**George Panopoulos, Golfo Moatsou, Chrysanthi Psychogyiopoulou and Ekaterini Moschopoulou \***

Laboratory of Dairy Research, Department of Food Science and Human Nutrition, Agricultural University of Athens, Iera Odos 75, 118 55 Athens, Greece; g.panopoulos@yahoo.gr (G.P.); mg@aua.gr (G.M.);

ps.chrysanthi@gmail.com (C.P.)

**\*** Correspondence: catmos@aua.gr

Received: 9 February 2020; Accepted: 2 March 2020; Published: 4 March 2020

**Abstract:** The aim of this research work was to assess the effect of the microfiltration (ceramic membranes 1.4 μm, 50 ◦C) of partially defatted ovine milk (fat 0.4%) and bovine milk (fat 0.3%) characteristics. Feed milks, permeates and retentates were analyzed for microbial counts, gross composition, protein fractions, the indigenous enzymes cathepsin D and alkaline phosphatase and the behavior during renneting. It was showed that the microbial quality of both ovine and bovine permeate was improved by reduction of the total mesophilic microflora about 4 Log and 2 Log, respectively. The protein contents and the total solids contents of both permeates were significantly (*p* < 0.05) reduced. A further analysis of protein fractions by Reversed Phase -High Performance Liquid Chromatography (RP-HPLC) revealed lower αs1- and β-casein and higher κ-casein contents in permeates. The activity of alkaline phosphatase followed the allocation of the fat content, while activity of cathepsin D in permeates was not influenced, although somatic cells counts were removed. Regarding cheesemaking properties, the firmness of ovine curd made from the feed milk did not differ significantly from that made from the permeate. The obtained results suggested that microfiltration could be used for pre-treating of ovine milk prior to cheesemaking.

**Keywords:** microfiltration; ovine milk; bovine milk; casein fractions; alkaline phosphatase; cathepsin D; milk renneting properties
