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. 2007 Apr 30;12(4):917–931. doi: 10.3390/12040917

Effects of Different Carriers on the Production of Isoflavone Powder from Soybean Cake

Tsai-Hua Kao 1, Bing-Huei Chen 1,*
PMCID: PMC6149415  PMID: 17851444

Abstract

The objectives of this study were to use soybean cake as the raw material for the production of isoflavone powder and compare the effects of different carriers as well as drying methods on the powder quality. Results showed that with spray drying, a level of 40 % maltodextrin as carrier produced the highest yield (mass) of isoflavone powder, followed by 10 % gelatin and 1 % sodium alginate. However, a reversed trend was observed for the isoflavone content. With 1 % sodium alginate, freeze drying generated the greatest yield of isoflavone powder, followed by vacuum drying and spray drying. The isoflavone content also exhibited the same tendency. With poly-γ-glutamic acid (γ-PGA) as carrier, all six levels studied (0.57, 0.28, 0.14, 0.028, 0.014 and 0.003 %) were capable of forming powder containing high amounts of total isoflavone, which was comparable to that using 1% sodium alginate by freeze drying. Both high- and low-molecular-weight γ-PGA showed similar effects in terms of powder yield and isoflavone content.

Keywords: Isoflavone powder, soybean cake, γ-PGA, sodium alginate, maltodextrin

Introduction

Isoflavones, a major class of flavonoids in soybeans, have received great attention in recent years because of their possible roles in the prevention of chronic diseases such as osteoporosis and hypercholesterolemia, as well as alleviation of postmenopausal syndromes [1,2,3]. Twelve isoflavones have been found in soybeans and are divided into four groups, i.e., malonylglucoside, glucoside, acetylglucoside and aglycone, in which the glucoside forms are dominant [4,5]. Soybean cake (defatted soybean meal), a by-product obtained during processing of soybean oil, was found to contain high amounts of isoflavone [6,7]. Thus, it would be a great advantage to the health food industry if the isoflavone in soybean cake could be extracted and processed into powder.

Powder products are often processed by vacuum, freeze or spray drying, but the powder yield and quality can vary depending upon the drying methods and conditions used [8]. For instance, freeze drying is generally considered the most appropriate method to maintain high powder quality, but the capital cost is high. Conversely, spray drying is suitable for commercial powder production, however, this method requires control of several variables like both inlet and outlet temperatures, and the powder quality may be affected during high-temperature drying [9].

Different carriers like gelatin, gum arabic, maltodextrin, cellulose and glycerol monostearate have been used commercially to obtain nonsticky and free flowing powders [10,11], but these carriers suffer a major drawback, namely, a large quantity has to be used for powder formation, which may increase production cost substantially.

Poly-γ-glutamic acid (γ-PGA), a nontoxic and biodegradable polymer consisting of many glutamic acid units linked by amide bonding between α-amino and γ-carboxylic acid groups, is produced from Bacillus sp. [12,13,14]. Both high-molecular-weight γ-PGA (H-γ-PGA) and low-molecular-weight γ-PGA (L-γ-PGA) ranging from 10,000 to 2 million Daltons have been commercialized and they are produced in different ionic forms, i.e., Ca, Na and H-forms. The applications of γ-PGA in removing heavy metals, toxic compounds and artificial dyes have been well documented [12,13,14,15], but the feasibility of using a low level of γ-PGA as carrier for powder formation remains unknown and requires further investigation. The objectives of this study were to isolate isoflavones from soybean cake and determine the effects of various drying methods and carriers, especially γ-PGA, on the yield of isoflavone powder product. The isoflavone content changes as affected by drying conditions were also investigated.

Results and Discussion

Isoflavone content in soybean cake

In a previous study we demonstrated that all 12 isoflavones in soybean cake plus the internal standard formononetin could be separated by HPLC within 15 min using a Vydac 201TP54 C18 column [7]. This method is much faster than those reported in the literature [6,16,17]. Figure 1 shows the chemical structures of the 12 isoflavones present in soybean cake. High r2 values ranging from 0.9894~1 were observed for all the calibration curves of the 12 isoflavone standards. The linear regression equations of the 12 isoflavones were: y = 0.2049x–0.0016 (malonyldaidzin), y = 0.1686x+0.0218 (malonylglycitin), y = 0.4492x+0.0081 (malonylgenistin), y = 0.6777x+0.0018 (daidzin), y = 0.2729x–0.0164 (glycitin), y = 0.5138x+0.007 (genistin), y = 0.7899x+0.0048 (acetyldaidzin), y = 0.3716x+0.0087 (acetylglycitin), y = 0.9027x+0.022 (acetylgenistin), y = 0.8639x+0.0313 (daidzein), y = 0.4298x–0.0008 (glycitein) and y = 1.3841x+0.0679 (genistein), respectively. Malonylglucoside was the compound present in the largest amount in soybean cake (2,411 μg/g), followed by glucoside (2,184 μg/g), acetylglucoside (256 μg/g) and aglycone (159 μg/g) for a combined total of 5,010 μg/g [7]. These levels were much higher than those reported by Wang et al. [18] or Coward et al. [19], who found malonylglucoside, glucoside, acetylglucoside and aglycone levels to be 1,013 and 1,340 μg/g, 475 and 249 μg/g, 0 and 207 μg/g, and 24 and 11 μg/g, respectively. These differences may be accounted for by variations in cultivar, growth environment, harvest time and storage conditions [6,20].

Figure 1.

Figure 1

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Chemical structures of 12 isoflavones in soybean cake.

Processing of isoflavone powder by spray drying

With gelatin as carrier, it was shown a 5 % level would make spray drying difficult because of the resulting low solids contents. By raising the gelatin level to 15 or 20 %, the isoflavone powder could be processed by spray drying, but the isoflavone content was then too low. Thus, the optimum level of gelatin was chosen to be 10 %. With the inlet temperature set lower than 170 °C, the isoflavone homogenate stuck to the inner tube in the spray dryer and complete drying could only be attained when the inlet temperature reached 180 °C or above with the outlet temperature maintained at 120°. For feed rate, a high value (>10 %) resulted in incomplete drying, while a low one (<10 %) required a longer drying time. Therefore, a value of 10 % was selected as the most suitable feed rate. By choosing the most favorable conditions shown above, that is, gelatin level 10 %, inlet temperature 180 °C, outlet temperature 120 °C and feed rate 10 %, a total amount of 3.6 g powder (6.5% H2O) containing 10,009 μg/g isoflavone was produced after drying.

