| Summary: | 碩士 === 國立嘉義大學 === 食品科學系碩士班 === 91 === Abstract
Isoflavones are novel functional ingredients of soybeans and other related bean products. With various processing conditions and degrees, the amount of isoflavone contained in soybean products also changes substantially. This thesis aimed at functional enhancement of tofu products, addressing the influences of different processing conditions on transformation of isoflavones by two aspects of small-amount and large-amount tofu preparation. Soybeans were soaked with water, steam-cooked, inoculated with the conidia of Aspergillus oryzae , incubated 3 days for koji , and pulverized for koji power preparation. The koji powers were mixed and extracted with water in various proportions to prepare crude koji enzyme extractives as the source of β-glucosidase. When making soymilk, the soybeans were soaked with water at ambient temperature for 8 hours, daidzein and genistein contents of soybeans increased remarkably after soaking while the amount of isoflavone glucosides of daidzin and genistin decreased. In addition, there was some isoflavones existing in the water where the soybeans were soaked in. This indicates that during the process of soaking, there was a small amount of isoflavone lost from the soybeans. When determining the activity of β-glucosidase within crude koji enzyme extractives through different extraction ratio (50%, 25%, 16.7%, 12.5% and 10%, w/w) at 30℃, increased remarkably with an increase of extraction ratio. Aliquots of 3kg soymilk were taken, supplemented with the crude koji enzyme extractive of the extraction ratio 25% at 35±1.5℃ and reacted for various periods of time (0, 30, 60, 120 and 300 min), and then were made into tofu. The experiment results indicated that the amount of daidzein and genistein contained in soymilk was greatest during the 120-min reaction time and was smallest when the reaction time was 0 min; and the amount of daidzin and genistin was greatest when the reaction time was 0 minute, and was smallest during the 120 min reaction time. The amount of daidzein and genistein contained in tofu was greatest during the 120 min reaction time and was smallest when the reaction time was 0 min. When the reaction time was was within less than 120 min, the yield of tofu was virtually the same (P>0.05); however, when the reaction time was up to 300 min, the yield of tofu decreased remarkably (P<0.05). In respect of quality evaluation, after being supplemented with crude koji enzyme extractives, the pH values and microbial populations of the soymilks was the same when the reaction times were in with 120 min; but when the reaction time was up to 300 min, the pH value went down strikingly and the microbial populations also increased substantially. To integrate all experiment results, it was obvious that tofu, which was made from soymilk kept under the temperature of 35±1.5℃, supplemented with crude koji enzyme extractive of extraction ratio 25% (0.33%), and reacted for 120 min, was of the highest yield, containing the highest amount of active isoflavones and rendering acceptable quality.
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