The effect of temperature and time on the quality of naturally fermented marula (Sclerocarya birrea subsp. Caffra) juice

•Fermented marula juice is a good source of ascorbic acid.•Fermentation at lower temperatures and longer times results in lower ascorbic acid.•Phenolic compounds in marula juice are stable during fermentation.•Fermented marula juice can retain over 80% of its initial antioxidant activities.•Marula juice can be used as a good source for natural antioxidants.

This paper presents the effects of fermentation on the retention of vitamin C, total polyphenols and antioxidant activity in the naturally fermented marula juice. The fermentation conditions have been varied: temperature ranged between 20 and 40 °C and fermentation time from 1 to 8 days. Marula juice fermented at higher temperatures ranged between 30 and 40 °C for 6 to 4 days retained high antioxidant activities, and they were positively correlated to its ascorbic acid and phenolic content. The values obtained ranged between 0.0239 ± 0.0051 and 0.029 ± 0.0038 μmol/mg for Trolox Equivalence Antioxidant Capacity, 870 ± 80 and 960 ± 130 mg/100 ml for total phenolic content and 90 ± 6 and 159 ± 15 mg/100 ml for ascorbic acid. Overall, fermented marula juice can be used as a good source for natural antioxidants.