Changes in the quality of kefir fortified with anthocyanin-rich juices during storage

Changes in sensorial, chemical and microbiological qualities of kefirs fortified with black carrot (KBCJ), black mulberry (KBMJ), pomegranate (KPJ), and strawberry (KSJ) juices at different concentrations (10, 25 and 50%, w/w) were monitored throughout storage at 4 degrees C for 12 weeks. The most preferred kefirs by the sensorial panel were KSJ and KPJ, followed by KBMJ and KBCJ. KBMJ was associated with the highest anthocyanin stability, followed by KPJ, KSJ, and KBCJ. Lactic acid [r = (-0.688)-(-0.970)], glucose [r = (-0.563)-(-0.793)] and microorganisms [r = (-0.633)-(-0.961)] in kefirs had significant effect on anthocyanin stability and colour (p < 0.05). Copigmentation between lactic acid and anthocyanins were observed. Fortification with 25% juices led to an increase (1.8-4.8 times) in antioxidant activity (AA). Shelf-lives of samples, except for KPJ, ended after 12 weeks of storage, due to low sensorial scores. Additions of SJ, PJ and BMJ at 25% concentration are recommended for the production of more palatable kefir with high AA.