Nutritional Qualities and Shelf Life Extension of Gamma Irradiated Dried Pleurotus ostreatus (Jacq. Ex. Fr.) Kummer Preserved in Two Different Storage Packs

Food Science and Technology 5(1): 9-16, 2017 http://www.hrpub.org
DOI: 10.13189/fst.2017.050102
Nutritional Qualities and Shelf Life Extension of Gamma
Irradiated Dried Pleurotus ostreatus (Jacq. Ex. Fr.)
Kummer Preserved in Two Different Storage Packs
Nii Korley Kortei1,*
, George Tawia Odamtten2
, Mary Obodai3
, Michael Wiafe- Kwagyan2
1
Department of Nutrition and Dietetics, School of Allied Health Sciences, University of Health and Allied Sciences, PMB 31, Ho, Ghana
2
Department of Plant and Environmental Biology, College of Basic and Applied Sciences, University of Ghana, Ghana
3
Food Microbiology Division, Food Research Institute Council for Scientific and Industrial Research, Accra
Copyright©2017 by authors, all rights reserved. Authors agree that this article remains permanently open access under the
terms of the Creative Commons Attribution License 4.0 International License
Abstract Pleurotus ostreatus has high nutritional value
as an important source of protein, carbohydrates, vitamins,
mineral elements and is among most favorite mushrooms of
the world. Proximate composition and metabolizable energy
of these mushrooms were evaluated for their dietary value.
Fruit bodies were solar dried to a moisture content of 12%
and exposed to low dose ionizing (gamma) radiations of 0,
0.5, 1, 1.5 and 2 kGy at a dose rate of 1.7kGy/hr and stored in
polyethylene and polypropylene packs at room temperature
(28- 30 o
C) for a period of 12 months. Values ranged 14.11-
15.80%, 6.16- 8.31%, 0.65- 1.24%, 13.56- 15.39%, 12.51-
15.25%, 61.16- 65.50% respectively for moisture, ash, fat,
fibre, protein and carbohydrate. Metabolizable energy also
ranged 247.8- 284.6 Kcal./100g for 12 months storage.
Although there were some significant (p<0.05) changes
observed for some nutrients due to gamma irradiation and
storage, the results obtained showed that the integrity of
these nutrients in this mushroom were minimally affected as
no adverse effects were observed.
Keywords Pleurotus ostreatus, Proximate, Nutritional,
Metabolizable Energy, Gamma Irradiation
1. Introduction
Pleurotus ostreatus is a macrofungus which exploit
polysaccharides (cellulose and hemicelluloses) usually from
a wide range of lignocelluloses to produce expensive
protein for human consumption [1]. Their global economic
value is now inconceivable, and the reason for the rise in
consumption is a combination of their value as food [2, 3]
and their medicinal or nutraceutical properties [4–7].Their
nutritive as well as medicinal attributes dates back to ancient
times as early as 1500 BC culled from ancient literatures.
Mushrooms are highly perishable and deteriorate within a
short time after harvest due to its high moisture content and
inability to maintain their physiological status.
In Ghana and most parts of the world, drying remains one
of the best alternatives of preprocessing this mushroom.
Drying of different species of mushrooms have been
reported in previous studies [8–11]. It is one of the oldest
means of food preservation and is applicable to a wide
range of food products including P.ostreatus strain EM–1
[12] .The principle behind drying according to Labuza and
Altunakar [13] is primarily reduction of moisture to levels
low enough to inhibit microbial growth and also slow down
enzymatic and other biological reactions that may
contribute to food spoilage.
Food irradiation is the intentional exposure of food to
ionizing radiation (such as gamma and electron beam) in
order to enhance its shelf life without any detrimental effect
on food quality as well as the safety of food. After decades of
research, development, public debate and consumer
acceptance trials in many countries, irradiation has emerged
as a safe and viable technology for ensuring the safety and
quality of food and for combating food-borne diseases.
Indeed it is currently the best available technology according
to IAEA, [14] as suitable for treating raw and partially raw
food products and those countries which adopt it will benefit
greatly in both domestic and international markets.
Perusal of pertinent literature revealed that scanty work
had been done in this area of study. The objective of this
study was to assess the effect of drying and gamma
irradiation on the nutritional quality of mushroom (Pleurotus
ostreatus) stored in polyethylene and polypropylene packs
and stored over a period of 12 months.
