Waste-Free Glucose to Erythritol Conversion—Innovations with Yarrowia lipolytica Wratislavia K1 UV15

Abstract

This study investigates the waste-free bioconversion of glucose to erythritol using the UV-mutagenized strain Yarrowia lipolytica Wratislavia KI UV15. This research focuses on optimizing fermentation parameters to enhance erythritol yield, with a key emphasis on utilizing post-crystallization erythritol filtrate as a primary carbon source, promoting a cost-effective and sustainable approach to erythritol production. The experimental design included systematic variations in ammonium sulfate concentration, yeast extract supplementation, and initial glucose concentration. The results demonstrate that the UV15 strain achieves high erythritol production efficiency. An optimal nitrogen source concentration (3.1 g/L) and reduced yeast extract levels (0.25 g/L) provided the best results, achieving a maximum erythritol concentration of 174.8 g/L with a yield of 58.2%. Furthermore, lowering the initial glucose concentration further improved process efficiency, confirming the feasibility of using post-crystallization filtrate as an effective and sustainable carbon source. These findings highlight the biotechnological potential of Y. lipolytica UV15 in erythritol production, demonstrating its adaptability to waste-derived substrates and advancing the development of economically viable, environmentally sustainable production methods.

1. Introduction

Glucose is widely used in biotechnology, the food, pharmaceutical, and cosmetic industries, serving as an important raw material for the production of alcohols, organic acids, proteins, and enzymes [1,2]. Over the past few decades, its role in biotechnology has significantly increased, particularly with the development of bioethanol production [3]. The price of glucose has shown mild fluctuations and slight decreases over the years for both import and export markets. According to a report on the industrial glucose market (https://www.gminsights.com/industry-analysis/industrial-glucose-market, accessed on 6 January 2025), the global industrial glucose market size in 2022 was estimated at approximately USD 40 billion, reflecting significant demand and use in the food, pharmaceuticals, and fermentation industries. While there are some variations, the market price of glucose for biotechnological applications appears to range from about USD 0.10/kg to USD 0.26/kg [4,5,6]. However, the total cost of the final product, in this case erythritol, is influenced not only by the price of the substrate but also by the technology used to obtain pure crystals and the management of by-products.

Erythritol is sought after primarily for its low-calorie sweetening properties, and because its consumption does not affect insulin or glucose levels, it is gaining increasing popularity among sweeteners [7]. In recent years, there has been significant growth in erythritol production, with its production value expected to exceed USD 150 million by 2023 [8]. However, its biosynthesis is accompanied by various metabolic by-products, which can affect both production efficiency and economic viability in industrial applications. There are few studies in the available literature reporting erythritol production from glucose by Y. lipolytica yeasts, and the described research has confirmed that these yeasts can convert glucose into erythritol with high efficiency when their metabolism is properly engineered. Targeted metabolic and process engineering—through overexpression of enzymes, enhancement of NADPH, disruption of pathways, and advanced gene editing—enables the achievement of erythritol yields from glucose in the range of 171–256 g/L [3,9,10,11,12,13]. The biosynthesis of erythritol, using Y. lipolytica yeast, can yield several by-products, the quantities of which vary depending on the strain [14]. However, microorganisms designed for higher erythritol yields can minimize by-product formation [5]. Another important factor influencing the production of other compounds during erythritol biosynthesis is the type and purity of the substrate. For instance, using crude glycerol may result in higher levels of undesirable compounds compared to pure substrates [6]. Primarily, mannitol is often produced during the biosynthesis of both erythritol and citric acid from glycerol, but another sugar alcohol, arabitol, can also form. The presence of sodium chloride (NaCl) in the medium can enhance erythritol production while inhibiting mannitol synthesis [15]. Various organic acids, mainly citric acid, may also be produced during erythritol biosynthesis, contributing to the overall by-product profile. Environmental conditions, such as pH, temperature, and osmotic pressure (e.g., due to NaCl addition), cannot be overlooked as they can alter metabolic pathways, affecting both erythritol yield and the profiles of by-products [6].

