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

•Black carrot, black mulberry, pomegranate and strawberry juices were added to kefir.•The most preferred samples by the panelist were kefir with strawberry juice.•Lactic acid, glucose, microorganisms had important effect on anthocyanin stability.•Copigmentation between lactic acid and anthocyanins were observed.•Fortification with juice caused an increase (up to 4.8 times) in antioxidant activity. 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 °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