Control of foaming during microbiological analysis of foods and recovery of indicator organisms [Escherichia coli, Stpahylococcus aureus, Stroptococus faecalis]

Persistent foam formation occurring during blending of jelly powder (JP), whole egg powder (WEP) and skim milk power (SMP) was demonstrated. Reduction of foaming was uniformly best achieved by using the Colworth Stomacher 400 (STOM) for mixing or blending under a vacuum (VAC). Two hundred, 1000 and 6000 ppm of Dow Corning Antifoam Agent (DAF) was necessary to reduce foaming of JP, SMP and WEP, respectively. Escherichia coli was recovered in similar numbers from JP, SMP and WEP by normal blending (N), STOM, VAC or by the application of 200 ppm of DAF. Significantly lower recovery of Staphylococcus aureus from JP resulted when N or VAC was employed and from SMP when STOM was used. Streptococcus faecalis showed significantly lower recoveries from JP and WEP when STOM or VAC and DAF at 200 ppm were used.