Food Science and Applied Biotechnology, 2021, 4(1), 86-91 Food Science and Applied Biotechnology Journal home page: www.ijfsab.com https://doi.org/10.30721/fsab2021.v4.i1 ✉ Corresponding author: Chief Assist. Professor Siyka Kodinova, PhD; Department of Process Engineering, Technical Faculty, 26 Maritza blvd. BG-4002 Plovdiv, Bulgaria, tel.: ++359 32 603 874; E-mail: sisi.kozludjova@abv.bg Article history: Received 16 December 2020 Reviewed 11 January 2021 Accepted 23 February 2021 Available on-line 19 March 2021 https://doi.org/10.30721/fsab2021.v4.i1.135 © 2021 The Authors. UFT Academic publishing house, Plovdiv Kodinova and Dushkova, 2021 Concentration and retention factors during ultrafiltration of goat's milk Page 86 Short Communication Effect of volume reduction ratio on the concentration and retention factors during ultrafiltration of goat’s milk Siyka Kodinova 1✉ , Mariya Dushkova 1 1 Department of Process engineering, Technical Faculty, University of Food Technologies, Plovdiv, Bulgaria Abstract This experimental work aimed to study the effect of volume reduction ratio on the concentration and retention (selectivity) factors during ultrafiltration of goat’s milk with UF25-PAN polyacrylnitrile membrane. They were calculated on the basis of dry matter, total protein, fat and ash content in retentates and permeate at volume reduction ratios of 2 and 3. The results showed that the increase in the volume reduction ratio from 2 to 3 led to an increase in the concentration factors of dry matter - from 1.34 ± 0.05 to 1.87 ± 0.03, total proteins – from 1.70 ± 0.02 to 2.72 ± 0.06, fat – from 1.71 ± 0.03 to 2.71 ± 0.03, ash – from 1.13 ± 0.02 to 1.52 ± 0.02 (p  0.05). At these conditions, the retention factor (selectivity) of ash increased from 37.40 ± 2.19% to 53.50 ± 2.21% (p  0.05). There was no significant difference (p  0.05) of the selectivity of the membrane according to the proteins when volume reduction ratio increased. The results showed that these two volume reduction ratios and this membrane could be successfully used for the production of yoghurts with improved quality making them an excellent functional food. Keywords: ultrafiltration, concentration factor, retention factor, goat’s milk Abbreviations: ultrafiltration polyacrylonitrile membrane with molecular weight cut-off 25 kDa (UF25- PAN); volume reduction ratio (VRR)