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  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, selected from prior nano-milk-filtrations) with an average flux (J_P) increasing from 48 L.m⁻².h⁻¹ at 20°C and over 67 L.m⁻².h⁻¹ at 50°C until reaching a volume reduction of  5 . The DPPH antioxidant activity was effectively improved (~3 fold) with some insignificant loss due to fouling. Despite the high rejection, transmission of low-molecular weight components is detectable in the permeates, additionally the latter have astoundingly an antioxidant capacity, so each permeate can be divided into time interval fractions-aliquots each showing different DPPH antioxidant activity. This is further confirmed with statistical analysis where р < 0.05. As conclusion, because temperatures up to 50°C significantly increase the flux without much effect on the antioxidant activity, such conditions (temperature, pressure, dilution) are viable options for large-scale production applications.