The aim of this study was to investigate the impact of medium composition, including the concentration of nitrogen sources, glucose, and yeast extract (YE), on the efficiency and selectivity of erythritol biosynthesis by the Y. lipolytica K1UV15 strain. This research aimed to determine the optimal production conditions using waste substrates, such as post-crystallization erythritol filtrate, and to minimize the use of components that negatively affect the crystallization process of the product. Figure 1 shows the exact course of the fermentation experiment and the origin of the substrate components. Particular attention was given to evaluating the optimal concentration of ammonium sulfate ((NH₄)₂SO₄) as a nitrogen source, examining the impact of reducing or eliminating yeast extract (YE), combined with thiamine supplementation on yeast growth and erythritol production parameters. The potential was analyzed for reducing the initial glucose concentration and the utilization was studied of organic compounds present in the erythritol post-crystallization filtrate as an alternative carbon source. Glucose feeding strategies during cultivation to enhance process selectivity and efficiency were evaluated. This study also aimed to provide practical guidelines for optimizing fermentation processes using waste substrates, enabling cost reduction and improving the purity of the final product.

2. Materials and Methods

2.1. Microorganism

These studies utilized the yeast strain Y. lipolytica K1UV15, which was obtained through UV-induced mutagenesis of the Wratislavia K1 strain [16]. The strain is characterized by a lack of ability to utilize erythritol, similar to the parental strain.

2.2. Media

The composition of the individual media used in the experiments is presented in

Table 1. Media composition used in the present study.

Lp.	Name	Composition (g/L)	Purpose
1.	Inocula	glucose—40.0; peptone—2.0; yeast extract—3.0; distilled water up to 1.0 L	Inoculum preparation
2.	Filtrate originating from erythritol crystallization	erythritol—224.0 ± 2.9, mannitol—82.6 ± 5.1, arabitol—42.8 ± 2.1, citric acid—60.2 ± 0.6	Carbon source in the production medium
4.	Production medium 1	glucose 300.0 (25.0 g/L at the beginning of the process, 200.0 g/L and 75.0 g/L added after 24 h and 48 h), filtrate (130.0 mL), (NH4)2SO4—2.6, 3.1, 3.6, 4.1), MgSO4·7H2O—1; KH2PO4—0.22; yeast extract—1.0	Selection of optimal nitrogen source concentration
5.	Production medium 2	glucose 300.0 (25.0 g/L at the beginning of the process, 200.0 g/L and 75.0 g/L added after 24 h and 48 h), filtrate (130.0 mL), (NH4)2SO4—3.1 g/L, MgSO4·7H2O—1.0; KH2PO4—0.22; yeast extract—0.0, 0.25, 0.5, 0.75, 1.0; thiamine 200 µg/L in medium with 0.0, 0.5, 0.75 of yeast extract	Selection of optimal yeast extract concentration
6.	Production medium 3	Glucose 300.0 (0.0, 5.0, 10.0, 15.0, 25.0 at the beginning of the process and 250.0 g/L and the rest to 300.0 g/L added after 24 h and 48 h), filtrate—250.0 mL, (NH4)2SO4—3.1 g/L, MgSO4·7H2O—1; KH2PO4—0.22; yeast extract—0.25.	Analyzing the potential for reducing the initial glucose concentration

. The medium used for preparation of inoculum for the bioreactor production culture contained (g/L) glucose—40.0; peptone—2.0; yeast extract—3.0; and distilled water up to 1.0 L.

The production medium 1, 2, and 3 consisted of (g/L) (NH₄)₂SO₄—ranged from 2.6 to 4.1; MgSO₄·7H₂O—1.0; KH₂PO₄—0.22; yeast extract—ranged from 0.0 to 1.0, total glucose 300.0, filtrate originating from erythritol crystallization (Figure 1)—130.0 and 250.0 mL. At the start of the cultivation, the initial glucose concentration ranged from 0.0 to 25.0 g/L, with additional portions added at 24 and 48 h, as specified in the captions of Figure 2, Figure 3 and Figure 4.