With maltodextrin as carrier, a 10 % solution was prepared by dissolving 10 g of maltodextrin in 90 g of isoflavone extract and homogenizing for 10 min before spray drying, but the spray-dried powder was found to have a low solids content. By comparing maltodextrin concentrations of 20, 30 and 40 %, a level of 40 % was shown to be the most appropriate. Four feed rates of 10, 15, 20 and 25 % were also compared and the optimum level was found to be 20 %. By controlling the inlet temperature at 180 °C and outlet temperature at 120 °C, a total amount of 7.9 g powder (6.1% H2O) containing 1,887 μg/g isoflavone was obtained after spray drying.

Because of its poor solubility in isoflavone extract, sodium alginate was first dissolved in deionized water and then mixed with isoflavone extract. A concentration of 4 % sodium alginate in water was found to be adequate to maintain a medium viscosity. A final concentration of 1 % sodium alginate in isoflavone extract was prepared by mixing 25 g of aqueous sodium alginate solution and 75 g of isoflavone extract. After homogenization for 10 min, the mixture was subjected to spray drying. By comparing four inlet temperatures (110, 130, 150 and 180 °C), it was shown that higher temperatures (150 and 180 °C) may cause degradation of the isoflavone powder particles, whereas a low temperature (110 °C) could result in inadequate drying. Therefore, the most favorable inlet and outlet temperatures were 130 and 100 °C, respectively. As for feed rate, a 7 % level was optimum as a higher feed rate (≥10 %) led to incomplete drying. A total amount of 1.9 g powder (6.9 % H2O) containing 23,847 μg/g isoflavone was thus generated after spray drying (Table 1).

Table 1.

Effect of drying methods on isoflavone contents (μg/g) A in a powder with 1 % sodium alginate as carrier B.

Isoflavone Spray drying Vacuum drying Freeze drying
Mdin 4,619±383c 6,745±135b 10,246±333a
Mglin 3,321±331c 3,788±261b 4,625±137a
Mgin 4,501±142b 6,739±22a 6,640±242a
Sub total 12,441±572c 17,272±657b 21,510±437a
Din 1,896±24b 2,689±82a 2,736±75a
Glin 1,844±41b 2,657±213a 2,765±65a
Gin 5,606±61b 10,075±113a 9,964±183a
Sub total 9,346±44b 15,421±408a 15,464±322a
Adin 285±4b 635±38a 638±42a
Aglin 232±10c 429±4b 502±21a
Agin 702±30b 1,192±74a 1,161±46a
Sub total 1,219±44b 2,255±208a 2,300±67a
Dein 428±44c 1,138±20b 1,255±10a
Glein 182±10c 946±18a 606±47b
Gein 230±59b 1,408±33a 1,288±128a
Sub total 840±5c 3,492±71a 3,148±92b
Total 23,847±577c 38,240±1,061b 42,423±734a
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A Average of duplicate analyses±standard deviation. B Symbols bearing different letters (a-c) in the same row are significantly different (P<0.05). Mdin: malonyldaidzin; Mglin: malonylglycitin; Mgin: malonylgenistin; Din: daidzin; Glin: glycitin; Gin: genistin; Adin: acetyldaidzin; Aglin: acetylglycitin; Agin: acetylgenistin; Dein: daidzein; Glein: glycitein; Gein: genistein.

Evidently, the yield of isoflavone powder can be affected by both the type of carrier and spray-drying conditions. Fernandez-Perez et al. [21] studied the effects of inlet temperature (100-200 °C) and feed rate (2.5-10 mL/min) on the quality of spray-dried instant soup powder and found that the powder yield increased as the inlet temperature increased (<160 °C). However, a high inlet temperature (200 °C) would decrease the yield of powder, probably due to powder particle degradation. In addition, these authors pointed out that the faster the feed rate and the lower the outlet temperature, the lower the yield of powder. Goula and Adamopoulos [22] also reported that the lower the inlet temperature and the slower the hot air rate, the higher density of the powder was. Likewise, the higher the inlet temperature and the slower the hot air rate, the lower the moisture content of the powder was. Some other authors have suggested that a high feed rate may increase the volume of liquid droplets to thus produce a low yield of powder [23]. Krishnan et al. [24] further stated that carriers such as gelatin and sodium alginate possessed higher viscosity than maltodextrin, which was less efficient in terms of active material or core material encapsulation. Theoretically, the higher the solid content, the larger the yield of powder [21]. But, a high solids content would result in a low amount of active material being encapsulated into the powder. For example, in our study the highest yield of powder (7.9 g) was produced with 40 % maltodextrin as carrier, followed by 10 % gelatin (3.6 g) and 1 % sodium alginate (1.9 g). In contrast, the isoflavone content in the powder followed an increasing trend, with values of 1,887, 10,009 and 23,847 μg/g, respectively.

Production of isoflavone powder by vacuum drying

The results shown above clearly indicate that with 1 % sodium alginate as carrier, a powder product containing high level of isoflavone could be obtained by spray drying. Thus, we further investigated the possibility of processing isoflavone extract into powder with sodium alginate as carrier by vacuum drying. Of the five proportions studied, a powder product of 5.3 and 4.9 g was obtained for the isoflavone solutions containing 1 and 0.4 % sodium alginate, respectively, while the other three levels (0.2, 0.1 and 0.05 %) failed to form powder, probably because of low solids content. In contrast, powder products of 5.9, 5.6, 5.5 and 5.4 g resulted from the isoflavone solutions containing 1, 0.4, 0.2 and 0.1 % H-γ-PGA, respectively, whereas the level of 0.05 % H-γ-PGA failed to produce powder. The isoflavone content in the powder increased with the decreasing concentration of both carriers (Table 2). A concentration of 0.1% H-γ-PGA in the isoflavone extract produced the highest yield (51,564 μg/g) of total isoflavone, followed by the other three concentrations of 0.2, 0.4 and 1 %, which gave 49,900, 46,689 and 38,165 μg/g, respectively. Similarly, a level of 0.4 % sodium alginate in the isoflavone extract generated a greater yield (49,041 μg/g) of total isoflavone than that of 1% (38,661 μg/g). All four groups of isoflavones, namely, malonylglucosides, glucosides, acetylglucosides and aglycones showed the same trend.

Table 2.

Isoflavone contents (μg/g) A in the vacuum-dried powder with sodium alginate and H-γ-PGA (Na) B as carrier C.

