RETENTION OF VARIOUS MICROBIAL SPECIES DURING MILK EPURATION BY CROSS-FLOW MICROFILTRATION

Retention of 7 bacterial species representative of typical contaminant flora of raw milks by microfiltration membranes used for the Bactocatch process was studied. These bacteria were added to 4 dairy liquids: milk ultrafiltrate; milk microfiltrate obtained with 0.2-mu-m membrane; native phosphocaseinate solution and HTST pasteurized skim milk. The results show that the average decimal reduction equals 2.6 and is independent of the initial level of the bacterial population. This indicates that membranes were acting as depth filters and not as screen filters. Bacterial retention rates on 1.4-mu-m membrane were between 99.93-99.99%. They were slightly linked to average cellular volume. Comparison of retention observed in function of the biochemical composition of liquids experimented with, led to the conclusion that there is a non-negligible effect of soluble milk components which interact with alumina particles before favorising internal adsorption of microorganisms.