The filtrate was obtained from the liquid remaining after cultivation under conditions promoting erythritol overproduction. After separating the biomass, the resulting liquid was concentrated using a vacuum evaporator (Buchi Labortechnik AG, Flawil, Switzerland) to an erythritol concentration of approximately 650.0 g/L. It was then used to produce erythritol crystals. Following the separation of erythritol crystals, a filtrate was obtained, with the composition given in Table 1.

2.3. Culture Conditions

Inoculation cultures were performed in 300 mL conical flasks containing 50 mL of inoculation medium and cultivated for 72 h on a rotary shaker at 30 °C and 140 rpm. Each time, 100 mL of inoculation culture was used to inoculate the production culture in the bioreactor. Bioreactor production cultures were carried out in duplicate in a 5 L Biostat B Plus fermentor (Sartorius, Göttingen, Germany) with a working volume of 2 L. Production cultures were conducted at 29.0 °C, with agitation at 700 rpm, aeration at 0.8 vvm, and a pH of 3.0–3.1, maintained by automatic addition of 20% (w/v) NaOH.

2.4. Analytical Methods

Biomass (X) was determined using the gravimetric method after filtration of 10 mL of culture sample. The HPLC was performed to determine the concentration of the substrate (glucose, GLU) and products, i.e., citric acid (CA), erythritol (ERY), mannitol, and arabitol [17]. Data were analyzed using the Statistica 13.3 software. One-way analysis of variance was performed to detect significant differences in the data. Homogeneous groups were determined using Duncan’s test (p ≤ 0.05). Data are presented as mean values of three samples, and error bars represent standard deviation.

2.5. Calculation of Fermentation Parameters

The total yield of erythritol process production (Y), which includes the production of erythritol from glucose and the concentration of erythritol present in post-crystallization erythritol filtrate, expressed in g/g, was calculated using Equation (1):

$$\mathrm{Y}={\displaystyle \frac{\mathrm{E}\mathrm{R}\mathrm{f}+\mathrm{E}\mathrm{R}}{\mathsf{\Delta }\mathrm{G}\mathrm{L}\mathrm{U}}}$$

(1)

The productivity of total erythritol process production (Q), expressed in g/Lh, was calculated using Equation (2):

$$\mathrm{Q}={\displaystyle \frac{\mathrm{E}\mathrm{R}\mathrm{f}+\mathrm{E}\mathrm{R}}{\mathsf{\Delta }\mathrm{t}}}$$

(2)

The erythritol specific production rate (q), expressed in g/gh, was calculated using Equation (3):

$$\mathrm{q}={\displaystyle \frac{\mathrm{Q}}{\mathrm{X}\mathrm{s}\mathrm{t}}}$$

(3)

The selectivity of erythritol production (S) as the percentage share of erythritol in the total sum of products, expressed in %, was calculated using Equation (4):

$$\mathrm{S}={\displaystyle \frac{\mathrm{E}\mathrm{R}\times 100\mathrm{\%}}{\mathrm{S}\mathrm{U}\mathrm{M}}}$$

(4)

In all these equations, ERf indicates the concentration of erythritol in post-crystallization erythritol filtrate (g/L); ER indicates the concentration of erythritol produced at the end of the cultivations (g/L); ΔGLU denotes the concentration of glucose consumed (g/L); Xst denotes the concentration of biomass in stationary phase (g/L); t denotes the duration of the fermentation process (h); and SUM denotes the combination of concentrations of arabitol, mannitol, erythritol, and citric acid at the end of cultivation (g/L).

