need to explore possible source of protein production to help the country overcome malnutrition. Mushrooms are one of the highest protein producers per unit area and time. Their production from agro wastes can be a very effective weapon in fighting malnutrition (Singh and Singh, 2011). There is a very high incidence of malnutrition, especially of protein and micronutrient deficiency in developing countries (FAO, 2010). The production of protein rich food is required to meet the demand of protein and overcome malnutrition in the developing parts of the world (Oyetayo et al. 2007). The importance of a foodstuff as a source of protein depends on the kinds of amino acids that form the protein (Oyetayo et al. 2007).

Several species of mushrooms are known for their characteristic biting texture and pleasant aromas (Kumari et al., 2011). These properties have given meaning to mushrooms as food items (Kumari et al., 2011). Edible mushrooms are valued for their unique taste, aroma, texture and nutritive value. Of particular significance among constituents of mushroom tissue are nitrogen compounds, especially protein, free amino acids, amines, nucleic acids, urea and chitin (Jaworska et al., 2011). Both wild and cultivated mushrooms have been consumed by humans for their nutritional and medicinal benefits and they have unique aroma, taste and texture (Cheung, 2010; Jaworska et al., 2011). Mushrooms are low in energy and fat but high in protein, carbohydrate and dietary fibre and contain a variety of minerals (Cheung, 2010).Mushrooms have been recognized as a good source of amino acids which play an important role in their flavours (Tseng and Mau, 1999).They have been used as food and flavouring material in soups for centuries due to their unique and subtle flavour (Chye et al., 2008).

In the recent years, it has been well proven and documented in the world literature that mushrooms provide nutrition and health benefits for humans (Kumari et al., 2011). Wild mushrooms have been a delicacy in western Kenya for many years and are meat substitute especially for the rural population. The inhabitants of western Kenya usually utilize several species of mushrooms belonging to the genera Termitomyces, Pleurotus and Auricularia for food and trade. The residents have great knowledge about wild edible mushrooms. They are able to characterize them by simple characteristics such as colour, size and habitat. But only little information is available about the cultivation and chemical composition and anti-oxidative properties of these mushrooms. In addition, there are limited data in the literature concerning the nutritional profile of the wild edible mushrooms in Kenya.

The members of Pleurotus species are well known edible mushrooms and some studies have confirmed that they are nutritious and rich source of nutrients (Lewinsohn et al., 2005).There are several species of wild edible mushrooms whose nutritive profiles have not been described (Kumari et al., 2011).The indigenous Pleurotus citrinopileatus mushroom from Kakamega forest in Kenya is one of the wild edible mushrooms that needs to be studied.

The indigenous P. citrinopileatus was collected from Kakamega forest in western Kenya, characterized and grown at the Kenya Industrial Research and Development Institute laboratories. The nutritional properties of this mushroom are not yet known. To our knowledge, the composition and properties of the P. citrinopileatus mushrooms has not been investigated particularly in Kenya contrary to other countries such as China and western countries.

The objective of this study was to evaluate indigenous P. citrinopileatus mushroom with the aim of qualifying and quantifying chemical information that might serve as a guide to exploit its potentials and benefits for human nutrition. The proximate composition (moisture, energy, fibre, crude fat, ash, minerals and protein) and amino acids contents (by high performance liquid chromatography) and vitamins of the indigenous P. citrinopileatus mushroom were determined.

MATERIALS AND METHODS

Sample preparation: Indigenous Pleurotus citrinopileatus mushroom used in the study was grown at the Mushroom Pilot Plant facility of the Kenya Industrial Research and Development Institute (KIRDI) between October and December, 2011. It had been previously collected from Buyangu forest reserve within the Kakamega forest and phenetically characterized by the first author of this manuscript and maintained as pure culture at mushrooms culture bank at KIRDI. The fruits were harvested, sorted and spliced before drying them in a hot air drier at a temperature of 35°C for 2 days before being crushed in a fine mill (Bauermeister, Germany).

Proximate analyses: The moisture, ash and crude fibre contents were analysed according to standard methods (AOAC, 2006). Nitrogen was assayed using Kjeldahl method and the nitrogen content converted to protein by a multiplication factor of 6.25. Proximate analyses were carried out in triplicate and results expressed as percentage of the sample analyzed.

