Microfiltration of bovine and ovine milk for the reduction of microbial content: Effect of some operating conditions on permeate flux and microbial reduction

In the present work a study on bovine and ovine milk microfiltration in a tubular ceramic membrane is reported. The study was aimed at the reduction of milk microbial content through a cold technology, with the obvious advantages for the preservation of essential elements. Considering the low availability of ovine milk, which was daily provided by local farmers, most of the tests were performed with bovine milk, which was commercially available. Few tests were then performed also with ovine milk. Firstly, some tests were performed using bovine milk with different fat content. In the presence of fats, a gradual start-up procedure (realized by treating a milk diluted with distilled water prior to microfiltration of pure milk) was demonstrated to be fundamental for the achievement of a permeate. Further tests with skim bovine milk evidenced the positive effect of temperature and the negative effect of transmembrane pressure on permeate flux: in fact, average permeate fluxes were 850 and 650 L h(-1) m(-2) when trans-membrane pressure was 0.6 and 1.9 bar, respectively, at 40 degrees C, and 650 and 400 L h(-1) m(-2) respectively, at 30 degrees C. The subsequent tests with ovine skim milk, performed at 40 degrees C and 0.6 transmembrane pressure, revealed a significant flux decline from 700 to 200 L h(-1) m(-2) in the first 60 min processing and a relatively stable permeate flux around 200 L h(-1) m(-2) for further 30min. In any case, the microbial decimal reduction was about 2-3, in agreement with values found in the literature.