3. Results and Discussion

3.1. Optimization of (NH₄)₂SO₄ Concentration for Efficient Erythritol Biosynthesis by Y. lipolytica Using Glucose and Post-Crystallization Filtrate

In the first stage of this study, the concentration of the nitrogen source, (NH₄)₂SO₄, was optimized for efficient biosynthesis of erythritol from glucose. (NH₄)₂SO₄ had already been used in preliminary studies involving the Wratislavia K1UV15 strain [16]. Notably, this compound was identified as the optimal nitrogen source for erythritol production from glycerol [17]. Four cultivation processes were conducted with (NH₄)₂SO₄ concentrations of 2.6, 3.1, 3.6, and 4.1 g/L, respectively (Table 1—Production medium 1).

The total glucose concentration was 300.0 g/L, with initial cultures grown in a medium containing both glucose (25.0 g/L) and compounds present in the filtrate obtained after erythritol crystallization from the post-culture liquid (130.0 mL), including erythritol, mannitol, arabitol, and citric acid. The working volume at the start of cultivation was approximately 1400 mL, and additional portions of concentrated glucose solution, 200.0 g/L and 75.0 g/L, were added after 24 and 48 h, respectively. The working volume of the bioreactor reached 2 L after the final glucose addition. Results obtained from these cultivations are presented in Figure 2. The cultivations continued until all glucose was consumed, which took between 140 h for 4.1 g/L (NH₄)₂SO₄ and 216 h for 2.6 g/L (NH₄)₂SO₄ (Figure S1). The highest erythritol concentration, 146.3 g/L, was achieved in the process conducted with 3.1 g/L (NH₄)₂SO₄ (Figure 2A). Under these conditions, key cultivation parameters such as yield (0.49 g/g) and volumetric erythritol production rate (0.87 g/Lh) were also the highest and significantly differed from the parameters obtained in the other three cultivations (Figure 2B).

In the collected samples, the presence of other polyols, such as mannitol and arabitol as well as small amounts of citric acid, was also detected. The contribution of these products to the total metabolites produced did not exceed 19%. The highest selectivity, 86% (with the lowest relative amount of by-products), was observed in the cultivation conducted with 3.6 g/L (NH₄)₂SO₄ (Figure 2B).

Figure 2. The increase in erythritol concentration depending on the amount of (NH₄)₂SO₄ in the cultivation medium (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B). Cultivation conditions: initial glucose concentration 25.0 g/L; 1 g/L of yeast extract; 130 mL of post-crystallization erythritol liquid. Mean values with different letters (A, B, C) (a, b, c) differ significantly at p ≤ 0.05.

Figure 2. The increase in erythritol concentration depending on the amount of (NH₄)₂SO₄ in the cultivation medium (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B). Cultivation conditions: initial glucose concentration 25.0 g/L; 1 g/L of yeast extract; 130 mL of post-crystallization erythritol liquid. Mean values with different letters (A, B, C) (a, b, c) differ significantly at p ≤ 0.05.

3.2. Impact of Yeast Extract Reduction on Erythritol Production and Purity in Y. lipolytica

For the second stage of this project, a nitrogen source concentration of 3.1 g/L was selected. The aim of this experiment was to compare erythritol production parameters at different concentrations of YE, which is commonly used as a source of thiamine in media for erythritol production, as well as for the biosynthesis of citric acid by Y. lipolytica.

Y. lipolytica yeast strains are natural thiamine auxotrophs, as they cannot synthesize the pyrimidine moiety of the thiamine molecule. Without thiamine, they fail to grow [18]. According to the literature data, the concentration of this vitamin required for proper growth is 200 μg/L [19]. However, other studies have highlighted varying sensitivities of strains to thiamine deficiency/concentration [20]. In microbiological media, pure thiamine is often replaced with natural ingredients such as corn steep liquor (CSL) or YE. CSL originates from a waste stream in the corn starch wet-milling process. It is rich in organic nitrogen, amino acids, lactic acid, minerals, vitamins, and reducing sugars [21]. However, CSL’s batch-to-batch variability, high solids’ content, and strong coloration are significant disadvantages for its use as a nutrient source in fermentation processes [22]. YE is a product primarily derived from waste brewer’s yeast. It is rich in nucleotides, proteins, amino acids, sugars, and various trace elements. Its advantages include low production costs and abundant raw material supply. However, the presence of YE can result in yellow discoloration of erythritol crystals. Therefore, reducing or even eliminating YE in the medium composition could eliminate the decolorization step, improving crystallization efficiency and erythritol purity. Decolorization is also widely used for other polyols, such as xylitol [23].

