Scale-down of vinegar production into microtiter plates using a custom-made lid

As an important food preservative and condiment, vinegar is widely produced in industry by submerged acetic acid bacteria cultures. Although vinegar production is established on the large scale, up to now suitable microscale cultivation methods, e.g. using microtiter plates, are missing to enable high-throughput cultivation and to optimize fermentation conditions. In order to minimize evaporation losses of ethanol and acetic acid in a 48-well microtiter plate during vinegar production a new custom-made lid was developed. A diffusion model was used to calculate the dimensions of a hole in the lid to guarantee a suitable oxygen supply and level of ventilation. Reference fermentation was conducted in a 9-L bioreactor to enable the calculation of the proper cultivation conditions in the microtiter plate. The minimum dissolved oxygen tensions in the microtiter plate were between 7.5% and 23% of air saturation and in the same range as in the 9-L bioreactor. Evaporation losses of ethanol and acetic acid were less than 5% after 47 h and considerably reduced compared to those of microtiter plate fermentations with a conventional gas-permeable seal. Furthermore, cultivation times in the microtiter plate were with about 40 h as long as in the 9-L bioreactor. In conclusion, microtiter plate cultivations with the new custom-made lid provide a platform for high-throughput studies on vinegar production. Results are comparable to those in the 9-L bioreactor.