1. The growth in synthetic cream of certain pathogenic bacteria may be inhibited by two methods:
(a) By limiting the ingredients to cooking fat or other fatty material, excluding margarine or butter, emulsifying agent such as methyl cellulose, sugar and salt. The cream must not then be left in contact with confectionery from which nutritive material may be absorbed. This last condition renders the method impracticable as a means of control.
(b) By the addition to synthetic cream, including those containing milk and egg, of a bacteriostatic agent such as hydrogen peroxide.
2. Contaminants may grow in emulsified fats in the absence of protein. These are probably lipolytic organisms which are able to utilize the products split from the fat. Organisms such as coagulase-positive staphylococci, Salmonella paratyphi B, and Bacterium coli, tend to die out within 24 hr. or after a few days in creams lacking protein.
3. The concentration of H2O2 necessary to inhibit the growth of test organisms is dependent on the ingredients of the cream. In the presence of butter, milk and egg yolk at least three times the concentration of H2O2 is necessary as when emulsified fat without added protein is used. The suggestion is made that concentrations of H2O2 from 0·005 to 0·02% should be added to all commercially produced synthetic cream, the actual concentration used depending on the constituents of the cream.
4. To prevent the growth of contaminating organisms in commercially produced synthetic cream, H2O2 should be added immediately after pasteurization and cooling when the bacterial count is still low. Even comparatively high concentrations of H2O2 will not inhibit or control the growth of bacteria already present in large numbers.
5. The inhibiting power of 0·012% of H2O2 remained effective in a fat-emulsion cream and also in a laboratory cream containing margarine, egg and milk for 3 weeks at + 4 and 20° C.; at higher temperatures of storage the stability of the oxidizing agent is doubtful.
6. Since synthetic cream is exposed to so many different sources of contamination, particularly in the bakery, and since there is no method of controlling the growth of pathogenic organisms that have gained access to it other than by the addition of a bacteriostatic agent, it is strongly recommended that the present regulations on preservatives should be altered to allow the addition of H2O2 in suitable concentration to synthetic cream.
We are grateful to all those who have helped in the supplies of material, and in particular we wish to thank the Public Health Department, St Pancras Town Hall; Mr E. Capstick, United Dairies Ltd.; Mr J. Valentine Backes, President, Bakery Allied Traders' Association; and also Messrs Bakcos Catering Supplies Ltd., A. Bellamy and Co. Ltd., Farma Cream Products Ltd., Krema Ltd., Malga Products Ltd., Ramsay, Braddon and Co. Ltd., Quality Foods Ltd., Sunnyside Products Ltd., Unicream Ltd., and Vitacream Ltd.
We are indebted to Mr L. Bailey for his technical assistance.