Báo cáo khoa học " Characterization of stipe and cap powders of mushroom (Lentinus edodes) prepared by different grinding methods " ppt

Characterization of stipe and cap powders of mushroom (Lentinus edodes) prepared by different grinding methods Zipei Zhang a , Huige Song a , Zhen Peng a , Qingnan Luo a , Jian Ming a , Guahua Zhao a,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 article info 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 abstract 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 extendtheir shelf life andfor 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. doi:10.1016/j.jfoodeng.2011.11.007 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). Journal of Food Engineering 109 (2012) 406–413 Contents lists available at SciVerse ScienceDirect Journal of Food Engineering journal homepage: www.elsevier.com/locate/jfoodeng The 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 an AACC 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 54.77 l m and 40.90 l m, 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 using AOAC methods (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 by Zhang 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 = arctanH/R. The slide angle ( a ) was determined according to the procedure described by Zhou 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 (M 1 , g) was poured into it. Water (M 2 , g) was added to disperse the pow- der with a powder/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 (M 3 , g) was weighed again. WHC was calculated as following formula: WHC (g/g) = (M 3 À M)/M 1 . Water solubility index (WSI) was determined by an AACC meth- od of No. 44-19. The powder (S 1 , 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 (S 2 , g) and subjected to dry at 103 ± 2 °C, and the evaporating dish with residue was weighed again (S 3 , g). WSI was calculated as following formula: WSI (%) = (S 3 À S 2 )/S 1 Â 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 (V 1 ) 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 (V 2 ) of the wetted powder was then recorded. WSI was calculated as following formula: SC (mL/ g)=(V 2 À V 1 )/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 Z. Zhang et al. / Journal of Food Engineering 109 (2012) 406–413 407 the 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 (a w 0.070), MgCl 2 (a w 0.33), Mg(NO 3 ) 2 (a w 0.528), NaCl (a w 0.757), KBr (a w 0.807), KCl (a w 0.842), BaCl (a w 0.901) and K 2 Cr 2 O 7 (a w 0.986) 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 by Oboh 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 in Table 2. Particle size distribu- tions were characterized by D 0.1 , D 0.5 and D 0.9 values (Giry et al., 2006). Agglomeration ratio D 0.5 was 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 in Table 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 Parameters c Powders b SPS MMS JMS SPC MMC JMC Moisture (g/100 g) 8.16 ± 0.11 g 9.55 ± 0.11 e 9.25 ± 0.11 e 9.52 ± 0.29 e 8.56 ± 0.16 f 9.98 ± 0.16 d Fat (g/100 g) 1.58 ± 0.09 f 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 Protein (g/100 g) 6.35 ± 0.41 gh 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 Ash (g/100 g) 4.73 ± 0.21 g 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 SDF (g/100 g) 4.20 ± 0.16 i 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 Cd (g/kg) 0.35 ± 0.03 de 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 Pb (g/kg) 0.59 ± 0.02 d 0.47 ± 0.01 e 0.56 ± 0.04 de 0.43 ± 0.02 ef 0.37 ± 0.03 f 0.56 ± 0.03 de 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 Values bearing different superscript lowercase letters within the same row are significantly different (Duncan, p < 0.05). 408 Z. Zhang et al. / Journal of Food Engineering 109 (2012) 406–413 area 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 in Table 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 with Table 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 in Table 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 with Table 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 in Fig. 1. It was clear to see that both protein and polysaccharide solubility of all powders were linearly (R 2 = 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 ( l m) c Powders b SPS MMS JMS SPC MMC JMC D 0.1 8.71 7.53 4.04 9.73 6.09 4.32 D 0.5 40.90 32.01 12.71 54.77 22.13 13.16 D 0.9 194.42 92.00 27.03 333.39 62.26 28.34 Span 4.54 2.64 1.81 5.91 2.54 1.83 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 D 0.1 , D 0.5 and D 0.9 are the equivalent volume diameters at 10%, 50%, and 90% cumulative volumes, respectively; Span was determined by the equation: span = (D 0.9 À D 0.1 )/D 0.5 . 