## 3 Results and Discussion
### Optimizing Initial Glucose Concentration for Enhanced Selectivity in Erythririrol Production
Process parameters: total yield of the erythroid process production (Y), productivity of total erythroid process production (Q), erythroid specific production rate (q), and the selectivity of the process (S) (**B**) Cultivation conditions: 3.1 g/L of (NH4)2 SO4; 0.25 g/L of yeast extract, 250 mL of post-crystallization erythroid liquid. Mean values with different letters (A, C) (a, b) differ significantly at \(p\leq 0.05\). The theoretical yield of glucose conversion to erythroid is 67.8%. The process presented in this study had a yield of 58%, resulting in 174.8 g/L of erythroid. Upon analyzing the data in Table 2, 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 erythroid, 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 erythroid 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-erythnitol conversion reaction is also CO2, according to the reaction:  
\[\mathrm{C_{6}H_{12}O_{6}+3/2O_{2}\to C_{4}H_{10}O_{4}+2 CO_{2}+H_{2}O}\]  
The ability to produce erythroid from waste substrates like post- crystallization erythroid filtrate combined with the optimization of fermentation conditions could greatly reduce production costs and enhance the economic viability of erythroid production on an industrial scale. Additionally, the use of non GMO _Y. lipolytica_ K1 UV15, 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 erythroid 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 erythroid 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 erythroid 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 erythroid 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 \begin{table}
\begin{tabular}{c c c c} \hline  & & **Carbone [g/L]** & \\ \hline
**Name** & **Filtrate** & **Start Batch** & **End of Batch** \\ \hline Glucose & 0.0 & 120.0 & 0.0 \\ \hline Erythnitol & 88.0 & 11.2 & 68.7 \\ \hline Mannitol & 32.7 & 6.5 & 2.2 \\ \hline Arabitol & 17.1 & 4.5 & 1.2 \\ \hline Citric acid & 28.1 & 4.8 & 4.9 \\ \hline Biomass & 0.0 & 0.0 & 10.0 \\ \hline CO2 & - & - & 40.0 \\ theoretically from glucose & - & - & 127.0 \\ \hline SUM & 165.9 & 147.0 & 127.0 \\ \hline \end{tabular}
\end{table} 
Table 2: Mass balance of erythroid production in the process of conversion the glucose and post- crystallization erythroid filtrate. substrates and the high selectivity towards erythroid 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 erythroid production, which is highly attractive for the industry.