Using Ft-Nir Spectroscopy To Automate Constant Sugar Concentration Fed-Batch Fermentations With Saccharomyces Cerevisiae: Effects On Cellular Viability And Kinetics Of Osmotic Stress Associated Metabolites

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During alcoholic fermentations with Saccharomyces cerevisiae, high sugar concentrations lead to growth inhibition or yeast lysis and cause stuck or sluggish fermentations. Even sublethal sugar concentrations stimulate a yeast hyperosmotic stress response and cause increased formation of various byproducts, including glycerol and acetic acid, and decreased product yields. In order to avoid the problems associated with high substrate concentrations, fed-batch approaches are utilized in some industrial fermentation. However, this technique has not been applied to winemaking, even though the effects of ongoing climate change are causing grapes to be harvested with increasingly high sugar concentrations. Hence, this work focused on the engineering of an automated system for conducting constant, low sugar concentration fed-batch vinifications, and the effects of these fermentations on yeast metabolism and viability. An initial manually maintained fed-batch fermentation revealed significant reductions (45, 81, and 52 %, respectively) in the final concentrations of glycerol, acetic acid, and iii acetaldehyde and improved ethanol production kinetics and yeast viability, relative to a high gravity batch fermentation of the same juice. A fully automated fed-batch system that uses FT-NIR spectroscopy-based control of fermentation broth sugar levels was then engineered. Calibrations for glucose, fructose, total sugar, and ethanol were created using over 200 natural and semisynthetic fermentation samples. When used to maintain a test fermentation at a sugar concentration of 45 g l-1, the system performed very well, keeping the concentration within 5 g l-1 of this value. Automated fed-batch-produced wines confirmed earlier findings and demonstrated large reductions in glycerol and acetic acid concentrations relative to a high gravity batch fermentation, the latter of which was below the limit of detection (0.05 g l-1). Simultaneously, fed-batch fermentations exhibited a 3.4-fold increase in final [alpha]-ketoglutarate levels and modified concentrations of several aroma-relevant compounds. Automated fed-batch fermentations also rapidly achieve and maintain high ethanol concentrations with minimal volume delivery, and thus may reduce susceptibility to contamination by spoilage bacteria. An affordable and offline discontinuous fed-batch approach, where discrete additions of must are made to an active fermentation, may also allow for a lessening of the yeast osmotic stress response and decreased osmolyte formation. iv

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Saccharomyces cerevisiae; Fed-Batch Fermentation; Osmotic Stress Response


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Sacks, Gavin Lavi

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Walker, Larry P
Worobo, Randy W.

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Food Science and Technology

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Ph. D., Food Science and Technology

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Doctor of Philosophy

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Government Document




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dissertation or thesis

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