Continuous malolactic fermentation by Oenococcus oeni entrapped in LentiKats

A continuous process to deacidify apple juices and cider was developed by entrapping Oenococcus oeni in LentiKats, a new polyvinyl alcohol hydrogel. For a residence time of 0.55 h, malic acid was completely converted into lactic acid when the LentiKats bioreactor was fed with apple juice at pH 4.46 and 3.95 and thirty three percent of initial malic acid (6.7 g l(-1)) was converted when the initial apple juice pH was 2.30. The optimal malolactic activity of this bioreactor was obtained at 30 degreesC and a 50% reduction in malic acid conversion was measured between 15 degreesC and 20 degreesC, at a residence time of 0.3 h. The LentiKats bioreactor gave better performance than continuous reactor with Oenococcus oeni immobilised in alginate beads (specific malic acid consumption increased by a factor of 4.6) due to the increase of the ratio external surface to volume, allowing better mass transfer.