Characterization of stipe and cap powders of mushroom Lentinus edodesprepared by different grinding methods Zipei Zhanga, Huige Songa, Zhen Penga, Qingnan Luoa, Jian Minga, Guahua Zhaoa,
Trang 1Characterization of stipe and cap powders of mushroom (Lentinus edodes)
prepared by different grinding methods
Zipei Zhanga, Huige Songa, Zhen Penga, Qingnan Luoa, Jian Minga, Guahua Zhaoa,b,⇑
a
College of Food Science, Southwest University, Tiansheng Road 1, Chongqing 400715, PR China
b
Key Laboratory of Food Processing and Technology of Chongqing, Chongqing 400715, PR China
a r t i c l e i n f o
Article history:
Received 22 September 2011
Received in revised form 29 October 2011
Accepted 4 November 2011
Available online 13 November 2011
Keywords:
Mushroom
Lentinus edodes
Micronization
Particle size
Physico-chemical properties
a b s t r a c t
The effects of micronization methods, mechanical and jet millings, on the physico-chemical properties of mushroom (Lentinus edodes) powder were investigated in contrast to shear pulverization The powders of dried mushroom cap and stipe were prepared to obtain six powders Compared to shear pulverization, mechanical and jet millings effectively reduced particle size and brought about a narrow and uniform particle size distribution With the same material, powders from mechanical and jet millings had higher values in soluble dietary fiber content, surface area, bulk density, water soluble index and nutrient sub-stance solubility, but lower values in the angles of repose and slide, water holding and swelling capacities than shear pulverized powder These indexes were tightly dependent on particle size with absolute coef-ficients beyond 0.8330 With the same grinding method, cap powders possessed higher values in water soluble index, swelling capacity, bulk density, protein and soluble dietary fiber than stipe powders
Ó 2011 Elsevier Ltd All rights reserved
1 Introduction
Lentinus edodes, belongs to the family of Tricholomataceae, is
fa-mous for its high nutritional value and medicinal properties like
anticancer, antidiabetic, hypotensive, antinociceptive,
anti-inflam-matory, hypocholesterolemic (Wasser, 2005; Carbonero et al.,
2008) Also, it is important nutritionally because of its higher
pro-tein, dietary fibers and important mineral contents (Khan et al.,
2009) Due to their high moisture contents (typically greater than
85 g/100 g), fresh mushrooms start deteriorating immediately after
harvest and have to be processed to extend their shelf life and for
off-season use Drying is an inexpensive method that can extend the
shelf life of mushroom (Walde et al., 2006) Mushrooms have been
commonly dried as harvested or divided into small pieces prior to
drying The resulting products are mainly used as cooking material
To extend the application of mushrooms, dried mushrooms can be
further processed into a powder form which could be incorporated
into various foods as a functional food additive with distinct flavor
(García-Segovia et al., 2011) The degree of the above described uti-lization is decided by the physico-chemical properties of the pow-der, which are tightly depended on the particle size and the method applied in powder production The commonly used meth-ods could be classified as routine grinding and micronization Rou-tine grinding, such as shear pulverization, produced larger size particles than micronization, such as mechanical and jet millings Superfine powders obtained from micronization have properties that are not found in powders from conventional grinding methods (Tkacova and Stevulova, 1998; Zhao et al., 2009) With these supe-rior characteristics, the superfine powder might find a wider scope
of applications than conventional particle materials (Huang et al.,
2007) Moreover, effects of micronization treatment on the charac-teristics of gained powders may be different, which depends on the grinding methods and raw materials (Chau et al., 2007) The edible part of mushroom (L edodes) consists of cap and stipe, which account for approximate 75% and 25% of the mush-room on dry basis (Gao et al., 2010) Proximate composition anal-ysis implied that they are very different in chemical composition
In contrast to cap, stipe has a higher fraction of insoluble crude fi-ber (about 38 g/100 g) which is difficult to chew thereby limiting their utilization in foods (Jiang et al., 2010) In most mushroom processing factories, the stipes of L edodes are not fully utilized and treated as a waste The disposal of them causes many environ-ment problems mainly due to their large volume and high organic material content (Yen et al., 2007) Micronization has been proved
as an effective approach to modify the texture of fiber rich plant food materials (Wang et al., 2009; Zhao et al., 2009)
0260-8774/$ - see front matter Ó 2011 Elsevier Ltd All rights reserved.
