The combined antimicrobial effects of hop resins with sodium hexametaphosphate, glycerol monocaprate, and lysozyme were investigated aiming to make an effective agent against Escherichia coli. When they are used separately, the antimicrobial activity against E. coli was minimal. However, the combination of hop resins with sodium hexametaphosphate exhibited strong antimicrobial activity against E. coli, but no effect was found in combinations of hop resins with the other agents. The activity was strongest when the combination was added at the beginning of growth of the bacteria, resulting in a prolonged lag phase. However, when the antimicrobials were added during the log phase, growth was depressed considerably. By addition of these materials, cell components with absorbance near 260 nm were leaked out. This possibly may have resulted from damage to the cell membranes of the bacteria. The combined effect was also detected in model food systems such as mashed potatos. The use of hop resins and sodium hexametaphosphate in combination may thus be useful for controlling E. coli.

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The effects of addition of powdered protein (egg white, milk protein, soybean protein and bovine plasma protein) to kamaboko and ham on the growth of bacteria were studied. P. fluorescens IFO3081 could not grow on the surface of a model kamaboko prepared from surimi of codfish, salt, sugar, pota to starch and water but was able to grow on that containing egg white, milk protein or soybean protein. Since these powdered proteins are rich in low-molecular-weight nitrogen sources utilizable by microor ganisms which are unable to digest high-molecular-weight proteins, the strain grew on the kamaboko and ham containing these powdered proteins. On the other hand, bovine plasma protein was found to have activity to suppress proliferation of the strain. From these results, the use of powdered protein for kamaboko and ham has both advantages and disadvantages in terms of food preservation.