Mineral element analysis: Mineral element analyses were determined using atomic absorption spectrophotometer (Model-Shimadzu AA-6300). Flame technique was employed for P, Ca, Mg, K, Na, Fe, Zn and Cu determinations. Duplicate solutions were prepared for each sample and a minimum of three separate readings were taken to minimize error. The mean values were used to calculate the concentrations. Phosphorus content in mushroom was estimated by ultra violet spectrophotometer (Model: Carry Canc 50 UV visible Spectrophotometer) ammonium molybdovanadate method (AOAC, 2006).

Calorific value: The calorific values of the samples were determined by burning a weighed sample in oxygen, in a calibrated adiabatic bomb calorimeter (Ika-Kalorimeter C400 Adiabatic) under controlled conditions. The calorimeter was standardized by burning benzoic acid. The calorific value of the sample was computed from temperature observation made before, during and after combustion, making proper allowances for heat contributed by other processes and for thermometer and thermo-chemical corrections.

Amino acids: Amino acids profile of the mushroom was determined using AOAC (2006) official methods of analysis (AOAC, 2006).

Vitamins: The vitamins profile was determined following the methods described by British standards and AOAC official methods of analysis as outlined below. Vitamin C (Method derived from BS EN 14130), vitamin A (Method derived from BS EN 12823), vitamin B2 (Method derived from BS EN 14152), vitamin Niacin (Method derived from BS EN 15652), vitamin B6 (Method derived from BS EN 14164), vitamin H (Method NF EN 15607) derived from BS EN 15607), vitamin B (method derived from British Standard EN 14131), while vitamin B5 and B12 were determined using AOAC official methods of Analysis (AOAC, 2006).

Standards: Standard solutions of metals (1 mL = 1 mg), calcium (Ca), cobalt (Co), copper (Cu), iron (Fe), magnesium (Mg), nickel (Ni), phosphorus (P), potassium (K), sodium (Na) and zinc (Zn) were purchased from BDH Chemicals Ltd., Poole, England). Stock solutions were prepared from the standard solutions. Working standards were prepared by diluting the stock solutions.

Quality assurance: Analar grade chemicals were used to establish accuracy, reliability and reproducibility in the results. Volumetric glassware of class “A” quality was used for solution preparation. Double distilled water was used for solution preparation and dilution purpose.

Statistical data analysis: Data were statistically analyzed using statistical software Genstat Edition 13(VSN International Ltd., UK).

RESULTS

The results of the chemical composition and energy value (expressed on dry weight basis) of the indigenous P. citrinopileatus mushroom are shown in Table 1 and 2.

The protein content was 22.10% while the fat was 1.32% and fibre 20.78%.

The mushroom was found to contain variable amounts of minerals. The most predominant mineral found in the mushroom was Potassium with value of 2.28%. Copper, zinc and iron minerals were generally low with values from 0.0002, 0.0015 and 0.01%, respectively.

The results of vitamins composition obtained for the studied mushroom are shown in Table 3. Vitamin B3 (Nicotinic acid) was the most abundant vitamin with the value of 22.2 mg/100 g while vitamin B12 (cyanocobalamin) and vitamin A (retinol) were the least with values of <0.3 and <10 μg/100 g, respectively.

The nutriceutical analysis of P. citrinopileatus was done to elucidate its essential and non essential amino acids (Table 4). The analysis revealed 8 essential amino acids namely Leucine> Valine> Threonine> Lysine> Phenylalanine> Isoleucine> Methionine> Tryptophan in decreasing order of abundance. The most abundant amino acid glutamic acid with an average value of 3.07% and the lowest levels were those of cysteine (0.20%).