Abbreviations: DF, dietary fiber; EMC, equilibrium moisture content; IDF,
insoluble dietary fiber; JMC, jet milled cap powder; JMS, jet milled stipe powder;
MMC, mechanically milled cap powder; MMS, mechanically milled stipe powder;
SC, swelling capacity; SDF, soluble dietary fiber; SPC, shear pulverized cap powder;
SPS, shear pulverized stipe powder; WHC, water holding capacity; WSI, water
solubility index.
⇑Corresponding author at: College of Food Science, Southwest University,
Tiansheng Road 1, Chongqing 400715, PR China Tel.: +86 23 68 25 03 74; fax:
+86 68 25 19 47.
E-mail address: zhaogh@swu.edu.cn (G Zhao).
Contents lists available atSciVerse ScienceDirect
Journal of Food Engineering
j o u r n a l h o m e p a g e : w w w e l s e v i e r c o m / l o c a t e / j f o o d e n g
Trang 2The present work aims to observe the differences in
physico-chemical properties of cap and stipe powders of mushroom (L
edodes) produced by shear pulverization, mechanical and jet
millings
2 Methods
2.1 Materials
Fresh mushroom (L edodes) was purchased from a local market
(Chongqing, China) in October 2010 Insect and disease-free
sam-ples were chosen and cleaned The caps and stipes were manually
separated and hot-air dried in an oven (DHG-9140, Qixing,
Shang-hai, China) at 45 °C for 32 h and 38 h, respectively Under these
conditions, the moisture contents of cap and stipe were reduced
to 10 g/100 g and 11 g/100 g, respectively Moisture contents were
determined according to anAACC method (No 44-19) All
chemi-cals used were of analytical grade
2.2 Powder preparation
The shear pulverized cap and stipe powders of mushroom were
prepared with the aid of a DFT-200 high-speed pulverizer (Linda,
Wenling, China) Pulverization process lasted for 30 s This ensured
that all particles of the powder passed through an 80 mesh sieve
with average particle sizes of cap and stipe of 54.77lm and
40.90lm, respectively Shear pulverized powders were then
ground and sheared by the strong force between the lapping wheel
and rail of a YSC-701 type micronizer (Yanshanzhengde, Beijing,
China) for 8 min to result in mechanically milled powders Jet
milled powders were obtained by processing shear pulverized
powders in a LNJ-120 jet mill (Liuneng, Mianyang, Sichuan, China)
using compressed air at 145 psi As a result, six different powders
were obtained as: shear pulverized cap (SPC) and stipe (SPS)
pow-ders; mechanically milled cap (MMC) and stipe (MMS) powders
and jet milled cap (JMC) and stipe (JMS) powders The proximate
composition of powders, including moisture, ash, protein, fat,
soluble dietary fiber (SDF) and mineral elements (Pb, Cd), were
measured by usingAOACmethods(1998)
2.3 Particle size and bulk density measurement
The particle size of six mushroom powders was measured by a
Mastersizer 2000 E laser particle size analyzer (Malvern
instru-ment Ltd., UK) The bulk density was determined by pouring gently
2 g of mushroom powder into a 10 mL measuring cylinder, and
then holding the cylinder on a vortex vibrator for 1 min to obtain
a constant volume of the sample The volume of the sample was
re-corded against the scale on the cylinder The bulk density value
was calculated as the ratio of mass of the powder and the volume
occupied in the cylinder (Bai and Li, 2006)
2.4 Determination of the angles of repose and slide
The angle of repose (h) was defined as the maximum angle
sub-tended by the surface of a heap of powder against the plane which
supported it (Taser et al., 2005) The angle of repose was measured
according to the method reported byZhang et al (2005)with
min-or modification Firstly, filler was fixed vertically above a piece of
graph paper with the distance (H) from the paper to the outlet of
the filler was 1 cm Then the test powder was continuously poured
into the filler and went out freely until the tip of the powder cone
touched the outlet of the filler The diameter (2R) of the cone was
read against the scale of the paper The angle of repose (h) was
cal-culated as the following formula: h = arctan H/R
The slide angle (a) was determined according to the procedure described byZhou and Ileleji (2008) with some slight modifica-tions Five grams (5.000 g) mushroom powder were exactly weighed and separately poured on a rectangular glass plane with
