B.S., 1986, University of Pennsylvania

Ph.D., 1992, University of Minnesota

Research

Elucidating Ethanol Tolerance Mechanisms in Yeast

Stuck and sluggish alcoholic fermentations are an important problem in the wine industry. Many times, microbial strains with desirable traits such as flavor qualities are less ethanol tolerant. Therefore, it is our goal to understand the fundamental basis of alcohol tolerance in yeast, so that this tolerance can be increased in otherwise desirable production strains. Early on in our modeling of this system, it appeared that inactivation of yeast (i.e. lack of tolerance) could be a result of the composition and structure of the lipid bilayer composing the cell membrane, including the phenomenon of membrane bilayer interdigitation (complete overlap of the fatty acid side chains) as potentially responsible for physiological behavior of yeast in response to alcohol. This led us to develop a high-resolution liquid chromatography/mass spectrometer (LC/MS) method for identifying and quantifying membrane composition in yeast. We then used this method to relate membrane composition to ethanol tolerance using a range of 25 industrial Saccharomyces strains. We were able to use the data to show that there are likely to be two complementary mechanisms for alcohol tolerance, higher tolerance per cell and higher maximum cell concentration during fermentation. Our data showed that both of these mechanisms are related to membrane composition. This work expanded to include metabolomics measurements during alcoholic fermentations, as well as genome-scale modeling of S. cerevisiae to understand the metabolic differences between strains resulting in different efficiencies of cell growth and production of volatile aroma impact molecules (with Eddy Smid and Richard Notebaart, Wageningen) during fermentation.  We have now begun to use these models to direct promising genetic manipulations for strain improvement with Ben Montpetit (UC Davis) and Vladimir Jiranek (U Adelaide).

Wine Process Optimization and Intensification

Our group is also working on optimizing wine processing to achieve processing goals (like mouthfeel and color).  One of the key processes on which we have worked extensively is phenolic extraction in red wines.  Red wines are fermented with grape skins in order to extract color, tannins, and other flavor impact molecules (mostly affecting bitterness and astringency). During the fermentation, the skins float to the top of the fermentation and form a “cap.” The mechanisms of extraction from this cap have not been well understood, nor has the influence of temperature and ethanol concentrations. It is clear, however, that red wine fermentations present a heterogeneous environment that complicate this analysis. We have performed extensive pilot scale experiments to understand the underlying phenomena, examining cap temperature, liquid temperature, pumpover frequency and volume, and “cold soak” treatments.  These large-scale experiments led us to further explore the fundamental basis of our observations.  Recently, we developed the first comprehensive, computational fluid dynamics (CFD) model for red wine fermentations, combining fluid flow, heat transfer, mass transfer, yeast growth kinetics, and phenolic extraction.  This model, along with associated parameter measurements, was a major accomplishment and has given us the means to understand and control phenolic profiles at large production scale, along with giving us the basis for developing intensified wine processes—that is, producing the same wines with far less equipment, personnel, and other resources.

Single Vine Resolution Irrigation (SVRI)

California’s recurrent experiences with drought and water shortages have stoked competition between agricultural, municipal, and conservation needs, requiring irrigation in formerly non-irrigated areas. In vineyards, current drip irrigation and fertigation practices generally treat all vines in a block or management zone identically, even though it is clear that all plants do not require the same amount of water or fertilizer. An important means of increasing water-use and fertilizer-use efficiency and decreasing crop heterogeneity is to deliver a different amount of water or fertilizer to each vine according to its needs—Single-Vine Resolution Irrigation (SVRI). Technology to achieve this goal has yet to be developed, especially that is low cost and compatible with existing production systems (i.e., can be installed in existing vineyard)—two factors that will be critical to widespread and rapid adoption. Our long-term goal is to develop a comprehensive water/nutrient sensing and delivery system that can be used in high value specialty crops, such as grapes, thus increasing the overall sustainability of specialty crops.  To date, our lab, along with Mason Earles (UC Davis) and Mark Burns (University of Michigan) has identified a suite of inexpensive sensors that may accomplish the goal of estimating evapotranspiration rates for each vine.  We have also installed and operated a 640-vine proof-of-concept block for differential delivery of water.  We are now working on the computational parts of the method, as well as investigating inexpensive, compact sensor alternatives.

Cultivated Meat Process Optimization

Cultivated meat production is the process of growing animal muscle, fat, and connective tissue cells, such as beef, chicken, pork, turkey or fish, in large-scale fermentors to produce a protein-rich meat product. It addresses the compelling and immediate societal problem of feeding a growing global population with a nutritious and satisfying diet, while protecting our environment and limited resources. It requires the deep integration of stem cell engineering, tissue culture, animal and meat science, experimental process optimization and artificial intelligence, biochemical engineering, industrial fermentation and manufacturing, food science and engineering, materials science and biomaterials, sensory science, techno-economic modeling, life cycle analysis, and consumer science.   Our goal is to help establish the scientific and engineering foundation for the nascent cultivated meat industry, address critical scientific and engineering bottlenecks and knowledge gaps.  I am leading an NSF-funded comprehensive center on cultivated meat addressing all aspects of production.  This exciting new center includes 13 faculty on the UC Davis campus, and is the only comprehensive center of its kind in the US.  In our lab, we specifically focus (along with Keith Baar) on establishing a process for growing and differentiating cell lines in inexpensive, plant-based, serum-free medium up to pilot scale.  To do this, we are using our expertise in large-scale fermentation optimization, along with advanced AI-based tools for directing experimental process optimization.  However, others on campus will be working on developing stable embryonic cell lines, creating biomaterials and processes that allow creation of three-dimensional tissue structure (like a steak or chicken breast), and completing a techno-economic analysis (TEA) and life cycle analysis (LCA) for cultivated meat production.