The Production of Lactic Acid Bacteria Powder by Low-temperature Oven Drying Method
Chester S. Ho
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.
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