Recently, the authors have developed a new container used for liquid food products such as soy sauce and milk, which consists of a paper case made of a sheet of recycled paper and a liquid-packing bag made of plastic film. One of the major features of the new container is that the container is capable of delaying the discoloration and decay of liquid food products. It was inferred that this function is due to the prevention of the invasion of microorganisms from a simple pouring lip into the bag; the lip is made of the same plastic film as the bag and is located in the upper part of the container. However, the reason microorganisms could not enter the bag remains to be determined. In this study, as a first step toward determining the above reason, the velocity of movement of colon bacillus in liquid in microchannels made to simulate the lip of the new container was measured using a digital image correlation technique. Results indicated that the existence of nutrition and increase in the gap size of rectangular channels increased the swimming speed of colon bacillus, and the ratio of colon bacillus adhered to the wall surface of the channels increased with decrease in the gap size. The shape of bacteria changed due to the existence of nutrition.
