Presenter: Phillip Callihan, University of South Carolina
School of Medicine Greenville, Greenville, SC
Coauthor: William E. Roudebush, University of South Carolina
School of Medicine Greenville, Greenville, SC
Studies have reported that beer (moderate consumption)
can have a positive impact on health and disease prevention
(reviewed in Beer in Health and Disease Prevention, V. R.
Preedy, ed., Academic Press, London, 2009). Additionally,
there is emerging evidence demonstrating the antioxidant
capacity of beers (Zhao et al., J. Sci. Food Agric. 93:910-917,
2013). The health benefits of beer may be tied to its overall
quality. Beer quality is strongly influenced by the biochemical
performance of yeast (Saccharomyces cerevisiae) during
fermentation, with performance defined as the capacity of yeast
to exhibit cell growth, attenuation, flocculation, and flavor.
A number of biochemical compounds are produced by yeast,
including lipids. Yeast lipids have a substantial influence on
beer quality due to sterol synthesis controlling yeast growth. In
particular, yeast cells synthesize a unique and novel lipid, i.e.,
platelet-activating factor. Platelet-activating factor (1-O-alkyl-
2-O-acetyl-sn-glycero-3-phosphorylcholine; PAF) is a potent
signaling phospholipid that appears to be critical for many
of the events surrounding cell development and metabolism.
Yeast synthesis of PAF appears to control the cell cycle phase
in budding yeast. In a preliminary study, we described temporal
PAF production in ale and lager yeast at different culture
temperatures (Roudebush et al., Am. J. Brew. Chem. 64:135-
138, 2006). Little information is known on the direct impact
PAF has on the physiological biochemistry of yeast. Therefore,
the study objective was to determine the effect of exogenous
PAF on brewer’s yeast (S. cerevisiae) attenuation. A proprietary
strain of brewer’s ale yeast (No. 1028; Wyeast Laboratories,
Inc., Odell, OR) was cultured in sterile dried malt extract
(DME; 13.8°P; Crosby and Baker, Westport, MA) in water.
Individual static yeast cultures (50 mL total volume; 5 mL head
volume) were anaerobically incubated at 20°C. Samples (500
μL) of yeast-conditioned DME culture media were obtained
at specific intervals (0, 24, and 48 hr of culture), and specific
gravities (°P) were measured by refractometry (Grand Index,
Hong Kong; model RSG-100/ATC) and recorded. There was
a significant difference (P < 0.05) between the control (5.8°P)
and PAF (4.6°P) group attenuation at 24 hr. At 48 hr (final
attenuation), differences between the control (4.8°P) group and
the PAF (4.6°P) group approached significance (P = 0.065).
The data demonstrate that brewer’s yeast responds to PAF with
a lower attenuation and in a shorter time period. Additional
studies are warranted to determine the impact of PAF on yeast
fermentation time (potentially increasing beer production
throughput efficiency) and attendant beer quality.
Phillip Callihan completed his Ph.D. degree in pharmaceutical
and biomedical sciences at the University of Georgia in 2012
and is currently pursuing an M.D. degree at the University
of South Carolina School of Medicine Greenville. He is a
member of the American Society of Pharmaceutical Scientists
and the American Medical Association. In 2011, he delivered
an invited talk at the Southeastern Regional Lipid Conference
titled “Distinct Generation, Pharmacology, and Distribution
of Sphingosine 1-Phosphate and Dihydro-sphingosine
1-Phosphate in Human Neural Progenitor Cells.” Phillip has
authored multiple biochemistry and pharmacology publications
and is now investigating the potential roles of beer in improving
human health.
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