以低溫乾燥法生產食用乳酸菌菌粉

Abstract

乳酸菌發酵乳製品是在世界各地廣為流行的健康食品之一，在台灣，由於其特殊的風味(傳統上以液態及凝態產品為主)，國人接受的程度並不是很高。而以固體型式出現之乳酸菌發酵乳製品一方面因為沒有發酵產品所特有的味道，另一方面也由於其口味富於彈性(可隨著國人的喜好來作調整)，再加上產品之多樣性，在國內的健康食品市場上有逐漸受到重視的趨勢。 低溫乾燥法是有別於噴霧乾燥法及冷凍乾燥法的菌粉製作方法，其原理頗類似於傳統之烘箱烘乾法；相較於噴霧乾燥及冷凍乾燥法而言，低成本、設備及操作簡單、危險性低是低溫乾燥法特點。經低溫乾燥法處理後，標準乳酸菌菌株(CCRC14009,CCRC14080,CCRC10697,CCRC12936)之生長特性及菌體活性都不受影響；而菌體之存活率則在各菌株之間有極大的差異，由CCRC14009在35℃時將近98%的存活率，至CCRC12936在50℃時低於20%之存活率。一般而言，菌體之存活率會隨著溫度的升高而降低，但對大部份標準菌株而言，除CCRC14080及供試菌粉外，因溫度差異所造成之存活率變化不很顯著(<6%)；這顯示在實驗中若以脫脂奶粉為賦形劑，將可以對菌體提供相當的保護；而若改以馬鈴薯澱粉或乳糖為賦形劑時，菌體在乾造後的第4個小時內，存活率就不及原來菌液中的1%了。在水含量及水活性方面，溫度愈高，其值愈低；低的水含量及水活性將有助於乾燥菌粉之保存。而若在整個乾燥製程中加入乾燥劑(CaCl2)，可使乾燥菌粉之水含量及水活性於一短時間內(約四小時左右)即達一低值(水含量<5%，水活性<0.3)，對於以較低溫35℃處理之乾燥菌粉來說此種現象尤其顯著，這將有助於縮減低溫乾燥製程所需的時間。

Lactic acid bacteria (LAB) fermented products is one of the most popular health foods around the world, but in Taiwan, not so many people familiar to these products because of their specific flavor. Over the past few years, dried cell products of LAB has grown considerably in Taiwan, because these dried cell products don't have the specific flavor of fermented products. Besides, the formula and flavor can vary with the different tastes. Several investigators have considered the possibility of drying large quantities of bacterial cultures, with the idea of using it as a method to replace the usual liquid bulk starter in the production of fermented dairy products. For this purpose, low-temperature oven drying method would be preferable to freeze-drying and spray drying because of the lower cost, ease for operation and the safety reason. The growth kinetics and the pH evolution activities of these bacteria strains (CCRC14009, CCRC14080,CCRC12936, and CCRC10697) were not affected by this drying process; however, the viability of LAB upon drying varies between different strains. Strain CCRC14009 had the hightest survival ratio, 98%, at 35 ℃; strain CCRC12936 had the lowest one smaller than 20% when drying at 50℃,. Three different compatible excipients, including skim milk, patato starch and lactose, were used to investigate for their protective effects on the dried cell during drying process. The highest survival rate was observed when the skim milk was added as the excipient for all these tested strains or yoghurt powder. However, the survival ratio of LAB would be worse than 1% if potato starch and lactose was used as the exipients. Generally, the viability of microorganism decreased as the drying temperature incresed, but in our experiment there was little difference in the decline in numbers of total lactic acid bacteria owing to temperature changes with the exception of CCRC14080 and yoghurt powder. The amount of water present in the dried cell product has a significant impact on stability. It was found that placing a drying agent (such as CaCl2) in the oven made the drying process more quickly and efficiently. If we had it in the drying process, the water activity (ａw) and relative moisture content (rmc) could attain to a lower level (ａw <0.3， rmc<5%) at about four hours after the drying process was started and the survival ratio would not be affected.