a length of 130 mm After that, the glass plane was gradually lifted until the surface of the mushroom powder began to slide The ver-tical distance (H) from the top of inclined glass plane to horizontal was measured The angle of slide (a) was calculated as the follow-ing formula:a= arcsin H/L
2.5 Hydration properties determination Water holding capacity (WHC) was determined with the se-quence of steps stated here (Anderson, 1982) Firstly, a cleaned cen-trifuge tube (M, g) was weighed and approximate 0.5 g powder (M1, g) was poured into it Water (M2, g) was added to disperse the pow-der with a powpow-der/water ratio of 0.05/1 (w/w) at ambient temper-ature The dispersion was incubated in a water bath at 60 °C for
30 min and immediately followed by cooling in an ice-water bath for 30 min Then, the tube was centrifuged at 5000 rpm for
20 min The resulting supernatant was removed and the centrifuge tube with sediment (M3, g) was weighed again WHC was calculated
as following formula: WHC (g/g) = (M3 M)/M1 Water solubility index (WSI) was determined by anAACC
meth-od of No 44-19 The powder (S1, g) was dispersed in a centrifuge tube by adding water with a powder/water ratio of 0.02/1 (w/w)
at ambient temperature Then the dispersion was incubated in a water bath at 80 °C for 30 min, followed by centrifugation at
6000 rpm for 10 min The supernatant was carefully collected in
a pre-weighed evaporating dish (S2, g) and subjected to dry at
103 ± 2 °C, and the evaporating dish with residue was weighed again (S3, g) WSI was calculated as following formula: WSI (%) = (S3 S2)/S1 100%
Swelling capacity (SC) was determined according to a previ-ously reported method (Lecumberri et al., 2007) The initial of 1 g powder was recorded when poured into a graduate cylinder and its occupied bed volume (V1) was recorded Then 10 mL of distilled water was added into the tube and the tube was shaken until a homogeneous dispersion achieved The dispersion was incubated
in a water bath at 25 °C for 24 h to allow the complete swelling
of the powder The new volume (V2) of the wetted powder was then recorded WSI was calculated as following formula: SC (mL/ g) = (V2 V1)/M
2.6 Determination of protein and polysaccharide solubility Power sample (0.5 g) was weighed into a pre-weighed centri-fuge tube Fifteen millilitres of distilled water was added into the tube and the tube was shaken until a homogeneous dispersion achieved Then, the tube was incubated in a water bath (60 °C for protein solubility and 80 °C for polysaccharide solubility) for a re-quired time varied from 10 min to 90 and 100 min separately After incubation, the tube was taken out, cooled and weighed The lost water during incubation was compensated to obtain the weight
of the tube as it was before incubation After 20 min lay-aside at ambient temperature, the tube was subjected to centrifugation at
4500 rpm for 10 min and the supernatant was collected for further measurements
The amount of protein in above-obtained supernatant was determined by a Coomassie Brilliant Blue method as developed
by Bradford (1976) The polysaccharide in the supernatant was quantified by a phenol–sulfuric acid method (Dubois et al.,
1951) Protein solubility (%) was expressed as the percentage of the mass of protein of the supernatant to that of the powder and polysaccharide solubility (%) was expressed as the percentage of
Trang 3the mass of polysaccharide in the supernatant to that of the
powder
2.7 Determination of moisture sorption isotherm
Moisture sorption isotherm was determined according to the
method of Lee and Lee (2007) with some minor modifications
The moisture contents of powder samples were determined by
drying in an oven at 105 °C for 12 h (AACC method of No 44-19)
The equilibrium moisture content of the powders was determined
using a gravimetric technique by Conway dish method Saturated
salt solutions of NaOH (aw0.070), MgCl2(aw0.33), Mg(NO3)2(aw
0.528), NaCl (aw0.757), KBr (aw 0.807), KCl (aw0.842), BaCl (aw
0.901) and K2Cr2O7(aw0.986) were used in outer layer of the
Con-way dish To determine the sorption/desorption value, 1 g of the
test powder was accurately weighted into a weighing bottle and
put inside the inner layer of the Conway dish which was firmly
sealed and kept at 25 °C Sample were weighed every 24 h until
the equilibrium was achieved as indicated by the difference of
