以台灣式製程製備豆腐乳時風味物質組成及抗致突變性之變化

Abstract

豆腐乳 (Sufu) 是軟質乾酪狀由黃豆凝結塊(豆腐)製成之東方發酵黃豆食品。台式豆腐乳之釀造過程包括先製備鹽漬豆腐塊，以Aspergillus oryzae為發酵之豆米麴，然後再將鹽漬豆腐塊浸漬於麴醪 (豆米麴加糖水) 中發酵而成。本研究主要在探討台式豆腐乳發酵過程中 (揮發性成分，醣類與有機酸組成分) 與抗致突變活性變化之情形。 結果顯示隨著發酵時間增加，大部分揮發性成分之含量亦隨之上升，尤其是醇類及酯類。豆腐乳樣品中共鑑定出90種揮發性成分，其中包括22種醇類，22種酯類，21種醛類，10種脂肪酸，9種酮類與6種其它成分。 未發酵之豆腐中主要之醣類為水蘇糖，棉子糖，蔗糖，葡萄糖與果糖。而豆米麴醪中除發現上述之醣類外還含有麥芽糖與半乳糖且有大量之棉子糖與葡萄糖。大致而言，水蘇糖、棉子糖及蔗糖含量隨發酵時間之增加而減少，但單醣含量則隨發酵時間增加而上升，發酵46天後，豆腐乳與豆米麴中以葡萄糖之含量最多。 在發酵8天後豆腐乳與豆米麴中檢測出四種有機酸，包括草酸，乳酸，醋酸及檸檬酸，其中以醋酸含量最高。大致而言，除檸檬酸外，豆腐乳中有機酸含量皆於發酵第8天達到最高。隨著發酵時間增加，豆米麴中之乳酸，醋酸及檸檬酸含量也隨發酵時間之延長而增加，但草酸則呈現下降之趨勢。 此外，豆腐塊對4-NQO (4-nitroquinoline N-oxide) 與DMAB (3, 2-Dimethyl-4-amino-biphenyl hydrochloride) 所呈現之抗致突變活性隨著發酵時間之延長而增加。

Sufu, the oriental fermented product of soy bean, is a soft cheese-like product made from cubes of soy bean curd (tofu). During the Taiwanese manufacturing process of sufu, the salted-tofu cubes and koji mash were first prepared. Fermentation was then proceeded by soaking the salted-tofu cubes in the prepared koji mash. Koji mash was prepared by mixing Aspergillus oryzae fermented rice-soybean koji with syrup containing 65% sucrose. In this study, changes in volatile, sugar, organic acid constituents and antimutagenicity of sufu during fermentation were investigated. A total of 90 compounds of volatiles including 22 alcohols, 22 esters, 21 aldehydes, 10 fatty acids, 9 ketones and 6 other compounds from the sufu samples examined were identified. It was found that as the fermentation period was extended, contents of nearly all volatile fractions increased gradually, especially alcohols and ester. The main sugars noted in the non-fermented tofu were stachyose, raffinose, sucrose, glucose and fructose. As the fermentation time extended, generally, content of stachyose, raffinose and sucrose decreased, while content of glucose and fructose increased. Glucose was the most abundant sugar detected in the 46-day-sufu. Four organic acids including oxalic, lactic, acetic and citric acid were detected from the tofu and rice-soybean koji samples after fermentation for 8 days or longer. Acetic acid was the most predominant organic detected. It was generally found that content of these organic acids, except citric acid in the tofu cube increased to the highest point after 8 days of fermentation. The level of lactic, acetic and citric acid also increased in the collected koji as the fermentation time was extended. Methanol extract of tofu showed antimutagenicity against 4-nitroquinoline-N-oxide (4-NQO) and 3, 2′-dimethyl-4-amino-biphenyl (DMAB). Fermentation was found to enhance the antimutagenicity of tofu extract. Antimutagenicity of tofu extract increased with the extension of fermentation time. Beside, sufu extract exerted a significantly higher (p < 0.05) antimutagenicity against DMAB than 4-NQO.