[Studies on the reduction of microorganisms in icecream in production and storage (author's transl)]

Experimental analyses referred to in this publication were to clarify two important hygienic-bacteriological issues: 1. Which is the capacity of survival owned by microorganisms in icecream in correspondence to temperature and storing time, and what significance have the results in regard to the length of intervals between the taking of samples of icecream and their examination. 2. Which nutritient media are suitable for a routine diagnostic of coliforms? Analyses were being made with an artificially contaminated, industrially produced icecream (Vanilla icecream with 10 per cent milk fat and strawberry icecream with 6,6 per cent milk fat and 21 per cent strawberries). Inoculations were only done with strains of bacteria isolated from icecream. We employed one strain of Escherichia coli, Staphyloccus aureus, Pseudomonas aeruginosa and three strains of Coliforms for each inoculation. Contaminated samples were stored in deep-freeze units at three different temperatures(-28, -18, -8 degrees C). In the beginning inspections in regard to microbial content were performed in daily intervals, but intervals grew longer in the course of time. At the utmost samples were under observation for 140 days. For quantitative measurement of Coli and Coliform microorganisms five different culture media were used (Endoagar, Hexachlorophene Endoagar, Desoxycholatcitrat Agar, Violet Red Bile Agar and Brilliant Green Broth). Generally results showed, that icecream, if being stored, looses approximately one to two quarters of the bacteria within hours after production, the third dies within days and the rest after weeks and months. Within the given period of observation sterility can only be reached with rather sour kinds of icecream. E. coli proved to be moderately resistant, Coliforms were somewhat more sensitive. Staphylococci showed in the beginning a lower drop, but in the course of time similar rates as Coli and Coliforms. Only with Pseudomonas inactivation was distinctly more rapid. Differences concerning kinds of icecream and temperatures were not to be secured statistically. Examination of cultur media for the demonstration of E. coli and Coliforms resulted that Hexachlorophene Endoagar is the best one. It is recommended, to take icecream samples at the earliest at the time the icecream is to be sold. Bacteriological cultures should be prepared within 14 days. Controls are to be made at the earliest possible date, but not later that two weeks after the official analysis. Findings with a lower count reached at a later date do not contradict an earlier result of two to five times higher rates. Reliable constants for the retrospect establishment of balances of microbial content were not to be found.