Flora of Lactic Acid Bacteria in a Soaked Fluid of Salted "Daikon" under a Nitrogen Gas-Packing System

Abstract

By using a nitrogen gas-packing system, salted "Daikon" (Japanese radish) containing 5-6% NaCl could be stored for six months, from December to June, in the atmospheric temperature. However, it begen to putrefy with the accumulation of an excess amount of lactic acid causing acidification when the temperature rose over 20°C. The change in flora of lactic acid bacteria was studied in both the nitrogen gas-packing system and the conventional open system, since the acidification might be caused by the growth of this group bacteria. In the early stage of storage, about 10⁵ cells/ml of unidentified lactobacilli were found in both systems, then after about 40days, they decreased to below 1×10³ cells/ml probably due to the lowering pH and the atmospheric temperature. In the middle to late stages, Lactobacillus bavaricus, Lactobacillus curvatus, Lactobacillus corynifcrmis subsp. torquens, Lactobacillus brevis, Lactobacillus plantarum, Lactobacillus coryniformis subsp. coryniformis, and some unidentified lactobacilli were found in both systems. The growth of L. bavaricus, L. breuis, and L. coryniformis which are regarded as undesirable lactobatilli producing hydrogen sulfide, ammonia and slimes were fairly suppressed in the nitrogen gas-packing system as compared with the conventional open system. Namely, in the nitrogen gas-packing system, the number of those lactobacilli was 1/100 of that in the open system and their growth delayed about one month. This phenomenon can explain why salted "Daikon" can be stored for a long period of time in the nitrogen gas-packing system. In the late stages, however, salted "Daikon" tended toward putrefaction even in the nitrogen gas-packing system, causing acidification acompanied with the increase of the cell number of L. brevis, L. coryniformis, and L. plantarum, which reached to about 10⁵-10⁶/ml. It is considered that the development of some means to suppress the growth of those bacteria is the most important for further improvement of the nitrogen gas-packing system.