Aeration, Agitation and Cell Immobilization on Corncobs and Oak Wood Chips Effects on Balsamic-Styled Vinegar...

Optimum fermentor conditions are essential for desired microbial growth and activity in fermentations. In balsamic vinegar fermentation systems, the microorganisms used must endure several stressful conditions including high sugar concentration, low water activity, high osmotic pressure and high acetic acid concentration. Consequently, the present study was aimed at improving the performance of a microbial consortium of non-Saccharomyces yeast and acetic acid bacteria during balsamic-styled vinegar fermentation. Cell immobilization via adsorption on corncobs and oak wood chips in combination with aeration and agitation effects, have never been tested during balsamic-styled vinegar fermentation. Therefore, fermentations were initially conducted under static conditions without aeration with successive fermentations also being subjected to low (0.15 vvm min^-1) and high (0.3 vvm min^-1) aeration. The results showed improved acetification rates when cells were immobilized on corncobs under static conditions. Low aeration showed better acetification rates (1.45-1.56 g·L·day^-1), while only free-floating cells were able to complete fermentations (1.2 g·L·day^-1) under high aeration conditions. Overall, cells immobilized on corncobs showed higher acetification rates of 1.56 and 2.7 g·L·day^-1 under low aeration and static fermentations, respectively. Oak wood chips were determined to be less efficient adsorbents due to their relatively smooth surface, while the rough surface and porosity of corncobs led to improved adsorption and, therefore, enhanced acetification rates.