Table 1: Chemical composition of P. citrinopileatus in g/100 g dry matter
Image for - Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus 
  citrinopileatus Singer: An Indigenous Mushroom in Kenya
Data are expressed as Mean±SD (n = 4)

Table 2: Mineral composition of P. citrinopileatus in mg/100 g dry matter
Image for - Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus 
  citrinopileatus Singer: An Indigenous Mushroom in Kenya
Data are expressed as Mean±SD (n = 4)

Table 3: Vitamins profile of P. citrinopileatus
Image for - Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus 
  citrinopileatus Singer: An Indigenous Mushroom in Kenya

Table 4: Amino acids profile of P. citrinopileatus mushroom
Image for - Proximate Composition, Amino Acids and Vitamins Profile of Pleurotus 
  citrinopileatus Singer: An Indigenous Mushroom in Kenya

DISCUSSION

Proximate analysis of P. citrinopileatus revealed that it contained 22.10% protein while the fat was 1.32% and fibre 20.78%. The values presented here fall within the range reported for most mushrooms (Crisan and Sands, 1978; Yang et al., 2001; Mau et al., 2001).

Mineral composition showed the mushroom to be a good source of potassium. Potassium was the most predominant mineral with value of 2.28%. These findings were in agreement with those of Chye et al. (2008) for Hygrocybe sp. and Okwulehie et al. (2007). Zinc was not detected. This finding is great biological significance, because it means that indigenous P. citrinopileatus mushroom is not a zinc accumulator.

Glutamic acid was the most predominant amino acid in all samples analyzed. While cysteine was the least abundant. The high content of glutamic acid suggests that P. citrinopileatus has very good flavouring ingredients useful in food preparation. These findings concur with those of Reyes et al. (2009) who found high proportion of glutamic acid in Coprinus comatus mushroom. Kumari et al. (2011) also reported similar results for Cantharellus species. The report of Chirinang and Intarapichet (2009) for P. ostreatus and P. sajor caju also concurs with our findings. Liu et al. (2010) also reported abundance of glutamic acid, aspartic acid and leucine in Tricholoma matsutake. Li et al. (2011) also reported similar results where glutamic acid was observed as the major amino acid in button mushroom soup. Similar results for canned mushrooms were obtained by Jaworska et al. (2011).

The high concentration of the acidic amino acids like glutamic acid may be because of their use as precursors from which the backbone of other amino acids is formed (Oyetayo et al. 2007). Previous studies have reported glutamic acid as an active participant in metabolism and synthesis of nucleotide and some amino acids (Liu et al., 2010). It also reported to play a role in brain functioning, nerve system and participates in the disintoxication of ammonia in liver, muscle and brain (Liu et al., 2010).

It is well known that amino acids, especially highly basic amino acids and glutamic acids contribute to the flavour properties of mushrooms (Maga, 1981; Sugahara et al., 1975), thus the high levels of glutamic acids in P. citrinopileatus contribute to their characteristic flavour. The results of this study clearly indicate the potential of this mushroom species for its use as source of flavour in soups and stews.

Tsai et al. (2008) reported the presence of glutamic acid and alanine amino acid in mushroom soup and proved that these acids were the main factor for umami and sweet taste in many species of mushrooms. Aspartic and glutamic acids are monosodium glutamate-like (MSG) components which give the most typical mushroom taste, i.e., the umami or palatable taste that is characteristic taste of MSG and 5'-nucleotides (Tseng and Mau, 1999). The characteristic taste of some mushrooms can be classified into non volatile (taste) and volatile components (smell) (Li et al., 2011).

Vitamin content is an important factor in the overall nutritional value of food (Mshandete and Cuff, 2007). Vitamin B3 (Nicotinic acid) was the most abundant vitamin in all samples analyzed. However, this amount was lower than that reported by Crisan and Sands (1978) for Pleurotus ostreatus. In the literature no data were obtained on vitamins composition of Pleurotus citrinopileatus, so comparisons with published data are not possible.

CONCLUSION

The nutritional and nutriceutical properties of this mushroom had not been reported before. It is the first time indigenous P. citrinopileatus mushroom was submitted for these studies.

The data presented in this study suggested that the indigenous P. citrinopileatus mushroom is highly nutritious and compare well with exotic species. It can be concluded that this mushroom holds great promise in addressing the protein and minerals deficiency prevalent in the diet of rural population.

Detailed analysis of the mushroom species for other nutrients, anti-nutrients and secondary metabolites with medicinal potential should be undertaken.

ACKNOWLEDGMENT

The authors are thankful to Director, Kenya Industrial Research and Development Institute (KIRDI) and management for funding this research under the ‘Domestication and Characterization of wild edible mushrooms’ project and for providing experimental facilities.

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