two consecutive weights less than ±0.0005 g The isotherm models,
including BET, Kuhn, Oswin, Biadley, Caurie, Halsey and Chung-P,
were used to fit the experimental moisture sorption date
2.8 Statistical analysis
All experiments were done in triplicate and the results were
ex-pressed as mean ± standard deviation (SD) The difference between
means was determined by Duncan’s multiple range tests by using
the SPSS16.0 statistics software (SAS Inc., NC, USA) Results were
considered statistically significant at p < 0.05 Correlation analysis
was also performed using the same software
3 Results and discussion
3.1 Proximate composition
The proximate composition of the powders was shown in
Ta-ble 1 Cap powders had higher values in fat and ash than stipe
pow-ders (p < 0.05) The protein content (5.61–7.20 g/100 g) in stipe
powders was much lower than that (16.71–18.29 g/100 g) in cap
powders (p < 0.05) In terms of the nutrients, the cap of mushroom
was superior to the stipe This finding was consistent with the
re-sult byOboh and Shodehinde (2009) With the same size-reduction
method, the SDF fraction in cap powders was dramatically higher
than that in stipe powders (p < 0.05) For example in powders by
shear pulverization, they were 8.11 and 4.20 g/100 g, respectively
It was valuable to emphasize that micronization methods highly
increased the SDF fraction in the powders and jet milling behaved
in a more effective way than mechanical milling Previous reports had specified the increased SDF fraction in carrot insoluble fiber-rich fraction and water caltrop pericarp after ball milling micron-ization (Chau et al., 2007; Wang et al., 2009) This fact was ex-plained by the redistribution of fiber components from insoluble
to soluble fractions In general, insoluble dietary fiber (IDF) was beneficial to intestinal function as it could help to increase fecal bulk and to enhance intestinal peristalsis and SDF had beneficial properties associated with their significant role in human physio-logical function like reductions in cholesterol level and blood pres-sure, prevention of gastrointestinal problems and protection against onset of several cancers (Gallaher and Schneeman, 2001)
In this context, a well functioned dietary fiber (DF) should have a suitable ratio of SDF/IDF and micronization was effective in the modification of insoluble fiber-rich foodstuffs
3.2 Particle size The particle size distributions of the powders obtained by laser particle size analyzer were shown inTable 2 Particle size distribu-tions were characterized by D0.1, D0.5and D0.9 values (Giry et al.,
2006) Agglomeration ratio D0.5was considered to be the average median diameter which was representative of the degree of pow-der cohesiveness In contrast to shear pulverization, both mechan-ical and jet millings significantly reduced the average particle size
of the powders The width of particle size distributions was mea-sured by span according to a British Standards A smaller span va-lue indicated a narrower particle size distribution and more uniform size The span values of shear pulverized powders were much higher than those of micronized powders In other words, powders obtained by mechanical and jet millings were more homogeneous than shear pulverized powders However, there were no significant differences observed between cap and stipe powders prepared by the same method As expected, the reduction
in particle size resulted in an increase in specific surface area of the powder (Table 3)
3.3 Bulk density The bulk density of the mushroom powders produced by differ-ent size-reduction methods was shown inTable 3 The bulk density
of the powders increased in the size-reduction method sequence of shear pulverization < mechanical milling < jet milling The reason might be attributed to that lower particle size had a larger contact surface with the surroundings and higher homogeneous form, which would lead to decrease the pore spaces between particles and increase the value of bulk density (Zhao et al., 2009, 2010a,b) Bulk density was highly correlated to specific surface
Table 1
Proximate composition of mushroom (L edodes) powders as affected by grinding methods a
1.37 ± 0.07 f
1.49 ± 0.12 f
2.61 ± 0.09 d
2.67 ± 0.19 d
2.35 ± 0.02 e
7.20 ± 0.22 g
5.61 ± 0.37 h
18.29 ± 0.68 d
16.71 ± 0.79 f
17.94 ± 0.83 ef
5.04 ± 0.23 f
4.98 ± 0.19 f
