MOISTURE ACTIVITY ON GERMINATION 51 



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Discugsion 



Morton M. Rayman 



Mr. Chairman and members of the Conference: Dr. Beers has presented 

 an excellent review of the important role of moisture relationships in bacterial 

 spore germination and growth. You are to be congratulated, Dr. Beers. 

 Research in this field is difficult. Very little systematic work has been pub- 

 lished. Nevertheless, the need for establishing the critical moisture levels 

 for germination exists. Not only is there an intrinsic interest, but also for 

 the solving of practical problems; it is of particular importance in the preser- 

 vation of certain food products as well as pharmaceutical products. 



I shall confine my remarks mainly to some aspects of the moisture limita- 

 tion problem aimed at preventing spores from germinating in food stuffs. 

 Since the beginning of World War II the dehydrated food industry has 

 expanded enormously, and hundreds of millions of pounds of dehydrated 

 vegetables, milk, and eggs are now produced annually. Substantial amounts 

 of dried or dehydrated fruits and cereal products are also processed today. 

 Currently there is a trend toward the dehydation of precooked foods for 

 convenience feeding. For all these products it is essential that the water 

 content be reduced to a point at which germination and bacterial growth 

 are restricted. In addition to the aforementioned items, there is a variety of 

 nonsterile canned foods which are of special interest. These include canned 

 white bread, canned steamed puddings, dehydrated sliced bacon, canned 

 cheese spreads, and canned chocolate nut rolls. 



I am glad to note that progress has been made in relating spore germina- 

 tion to the role of moisture. Certainly we do not yet have everything in 

 sharp focus, but the outlined shadows are emerging. Perhaps a diagram 

 will illustrate the general pattern. In Fig. 1 three zones of differing effective 

 water concentrations are shown. From essentially 100 percent water down- 

 ward to a limiting concentration A, one encounters a region in which germi- 

 nation and growth are normal and unrestricted. As dehydration proceeds 

 within the second zone, between water concentrations A and B, delayed 

 germination and restricted growth are met. In this range of moisture values 

 the phenomenon of dormancy may occur. It further appears that below the 

 critical water concentration B no germination or growth can take place. 