2. Material and Methods
2.1. Mushroom Samples
Pleurotus ostreatus strain EM 1 were grown on

10 Nutritional Qualities and Shelf Life Extension of Gamma Irradiated Dried Pleurotus ostreatus (Jacq. Ex. Fr.) Kummer
Preserved in Two Different Storage Packs
composted sawdust as described by Kortei et al [15] and
harvested at maturity from the cropping house of the
Mycology Unit, Food Research Institute- Council for
Scientific and Industrial Research, Accra, between the
periods of February to May 2013.
2.2. Processing
Drying of Mushroom Samples
Drying was carried out by using a solar dryer at a
temperature of 50- 60o
C to reduce moisture content to about
12% for an average period of 12 days.
Irradiation of Mushroom Materials
Fruitbodies were solar dried to a moisture content of 12%
and exposed to low dose ionizing (gamma) radiations of 0,
0.5, 1, 1.5 and 2 kGy at a dose rate of 1.7kGy/hr in air from
a Cobalt 60 source (SLL 515, Hungary) batch irradiator.
Doses were confirmed using Fricke’s dosimetry system
which is a reference chemical dosimeter based on the
chemical process of oxidation of ferrous ions (Fe2+
) in
aqueous sulphuric acid solution to ferric ions by ionizing
radiation at the Radiation Technology Centre of the Ghana
Atomic Energy Commission, Accra, Ghana.
Storage
Forty (40) grams of dried oyster mushrooms (Pleurotus
ostreatus) were packed and stored in polyethylene and
polypropylene packs at room temperature (28- 30 o
C) for a
period of 12 months.
Nutritional Analysis
This study was carried out in the laboratories of
Department of Food Science and Nutrition (University of
Ghana) from March 2013 to March 2014.
Determination of Moisture:
The moisture content was determined by the gravimetric
method of AOAC [16]. Two crucibles were each washed,
dried, weighed and 2 g of fresh mushrooms weighed into
each of the crucibles. The crucibles were placed in a
thermostatically controlled oven (Gallenkamp oven 300 plus
series, U.K) and the temperature maintained at 105 o
C for 5
hours, after which they were removed and placed in a
dessicator to cool. They were then reweighed. The procedure
was repeated until a constant weight was obtained. The
moisture content was found by subtracting the final mass
from the initial mass.
Determination of Fat Content
Procedure was carried out in accordance with AOAC [16]
with modifications. Two grams of dried sample was
transferred into a 22 mm x 80 mm paper thimble and a small
ball of cotton wool placed in the thimble to prevent loss of
sample. A 250 ml round bottom flask was washed and dried
at 100 o
C and weighed. Some anti ̶ bumping granules were
put into the flask. Fifteen millilitres (15 ml) petroleum spirit
of boiling point 60 – 80 o
C was added. A quick fit condenser
was connected to a Soxhlet extracter and refluxed for 4 hours
at high heat using a heating mantle. The flask was removed
and the solvent evaporated on a steam bath. The flask with its
contents was put into a dessicator to cool to room
temperature. It was then weighed and the mass of fat
determined by subtraction.
Determination of Ash Content
Procedure was carried out in accordance with AOAC [16]
with modifications. Two crucibles were each washed, dried
and weighed and 2 grams of the whole mushrooms weighed
into the crucibles. They were then placed in a muffle furnace,
pre heated to 600 o
C for 2 hours. The crucibles were then
removed, allowed to cool in air, placed in a dessicator to cool
completely and re-weighed. The masses of the crucibles and
their contents were found by subtraction.
Determination of Total Protein:
According to a modified Buiret method by Burtis &
Ashwood [17]. Ten grams of ground mushroom was taken
with 50ml of 1N NaOH and boiled for 30 minutes. The
solution was cooled in room temperature and centrifuged at
1000 × g by a table centrifuge machine
(Hardwarefactorystore.com, China). The supernatant was
collected and total protein content was measured.
Determination of Crude Fiber:
The method outlined by AOAC [18] was used in this
experiment. Half gram (0.5g) of ground dehydrated
mushroom was weighed (W1) and passed through a one
milliliter (1mm) mesh or screen into 600 ml beaker (without
spout). Fifty milliliters (50 ml) cold (room temperature)
NDS (the NDF solution) was placed in a beaker on a
refluxing unit and allowed to boil. Heat was adjusted to even
boiling, keeping the sample particles suspended. Heat was
reduced as boiling began, to avoid foaming. It was refluxed
for 60 minutes from onset of boiling. Gooch crucible was
placed on the filter manifold and rinsed with hot water. The
residue was filtered on to the crucible using light suction. It
was washed twice with hot water. Mixture was allowed to
stand for 5-10 minutes, washed twice with hot water, twice
with acetone and dried using suction. For recovery reasons,
acetone washing was done separately. The crucible was air
dried for 10-15min (some of the acetone will escape) and
oven dry for 8 hours or overnight in a forced-air oven at
105°C. It was cooled in a desiccator and weighed (W2) to
obtain yield of cell wall. Crucible was ashed at 510°C for 3
hours, allowed to cool and removed from furnace, put in an
oven (set at 105°C) cooled and weighed (W3). The loss in
weight was the ash free cell wall

Food Science and Technology 5(1): 9-16, 2017 11
W0 = Empty crucible weight.