Isoflavones Carriers
Sodium alginate H-γ-PGA (Na)B
1 % 0.4 % 1 % 0.4 % 0.2 % 0.1 %
Mdin 8,345±57c 9,857±91b 8,170±264c 9,986±270b 10,855±255a 11,315±197a
Mglin 2,853±40e 3,696±166c 2,865±23e 3,137±2d 4,357±196b 4,793±32a
Mgin 5,017±148c 6,410±101a 4,912±3c 5,791±117b 6,507±88a 6,385±112a
Sub total 16,214±246e 19,963±358c 15,947±286e 18,914±389d 21,719±29b 22,492±341a
Din 3,407±12c 4,480±113a 3,327±12c 4,290±24b 4,345±30ab 4,338±3ab
Glin 4,217±21d 5,401±119ab 3,983±45d 4,830±96c 5,277±121b 5,657±170a
Gin 9,315±42c 12,356±416a 9,417±79c 12,147±165ab 11,743±126b 12,087±15ab
Sub total 16,939±51c 22,238±410a 16,728±135c 21,266±237b 21,365±35b 22,083±153a
Adin 509±4b 665±26a 501±8b 652±13a 651±11a 679±2a
Aglin 482±5d 787±9a 466±10d 567±17c 734±49ab 689±17b
Agin 898±99b 1,098±46a 873±20b 1,123±23a 1,101±29a 1,124±22a
Sub total 1,889±98c 2,550±64a 1,840±19c 2,342±7b 2,486±67a 2,493±37a
Dein 546±5c 729±13ab 537±6c 765±6a 741±33ab 714±27b
Glein 365±6c 580±43a 357±3c 461±0b 445±51b 479±19b
Gein 2,708±64d 2,983±82c 2,757±6d 2,941±26c 3,144±31b 3,304±3a
Sub total 3,618±53d 4,291±52c 3,651±3d 4,167±32c 4,330±115b 4,497±22a
Total 38,661±448d 49,041±168b 38,165±172d 46,689±652c 49,900±117b 51,564±478a
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A Average of duplicate analyses±standard deviation. B γ-PGA (Na) with high molecular weight. C Symbols bearing different letters (a-e) in the same row are significantly different (P<0.05). Mdin: malonyldaidzin; Mglin: malonylglycitin; Mgin: malonylgenistin; Din: daidzin; Glin: glycitin; Gin: genistin; Adin: acetyldaidzin; Aglin: acetylglycitin; Agin: acetylgenistin; Dein: daidzein; Glein: glycitein; Gein: genistein.

The above results indicated the most appropriate concentrations for sodium alginate and H-γ-PGA in isoflavone extract were 0.4 and 0.1 %, respectively, with the proportion of carrier to isoflavone extract being 1:4 and 1:19 (w/w). Therefore, it is necessary to investigate the possibility of producing powder product by lowering the levels of both carriers. Four levels of 0.4, 0.2, 0.04 and 0.02 % of sodium alginate, and 0.1, 0.05, 0.01 and 0.005 % of both H-γ-PGA and L-γ-PGA, were each prepared in isoflavone extract as described above.

A powder product of 4.9, 4.7 and 4.6 g was formed for alginate levels of 0.4, 0.2 and 0.04 %, respectively. For both H-γ-PGA and L-γ-PGA levels at 0.1, 0.05 and 0.01 %, a powder product of 5.4, 5.2 and 5.2 g was generated for the former and 5.6, 5.3 and 5.3 g for the latter. Levels of 0.02 % sodium alginate and 0.005 % of H-γ-PGA or L-γ-PGA both failed to form powder, which may be due to the presence of a low solids content. The highest amount of malonylglucoside was found for 0.01 % H-γ-PGA and L-γ-PGA, which equaled 27,052 and 26,868 μg/g, respectively, followed by 0.05 % H-γ-PGA and L-γ-PGA (25,498 and 25,059 μg/g), and 0.04 and 0.2 % sodium alginate (24,764 and 21,978 μg/g). The same trend also occurred for both acetylglucoside and aglycone. However, only minor differences were shown for glucoside (Table 3). For total isoflavone, it also followed a similar trend as the four groups of isoflavones.

Table 3.

Isoflavone contents (μg/g) A in the vacuum-dried powder with H-γ-PGA (Na) B and L-γ-PGA (Na) C or sodium alginate as carrier D.

Isoflavones Carriers
Sodium alginate H-γ-PGA (Na)B L-γ-PGA (Na)C
0.20% 0.04% 0.05% 0.01% 0.05% 0.01%
Mdin 10,915±47e 12,459±110c 12,934±247b 13,613±187a 12,971±283b 13,693±74a
Mglin 5,287±39a 5,377±187a 5,389±110a 5,558±26a 5,323±64a 5,444±135a
Mgin 5,776±407d 6,928±21b 7,176±171b 7,882±77a 6,765±187bc 7,731±248a
Sub total 21,978±415c 24,764±318b 25,498±529b 27,052±290a 25,059±534b 26,868±309a
Din 3,992±235b 4,365±115a 4,471±128a 4,390±175a 4,419±24a 4,448±144a
Glin 5,073±294b 5,099±366b 5,104±64b 5,182±80ab 5,073±19a 5,148±33a
Gin 1,2051±58b 12,731±352a 12,798±217a 12,772±93a 12,513±186a 12,669±214a
Sub total 21,117±587b 22,195±101a 18,777±326a 22,344±348a 22,005±182ab 22,266±324a
Adin 849±44b 951±24a 759±28c 887±29ab 778±28c 868±2b
Aglin 680±28c 717±20bc 667±8c 856±64a 657±14d 880±31a
Agin 1,121±22b 1,211±71ab 954±32c 1,313±61a 968±15d 1,360±6a
Sub total 2,650±6b 2,879±114a 2,380±53c 3,056±154a 2,403±57d 3,109±27a
Dein 637±51c 688±6bc 636±20c 806±27a 652±16bc 816±40a
Glein 558±1b 595±27ab 632±15ab 664±47a 623±15a 614±51a
Gein 3,287±35b 3,397±59ab 3,402±156ab 3,518±95a 3,355±9ab 3,458±56a
Sub total 4,482±86bc 4,679±91b 4,670±151b 4,989±169a 4,630±8b 4,888±67a
Total 50,227±92d 54,517±625b 54,922±150b 57,441±962a 54,098±765b 57,130±673a
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A Average of duplicate analyses±standard deviation. B γ-PGA (Na) with high molecular weight. C γ-PGA (Na) with low molecular weight. D Symbols bearing different letters (a-f) in the same row are significantly different (P<0.05). Mdin: malonyldaidzin; Mglin: malonylglycitin; Mgin: malonylgenistin; Din: daidzin; Glin: glycitin; Gin: genistin; Adin: acetyldaidzin; Aglin: acetylglycitin; Agin: acetylgenistin; Dein: daidzein; Glein: glycitein; Gein: genistein.

