BACTERIOLOGICAL STUDY OP RETAIL ICE CREAM. 



13 



THE PEPTONIZING GROUP. 



The peptonizing group is probably the most interesting if not the 

 most important group of bacteria in ice cream. This group consists 

 of what are commonly known as the putrefactive bacteria ; that is to 

 say, they attack primarily the proteins, decomposing them into less 

 complex organic bodies. Bacteria of this class are usually considered 

 undesirable in articles of food, and it is to them that intestinal 

 troubles are sometimes attributed, perhaps with or without justifica- 

 tion. Whatever their true effect is will not be discussed in this 

 paper, but because bacteria of this group are looked upon with sus- 

 picion it is therefore of great importance. In Table 8 will be found 

 the averages of the number of peptonizing bacteria in ice cream 

 during the summer and winter seasons from a number of different 

 plants. 



Table 8. — Average number of peptonizing bacteria per cubic centimeter of ice cream from 



various manufacturers. 





Summer. 



Winter. 



Manufacturer. 



Number 



of 

 samples. 



Average 

 number of 

 peptonizing 



bacteria 

 per cubic 

 centimeter. 



Number 



of 

 samples. 



Average 

 number of 

 peptonizing 



bacteria 

 per cubic 

 centimeter. 



A 



15 

 7 

 8 

 6 

 3 

 3 

 5 

 1 

 1 

 1 

 4 

 4 

 4 

 2 

 3 

 1 



909, 132 

 3,579,261 

 2, 752, 681 

 2,587,978 

 1,064,463 

 1,018,440 



567, 409 



328,119 



406,400 

 1,128,000 



415,018 

 4,370,497 



874, 754 



72,253 



2,879,467 



247, 656 



3 

 7 

 2 

 3 



30,358 



1, 159, 888 



2,097 



247,944 



B 



C 



D 



E 



F 



3 



3 



104,008 

 197,314 



G 



H 



I 







J 



2 

 2 



290,623 

 117,316 



K, 



L 



M 







N 















P 















68' 



1,449,533 



21,000,000 



36,063 



25 



268,693 



Maximum count 



Minimum count 







1 194 











The bacterial averages were much higher in the summer than 

 during the winter. It is evident from these figures that the average 

 commercial ice cream contains a large number of peptonizing bac- 

 teria. In order t <> show the range in the percentage of peptonizers, the 

 entire lot of summer and winter samples has been plotted in a fre- 

 quency curve, as shown in figure 4. It will be seen that the majority 

 i.l' samples contained from 0.1 to 5 per eenl, of peptonizing bacteria. 

 A large proportion contained, however, as high as 25 to 30 per 

 cent, and in a few samples they were present to the extent of from 

 90 to 95 per cenl of aJl the bacteria. 