Two commonly employed approaches involve decolorization during either the recovery or purification stage, typically using activated carbon. In both cases, the key parameters identified include dose, temperature, contact time, and mixing speed [24,25]. Nevertheless, a virtually colorless post-culture liquid can be obtained by minimizing the addition of coloring components to the culture—in this case, YE. Studies on erythritol biosynthesis from glycerol by Y. lipolytica [20] identified a YE concentration of 1.0 g/L as optimal. Therefore, earlier experiments were conducted at this concentration (Figure 2). However, in the following study, erythritol production parameters were examined with a reduced YE content (Figure 3).

Figure 3. The influence of yeast extract (YE) concentration on the final erythritol concentration and on the biomass concentration in the stationary phase (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B). Cultivation conditions: initial glucose concentration 25.0 g/l; 3.1 g/L of (NH₄)₂SO₄; 130 mL of post-crystallization erythritol liquid. Mean values with different letters (A) (a) differ significantly at p ≤ 0.05.

Figure 3. The influence of yeast extract (YE) concentration on the final erythritol concentration and on the biomass concentration in the stationary phase (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B). Cultivation conditions: initial glucose concentration 25.0 g/l; 3.1 g/L of (NH₄)₂SO₄; 130 mL of post-crystallization erythritol liquid. Mean values with different letters (A) (a) differ significantly at p ≤ 0.05.

Four cultivation processes were conducted in the presence of 3.1 g/L (NH₄)₂SO₄, with YE concentrations ranging from 0.00 to 0.75 g/L (Table 1—Production medium 2). Any potential thiamine deficiency in cultures with 0.00–0.75 g/L YE was supplemented with the addition of 200 µg/L of pure vitamin. For comparison, Figure 3 also includes results from the cultivation conducted at YE = 1.0 g/L (from the previous experiment). The time required for complete glucose utilization ranged narrowly from 168 to 182 h, and the final erythritol concentration varied from 141.9 g/L (YE = 0.75 g/L) to 155.0 g/L (YE = 0.25 g/L) (Figure 3A). No statistically significant differences were observed in the erythritol production parameters; however, the highest values of yield (Y = 0.52 g/g) and volumetric productivity (Q = 0.85 g/Lh), as well as the highest selectivity (87%), were noted at a YE concentration of 0.25 g/L (Figure 3B).

Based on these results, it can be concluded that the medium for erythritol production from glucose does not necessarily require YE in its composition, but only 200 μg/L of thiamine. However, due to the lower biomass level in the cultivation without YE addition (Figure 3A) and the slightly higher erythritol production parameters achieved at 0.25 g/L YE (Figure 3B), this YE concentration was chosen for subsequent experiments.

3.3. Optimizing Initial Glucose Concentration for Enhanced Selectivity in Erythritol Production

In the last experiment, the possibility of reducing the initial glucose concentration was tested to improve the selectivity of erythritol production. At the start of the cultivation, the carbon source in all the processes described above was glucose (25.0 g/L) and the compounds contained in the crystallization liquid of erythritol, which was added to the medium in an amount of 130 mL. This amount of liquid resulted in initial concentrations of erythritol (approximately 20.0–22.0 g/L), as well as mannitol, arabitol, and citric acid at 8.5 g/L, 5.8 g/L, and 5.4 g/L, respectively. In subsequent cultivations, 250 mL of the crystallization liquid was used, generating approximately double the initial concentrations of erythritol, mannitol, arabitol, and CA. Four cultivations containing 250 mL of crystallization liquid were carried out, with initial glucose concentrations ranging from 0.0 to 15.0 g/L (Figure 4).