Processing of isoflavone powder by freeze drying

Following the same approach, a mixture (100 g) containing sodium alginate and isoflavone extract was freeze dried at –40° under a 60 millitorr vacuum and with a drying time of 24 h. A powder product of 6.6 g (9.1 % H2O) was obtained which contained the highest level of malonylglucoside, glucoside, acetylglucoside and aglycone (Table 1). Of the various dried products, freeze-dried powder contained the highest content of total isoflavone, followed by vacuum-dried and spray-dried powder (Table 1). However, for aglycone, vacuum drying was shown to produce a higher level than freeze drying, probably caused by conversion from glucose-containing isoflavone during extensive vacuum drying at 60 °C. In a study dealing with the conversion and degradation of isoflavone during heating, Chien et al. [5] demonstrated that aglycone can be formed from malonylglucoside, glucoside or acetylglucoside depending on heating temperature and time. Compared to vacuum drying, freeze drying showed a higher level of malonylglucoside, but no significant difference was found in the contents of acetylglucoside (Table 1). Obviously, the highest yield of total isoflavone was accomplished by freeze drying, since both conversion and degradation of isoflavones were minimized. Nevertheless, vacuum drying generated a higher yield of powder (7.2 g) than either freeze drying (6.6 g) or spray drying (1.9 g).

A similar outcome was reported by Monsoor [25], who evaluated the effects of several drying methods on the functional properties of soy hull pectin, the lowest yield of powder being observed for spray drying, whereas there is no significant difference between freeze drying and vacuum drying. In our study, freeze-dried powder contained a higher amount of moisture (9.1 %) than vacuum dried (7.2 %) and spray dried (6.9 %), which may be explained by formation of porous structures in the powder during sublimation, which should be more prone to moisture absorption after drying [26]. The same phenomenon was reported by Tsami et al. [27], who found that freeze-dried powder could absorb moisture more readily than vacuum-dried powder, which can be attributed to the former being capable of forming a large number of pores with much smaller diameter.

By comparing the results shown above, freeze drying was proven to be the best method for production of powder with high-levels of isoflavone. Thus, we further investigated the effects of H-γ-PGA and L-γ-PGA on the production of isoflavone powder by freeze drying. Because of the high moisture absorption capacity and poor solubility in isoflavone extract, both H-γ-PGA and L-γ-PGA were dissolved separately in water to obtain a medium viscosity and a concentration of 2 %. In the beginning a mixture containing 25 g of H-γ-PGA or L-γ-PGA solution and 75 g of isoflavone extract was placed in a freezer (–30°) for 24 h. However, this mixture failed to freeze, mainly due to the presence of ethanol in the isoflavone extract. After various studies, a mixture containing 40 g of H-γ-PGA or L-γ-PGA solution and 100 g of isoflavone extract (0.28 % H-γ-PGA or L-γ-PGA in isoflavone extract) was frozen after 24 h at –30 °C. Six concentrations of 0.57, 0.28, 0.14, 0.028, 0.014 and 0.003 % H-γ-PGA or L-γ-PGA in isoflavone extract were prepared separately and placed in a freezer until frozen, after which each mixture was freeze dried at –40 °C under 60 millitorr for 24 h, and powder products of 8.4, 7.8, 7.9, 7.9, 7.6 and 7.5 g were produced, respectively, for H-γ-PGA, whereas for L-γ-PGA, a powder product of 8.4, 8.1, 7.7, 7.1, 7.5 and 7.7 g was formed. Of the four groups of isoflavones, both malonylglucosides and glucosides dominated for both powders containing H-γ-PGA and L-γ-PGA at all six levels (Table 4 and Table 5). Only slight differences between acetylglucoside and aglycone were noted, probably because they are present in much smaller amounts in isoflavone extract. With 0.003 % H-γ-PGA or L-γ-PGA, the contents of total isoflavone in the freeze dried powder were 48,144 and 48,155 μg/g, respectively (Table 4 and Table 5). Only minor differences were observed for 0.014 % H-γ-PGA and L-γ-PGA, which gave 48,204 and 47,245 μg/g, respectively. The same phenomenon also applied to H-γ-PGA and L-γ-PGA with levels at 0.28 and 0.57 %. No significant difference was found between 1 % sodium alginate and 0.57% H-γ-PGA or L-γ-PGA (Table 4 and Table 5) for total isoflavone in the freeze dried powder. This result further demonstrated that a high yield of powder containing a large amount of isoflavone could be attained by using an extremely low level of 0.003 % H-γ-PGA or L-γ-PGA, and was comparable to that using 1 % sodium alginate as carrier. As mentioned before, with γ-PGA as carrier the powder production cost could be reduced greatly.

Table 4.

Isoflavone contents (μg/g) A in the freeze-dried powder with H-γ-PGA (Na) B or sodium alginate as carrier C.

Isoflavones Carriers
1 % sodium alginate H-γ-PGA (Na)B
0.57 % 0.28 % 0.14 % 0.028 % 0.014 % 0.003 %
Mdin 9,160±92d 9,562±258d 10,527±166c 10,768±13c 12,476±273ab 12,802±454a 12,055±195b
Mglin 3,118±141ef 3,620±442bcd 3,930±10b 3,848±1bc 3,436±365cde 3,868±43bc 3,982±39b
Mgin 7,176±25d 7,404±162d 7,732±311c 7,791±45bc 7,958±75abc 7,867±122bc 8,056±29ab
Sub total 19,455±258e 20,586±538d 22,189±466c 2,2407±30c 23,870±563b 24,537±534ab 24,093±205ab
Din 3,579±18a 3,707±27d 3,902±64bc 3,950±3abc 4,030±85a 3,896±41bc 3,984±16ab
Glin 4,071±21a 3,917±131a 4,106±135a 4,241±52a 4,253±67a 4,159±184a 4,323±10a
Gin 10,437±77e 11,094±157def 11,770±332a 11,648±336ab 11,441±3abcde 11,174±102cdef 11,315±37bcde
Sub total 18,088±116cd 18,719±1cde 19,779±531a 19,838±385a 19,724±156a 19,230±327abc 19,622±43ab
Adin 651±8ab 696±22abcd 716±46ab 731±20a 699±24abcd 679±14abcd 726±6a
Aglin 641±5d 672±68ab 643±5ab 667±23ab 719±119ab 795±130a 735±50ab
Agin 1,078±2b 1,148±38bcd 1,183±41abc 1,192±5abc 1,218±2ab 1,184±67abc 1,193±1abc
Sub total 2,370±11a 2,516±127ab 2,543±93ab 2,590±3ab 2,637±74a 2,658±210a 2,654±55a
Dein 715±8b 740±46a 768±61a 784±18a 727±24a 718±43a 764±5a
Glein 441±9abc 462±40b 474±46b 523±51ab 486±45b 470±42b 591±12a
Gein 539±29abcde 542±28abc 573±14a 554±19ab 429±12d 430±5d 419±2d
Sub total 1,694±27e 1,744±58abcde 1,814±120abc 1,860±52a 1,642±81cde 1,618±79de 1,774±19abcd
Total 41,607±126e 43,565±352d 46,325±1210bc 46,695±306abc 47,873±400ab 48,204±923a 48,144±198a
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A Average of duplicate analyses±standard deviation. B γ-PGA (Na) with high molecular weight. C Symbols bearing different letters (a-f) in the same row are significantly different (P<0.05). Mdin: malonyldaidzin; Mglin: malonylglycitin; Mgin: malonylgenistin; Din: daidzin; Glin: glycitin; Gin: genistin; Adin: acetyldaidzin; Aglin: acetylglycitin; Agin: acetylgenistin; Dein: daidzein; Glein: glycitein; Gein: genistein.