W1= Weight of ground sample
W2 = Weight of sample after cooling in dessicator
W3= Weight of reweighed sample
Determination of Total Carbohydrate
According to Raghuramalu et al., [19] the content of the
available carbohydrate was determined by the following
equation [20] :
Carbohydrate (g/100g sample) = [100 – (Moisture + Fat +
Protein + Ash + Crude Fiber)]
Determination of Metabolizable Energy Content:
Fat, protein or carbohydrates can supply energy.
Metabolizable energy was calculated as described by [16]
using the following formula:
ME (Kcal /100g) = [(3.5 X CP) + (8.5 X CF) + (3.5 X NFE)]
Where, ME = Metabolic Energy; CP= % Crude Protein;
CF = % Crude Fat; NFE = % Nitrogen Free Extract
(carbohydrate)
3. Results and Discussion
3.1. Nutritional Analysis
The results of chemical (nutritional) analysis of gamma
irradiated dried mushrooms stored in polythene and
polypropylene packs are presented in Figures 1 and 2. The
nutritional attributes of edible mushrooms are directly linked
to their chemical composition. There is species variation in
nutrients but it is dependent on type of substrate, stage of
development, environmental conditions and essentially the
post-harvest condition of storage [21, 22]. Likewise, the
physical status of food (frozen or fresh, solid, liquid or
powder) and also its composition influence the reactions
induced by radiation [23].
Protein content for 0 month storage ranged from 12.51-
15.25%. Post irradiation storage studies revealed a
decreasing trend of protein content which was however not
significantly different (p>0.05) irrespective of ionizing
radiation dose and storage package used. After 12 months of
storage, protein content ranged from 12.48 - 15.22%.
According to Mostafarvi [24], an interaction of ionizing
irradiation and proteins could produce chemical reactions
depending on the protein structure, state (native or
denatured), physical status, amino acid composition, the
presence of other substances and the radiation treatment. The
most important changes include dissociation, aggregation,
cross-linking and oxidation. Arvanitoyannis [23], indicated
that low and medium doses induce only a small breakdown
of food proteins into lower molecular weight protein parts
and amino acids which cause less chemical reactions than
steam heat interactions. Protein is an important constituent of
dry matter of mushrooms [25, 26]. The digestibility of
mushroom protein can be as high as 72 to 83%. Protein
content of mushrooms depends on the composition of the
substratum, size of pileus, harvest time and species of
mushrooms [27]. The average protein content of cultivated
edible mushrooms ranges from 3.5-4% of their fresh weight
[28].
Protein content range obtained for P.ostreatus in this
study, generally fell within the range (12.51- 15.25%)
reported by several authors [28, 29, 30, 31] who worked on
Pleurotus spp. [32] Egwim et al., reported low protein
content values for P. ostreatus (14.03 ± 0.01%) and also
investigated some selected wild edible Nigerian mushrooms
and recorded higher protein contents of range 26.25±1.93-
60.38±0.20% for mushroom species Cantharella cibarius,
Laccaria amethysta, Clitocybe odora, Lepista nuda,
Macrolepiotata procera, Lepista saeva, Lactarius
deliciousus, Laccaria laccata, and Hericium erinaceus.
Al-Momany and Salih, [33] found values of 16.0- 16.8%
range for Pleurotus spp. amongst other edible fungi such as
Agaricus macrosporus and Tricholoma saponaceum var
squamosum. In terms of the amount of crude protein,
mushrooms rank below animal meats but well above most
other foods including milk [34]. On a dry weight basis,
mushrooms normally contain 19 to 35% proteins compared
to 7.3% in rice, 12.7% in wheat, 38.1% in soybean and 9.4%
in corn [35, 27]. A 100g serving can provide about
12.5-15.1% of the recommended dietary allowance (RDA)
or recommended nutrient intake (RNI). This high protein
content implies that this fungus can contribute significantly
to the daily human protein requirements, usually about
23-56g [36, 37].
