柵欄技術應用於桃園大溪地區豆腐乾衛生品質之改善

Abstract

本研究進行桃園大溪地區豆腐乾製程與產品之衛生概況結果為生豆、豆乳至豆腐乾，半成品至成品的過程中，水分含量70 %至90 %不等，pH值介於6至7左右，為一般微生物適合生長的環境。該地區豆腐乾防腐劑添加過量的情況已豆腐乾類產品最為嚴重，11件豆腐乾樣品中有6件苯甲酸使用過量的情形。桃園縣大溪地區市售四種豆腐乾產品於25℃儲存12小時後，除了過氧化氫殘留量超過0.1 %之產品菌數沒有明顯增加外，菌數均達107 CFU/g~108 CFU/g，且表面有粘性物質產生及不良氣味，於5℃之儲存下市售產品儲存期間菌數之下降不明顯。實驗自四種豆腐乾產品中所分離出之腐敗微生物為Acinetobacter lwoffii，此菌為不具發酵特性之格蘭氏陰性桿菌。 本實驗目的為應用符合GRAS之物質於豆腐乾製程以改目前善大溪地區豆腐乾之儲存情況與衛生品質。依據反應曲面法之結果找出培養溫度25℃下，苯甲酸濃度400~500 ppm、磷酸濃度300~400 ppm時，Serratia liquefaciens有較低之平均生長速度0.002至0.004 (OD600/hr)。中藥水溶液對豆腐乾腐敗菌之抑制實驗結果丁香與肉桂對A. lwoffii最小抑制濃度為3 % (w/v)，丁香對P. fluorescens最小抑制濃度為16 %，大茴香對S. liquefaciens最小抑制濃度為6 %。 豆腐乾經由以下列滷汁配方：苯甲酸420 ppm、檸檬酸鈉300 ppm或磷酸300 ppm、10 %中藥(肉桂:大茴香:丁香=3 :4 :3)以100℃滷煮15分鐘處理後，豆腐乾pH値從6.4降至5.5或5.2，並且於25℃儲存二天，表面未有粘性物質產生且無不良氣味，相較於大溪地區市售豆腐乾之儲存情況儲存期限從12小時延長至48小時，4℃下豆腐乾之總生菌數 隨著儲存時間之延長而下降，顯示本實驗配方可延緩豆腐乾在儲存期間之腐敗速度。

The dried soybean curds from Taoyuan County contains about, 70-90 % water, and water activity is about 0.8.The pH is around 6.0 - 7.0 which provides a good growth condition for spoilage organisms. Generally, after 12 hours of storage under room temperature, dried soybean curd will spoil and form slime on the surface. The spoilage organism isolated from dried soybean curd of Taoyuan County in this study was found to be Acinetobacter sp. Objective of this study is to improve the microbial quality of dried soybean curd in Taoyuan- Daxi area by combine several GRAS materials. According to the results of RSM, we decide the use of benzoic acid (420 ppm) and phosphoric acid (300 ppm) in treating dried soybean curd when the temperature of environment is 25℃ and the pH of soybean curd is 5 to minimize the growth of Serratia liquefaciens. The growth of indicator organisms, Serratia liquefaciens, can be inhibited by anise, cinnamon and clove and the minimum inhibitory concentration for anise, cinnamon, and clove are 6 %, 12% and 20 %, respectively. Pseudomonas fluorescens can be inhibited by clove, with a minimum inhibitory concentration of 16 %. While Acinetobacter lwoffii can be inhibited by cinnamon and clove, both with a minimum inhibitory concentration of 3 %. The combinations of benzoic acid 420 ppm, phosphoric acid or citric acid 300 ppm, cinnamon 3 %, anise 4 %, and clove 3 % in the bittern could extend the shelf life of dried soybean curd from 12 hours to 48 hours under 25℃. The total count of dried soybean curd decrease with the storage time under 5℃.