Dairy manufacturing generates whey by-products, many of them considered waste; others, such as whey permeate, a powder high in lactose and minerals from deproteinated whey, have unrealized potential. This study identified yeast species capable of utilizing lactose from whey permeate to produce ethanol or organic acids, and identified fungal species that reduced the acidity of whey by-products. Reconstituted whey permeate was fermented anaerobically or aerobically for 34 days, using species from Cornell University’s Food Safety Lab, Alcaine Research Group, and Omega Labs. Yeast species: Kluyveromyces marxianus, Kluyveromyces lactis, Dekkera anomala, Brettanomyces claussenii, Brettanomyces bruxellensis; mold species: Mucor genevensis and Aureobasidium pullulans. Density, pH, cell concentrations, organic acids, ethanol, and sugar profiles were monitored. Under anoxic conditions, K. marxianus exhibited the greatest lactose utilization and ethanol production (day 20: lactose non-detectable; 4.52% ± 0.02 ethanol). Under oxic conditions, D. anomala produced the most acetic acid (day 34: 9.18 ± 3.38 g/L), and A. pullulans utilized the most lactic acid, increasing the fermentate’s pH (day 34: 0.26 ± 0.21 g/L, pH: 7.91 ± 0.51). This study demonstrates that fermentation of whey could produce value-added alcoholic or organic acid beverages, or increase the pH of acidic by-products, yielding new products and increasing sustainability.

Acid whey is a by-product generated in large quantities during dairy processing, and is characterized by its low pH and high chemical oxygen demand. Due to a lack of reliable disposal pathways, acid whey currently presents a major sustainability challenge to the dairy industry. The study presented in this paper proposes a solution to this issue by transforming yogurt acid whey (YAW) into potentially palatable and marketable beverages through yeast fermentation. In this study, five prototypes were developed and fermented by Kluyveromyces marxianus, Brettanomyces bruxellensis, Brettanomyces claussenii, Saccharomyces cerevisiae (strain: Hornindal kveik), and IOC Be Fruits (IOCBF) S. cerevisiae, respectively. Their fermentation profiles were characterized by changes in density, pH, cell count, and concentrations of ethanol and organic acids. The prototypes were also evaluated on 26 sensory attributes, which were generated through a training session with 14 participants. While S. cerevisiae (IOCBF) underwent the fastest fermentation (8 days) and B. claussenii the slowest (21 days), K. marxianus and S. cerevisiae (Hornindal kveik) showed similar fermentation rates, finishing on day 20. The change in pH of the fermentate was similar for all five strains (from around 4.45 to between 4.25 and 4.31). Cell counts remained stable throughout the fermentation for all five strains (at around 6 log colony-forming units (CFU)/mL) except in the case of S. cerevisiae (Hornindal kveik), which ultimately decreased by 1.63 log CFU/mL. B. bruxellensis was the only strain unable to utilize all of the sugars in the substrate, with residual galactose remaining after fermentation. While both S. cerevisiae (IOCBF)- and B. claussenii-fermented samples were characterized by a fruity apple aroma, the former also had an aroma characteristic of lactic acid, dairy products, bakeries and yeast. A chemical odor characteristic of petroleum, gasoline or solvents, was perceived in samples fermented by B. bruxellensis and K. marxianus. An aroma of poorly aged or rancid cheese or milk also resulted from B. bruxellensis fermentation. In terms of appearance and mouthfeel, the S. cerevisiae (IOCBF)-fermented sample was rated the cloudiest, with the heaviest body. This study provides a toolkit for product development in a potential dairy-based category of fermented alcoholic beverages, which can increase revenue for the dairy industry by upcycling the common waste product YAW.

Acid whey from Greek-style yogurt (YAW) is an underutilized byproduct and a challenge for the dairy industry. One alternative is the fermentation of YAW by yeasts such as Saccharomyces, Brettanomyces, and Kluyveromyces spp., to produce new styles of fermented beverages. Previous research in our group suggested that the sugar profiles of the dairy coproducts impacted the fermentation profiles produced by B. claussenii. The present work aims to describe the fermentation of dairy sugars by S. cerevisiae, K. marxianus, and B. claussenii, under conditions comparable to those of YAW. For this purpose, four preparations of yeast nitrogen base, each containing 40 g/L of either lactose (LAC), glucose (GLU), galactose (GAL), or a 1:1 mixture of glucose and galactose (GLU:GAL), all at pH 4.20, were used as fermentation media. The fermentation was performed independently by each organism at 25 °C under anoxic conditions, while density, pH, cell count, ethanol, and organic acids were monitored. Non-linear modeling was used to characterize density curves, and Analysis of Variance and Tukey’s Honest Significant Difference tests were used to compare fermentation products. K. marxianus and S. cerevisiae displayed rapid sugar consumption with consistent ethanol yields in all media, as opposed to B. claussenii, which showed more variable results. The latter organism exhibited what appears to be a selective glucose fermentation in GLU:GAL, which will be explored in the future. These results provide a deeper understanding of dairy sugar utilization by relevant yeasts, allowing for future work to optimize fermentations to improve value-added beverage and ingredient production from YAW.

