SOYBEAN AND HEALTH - University of Macau Library

26Soybean and HealthIsoflavones, which are mostly present as 6-O-malonylglucoside and β-glucoside conjugatesand associated with proteins in soybean, are also broken down by heat treatment andfermentation (Barnes et al., 1998; H.K. Choi et al., 2007). During preparation of fermentedsoy foods, 6-O-malonylglucosides, the most prevalent soybean isoflavones, are converted to6-O-acetylglucosides or β-glucosides by heating, and β-glucosides are de-conjugated by theaction of β-glucosidases secreted by fermentation microorganisms (Murphy et al., 1999).Most isoflavones are not enzymatically hydrolyzed during short-term fermentation, incontrast to long-term fermentation in which 6-ο-malonylglucoside content declines withincreasing fermentation time with concomitant increases in unconjugated aglycones(genistein and daizein). Total isoflavone content in raw soybeans was about 3,000mg/kgand this decreased by about 50% during cooking prior to chungkukjang preparation. Totalisoflavone content of chungkukjang changed slightly during 45 hr fermentation. However,the content of isoflavone glycosides, consisting mainly of daizein, glycitin and genistin,decreased by about 40% during 45 hr fermentation, while the contents of free isoflavonesincluding, daidzein, glycitein and genistein showed a dramatic increase duringchungkukjang fermentation, with 2.9-, 54.0-, and 20.6 fold increases in concentration,respectively, by end of fermentation (45 hr) (Jang et al., 2006) (Table 1).IsoflavoneFermentation time (hr)raw 0 5 10 15 20 25 30 35 40 45Daidzin 99±31 1) 454±17 425±24 401±25 327±28 280±5 245±22 191±5 192±7 212±7 204±10Glycitin 45±15 101±5 101±5 87±6 77±6 60±6 65±26 69±4 34±5 41±4 35±4Genistin 184±50 548±22 568±19 513±30 476±32401±14 333±16 295±12 289±17 281±14 259±22M-Daidzin 1009±29 129±41 127±29 82±7 97±12 75±9 120±54 96±30 113±22 134±10 120±27M-Glycitin 157±2 10±5 3±0 12±5 63±5 144±3 217±1 220±0 225±7 244±5 231±1M-Genistin 1111±8 tr 2) tr tr tr tr tr tr tr tr trA-Daidzin 85±47 75±3 64±8 54±2 56±5 83±2 93±2 91±3 94±2 99±5 97±6A-Glycitin 101±174 10±2 7±1 5±4 11±5 29±12 44±7 50±10 46±9 38±12 33±12A-Genistin tr 43±3 47±3 37±3 35±3 45±0 38±5 41±6 39±5 31±6 27±5Total glycoside 2818 1370 1341 1191 1142 1117 1156 1020 1033 1079 1006Daidzein tr 33±6 50±8 36±2 69±6 79±2 82±2 107±3 112±5 102±6 114±7Glycitein tr 4±3 3±4 5±3 43±6 100±0 141±4 152±2 156±2 171±1 165±2Genistein 7±2 5±4 16±3 9±1 32±9 45±1 39±1 71±4 72±5 52±3 64±4Total aglycone 7 43 69 51 143 223 262 330 341 325 342Total isoflavones 2825 1413 1410 1242 1285 1340 1418 1350 1370 1404 13481)Values are mean ± SD (n-3). 2) tr : trace.Table 1. Isoflavone contents (μg/g dry water) of chungkukjang collected at variousfermentation times (Jang et al., 2006).We also investigated changes in isoflavone contents during the fermentation of meju anddoenjang (Jang et al., 2008) (Table 2-3). Most of isoflavones in cooked and unfermentedsoybean existed as glycosides (Table 2), accounting for total isoflavones. While isoflavone