The concentration of milk with different fat contents by freeze concentration assisted by centrifugation

Freeze concentration technique involves the removal of water as ice crystals by cooling the fluid to be concentrated at temperatures below the freezing point. The aim of this study was to provide concentrated milk by applying the freeze concentration assisted by centrifugation technique for milk samples with different fat contents (whole milk (3.3%), semi-skimmed milk (1.5%) and skimmed milk (0.1%)) and to detect the applicability of this technique in the production of concentrated milk. According to this purpose, whole milk (11.75ºBrix), semi-skimmed milk (10.57ºBx) and skimmed milk (9.10ºBx) were filled in centrifuge tubes, frozen in a static freezer (24ºC, 12 h) and the frozen samples were centrifuged (4500 rpm, 35 min, 25ºC). The concentrated solution which was obtained after the removal of formed ice by filtration was frozen again at the same conditions and the same processes were repeated (cycle). The moisture content (%), total soluble dry matter contents (ºBx), color, protein and fat contents (%), the thawing fraction (f), percentage of concentrate (KY), efficiency of concentration (ɳ) and recovered solute values (Y) were calculated for each cycle by using the weight of the seperated phases. In addition, freezing and thawing behaviors of concentrated milk samples were determined by following the sample temperature with respect to time. In order to determine the usability of freeze concentration assisted by centrifugation technique for concentrated milk productions, sensory evaluation was also applied. As a result of the first and second cycles of the milk concentration process, moisture values decreased. At the end of the second cycle, it was observed that the concentrated milk samples reached 25.43ºBx, 18.56ºBx and 17.40ºBx for whole, semi-skimmed and skimmed milk, respectively. By the freeze concentration process, it was determined that the milk protein and fat, which are the most valuable components of the milk, were kept in the concentrated part. The efficiency of concentration and recovered solute values of concentrated milks ranged between 83-63% and 0.85-0.61, respectively. The effect of the milk with different fat contents on freezing time was found to be insignificant (p>0.05). According to the results of sensory analysis, it was determined that the effect of concentrated samples obtained from milk with different fat content at color and appearance properties were significant (p <0.05).