MOISTURF, VCTIVITY ON GERMINATION 



53 



Table I 



Relationship of Total Water Content to Moisture Activity^ 

 for Different Substrates 



White Bread, crumb^ 



Total 



Moisture 



(percent) 



38 

 33 

 30 

 28 

 27 

 25 

 22 

 20 



Beef Liver, paste^ 



Moisture 



Activity 



(percent) 



97-100 



96-98 



94-96 



90-95 



90-95 



90-95 



^Approximate values are given. 



^Data based on work of Halvorson, 1949. 



^Data based on work of Williams, 1950. 



canned white bread for the armed forces, it became necessary to establish 

 bakery formulation limits for safety to have assurance that spores of CI. 

 botulinum in the flour would not germinate in the baked product. Investiga- 

 tions (Halvorson, 1949; Kadavy and Dack, 1951; Ulrich and Halvorson, 

 1948-49; Wagenaar and Dack, 1954) demonstrated that the control of mois- 

 ture content when combined with pH control was effective in preventing toxin 

 production in canned bread. In experimentally inoculated packs of canned 

 bread at moisture levels above 36 percent and with the pH adjusted to 5.8, 

 botulinum toxin was produced on storage of the cans at 32° C. (90° F.). 

 While toxin formation occurred within 2 weeks of incubation in canned 

 bread containing 40 percent moisture if the pH was set at 5.8, no toxin was 

 found in a year's storage for bread at the same moisture level when the pH 

 was adjusted to 4.8. Government specifications for canned bread, drafted 

 after extensive experimentation, now require that the moisture content of 

 the product shall not exceed 35.0 percent and the pH shall not exceed 4.8. 

 A value of 35 percent for the total moisture in canned bread corresponds to 

 abou*! 93 to 95 percent moisture activity. Under these moisture conditions 

 with added pH control a margin of safety is provided for this canned food 

 to preclude spore germination. 



