Graduate Thesis Or Dissertation
 

Sweet Whey Fermentation: An Exploration of Optimizing the Alcohol Production of Kluyveromyces marxianus and Measuring the Nitrogen Content of Sweet Whey

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  • It is estimated that for every 1 kg of cheese produced, approximately 9 kg of whey is created. For smaller producers something needs to be done to keep it out of water ways and potentially to valorize it. However, access to efficient secondary whey processing to isolate protein and lactose is almost exclusive to large cheese producers because the associated high costs of equipment and infrastructure and because some secondary processes require a production volume that is beyond the scale of all but the largest producers. Due to these factors, most artisanal creameries are forced to dispose of whey into water treatment streams or landfills, which also have economic and environmental costs of their own. These costs have led cheese producers to look for alternative methods of processing or disposing of their whey. One of the more popular methods of whey processing to emerge from the first decades of the 21st century is using it to make potable alcohol as a value-added product. This can be done through the fermentation and distillation of whey, although results are varied and uncertain in many cases. The aim of this study was to optimize the production of ethanol from whey using a monoculture that was capable of fermenting lactose. To that end, this work focuses on the exploration of fermenting sweet whey using the organism Kluyveromyces marxianus. K. marxianus is a thermotolerant yeast species that has been demonstrated to be capable of producing ethanol from lactose as its sole carbohydrate source. The first body of work focuses on how the environmental conditions of whey as a substrate affect the alcohol production by K. marxianus. Four variables important for fermentation systems were identified and tested in a series of experiments. Those variables were lactose content, pH, zinc supplementation, and diammonium phosphate (DAP) supplementation. Each variable had two levels of adjustment in the initial substrate and were allowed to ferment for twelve days. Post fermentation analysis of yeast health and alcohol concentration revealed significant results for most variables. Decreased initial pH of the whey caused a decrease in alcohol production. Supplementation by both zinc and DAP also showed a significant decrease in alcohol production. The second body of work was developed to further our understanding of whey as a fermentation system. Unbound amino nitrogen content of fermentable materials is considered one of the most important variables for alcohol production. The concentration of free amino acids in whey was explored with the use of common methods for measuring them from the beer and wine industries. It was found that the formaldehyde pH method over estimated fermentable nitrogen in whey due to the other protein content in solution. It was also discovered that the ninhydrin and NOPA methods may measure free amino nitrogen and yeast-assimilable nitrogen accurately. Although only ninhydrin was able to be confirmed as accurate through statistical analysis. Overall, the experiments in this study were able to provide some insight into the nature of whey fermentation systems. We found valuable information regarding the alcoholic fermentation of whey using K. marxianus such as how pH, DAP, and zinc may affect the production of alcohol. We were also able to provide evidence that an already existing method of amino nitrogen measurement, ninhydrin FAN, may provide accurate results for use with whey.
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