6.43 ± 0.18 d
5.89 ± 0.16 e
5.68 ± 0.23 e
13.86 ± 0.48 h
15.67 ± 0.67 g
8.11 ± 0.47 f
19.94 ± 0.91 e
23.62 ± 0.62 d
0.26 ± 0.02 e
0.28 ± 0.02 e
0.40 ± 0.008 d
0.43 ± 0.07 d
0.27 ± 0.04 e
a
Values are expressed as mean ± standard deviation of triplicate analysis Data, except that of moisture, were calculated on the dry basis.
b
SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder; JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC, mechanically milled cap powder; JMC, jet milled cap powder.
c
DF, soluble dietary fiber; Cd, cadmium; Pb, plumbum.
d–i
Trang 4area with coefficients for cap and stipe powders of 0.9945 and
0.9983, respectively The mushroom powders with high bulk
den-sity were potential ingredients that could be used in instant
beverages
3.4 The angle of repose and slide
The angles of repose and slide are used to describe the fluidity
of the powders As shown inTable 3, micronized powders had
sig-nificant lower values in repose and slide angles than shear
pulver-ized powders derived from the same material (cap or stipe), except
of the slide angle of the mechanically milled stipe powder
(p < 0.05) On the other hand, when cap and stipe powders
pro-duced by the same size-reduction method were compared,
signif-icant differences in values of repose angle were only observed
between the two powders prepared by jet milling (p < 0.05)
Com-bined withTable 2, it was easy to conclude that the smaller the
particles, the better the fluidity of the powder was The fact might
be due to span or particle size distribution in that smaller particles
filled the voids of larger particles and creating less fluidity This
re-sult was in agreement with the investigation of Zhao et al
(2010a,b)
3.5 Hydration properties
Hydration properties including WHC, WSI and SC of the
pow-ders were shown inTable 4 With the same material (cap or stipe),
mechanically and jet milled powders had significantly lower values
in WHC and SC than shear pulverized powders (p < 0.05) However,
significantly higher values in WSI were observed both for
mechan-ically and jet milled powders than shear pulverized powders
(p < 0.05) Together withTable 2, WSI was negatively but tightly
correlated to particle size of the powders A similar observation
was presented for cryomilled sorghum grain powders by
Mahasuk-honthachat et al (2010) With the same size-reduction method,
WSI and SC values of cap powders were significantly higher than those of stipe powders (p < 0.05) Although there was no significant difference between cap and stipe powders by mechanical milling, the WHC values of jet milled powders were significant lower than those of mechanically milled and shear pulverized powders (p < 0.05) This was might be due to the differences in the proxi-mate composite of cap and stipe powders, especially the contents
of protein and SDF
3.6 Protein and polysaccharide solubility The solubility of protein and polysaccharide of the powders as a function of soaking time were shown inFig 1 It was clear to see that both protein and polysaccharide solubility of all powders were linearly (R2= 0.9504–0.9973) increased with the prolonging of soaking time from 10 min to 90 and 100 min separately With the same material (cap or stipe), the protein and polysaccharide solubility of the powders increased in the size-reduction method order of shear pulverization < mechanical milling < jet milling Similar result about the effect of particle size on protein and poly-saccharide solubility was also observed by Zhao et al (2009, 2010b) With respect to materials, cap powders had higher values
in polysaccharide solubility but lower values in protein solubility than stipe powders with the same size-reduction method The fact might relate to protein content in the powders Assuming the pro-tein solubility, at a fixed sample/extractant ratio, was mainly de-pended on the protein content in the powder as observed in various industrial extractions The higher the protein content in the test powder, the higher the protein concentration in extract was The protein contents of cap powders (16.71–18.29 g/100 g) were much higher than that of stipe powders (5.61–7.20 g/
Table 2
Effect of grinding methods on particle size of mushroom (L edodes) powders a
Volume diameters (lm) c
Powders b
a
Values are expressed as mean of triplicate analysis.
