Fermentation of an aqueous ice cream byproduct by lactose-utilizing yeast species

Authors: Miller, Amanda; Renye Jr, John; Thomas, Jennifer; Oest, Adam; Johnston, David; Garcia, Rafael

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/12/2025
Publication Date: N/A
Citation: N/A

Interpretive Summary: The ice cream industry generates large amounts of wasted product each year which is an economic burden for manufacturers due to lost product and costly disposal fees due to potential environmental impacts of this waste. This challenge has led researchers to look for new ways to convert waste streams into desirable products, including beverage alcohol. Previous work showed the potential to generate beverage alcohol from waste ice cream using traditional brewer’s yeast, and this study investigated the potential for using other yeasts, commonly associated with dairy products, to improve the fermentation process. Results from this confirmed the other yeasts could ferment the milk sugar lactose, but they did not utilize this sugar when sucrose was present. The lack of lactose utilization within waste ice cream showed there was no benefit to using the other yeast strains tested when brewer’s yeast was shown to produce the highest ethanol yield under optimized conditions. Optimizing this fermentation process is expected to benefit the ice cream industry by offering a potential solution for reclaiming value from their waste material and minimizing the industry’s environmental impact.

Technical Abstract: Abstract: This study evaluated the fermentative performance of several yeast strains on the aqueous byproduct of waste ice cream (WIC) to ethanol, comparing three reported lactose-utilizers, Kluyveromyces marxianus Y-329, Dekkera anomala Y-1414, and Kluyveromyces lactis 8585, with the non-lactose utilizer, Streptomyces cerevisiae Y-45. Fermentation progression was monitored by weight loss, and high-performance liquid chromatography was used to analyze the composition of the fermentates. Ethanol production reached >10% for S. cerevisiae and K. marxianus, but was < 5% for D. anomala and K. lactis, possibly due to catabolite repression from the hydrolysis of sucrose. Treatment of the WIC byproduct with lactase increased the availability of fermentable carbohydrates, resulting in greater ethanol yields for all strains, except K. marxianus Y-1414, which may be limited by its ethanol tolerance. A minimal medium supplemented with lactose, sucrose or a combination of both sugars was used to test if the yeast could metabolize lactose alone or in the presence of sucrose. Sucrose was utilized by all four strains and produced ethanol in the absence and presence of lactose. Lactose was only utilized by D. anomala Y-1414 and K. lactis 8585 in the absence of sucrose, confirming that the presence of sucrose can prevent lactose utilization by yeasts in this study. Fermentation efficiency was also determined, with S. cerevisiae Y-45 having achieved the greatest efficiency in sucrose alone, while K. lactis 8585 showed the greatest efficiency in lactose alone. Results from this study showed S. cerevisiae remains the ideal candidate for the valorization of waste ice cream as it had the highest ethanol yield in WIC byproduct with lactose; and increased when lactose was hydrolyzed with lactase, reaching 12.5% at 72 h.