The final concentration of erythritol in these cultures ranged from 156.6 g/L to 174.8 g/L (Figure 4A). The erythritol production yield (0.55 and 0.58 g/g) was highest in the process without glucose or with 5.0 g/L of glucose, while the Q parameter showed similar values of 0.90 ± 0.03 g/Lh at glucose concentrations ranging from 5.0 to 15.0 g/L. The conducted cultivations demonstrated the highest production selectivity in cultures with the lowest glucose concentration or no glucose in the medium, at 89% and 90%, respectively (Figure 4B). Thus, it can be concluded that the crystallization liquid of erythritol and a minimal initial glucose concentration of 5.0 g/L can be effectively used for the erythritol production.

One of the key objectives of this study was to assess the potential of organic compounds in the post-crystallization erythritol filtrate as alternative carbon sources. To achieve this goal, a detailed analysis was performed to monitor changes in the concentrations of mannitol, arabitol, and citric acid during cultivation. This analysis was carried out both in the absence of glucose and in the presence of 15.0 g/L glucose in the medium. The results of these experiments are presented in Figure 5A,B. However, it should be noted that the erythritol present in the filtrate was not utilized, as seen in Figure 4A, because the K1UV15 strain, like the Wratislavia K1 strain, does not utilize this polyol [16]. Nevertheless, in the case of many other strains, erythritol is utilized [26], which increases the pool of available carbon sources.

Figure 4. The increase in erythritol concentration at different initial glucose concentrations (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B) Cultivation conditions: 3.1 g/L of (NH₄)₂SO₄; 0.25 g/L of yeast extract, 250 mL of post-crystallization erythritol liquid. Mean values with different letters (A, C) (a, b) differ significantly at p ≤ 0.05.

Figure 4. The increase in erythritol concentration at different initial glucose concentrations (A). Process parameters: total yield of the erythritol process production (Y), productivity of total erythritol process production (Q), erythritol specific production rate (q), and the selectivity of the process (S) (B) Cultivation conditions: 3.1 g/L of (NH₄)₂SO₄; 0.25 g/L of yeast extract, 250 mL of post-crystallization erythritol liquid. Mean values with different letters (A, C) (a, b) differ significantly at p ≤ 0.05.

In these processes, the yeast utilized the compounds in the crystallization liquid; however, the use of these compounds as a carbon source for yeast growth was strongly dependent on the presence of glucose in the medium, as shown in Figure 5. In the absence of sugar in the medium, the yeast utilized the available citric acid and nearly 50% of mannitol within the first 24 h. The concentration of arabitol also decreased by approximately 3.0 g/L (Figure 5A). In the next 24 h, further reductions in mannitol concentration were observed, down to 5.5 g/L. Subsequently, a slight increase in the amount of mannitol was noted, as well as citric acid and arabitol, whose final concentration was the highest among all the cultivations conducted, reaching 10.5 g/L.

In the presence of sugar, however, glucose was the preferred carbon source. Nonetheless, a significant decrease in citric acid concentration, to below 1.0 g/L, was observed during the first 24 h. Mannitol and arabitol remained at unchanged levels during this period (Figure 5B). In this cultivation, during the following hours, the concentrations of mannitol and arabitol stabilized and remained within the range of 6.0–9.6 g/L, while the concentration of citric acid increased to 9.1 g/L by the end of the process.

The theoretical yield of glucose conversion to erythritol is 67.8%. The process presented in this study had a yield of 58%, resulting in 174.8 g/L of erythritol. Upon analyzing the data in

Table 2. Mass balance of erythritol production in the process of conversion the glucose and post-crystallization erythritol filtrate.

	Carbone [g/L]
Name	Filtrate	Start Batch	End of Batch
Glucose	0.0	120.0	0.0
Erythritol	88.0	11.2	68.7
Mannitol	32.7	6.5	2.2
Arabitol	17.1	4.5	1.2
Citric acid	28.1	4.8	4.9
Biomass	0.0	0.0	10.0
CO2 theoretically from glucose	-	-	40.0
SUM	165.9	147.0	127.0

Cultivation conditions: 300 g/L glucose, 3.1 g/L of (NH₄)₂SO₄; 0.25 g/L of yeast extract; 250 mL of post-crystallization erythritol liquid.