Mushrooms contain high moisture depending on the
mushroom species and other parameters related to harvest,
growth, culinary and storage conditions [38]. Moisture
content of dried P.ostreatus ranged from 14.11- 15.80% for
0-3 month while 6-12 months storage ranged 14.11-16.11%
and showed some significant differences (p<0.05). This
could be attributed to the difference in the extent of water
hydrolysis by gamma radiation doses [23]. The moisture
content of any food is an index of its water activity [39, 40],
and is used as a measure of stability and susceptibility to
microbial contamination [41, 42]. Dried mushrooms are not
prone to rapid deterioration due to the absence of medium of
transport of enzymes to facilitate chemical reactions which
cause deterioration.
Although mushrooms are generally low in fat, they do
contain essential unsaturated fatty acids and are also
cholesterol free and as such considered essential and
significant for human diet and health. Fat content ranged
from 0.65- 1.24% for 0-3 month while that of 6- 12 months
ranged 0.63- 1.24%. The average fat content of mushrooms
is reported to be generally low, ranging from 0.6-3.2%.
Gamma radiation had a significant (p<0.05) effect on the fat
content of dried mushrooms during storage. Radiation dose 2
kGy had an apparent significant (p<0.05) effect on the fat
content. Free radicals formation during irradiation has been
proven to increase lipid oxidation [43]. The range of fat

content values obtained (0.65-1.24%) were comparable to
the 1.23% – 0.53% reported by Musieba et al. [44] and
Nurudeen et al.[45] respectively.
Crude fibre contents obtained in this present study ranged
13.56- 15.39% and its analysis showed some significant
differences (p<0.05). Results obtained fell within range of
results (3–32%) reported by some researchers [44, 32]. On
the average, a 100g serving of mushrooms guarantees from 9
to 40 % of the daily recommendation of dietary fibre [22].
Dietary fibre content was high (approx. 45 % of dry matter).
The fairly high level of fibre in the mushroom was a
desirable characteristic since fibre plays an important role in
human diet [22, 46, 47], observed that glycogen and chitin
form the major constituent of fibre content of mushrooms.
Gordon [48] indicated that there is a “dietary fibre
hypothesis” which suggests that fibre helps to prevent many
diseases prevalent in affluent societies. Evidence from
epidemiological studies suggest that increased fibre
consumption may contribute to a reduction in the incidence
of certain diseases like diabetes, coronary heart disease,
colon cancer, high blood pressure, obesity, and various
digestive disorders [49, 50, 51]. Dietary fibres alter the
colonic environment in such a way as to protect against
colorectal diseases. It provides protection by increasing
faecal bulk, which dilutes the increased colonic bile acid
concentrations which occur with a high-fat diet [52].
Carbohydrate values obtained in this study ranged from
61.39- 65.50% which represents the bulk of fruiting bodies
accounting for on dry weight basis. Similar results have been
reported by other researchers for cultivated Pleurotus
mushroom [53, 20]. Pleurotus spp. dry matter usually
include 50- 60% carbohydrates composed of various
compounds; monosaccharides, their derivatives and
oligosaccharides (commonly called sugars) and both reserve
and construction polysaccharides (glycans). Kalac [4],
reported a decrease in mannitol and α, trehalose which are
the main constituents of oligosaccharides as well as polyols
respectively. In general, irradiation modifies mono and
polysaccharides, but thermal treatment can produce more
modifications [54]. [55] reported carbohydrate values of
Agaricus bisporus (56.47 ± 0.21 %) and Agaricus bitorquis
(39.94 ± 0.17 %). The amount of carbohydrates determined
in Agaricus bitorquis was comparable to results obtained
(61.39- 65.50%) as average value for P.ostreatus in this
present study. Carbohydrate that can be used by humans
produces four calories per gram as opposed to nine calories
per gram of fat and four per gram of protein. In areas of the
world where nutrition is marginal, a high proportion
(approximately 0.45- 0.9 kg) of an individual’s daily energy
requirement may be supplied by carbohydrate, with most of
the remainder coming from a variety of fat sources [56].
Ash content values ranged between 6.16- 8.31%.
Statistical analysis revealed no significant (p>0.05)
difference. Results obtained in these present studies were
within range of values of 5.69- 7.82% as reported by [57],
[58] and [44] respectively. However, [32] recorded higher
values of 20.55 ± 0.13 %. By and large, packaging had no
significant (p>0.05) effect on the proximate analyses.