Table 5.

Isoflavone contents (μg/g)A in the freeze-dried powder with L-γ-PGA (Na)B or sodium alginate as carrier C.

Isoflavones Carriers
1 % sodium alginate L-γ-PGA (Na)B
0.57 % 0.28 % 0.14 % 0.028 % 0.014 % 0.003 %
Mdin 9,160±92d 9242±125d 10256±320c 10665±66c 12230±75b 11949±637b 12386±570ab
Mglin 3,118±141ef 2940±111f 3402±289de 3936±93b 3955±99b 4760±83a 4718±38a
Mgin 7,176±25d 7186±58d 8200±127a 7891±92bc 7945±57abc 7455±160d 7946±23abc
Sub total 19,455±258e 19368±179e 21857±736c 22491±251c 24130±231ab 24164±880ab 25050±632a
Din 3,579±18a 3606±42e 3864±29c 3958±5abc 4048±50a 3857±88c 3864±40c
Glin 4,071±21a 4080±441a 4075±53a 4114±70a 4125±207a 4052±108a 4132±144a
Gin 10,437±77e 10796±30fg 11508±199bcd 11590±19abc 11550±109abc 11039±285ef 11123±63def
Sub total 18,088±116cd 18481±453de 19447±222ab 19661±94ab 19723±148a 18948±480cde 19119±247abcd
Adin 651±8ab 699±46abcd 711±10abc 689±27abcd 696±35abcd 642±12d 659±23bcd
Aglin 641±5d 648±15ab 682±98ab 652±43ab 597±7b 767±25a 587±37b
Agin 1,078±2b 1123±47cd 1188±1abc 1242±14a 1175±24abc 1124±24cd 1154±28bc
Sub total 2,370±11a 2470±79ab 2581±109ab 2582±2ab 2468±65ab 2533±60ab 2399±89b
Dein 715±8b 746±52a 783±38a 768±6a 712±23a 703±37a 711±29a
Glein 441±9abc 495±41ab 501±9ab 506±70ab 451±38b 472±44b 448±54b
Gein 539±29abcde 523±18bc 546±11abc 554±15ab 509±12c 424±19d 427±2d
Sub total 1,694±27e 1,764±111abcde 1830±58ab 1829±91ab 1672±28bcde 1599±100de 1586±85e
Total 41,607±126e 42083±465de 45715±347c 46564±435abc 47993±46ab 47245±1521abc 48155±1052a
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A Average of duplicate analyses±standard deviation. B γ-PGA (Na) with low molecular weight.C Symbols bearing different letters (a-g) in the same row are significantly different (P<0.05). Mdin: malonyldaidzin; Mglin: malonylglycitin; Mgin: malonylgenistin; Din: daidzin; Glin: glycitin; Gin: genistin; Adin: acetyldaidzin; Aglin: acetylglycitin; Agin: acetylgenistin; Dein: daidzein; Glein: glycitein; Gein: genistein.

Table 6 shows the characteristics of various isoflavone powders made by different drying methods. Both spray-dried and freeze-dried powder possessed a slightly yellow appearance, while vacuum-dried powder was deep yellow, which may be due to long-time drying at 60 °C.

Table 6.

Characteristics of the various isoflavone powder made by different drying methods.

Drying method Carrier Carrier content (%) Color Powder
weight (g)		 Water content (%) Isoflavone content (μg/g)
Spray-drying Gelatin 10 Light yellow 3.6 6.5 10,009
Maltodextrin 40 Light yellow 7.9 6.1 1,887
Sodium Alginate 1 Light yellow 1.9 6.9 23,847
Freeze-drying Sodium Alginate 1 Yellow to white 6.6 9.1 43,423
H-γ-PGA (Na) A 0.570 Light yellow 8.4 14.0 43,565
H-γ-PGA (Na) 0.280 Light yellow 7.8 14.8 46,325
H-γ-PGA (Na) 0.140 Light yellow 7.9 16.1 46,695
H-γ-PGA (Na) 0.028 Light yellow 7.9 17.5 47,873
H-γ-PGA (Na) 0.014 Light yellow 7.6 16.7 48,204
H-γ-PGA (Na) 0.003 Light yellow 7.5 17.9 48,144
L-γ-PGA (Na)B 0.570 Light yellow 8.4 13.2 42,083
L-γ-PGA (Na) 0.280 Light yellow 8.1 14.7 45,715
L-γ-PGA (Na) 0.140 Light yellow 7.7 15.9 46,564
L-γ-PGA (Na) 0.028 Light yellow 7.1 17.1 47,993
L-γ-PGA (Na) 0.014 Light yellow 7.5 17.4 47,245
L-γ-PGA (Na) 0.003 Light yellow 7.7 17.9 48,155
Vacuum-drying Sodium Alginate 1 Yellow 5.3 4.4 38,601
Sodium Alginate 0.40 Yellow 4.9 4.5 49,041
Sodium Alginate 0.20 Yellow 4.7 4.6 50,227
Sodium Alginate 0.04 Yellow 4.6 4.9 54,517
H-γ-PGA (Na) 0.10 Yellow 5.4 5.7 51,564
H-γ-PGA (Na) 0.05 Yellow 5.2 5.8 54,922
H-γ-PGA (Na) 0.01 Yellow 5.2 5.8 57,441
L-γ-PGA (Na) 0.10 Yellow 5.6 5.4 52,542
L-γ-PGA (Na) 0.05 Yellow 5.3 5.6 54,098
L-γ-PGA (Na) 0.01 Yellow 5.3 5.5 57,130
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A γ-PGA (Na) with high molecular weight. Bγ-PGA (Na) with low molecular weight.

