Technical Session 16: Yeast III Session
Martin Zarnkow, TU München
Co-author(s): Thomas Becker, TU München, Germany
ABSTRACT: The goal of this study was to find a normative parameter for the growth of lactic acid bacteria in barley malt wort, probiotic or not. Four bacteria (Lactobacillus brevis, L. casei, L. perolens, and Leuconostoc lactis) and five well-established probiotic bacteria of the food industry (L. rhamnosus, L. acidophilus, L. casei, Streptococcus thermophilus, and Bifidobacterium lactis) were selected. Out of three different initial cell counts, three different pH values, and three different incubation temperatures, the most appropriate parameter set to the growth should be found. With this set, a general statement should be made, which can be accepted for a multitude of probiotic lactic acid bacteria in barley malt wort as substrate. The pH value, absorbance at 600 nm, and percentage amount of lactate were measured daily for this experiment. At the first and last day of this test run, the concentration of the extract and the alcohol concentration were determined. The face centered design of response surface methodology and the analysis resulted from the software Stat Ease Design Expert. The absolute growth, difference in absorbance between the end and beginning of the experiment, pH value, and amount of lactate at the end of the experiment were analyzed. In four out of five tested strains, the pH value of the substrate had the highest impact on growth. A pH value of 5.6 caused maximum growth behavior of these strains, although the amplitude was quite different. The determined growth ranged between a doubled and a 25-fold growth. In four out of five strains, the percentage amount of lactate was dependent on the pH value of the substrate as well. The highest amount of lactate was produced between a pH value of 4.8 and 5.6. The averaged amount of lactate was between 0.07 and 0.38%. The decline in pH was conspicuous for all of the strains. Predominately, a pH value below 4.0 was reached at the end of the experiment. The consumption of the extract was very different. Between 0.21 to 6.12% of the extract was fermented by the end. Because of the differing results, a normative procedure for these lactic acid bacteria is not easy to determine. Thus, a compromise has to be made that is close to the optimum but that cannot be the optimum for all probiotic and non-probiotic strains.
Martin Zarnkow apprenticed as a brewer and maltster from 1989 to 1991 at a small brewery in Frankonia. Finished a Diplom-Ingenieur (FH) degree, option brewing technology, in 1996 at TU München, Weihenstephan. Worked as a brewmaster for one year in a medium-sized brewery in Germany. Since 1997 Martin has been head of the research group for brewing and beverage technologies and microbiology at the Lehrstuhl für Brau-und Getränketechnologie (Institute for Beer and Beverage Technology) at TU München in Weihenstephan. Finished his external Ph.D. research in 2010 at the University College of Cork, Ireland, on the subject “Proso Millet (Panicum miliaceum L.) a Sustainable Raw Material for the Malting and Brewing Process.”