Effect of substrates on the kefir grain biomass production and antioxidant activity

ABSTRACT Kefir is a fermented milk with proven bioactivities and popularity worldwide. However, kefir grains biomass (KGB) limits its production. The effect of different substrates on the KGB increase and antioxidant activity (AC) was investigated. Kefir grains were inoculated (6 % w/v) into nonfat goat milk (GMK), nonfat goat milk with brown sugar (GMBSK), cow (1 % fat) milk (CMK), and cow milk brown sugar (CMBSK). The substrates were fermented at 25 ± 3 °C and stopped at 4.7 pH, approximately. Samples were taken at 0, 4 and 8 h incubation time. KGB increase kinetics, productivity, growth rate parameters, physicochemical composition changes, and antioxidant activity were evaluated. Goat milk substrates kefirs had the highest AC values. GMBSK and GMK had 44.8 ± 1.4 % and 37.6 ± 3.6 % AC, respectively. GMK and GMBSK had the highest biomass increments, 147 ± 23 % and 136 ± 7 %, respectively. Also, GMK had the highest (p < 0.01) kefir grains biomass productivity, 2.49 ± 0.24 g/L.h. Goat milk substrate has the potential to increase kefir grains biomass and to improve the bioactivity of kefir beverages.