Tsami et al. [27] also reported that pectin-sugar powder made by vacuum drying exhibited deeper color than with freeze drying. With spray drying, the maltodextrin carrier produced the highest yield of powder, followed by gelatin and sodium alginate. With sodium alginate as carrier, freeze drying generated the greatest yield of powder, followed by vacuum drying and spray drying. It was also observed that the powder weight increased following a rise in carrier content, which resulted in a decrease of isoflavone level because of the dilution effect.

Conclusions

With spray drying, use of a level of 40 % maltodextrin as carrier results in a higher yield of isoflavone powder than with 10 % gelatin or 1 % sodium alginate as carriers. Freeze drying can generate a larger amount of isoflavone powder than vacuum drying and spray drying with 1 % sodium alginate as carrier. Compared to sodium alginate, an extremely low level of γ-PGA (0.003 %) as carrier can be used to produce powder containing high amount of total isoflavone. The results of this study may provide a basis for possible commercial production of isoflavone powder in the food industry. Further research is necessary to study the stability of isoflavone powder during storage.

Experimental Section

Materials

Soybean cake (50 kg) was purchased from Chung-Lian Oil Co. (Taichung, Taiwan), ground into powder and stored at -20° for use. Twelve isoflavone standards were obtained from LC Laboratories (Woburn, MA, USA), Sigma (St. Louis, MO, USA) and Nacalai (Kyoto, Japan). Formononetin (internal standard) was from Sigma. HPLC-grade acetonitrile was from Merck (Darmstadt, Germany). Analytical-grade ethanol (95%) was from Taiwan Tobacco and Wine Co. (Tainan, Taiwan). Deionized water was made using a Milli-Q water purification system (Millipore Co., Bedford, MA, USA). Gelatin, maltodextrin and sodium alginate were from Cheng-Fang Co. (Taipei, Taiwan). Both high-molecular-weight-γ-PGA (H-γ-PGA, MW 800 kDa) and low-molecular-weight-γ-PGA (L-γ-PGA, MW 200-400 kDa) in Na form were provided by Vedan Enterprise Corp. (Taichung, Taiwan).

Instrumentation

The HPLC instrument was composed of a Rheodyne 7161 injector (CA, USA), two Jasco pumps (PU 980 and PU 1980) and a Jasco MD-915 photodiode-array detector (Tokyo, Japan). Borwin computer software was used to process data. A Vydac 201TP54 C18 column (250 x 4.6 mm I.D., 5 μm) was used to separate the 12 isoflavones in soybean cake and powder. The Büchi Mini B290 spray dryer was from Büchi Co. (Flawil, Switzerland). The FD24 freeze dryer was from Ching-Ming Co. (Taipei, Taiwan). The KVED-1 vacuum dryer was from Tong-Yuan Co. (Taipei, Taiwan). The Sorvall RC5C high-speed centrifuge was from Du Pont Co. (Wilmington, Delaware, USA). The PT-MR 3000 homogenizer was from Kinematica Co. (Switzerland).

Extraction of isoflavone from soybean cake

Soybean cake (3 kg) was mixed with deionized water-ethanol (1:1, v/v, 9-L) in a flask, and the mixture was shaken for 2 h. Then the crude extract was divided into 10 portions and each subjected to centrifugation at 6,000 rpm for 20 min (25 °C), after which all the supernatants were collected and filtered through a glass filter paper. All the filtrates were combined to give approximately 4500-mL of filtrate that was used as raw material for processing the powder.

Processing of isoflavone powder by spray drying

Because of differences in solubility of the carriers in isoflavone extract, various proportions of gelatin, maltodextrin or sodium alginate to isoflavone extract have to be tried to find the optimum concentration. Four concentrations of 5, 10, 15 and 20 % gelatin in isoflavone extract were prepared by mixing 5, 10, 15 and 20 g of gelatin with 95, 90, 85 and 80 g of isoflavone extract, respectively. Similarly, four concentrations of 10, 20, 30 and 40 % maltodextrin in isoflavone extract were prepared by mixing 10, 20, 30 and 40 g of maltodextrin with 90, 80, 70 and 60 g of isoflavone extract, respectively. For sodium alginate, it was first dissolved in deionized water for a concentration of 4 % because of its poor solubility in isoflavone extract. Then a sodium alginate solution (25-g) was mixed with isoflavone extract (75-g) to obtain a final concentration of 1 %. Each carrier-containing isoflavone solution was subjected to homogenization for 10 min and then spray dried under the following conditions: feed rate 5, 10, 15 and 20 % and inlet temperatures 150, 160, 170 and 180 °C for gelatin solution; feed rates 10, 15, 20 and 25 % and inlet temperatures 150, 160, 170 and 180 °C for maltodextrin solution; feed rates 5, 7 and 10 %, and inlet temperatures 110, 130, 150 and 180 °C for sodium alginate solution. These conditions were chosen based on the different characteristics of carrier solutions like viscosity and solid content. After processing into powder, a sample (0.05 g) of either gelatin- and sodium alginate-containing powder or a sample (0.25 g) of maltodextrin-containing powder was separately dissolved in deionized water (5-mL). Then each solution (500 μL) was mixed with formononetin internal standard (200 μg/mL, 100 μL), followed by addition of deionized water (400-μL) and filtration through a 0.2-μm membrane filter. A 20-μL sample was injected for HPLC analysis.

Processing of isoflavone powder by vacuum drying

As the powder formation during vacuum drying can be affected by solids content, it is necessary to find out the optimum proportion of carrier to isoflavone extract. A concentration of 2 % sodium alginate and H-γ-PGA in deionized water was prepared separately, following by collecting 50, 20, 10, 5 and 2.5 g and mixing with 50, 80, 90, 95 and 97.5 g of isoflavone extracts, respectively. Proportions of carrier (sodium alginate or H-γ-PGA) to isoflavone extract at 1:1, 1:4, 1:9, 1:19 and 1:39 (w/w) were thus obtained with final concentrations of carrier of 1.0, 0.4, 0.2, 0.1 and 0.05%, respectively. After homogenization for 10 min, each solution was vacuum dried at 60 °C under 4 cm Hg for 48 h and then ground into powder. A powder sample (0.05 g) was dissolved in deionized water (5-mL), of which an aliquot (500-μL) was collected and mixed with formononetin internal standard (200 μg/mL, 100 μL) and diluted with deionized water (400 μL). The solution was filtered through a 0.2-μm membrane filter and 20 μL was injected for HPLC analysis.