b
SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder;
JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC,
mechani-cally milled cap powder; JMC, jet milled cap powder.
c
D0.1, D0.5 and D0.9 are the equivalent volume diameters at 10%, 50%, and 90%
cumulative volumes, respectively; Span was determined by the equation:
span = (D0.9 D0.1)/D0.5.
Table 3
Effect of grinding methods on surface area, bulk density and repose and slide angles of mushroom (L edodes) powders a
Powder b
Specific surface area (m 2
0.152 ± 0.004 g
47.29 ± 0.66 c
43.14 ± 1.08 cd
0.169 ± 0.003 f
45.48 ± 0.97 d
41.97 ± 1.24 de
0.210 ± 0.006 d
40.16 ± 0.96 f
39.27 ± 1.03 fg
0.183 ± 0.006 e
48.33 ± 0.77 c
44.26 ± 0.91 c
a
Values are expressed as mean ± standard deviation of triplicate analysis.
b
SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder; JMS, jet milled stipe powder; SPC, shear pulverized cap
powder; MMC, mechanically milled cap powder; JMC, jet milled cap powder.
c–g
Table 4 Effect of grinding methods on hydration properties of mushroom (L edodes) powders a
Powder b
Hydration properties c
21.621 ± 1.07 i
5.430 ± 0.053 e
23.143 ± 1.01 g
5.769 ± 0.086 d
25.209 ± 0.79 e
5.393 ± 0.069 e
27.358 ± 1.21 d
5.239 ± 0.058 f
a Values are expressed as mean ± standard deviation of triplicate analysis b
SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder; JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC, mechani-cally milled cap powder; JMC, jet milled cap powder.
c WHC, water holding capacity; WSI, water solubility index; SC, swelling capacity.
d–i Values bearing different superscript lowercase letters within the same column are significantly different (Duncan, p < 0.05).
Trang 5100 g) This brought about the fact that the protein solubilization
of the powders with higher protein content reached to equilibrium
with much more protein remaining in the powder than those with
lower protein content
3.7 Moisture sorption isotherms Moisture sorption isotherms, curves of equilibrium moisture content (EMC) against a of the powders at 25 °C were shown in
Fig 1 Effects of different grinding methods and soaking time on solubility of protein (A) and polysaccharide (B) of different mushroom (L edodes) powders SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder; JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC, mechanically milled cap powder; JMC, jet milled cap powder.
Trang 6Fig 2 Similar to trends that observed in numerous foods, EMC
val-ues of the powders increased with a When size-reduction
meth-ods were compared at the same EMC, awof the powders derived from the same material (cap or stipe) decreased in the same order
Fig 2 Effects of different grinding methods on moisture sorption isotherm characteristics of cap and stipe powders SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder; JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC, mechanically milled cap powder; JMC, jet milled cap powder.
