title: Isoflavone Profiles and Kinetic Changes during Ultra-High Temperature Processing of Soymilk.
abstract: Isoflavone profile is greatly affected by heating process. However, kinetic analyses of isoflavone conversion and degradation using a continuous industry processing method have never been characterized. In this study, Proto soybean was soaked and blanched at 80 °C for 2 min and then processed into soymilk, which underwent UHT (ultra-high temperature) at 135 to 150 °C for 10 to 50 s with a pilot plant-scale Microthermics processor. The isoflavone profile was determined at different time/temperature combinations. The results showed that all isoflavone forms exhibited distinct changing patterns over time. In the soymilk under UHT conditions, the degradation (disappearance) of malonyldaizin and malonylgenistin exhibited first-order kinetics with activation energies of 59 and 84 kj/mole, respectively. At all UHT temperatures, malonylgenistin showed higher rate constants than malonyldaidzin. However, malonylglycitin changed irregularly under these UHT temperatures. The increase of genistin, daidzin, glycitein and acetlydaidzin during heating demonstrated zero-order kinetics and the rate constants increased with temperature except for the conditions of 145 to 150 °C for 50 s. Overall, genistein series exhibited higher stability than daidzein series. Under all UHT conditions, total isoflavone decreased from 12% to 24%.
authors.affiliation: Dept. of Food Science, Nutrition and Health Promotion, Mississippi State Univ, Starkville, MS, 39761, U.S.A.
authors.forename: Yan
authors.initials: Y
authors.lastname: Zhang
authors.affiliation: Dept. of Food Science, Nutrition and Health Promotion, Mississippi State Univ, Starkville, MS, 39761, U.S.A.
authors.forename: Sam K C
authors.initials: SK
authors.lastname: Chang
mesh_terms: D005511:Food Handling / Q000379:methods*; D005960:Glucosides / Q000032:analysis; D006358:Hot Temperature; D006801:Humans; D007529:Isoflavones / Q000032:analysis*; D007700:Kinetics; D041942:Soy Milk / Q000737:chemistry*; D013025:Glycine max / Q000737:chemistry*
chemical_list: D005960:Glucosides; D007529:Isoflavones; C040641:genistin; C521200:malonylgenistin; C013908:daidzin; C459793:6''-O-malonyldaidzin; C004742:daidzein; C086566:glycitein; C433283:glycitin
keywords: UHT processing; conversion; degradation; isoflavones in soymilk; kinetic analysis