O-34. The effect of platelet-activating factor on yeast attenuation

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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