Nanofiltration process monitoring and antioxidant activity analysis of skimmed milk samples

Abstract

Dead-end stirred cell experiments were performed with reconstituted skimmed milk and model solutions of single components (lactic acid). When a low solids concentration is presented with the feed, dead-end filtration with a selected polymeric membrane with cut-off of 300 Da is a viable option to assure a high rejection of the dissolved organic compounds (> 90%), combined with a good transport at moderate pressures (20 bar) with an average flux increasing from 48 Lh−1m−2 at room temperature and over 67 L h−1m−2 at 50°C until reaching a volume reduction of about 5. The DPPH antioxidant activity was effectively improved (~3 fold) with some loss due to fouling, temperature and transmission of low-molecular weight components in the permeates in spite of high rejection in the process, whilst the latter have astoundingly an antioxidant capacity, so each permeate can be divided into time intervals of permeation per sample into aliquotes with different DPPH antioxidant activity. That is further confirmed with statistical analysis where р > 0.05. As conclusion, because the temperature of up to 50°C significantly increases the flux without much effect on the antioxidant activity, such temperatures, dilution and conditions are viable option for large-scale production uses.