Table 5
Mathematical expressions, coefficients of the determination (R 2
), mean relative percentage errors (E) and standard errors of estimate (SE) of selected sorption models for mushroom (L edodes) powders at a relative humidity range of 7–98% a
a
R 2
, E and SE were determined by following equations: R 2
¼
P
ðm i m pi Þ 2
Pm2 i
Pm2 pi
, E ¼ 100 n Pn i¼1ðmpi m i
m i Þ, SE ¼
ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi
P n i¼1 ðm pi m i Þ 2
ðn1Þ
r
, where n is the number of experimental observations; mi represents experimental moisture content values, and mpi denotes value predicted from model.
Table 6
Nonlinear regression parameters of Oswin model (m = k0[aw/(1 aw)] n0 ) for different
mushroom (L edodes) powders.
Powders a
Parameters b
a
SPS, shear pulverized stipe powder; MMS, mechanically milled stipe powder;
JMS, jet milled stipe powder; SPC, shear pulverized cap powder; MMC,
mechani-cally milled cap powder; JMC, jet milled cap powder.
b K, n and R 2 were determined by the mathematical expression of Oswin model:
m = k0[aw/(1 aw)] n0
.
Table 7 Correlation between particle size and physical–chemical properties of cap and stipe powders.
Trang 7of their particle sizes and soluble dietary fiber content The fact
suggested micronized powders were more stable than shear
pul-verized powders when they were stored under same conditions,
especially relative humidity This finding was in agreement with
the results reported byLee and Lee (2007) With the same material
(cap or stipe) and EMC, cap powders had lower awvalues than stipe
powders produced by the same size-reduction method The
differ-ence in sorption behavior between the powders derived from
dif-ferent material (cap and stipe) had been previously reported and
might be ascribed to the differences in the chemical composition
of cap and stipe as shown inTable 1(Khalloufi et al., 2000)
Seven sorption models presented inTable 5 were tested for
their goodness-of-fits in describing the isotherms of the powders
in terms of coefficient of the determination (R2), mean relative
percentage error (E) and standard error of estimate (SE) These
models were selected based on their simplicity of computation
and effectiveness at describing the sorption isotherms of several
foods All tested models show good ability to satisfactorily predict
the EMC of the mushroom powders with R2 beyond 0.912 and
absolute E values below 7.896% (Table 5andSup 1) Among these
models, the Oswin model showed the highest goodness-of-fit for
the moisture sorption isotherms of the powders indicated by its
highest value of R2and lowest absolute value of E The nonlinear
regression parameters of this model were shown inTable 6
3.8 Dependence of the physico-chemical properties on the particle size
The dependence of physico-chemical properties, such as aw, WSI,
SC, WHC, SDF, on the particle size (D0.5) of the powders were
eval-uated in terms of the coefficients of physico-chemical properties
and particle size The results were shown inTable 7 The absolute
values of coefficients derived from regression analysis were beyond
0.8330, which implied that the particle size exerted crucial effects
on the physico-chemical properties of the powders as mentioned
above Angles of response and slide, WHC and SC were positively
correlated with particle size However, negative relationships were
observed for aw, bulk density, specific surface area, SDF, protein and
polysaccharide solubility when they were related to the particle
size of the powders
4 Conclusion
In this study, physico-chemical properties of mushroom (L
edodes) powders prepared by three size-reduction methods, namely
shear pulverization, mechanical and jet millings were investigated
in a comparative way Cap powders were preponderant to stipe ones
in a nutritional view Although they were belonging to so-called
micronizations, jet milling was more effective in size reduction of
the mushroom powders than mechanical milling The particle size
played a dominated role in the physico-chemical properties of
mushroom powders In contrast to the powders prepared by shear
pulverization, micronized powders had smaller particle size and
higher fluidity, WSI, SC and protein and polysaccharide solubility
These improved properties facilitated the application of mushroom
powders in food additive and convenient food products The good
performance of stipe powders in holding water also allowed them
to be used as functional food additive
Acknowledgments
The authors gratefully acknowledge support for the jet milling
from Aocui Superfine Grinding Company (Sichuan) This work
was conducted with financial supports from National High-tech
R&D Program (863 Program) of China (2011AA100805-3) and the
Fundamental Research Funds for the Central Universities (XDJK2009B003)
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