, it is clear that 147.0 g/L of carbon enters the process (filtrate and glucose). In the products, 68.7 g/L of carbon in erythritol, 8.3 g/L of carbon in the analyzed by-products, and 10 g/L of carbon in biomass were obtained. Therefore, the amount of by-products is relatively low. Additionally, after the crystallization of erythritol and separation of biomass, the liquid can be recycled into the next cycle, as demonstrated in this work. A by-product of the glucose-to-erythritol conversion reaction is also CO₂, according to the reaction:

C₆H₁₂O₆ + 3/2O₂ → C₄H₁₀O₄ + 2CO₂ + H₂O

The ability to produce erythritol from waste substrates like post-crystallization erythritol filtrate combined with the optimization of fermentation conditions could greatly reduce production costs and enhance the economic viability of erythritol production on an industrial scale. Additionally, the use of non GMO Y. lipolytica K1UV15, a strain optimized through UV mutagenesis, further improves yield and purity, making it a more efficient option compared to conventional methods.

In comparison to other erythritol production platforms, Y. lipolytica UV15 shows promise for being more cost-effective. Traditional production platforms typically use glucose or glycerol as substrates, which are generally higher in cost compared to waste by-products. The use of waste-derived carbon sources such as the erythritol crystallization filtrate in this study represents a significant advantage. Not only does this reduce reliance on expensive raw materials, but it also offers a more sustainable approach by utilizing industrial by-products. Additionally, the optimization of fermentation conditions, such as reducing yeast extract concentration and adjusting glucose levels, contributes to lowering the overall costs associated with erythritol production.

Comparing Y. lipolytica UV15 with other platforms, this strain presents a competitive edge in terms of selectivity, yield, and the ability to minimize by-products, making it a more cost-effective choice for large-scale erythritol production. Conventional methods, such as those using Candida or Aspergillus strains, often face higher production costs due to the necessity of pure glucose as a carbon source and the requirement for extensive downstream processing to purify the final product. In contrast, Y. lipolytica UV15’s ability to utilize waste substrates and the high selectivity towards erythritol production reduces both operational and purification costs, offering a more commercially viable alternative.

Thus, this study has the potential to significantly lower production costs while improving the environmental footprint of erythritol production, which is highly attractive for the industry.

Figure 5. The utilization of compounds contained in the post-crystallization erythritol filtrate depending on the absence (A) or presence of glucose (B) in the medium at the start of cultivation. Cultivation conditions: 3.1 g/L of (NH₄)₂SO₄; 0.25 g/L of yeast extract; 250 mL of post-crystallization erythritol liquid.

Figure 5. The utilization of compounds contained in the post-crystallization erythritol filtrate depending on the absence (A) or presence of glucose (B) in the medium at the start of cultivation. Cultivation conditions: 3.1 g/L of (NH₄)₂SO₄; 0.25 g/L of yeast extract; 250 mL of post-crystallization erythritol liquid.

4. Conclusions

This study confirmed that the compounds contained in the filtrate remaining after erythritol crystallization can be used for yeast growth and subsequent biosynthesis of erythritol. The possibility of producing other compounds, such as citric acid, α-ketoglutaric acid, pyruvic acid, as well as biomass itself, is also not excluded. A simple production medium was formulated using the filtrate, with a minimal initial glucose concentration, containing 3.1 g/L (NH₄)₂SO₄, 0.25 g/L YE (as well as MgSO₄·7H₂O—1; KH₂PO₄—0.22 g/L), which enabled the production of 174.8 g/L erythritol with a yield and selectivity of 0.58 g/g and 90%, respectively. These results highlight the potential of using waste substrates in the biotechnological production of erythritol, which may contribute to cost reduction and increased efficiency of fermentation processes.