In Greek-style yogurt production, every kilogram of product yields 2 to 3 kg of acid whey (YAW); this coproduct’s composition and low pH pose challenges for its proper valorization and reinsertion into the food supply chain. However, 240 mL of YAW contains over 9 g of lactose and represents a good source of minerals; these traits can be leveraged to develop nutritious fermented beverages. The purpose of this study is to investigate the aerobic fermentation of dairy sugars by different yeasts by characterizing these processes and their products. This will determine whether such methods provide viable options for the production of acetic-acid-containing beverages from YAW. To achieve this, yeast nitrogen base was used to prepare four growth media formulations, each supplemented with lactose, glucose, galactose, or a 1:1 mix of glucose and galactose (GLU:GAL), and each adjusted to a pH of 4.20. Fermentations were performed by pure cultures of S. cerevisiae, K. marxianus, B. claussenii, or B. bruxellensis, and were held at 25 °C with agitation at 185 rpm. For each treatment, density, pH, and microbial enumeration were measured over time to obtain process profiles, while ethanol, organic acids, and sugars were analyzed at the beginning and the end of each fermentation via HPLC, to determine resulting products. ANOVA and Tukey’s honest significant difference test at a significance level of 0.05 were used to compare residual sugars and fermentation products. Variable rates of sugar consumption were observed for each species. In GLU:GAL, B. claussenii consumed all of the glucose, left behind most of the galactose, and produced a high concentration of acetic acid. These results suggest the potential to develop versatile processes that target glucose for acetic acid production, while leaving available galactose to confer products with prebiotic properties. The development of processes for the conversion of YAW into beverages with organic acids and other healthful components not only aligns with consumers’ demands for better-for-you products, but also promotes the valorization of this otherwise underutilized dairy coproduct.

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Under specific conditions, the fermentation of whey permeate (WP) by Brettanomyces claussenii can create bioproducts with high galactose concentrations and potential functionalities. The aims of this research are to optimize the fermentation of WP by B. claussenii using response surface methodology to maximize the production of ethanol and galactose, and to characterize various products obtained with this approach. For this purpose, five fermentation factors were studied to determine their impacts on ethanol and galactose: temperature (20 - 40°C), substrate concentration (5 - 15%TS), lactase enzyme/substrate ratio (0 - 40 IU/ g lactose), inoculation level (6 - 8 log cfu/mL), and time (6 - 30 days). Linear models, containing quadratic and interaction effects, were built for the optimization of both responses. Optimal levels were predicted for the maximum obtainment of ethanol and galactose simultaneously, which utilized the following parameters: 15%TS, 37 IU / g lactose, 28°C, 7.5 log cfu/mL, and 30 days, which together were predicted to produce 4.0%v/v ethanol and 51 g/L galactose in the final product. These parameters were then applied to 18-L fermentations, and the resulting fermentates were processed via distillation and freeze-drying. As a result, four product streams were obtained: a fermented product with 3.4%v/v ethanol and 56 g/L galactose; a 45%v/v ethanol distillate; a galactose-rich drink base (63 g/L); and a galactose-rich powder (55%w/w). These results demonstrate that it is possible to maximize the production of ethanol and galactose from the fermentation of WP and to design manufacturing processes based on these optimization models, to develop novel, potentially functional bioproducts from this stream.

As the Greek-style yogurt market continues to experience prosperous growth, finding the most appropriate destination for yogurt acid whey (YAW) is still a challenge for Greek yogurt manufacturers. This study provides a direct alternative treatment of YAW by leveraging the abilities of Mucor circinelloides and Mucor genevensis to raise the pH of YAW and to produce fungal biomass with a high lipid content. Aerobic cultivations of these species were conducted in YAW, both with and without the addition of lactase, at 30 °C, and 200 rpm agitation. The density, pH, biochemical oxygen demand (BOD), biomass production, lipid content, fatty acid profile, and sugar and lactic acid concentrations were regularly measured throughout the 14-day cultivations. The data showed that M. genevensis was superior at deacidifying YAW to a pH above 6.0—the legal limit for disposing of cultured dairy waste. On the other hand, M. circinelloides generated more fungal biomass, containing up to 30% w/w of lipid with high proportions of oleic acid and γ-linolenic acid. Additionally, the treatments with lactase addition showed a significant decrease in the BOD. In conclusion, our results present a viable treatment to increase the pH of YAW and decrease its BOD, meanwhile generating fungal oils that can be further transformed into biodiesel or processed into functional foods or dietary supplements.

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