Figure 1. Effect of irradiation on proximate composition of dried mushrooms in storage packs during storage period of 0- 3 months

Figure 2. Effect of irradiation on proximate composition of dried mushrooms in storage packs during storage period of 6-12 months
2.2. Metabolizable Energy
Table 3. Effect of irradiation and storage on the Metabolic Energy
(Kcal/100g) of Mushrooms
Storage
Time
(month)
Package
material
Applied Dose (kGy)
0 0.5 1.0 1.5 2.0
0
P1 280.4b
279.9b
278.9b
283.1c
272.7a
P2 279.9b
280.8b
279.7b
276.5bc
273.1a
3
P1 273.7a
279.3b
282.1bc
279.5c
276.9c
P2 274.4a
282.6c
284.6c
275.3a
279.9ab
6
P1 278.6b
281.7b
247.8a
282.9b
283.7b
P2 279.8b
280.0b
278.7b
277.5b
273.4b
12
P1 280.0b
279.9b
280.0b
284.9c
273.3a
P2 279.0b
281.8b
278.8b
282.3c
272.0a
Means with same letters in a row are not significantly (P>0.05) different
P1- Polythene, P2- Polypropylene
Generally, energy values of dried and gamma irradiated
mushrooms stored in the different packaging materials
ranged 247.8- 284.9 Kcal./100g of dried mushrooms and are
presented in Table 3. The initial energy values ranged
272.7-283.1 and 273.1- 280.0 Kcal/100g for polythene and
polypropylene respectively. There was no significant
(p>0.05) effect of storage packs on the metabolizable energy.
In terms of effect of gamma radiation, dose 2 kGy showed an
apparent effect (p<0.05) on fat content which affected the
energy content indirectly since it constitutes an integral part
of the energy equation. After 3 months, energy ranged from
273.7- 282.1 and 274.4- 284.6 Kcal./100g for polythene and
polypropylene respectively. There were significant
differences (p<0.05) in energy values obtained. Storage for 6
months, gave values ranging 247.8-283.7 and 273.4-280
kcal./100g for polythene and polypropylene respectively. In
polythene package, irradiation caused significant difference
(p<0.05). However, polypropylene showed no significant
difference (p>0.05) to irradiation effect. For storage for 12
month values, ranged from 273.3- 284.9 and 272.0- 282.3
Kcal./100g for both packages respectively. Energy values
due to irradiation showed significant differences (p<0.05) in
both polythene and polypropylene.
[22] emphasized that owing to their high water content
and low caloric value, mushrooms could be considered as a
dietetic food suitable for low-calorie diets. In terms of energy
values, the present results indicated that dry mushrooms
stored up to 12 months were of good quality, low in calorie
content and their energy value varied significantly (P<0.05).
Obodai et al [58], [6] and [59], reported energy values within
range of 272- 389 Kcal./100g and 381- 389 Kcal./100g
respectively for Pleurotus spp. Mshandete and Cuff [60]
reported energy values of 313 Kcal/100g dry matter for
Coprinus cinereus, 305 Kcal/100g dry matter for Volvariella
volvacea and 302 Kcal/100 g dry matter Pleurotus
flabellatus. Egwim et al [32] obtained energy values of 305
Kcal/100g and 302 Kcal/100g for Laccaria amethystea and
Lepista nuda respectively. These values fall within what was
recorded in the dry mushroom samples stored in both
packaging materials before and after irradiation. Recently,

[57] also found energy value of P.ostreatus on differently
formulated rice straw composts to vary from 305.81- 387.80
Kcal./100g.
4. Conclusions
Our study showed that this mushroom species are good
sources of proteins and carbohydrates. Several functional
properties have also been detected as favourable, making it
potentially useful in many food formulations. This research
also demonstrates the ability of gamma irradiation to be used
in the preservation of nutritional qualities of foods as
changes that occurred due to gamma irradiation were
minimal irrespective of the packaging material used in this
experiment. Averagely, non-irradiated dried mushroom last
not more than 6 months because of insect and pests damage.
Additionally, gamma irradiation eliminated all these insects
and pests to prolong its shelf life to 12 months. Gamma
irradiation with its enormous attributes could be employed in
food manufacturing industries to enhance product quality
and shelf life.
Acknowledgement
We are grateful to Mrs Leonora Wontumi, Department of
Nutrition and Food Science, University of Ghana and also to
Messers S.N.Y. Annan, J.N.O. Armah, S.W.N.O Mills and
SA Acquah of the Radiation Technology Centre, Ghana
Atomic Energy Commision, Kwabenya, Accra, for
undertaking the irradiation process.
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