Technical Session 09: Analytical II Session
Karl J Siebert, Dept. of Food Science, Cornell University, Geneva, NY, USA
ABSTRACT: A statistical experiment design (central composite face centered) was used to select combinations of conditions in a foam model system in which the levels of protein (ovalbumin), iso-alpha-acid, ethanol, and pH were varied. The results were used to construct a response surface model; this provided insight into some of the contradictions in the foam literature. Intermediate ethanol levels led to the best foam, with poorer foam at higher and lower ethanol contents. Increasing pH led to poorer foam. For predictions of a model system to be useful, it must behave like the modeled phenomenon (in this case beer foam). Ethanol was added to commercial non-alcoholic beer; the effect on foam behavior was similar to the model system. When a commercial lager was adjusted in pH, however, the foam increased with increasing pH, opposite to the model system. Dimethyl formamide, a hydrogen bond acceptor; dioxane, a non-polar but water-miscible solvent; and NaCl solution were each added to the model system and to beer. Salt greatly reduced foam in the model system, suggesting the bonding between ovalbumin and iso-alpha-acid is mainly ionic. DMF caused by far the largest reduction in the foam of the commercial beer, indicating a hydrogen bonding mechanism. These results show the mechanisms are different in this foam model system and beer. The barley proteins that have most often been associated with beer foam are lipid transfer protein 1 (LTP1) and proteins Z4 and Z7. Ovalbumin has considerable similarity to proteins Z4 and Z7 in the proportions of amino acids of different types and in the charge on the molecule at various pHs but is quite different from LTP1. The results suggest possible greater involvement of LTP1 than the other two proteins in beer foam.
Karl Siebert received a Ph.D. degree in biochemistry from Penn State in 1970. He then joined the Stroh Brewery Company in Detroit, MI, where he spent 18 years and held positions from research associate to director of research. In 1990, Karl joined Cornell University as professor of biochemistry in the Department of Food Science and Technology. He served five years as department chair and now has a predominantly research commitment. Karl is active as a consultant in beverage technology and chemometrics. He has twice received MBAA Presidential Award for papers he presented, and he and his colleague, Penny Lynn, received the ASBC Eric Kneen Memorial Award (for the best paper published in JASBC in the prior year) three times. Karl was made an honorary professor of the Moscow (Russia) State Academy of Food Processing in 1996, and in 1999 he received the ASBC Award of Distinction. He received the MBAA Award of Merit in 2011. He is currently a member of the JASBC Editorial Board and the ASBC Foundation. Karl’s research interests involve foam and haze in beverages, perception of astringency and other flavors, the application of chemometric methods in food science, and assessment of microbiological risk.