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.
VIEW PRESENTATION 31