To investigate the possibility of using a low level of carrier for production of isoflavone powder, four concentrations of 2, 1, 0.2 and 0.1 % of aqueous sodium alginate solution were prepared, and 20-g of each was collected and mixed with 80 g of isoflavone extract to obtain final concentrations of 0.4, 0.2, 0.04 and 0.02 %, respectively. Each solution was homogenized for 10 min and then vacuum dried at 60 °C under 4 cm Hg for 36 h. Likewise, four concentrations of 2, 1, 0.2 and 0.1 % aqueous solutions of both H-γ-PGA and L-γ-PGA were prepared, in which 5-g of each was collected and mixed with 95-g of isoflavone extract for the final concentrations at 0.1, 0.05, 0.01 and 0.005 %, respectively, and each solution was subjected to homogenization and vacuum drying. A 0.05-g of sample powder was collected for HPLC analysis following the same procedure described above.

Processing of isoflavone powder by freeze drying

For freeze drying, both sodium alginate and γ-PGA were not directly dissolved in isoflavone extract containing 50 % ethanol because of poor solubility. Instead, they were dissolved in deionized water to make freezing possible. Six concentrations of 4, 2, 0.4, 0.2, 0.04 and 0.02 % of sodium alginate in water were prepared, and 25-g of each was mixed with 75-g of isoflavone extract for the final concentrations of 1, 0.5, 0.1, 0.05, 0.01 and 0.005 %, respectively. After homogenization for 10 min, each solution was placed in a freezer (–30 °C) for 24 h for freezing. Similarly, six concentrations of 2, 1, 0.5, 0.1, 0.05 and 0.01 % of γ-PGA dissolved in water were prepared, and 40-g of each was mixed with 100-g of isoflavone extract giving final concentrations of 0.57, 0.28, 0.14, 0.028, 0.014 and 0.003 %, respectively. Each solution was homogenized for 10 min and then placed in a freezer (–30 °C) for 24 h. Next, all the sodium alginate and γ-PGA solutions were freeze dried at –40° under 60 millitorr for 36 h and subjected to grinding for powder production. A powder sample (0.05-g) was dissolved in deionized water (5-mL), of which 500 μL was collected and mixed with 100-μL internal standard formononetin (200 μg/mL) and 400-μL deionized water. The solution was filtered through a 0.2-μm membrane filter and a 20-μL sample was injected for HPLC analysis.

Identification and quantitation of isoflavone

The various isoflavones in soybean cake and powder were identified by comparing retention times and absorption spectra of unknown peaks with reference standards and co-chromatography with added standards. For quantitation, each isoflavone standard was dissolved in methanol for a concentration of 200 or 2000 μg/mL, while the internal standard (formononetin) was dissolved in methanol for a concentration of 200 μg/mL. Three standard concentrations of 1, 5 and 10 μg/mL of the 12 isoflavones were each prepared by mixing 25, 125 and 250 μL (from 200 μg/mL), respectively, with 500 μL internal standard (from 200 μg/mL) and diluting to 5 mL with methanol. Likewise, the other three standard concentrations of 20, 50 and 100 μg/mL for the 12 isoflavones were each prepared by mixing 50, 125 and 250 μL (from 2000 μg/mL), respectively, with 500 μL internal standard (from 200 μg/mL) and diluting to 5 mL with methanol. The final concentration of internal standard in each standard solution was 20 μg/mL. A 20-μL isoflavone standard solution of each was injected and 12 standard curves were prepared by plotting concentration ratio against area ratio, and the linear regression equation and correlation coefficient (r2) of each standard curve was calculated. A gradient mobile phase developed by Hsieh et al. [28] was used to separate the 12 isoflavones: a mixture of acetonitrile (A) and deionized water (B) (8:92, v/v) was used initially, increased to 10% A in 2 min, 12% A in 3 min, 22% A in 10 min, 23% A in 11 min, 35% A in 12 min, 50% A in 13 min, maintained for 3 min and returned to 8% A in 20 min. All 12 isoflavones were adequately resolved within 15 min with a flow rate of 2.0 mL/min and a column temperature of 35 °C and detection wavelength at 262 nm. Each isoflavone was quantified using a formula as described by Kao and Chen [6]. Duplicate analyses were performed, and the data were processed using SAS [29] and subjected to analysis of variance and Duncan’s multiple range test for comparison (α=0.05).

Footnotes

Sample Availability: Available from the authors.