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 /g) Bulk density (g/mL) Repose angle (°) Slide angle (°) SPS 0.338 ± 0.008 g 0.152 ± 0.004 g 47.29 ± 0.66 c 43.14 ± 1.08 cd MMS 0.402 ± 0.010 f 0.169 ± 0.003 f 45.48 ± 0.97 d 41.97 ± 1.24 de JMS 0.727 ± 0.014 c 0.210 ± 0.006 d 40.16 ± 0.96 f 39.27 ± 1.03 fg SPC 0.281 ± 0.012 e 0.183 ± 0.006 e 48.33 ± 0.77 c 44.26 ± 0.91 c MMC 0.459 ± 0.017 d 0.199 ± 0.010 c 45.15 ± 0.72 d 40.84 ± 0.55 ef JMC 0.718 ± 0.004 c 0.228 ± 0.009 c 41.88 ± 0.79 e 38.23 ± 0.51 g 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 Values bearing different superscript lowercase letters within the same column are significantly different (Duncan, p < 0.05). Table 4 Effect of grinding methods on hydration properties of mushroom (L. edodes) powders. a Powder b Hydration properties c WHC (g/g) WSI (%) SC (ml/g) SPS 3.923 ± 0.098 d 21.621 ± 1.07 i 5.430 ± 0.053 e MMS 3.614 ± 0.113 ef 22.932 ± 0.87 h 5.118 ± 0.094 f JMS 3.311 ± 0.101 g 24.112 ± 0.11 f 4.741 ± 0.068 g SPC 3.718 ± 0.113 e 23.143 ± 1.01 g 5.769 ± 0.086 d MMC 3.511 ± 0.085 f 25.209 ± 0.79 e 5.393 ± 0.069 e JMC 3.147 ± 0.145 h 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). Z. Zhang et al. / Journal of Food Engineering 109 (2012) 406–413 409 100 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 w 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. 410 Z. Zhang et al. / Journal of Food Engineering 109 (2012) 406–413 Fig. 2. Similar to trends that observed in numerous foods, EMC val- ues of the powders increased with a w . When size-reduction meth- ods were compared at the same EMC, a w of 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 Model Mathematical expression R 2 E (%) SE (%) BET m = aba w /[1 + (b À 2)a w À (b À 1)x 2 ] 0.912–0.955 À3.391–8.042 2.201–3.583 Kuhn m = a/lna w + b 0.945–0.963 2.134–7.896 0.987–1.268 Oswin m = k 0 [a w /(1 À a w )] n0 0.995–0.999 1.723–3.245 0.0531–0.1842 Bradley ln 1/a w = K 2 K 1 M 0.973–0.983 1.187–4.571 0.0871–0.6131 Caurie lnm =lnA À ra w 0.963–0.981 À1.986–3.871 0.0921–0.5732 Halsey aw = exp(Àa/m n ) 0.972–0.993 2.278–3.731 0.0712–0.3121 Chung-P lna w = ÀAexp(ÀBm) 0.983–0.993 2.112–2.877 0.0613–0.2478 a R 2 , E and SE were determined by following equations: R 2 ¼ P ðm i Àm pi Þ 2 P m 2 i P m 2 pi , E ¼ 100 n P n i¼1 ð m pi Àm i m i Þ, SE ¼ ffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffiffi P n i¼1 ðm pi Àm i Þ 2 ðnÀ1Þ r , where n is the number of experimental observations; m i represents experimental moisture content values, and m pi denotes value predicted from model. Table 6 Nonlinear regression parameters of Oswin model (m = k 0 [a w /(1 À a w )] n0 ) for different mushroom (L. edodes) powders. Powders a Parameters b K 0 nR 2 SPS 11.315 0.516 0.997 MMS 11.638 0.536 0.998 JMS 12.603 0.517 0.995 SPC 12.304 0.515 0.999 MMC 12.681 0.542 0.996 JMC 13.282 0.536 0.995 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 = k 0 [a w /(1 À a w )] n0 . Table 7 Correlation between particle size and physical–chemical properties of cap and stipe powders. Properties Correlation coefficient to particle size Cap powder Stipe powder WSI À0.9464 À0.9712 a w À0.9951 À0.9535 Bulk density À0.9997 À0.8858 Specific surface area À0.9115 À0.9873 Response angle 0.9475 0.9978 Slide angle 0.9714 0.9999 WHC 0.8894 0.9768 SC 0.9968 0.9879 SDF À0.9997 À0.8330 Polysaccharide solubility À0.9636 À0.9780 Protein solubility À0.8831 À0.9969 Z. Zhang et al. / Journal of Food Engineering 109 (2012) 406–413 411 of 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 by Lee and Lee (2007). With the same material (cap or stipe) and EMC, cap powders had lower a w values 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 in Table 1 (Khalloufi et al., 2000). Seven sorption models presented in Table 5 were tested for their goodness-of-fits in describing the isotherms of the powders in terms of coefficient of the determination (R 2 ), 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 R 2 beyond 0.912 and absolute E values below 7.896% (Table 5 and Sup. 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 R 2 and lowest absolute value of E. The nonlinear regression parameters of this model were shown in Table 6. 3.8. Dependence of the physico-chemical properties on the particle size The dependence of physico-chemical properties, such as a w , WSI, SC, WHC, SDF, on the particle size (D 0.5 ) of the powders were eval- uated in terms of the coefficients of physico-chemical properties and particle size. The results were shown in Table 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 a w , 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. 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Characterization of stipe and cap powders of mushroom (Lentinus edodes) prepared by different grinding methods Zipei Zhang a , Huige Song a , Zhen. 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. . 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