A Novel Approach for Assuring and Following Inoculum Activity during Kefir Grains Growth Studies – Application of Dynamic pH Profiles

Marko Tramšek and Andreja Goršek*
University of Maribor, Faculty of Chemistry and Chemical Engineering, Smetanova 17, SI–2000 Maribor, Slovenia
Tel: ++386 2 22 94 453, Fax: ++ 386 2 25 27 774,
E-mail: andreja.gorsek@uni-mb.si

The profiles of kefir grains growth curves strongly depend on bioprocess conditions and inoculum viability. Therefore, accurate growth curve studies require the use of optimally active kefir grains as inoculum. Accordingly, the main objective of our study was experimental optimization of classic kefir grains activation procedure and afterwards, comparison among growth curves of differently activated kefir grains. For this purpose some experiments were initially performed in computer-controlled RC1 reactor provided data of dynamic pH profiles during batch propagation of differently activated grains. Experimental data were mathematically analyzed and using the special methodology of minimizing the absolute deviation of pH(t) profiles the minimal time for grains activation was determined. We established that optimal inoculum activity could be ensured only by the kefir grains, which were previously activated at least over eleven successive days. In the second part of research the growth curve of optimally activated kefir grains was constructed using experimental measurements and fitted with Gompertz model. The present results were compared with the results obtained by our previous study14, where classically activated grains were used. We established that, in spite of equal daily kefir grain mass increase, considerable difference in growth curves of differently activated kefir grains exist.

Keywords: Kefir grains, minimal activation time, growth curve, dynamic pH profiles, Gompertz model