Characterisation of malolactic conversion by Oenococcus oeni to reduce the acidity of apple juice


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The high concentration of malic acid is responsible for the acidity and sourness in apple juice. Bio-conversion of malic acid to lactic acid through malolactic conversion (MC) in apple juice using Oenococcus oeni was investigated. When apple juice was inoculated with O. oeni (1 × 106 CFU mL−1), over 90% of malic acid was converted into lactic acid within 96 h at room temperature. When pH of apple juice was adjusted to 4.1 prior to inoculation, MC was completed within 60 h. MC was enhanced at a higher temperature (30°C) when compared with room temperature. The rate of MC was directly proportional to the number of bacteria added and MC was completed within 24 h at 1 × 109 CFU mL−1 initial cell density. MC occurred equally under aerobic and anaerobic conditions. The sensory analysis of partial MC-applied juice when compared against control revealed potential for use of MC for manufacture of low-acid apple juice.