ANNUAL REPORT, 1938 27 



The Influence of Bacteria on the Oxidation of Ascorbic Acid (Vitamin C). 



W. B. Esselen, Jr., and James E. Fuller.) The purpose of this study was to in- 

 vestigate the reported destruction of ascorbic acid by certain intestinal bacteria, 

 and to attempt to discover the mechanism of the vitamin's destruction. Pure 

 cultures of bacteria were cultivated in media containing ascorbic acid. It was 

 found that, instead of destroying ascorbic acid, the bacteria employed in this 

 study actually exerted a protective action which varied directly with the suit- 

 ability of the medium for bacterial growth, and vvith the numbers of bacteria 

 present. The experimental data suggest that growing bacteria may retard the 

 rate of oxidation of ascorbic acid by a combination of four factors, namely: 

 (1) the formation of un-ionized copper complexes whereby the catalytic action 

 of copper is destroyed, (2) the production of carbon dioxide with the subsequent 

 saturation of the medium with it, (3) the lowering of the oxygen tension of the 

 medium, and (4) the lowering of the oxidation-reduction potential of the medium. 



Additional work has been carried on using a miscellaneous group of forty-five 

 different bacteria, many of which may be present in foods. It was found that 

 most of these organisms significantly retarded the oxidation of ascorbic acid, 

 especially when they were grown in a medium containing a readily fermentable 

 carbohydrate. Thus it would appear that bacteria are not of importance in 

 causing a loss of ascorbic acid in foods. 



Gum Production by Aerobacter aerogenes. (Guy R. Vitagliano and James 

 E. Fuller.) Certain strains of Aerobacter aerogenes produce a great deal of viscous 

 growth in certain media, particularly those containing sugars. Ropy milk may 

 result from the growth of this organism, and it may cause similar ropy fermen- 

 tations of any sugar-containing substance. The object of this study was to 

 determine factors which would stimulate the organism to produce large quantities 

 of gum, in order that the gum might be more easily studied. 



Bacto tryptone and Bacto peptone were more suitable for quantitative gum 

 production than were ammonium salts or aspartic acid. Sucrose was the most 

 suitable carbohydrate, but lactose and dextrose also gave good results. Glycerol 

 and mannitol yielded less satisfactory quantities of gum. Sodium chloride, 

 calcium chloride, magnesium sulfate, and dipotassium phosphate in combination 

 stimulated gum production. This study will be submitted for publication in 

 detail. 



Relationship of Onion Juice to Bacterial Growth. (James E. Fuller and Ernest 

 R. Higgins.) In the course of some experiments on dried vegetables a few years 

 ago, it was observed that dried onions either had a very low bacterial content or 

 were entirely sterile. Since that time certain investigators have reported that 

 onion vapors have bactericidal power. In the present study several groups of 

 organisms were tested to determine their ability to grow in the presence of onion 

 juice. Aerobacter aerogenes strains were more resistant than were strains of 

 Escherichia coli, while Staphylococcus aureus and members of the Bacillus subtilis 

 group grew only in dilute concentrations of the juice. Salmonella and Pseudo- 

 monas strains were quite tolerant to the juice. Onion juice sterilized by steam 

 pressure was much less potent in preventing bacterial growth than was juice 

 sterilized by filtration through a Seitz filter. 



Bacteriological Study of Chocolate-Flavored Syrups and Cocoas. (Ralph L. 

 France, with W. S. Mueller.) This study is reported by the Dairy Department. 



Laboratory Service. (Ralph L. France.) Following is a list of the types and 

 numbers of examinations made during the past year. 