References

  • 1.Setchell K.D.R., Cassidy A. Dietary isoflavones: biological effects and relevance to human health. J. Nutr. 1999;129:758s–767s. doi: 10.1093/jn/129.3.758S. [DOI] [PubMed] [Google Scholar]
  • 2.Messina M., Gugger E.T., Alekel D.L. Handbook of Nutraceuticals and Functional Foods. CRC Press LLC; Boca Raton, FL, USA: 2001. Soy protein, soybean isoflavones and bone health: a review of the animal and human data; pp. 77–98. [Google Scholar]
  • 3.Demonty I., Lamarche B., Jones P.J.H. Role of isoflavones in the hypocholesterolemic effect of soy. Nutr. Rev. 2003;61:189–203. doi: 10.1301/nr.2003.jun.189-203. [DOI] [PubMed] [Google Scholar]
  • 4.Kao T.H., Lu. Y.F., Hsieh H.C., Chen B.H. Stability of isoflavone glucosides during processing of soymilk and tofu. Food Res. Intl. 2004;37:891–900. [Google Scholar]
  • 5.Chien J.T., Hsieh H.C., Kao T.H., Chen B.H. Kinetic model for studying the conversion and degradation of isoflavones during heating. Food Chem. 2005;91:425–434. doi: 10.1016/j.foodchem.2004.06.023. [DOI] [Google Scholar]
  • 6.Kao T.H., Chen B.H. An improved method for determination of isoflavones in soybean powder by liquid chromatography. Chromatographia. 2002;56:423–430. doi: 10.1007/BF02492004. [DOI] [Google Scholar]
  • 7.Kao T.H., Lu Y.F., Chen B.H. Preparative chromatography of four groups of isoflavones from soybean cake. Euro. Food Res. Technol. 2005;221:459–465. doi: 10.1007/s00217-005-1206-4. [DOI] [Google Scholar]
  • 8.Wang C.Y., Chen B.H. Tomato pulp as source for the production of lycopene powder containing high proportion of cis isomers. Euro. Food Res. Technol. 2006;222:347–353. doi: 10.1007/s00217-005-0058-2. [DOI] [Google Scholar]
  • 9.Bhandari B.R., Dumoulin E.D., Richard H.M.J., Noleau I., Lebert A.M. Flavor encapsulation by spray drying: application to citral and linalyl acetate. J. Food Sci. 1992;57:217–220. doi: 10.1111/j.1365-2621.1992.tb05459.x. [DOI] [Google Scholar]
  • 10.Jaya S., Das H. Effect of maltodextrin, glycerol monostearate and tricalcium phosphate on vacuum dried mango powder properties. J. Food Eng. 2004;63:125–134. doi: 10.1016/S0260-8774(03)00135-3. [DOI] [Google Scholar]
  • 11.Cano-Chauca M.P., Stringheta P.C., Ramos A.M., Cal-Vidal J. Effect of carriers on the microstructure of mango powder obtained by spray drying and its functional characterization. Innov. Food Sci. Emerg. Technol. 2005;6:420–428. doi: 10.1016/j.ifset.2005.05.003. [DOI] [Google Scholar]
  • 12.Inbaraj B.S., Chiu C.P., Ho G.H., Yang J., Chen B.H. Removal of cationic dyes from aqueous solution using an anionic poly-γ-glutamic acid-based adsorbent. J. Hazard. Mater. 2006;137:226–234. doi: 10.1016/j.jhazmat.2006.01.057. [DOI] [PubMed] [Google Scholar]
  • 13.Inbaraj B.S., Chiu C.P., Chiu Y.T., Ho G.H., Yang J., Chen B.H. Effect of pH on binding of mutagenic heterocyclic amines by the natural biopolymer poly(γ-glutamic acid) J. Agric. Food Chem. 2006;54:6452–6459. doi: 10.1021/jf061300o. [DOI] [PubMed] [Google Scholar]
  • 14.Inbaraj B.S., Chien J.T., Ho G.H., Yang J., Chen B.H. Equilibrium and kinetic studies on sorption of basic dyes by a natural biopolymer poly(γ-glutamic acid) Biochem. Eng. J. 2006;31:204–215. doi: 10.1016/j.bej.2006.08.001. [DOI] [Google Scholar]
  • 15.Gutnick D.L., Bach H. Engineering bacterial biopolymer for the biosorption of heavy metals: new products and novel formulations. Appl. Microbiol. Biotechnol. 2000;54:451–460. doi: 10.1007/s002530000438. [DOI] [PubMed] [Google Scholar]
  • 16.Murphy P.A., Song T., Buseman G., Barua K. Isoflavones in soy-based infant formulas. J. Agric. Food Chem. 1997;45:4635–4638. [Google Scholar]
  • 17.Franke A.A., Hankin J.H., Yu M.C., Maskarinec G., Low S.H., Cluster L.J. Isoflavone levels in soy foods consumed by multiethnic populations in Singapore and Hawaii. J. Agric. Food Chem. 1999;47:977–986. doi: 10.1021/jf9808832. [DOI] [PubMed] [Google Scholar]
  • 18.Wang C., Ma Q., Pagadala S., Sherrard M.S., Krishnan P.G. Changes of isoflavones during processing of soy protein isolates. JAOCS. 1998;75:337–341. [Google Scholar]
  • 19.Coward L., Smith M., Kirk M., Barnes S. Chemical modification of isoflavones in soyfoods during cooking and processing. Am. J. Clin. Nutr. 1998;68:1468s–1491s. doi: 10.1093/ajcn/68.6.1486S. [DOI] [PubMed] [Google Scholar]
  • 20.Lee S.J., Ahn J.K., Kim S.H., Kim J.T., Han S.J., Jung M.Y., Chung I.M. Variation in isoflavone of soybean cultivars with location and storage duration. J. Agric. Food Chem. 2003;51:3382–3389. doi: 10.1021/jf0261405. [DOI] [PubMed] [Google Scholar]
  • 21.Fernandez-Perez V., Tapaidor J., Martin A., Luque de Castro M.D. Optimization of the drying step for preparing a new commercial powdered soup. Innov. Food Sci. Emerg. Technol. 2004;5:361–368. doi: 10.1016/j.ifset.2004.05.001. [DOI] [Google Scholar]
  • 22.Goula A.M., Adamopoulos K.G. Spray drying of tomato pulp in dehumidified air: II. The effect on powder properties. J. Food Eng. 2005;66:35–42. doi: 10.1016/j.jfoodeng.2004.02.031. [DOI] [Google Scholar]
  • 23.Maury M., Murphy K., Kumar S., Shi L., Lee G. Effects of process variables on the powder yield of spray-dried trehalose on a laboratory spray-dryer. Euro. J. Pharm. Biopharm. 2005;59:565–573. doi: 10.1016/j.ejpb.2004.10.002. [DOI] [PubMed] [Google Scholar]
  • 24.Krishnan S., Bhosale R., Singhal R.S. Microencapsulation of cardamon oleoresin: evaluation of blends of gum Arabic, maltodextrin and modified startch as wall materials. Carbohydr. Polym. 2005;61:95–102. doi: 10.1016/j.carbpol.2005.02.020. [DOI] [Google Scholar]
  • 25.Monsoor M.A. Effect of drying methods on the functional properties of soy hull pectin. Carbohydr. Polym. 2005;61:362–367. doi: 10.1016/j.carbpol.2005.06.009. [DOI] [Google Scholar]
  • 26.Cohen J.S., Yang T.C.S. Progress in food dehydration. Trends Food Sci. Technol. 1995;6:20–25. doi: 10.1016/S0924-2244(00)88913-X. [DOI] [Google Scholar]
  • 27.Tsami E., Krokida M.K., Drouzas A.E. Effect of drying method on the sorption characteristics of model fruit powder. J. Food Eng. 1999;38:381–392. [Google Scholar]
  • 28.Hsieh H.C., Kao T.H., Chen B.H. A fast HPLC method for analysis of isoflavones in soybean. J. Liquid Chrom. Related. Technol. 2004;27:315–324. doi: 10.1081/JLC-120027102. [DOI] [Google Scholar]
  • 29.SAS Instruments; Cary, NC, USA: 2004. SAS/STAT Guide for Personal Computers. version 6. [Google Scholar]

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