THE USE OF ALGINATE AND NATURAL POLYMERS MIXTURES AS CARRIERS FOR MALOLACTIC BACTERIA CELL IMMOBILIZATION

Abstract

Malolactic fermentation (MLF) is defined as the enzymatic bioconversion of malic acid into lactic acid, a biological process of reducing the acidity of wine performed by lactic acid bacteria (LAB). The use of immobilized bacteria provides important advantages compared to the classic free cell inoculation, improving cell stability and process yield. The current study aimed at the immobilization of an autochthonous LAB strain (Oenococcus oeni, strain 13-7) cells, by entrapping in 2% sodium alginate, 1% alginate/1% k-carrageenan and 1% alginate/1% gellan gum mixtures, analysing the physical characteristics of the beads and the bioconversion yield in three successive fermentation cycles. An additional layer of 0.1% gel with the same composition was applied to the biocatalysts after initial extrusion of gels in 0.2 M CaCl2. The beads obtained were spherical, with a diameter between 3.39-3.62 mm. Inoculated in synthetic wine (12% vol. ethanol; 108CFU/mL), the immobilized LAB cells metabolized between 69-71 % of the malic acid in the initial fermentation cycle (10 days), the bioconversion yield decreasing by about 3% in the second cycle and by 10% in the final cycle of MLF. Blending of alginate (1%) with other natural polymers improved the structure of the beads, especially in combination with 1% gellan gum, the constant values of the optical transmittance at 550 nm (~99%) and the reduced number of cells released in the final fermentation cycle indicating a superior stability of the immobilization matrix compared to plain alginate beads.