**4. Conclusions**

Suitable substrates rich in nutrients are necessary for microbial growth in the fermentation processes to produce economical, sustainable high value-added bioproducts. In this study, whey from the dairy industry was investigated as a fermentation medium for red pigment production by *M. purpureus*. To optimize fermentation conditions and maximize the yield, the effects of whey type, fermentation methods, initial lactose concentration, MSG concentration, initial pH, and inoculation ratio on red pigment synthesis by *M. purpureus* were systematically investigated. The results showed that DM whey is a suitable substrate for the red pigment synthesis by *M. purpureus* and SHF was highly affected by the tested process parameters. This research provides new insights into the utilization of whey produced in massive amounts and presents a possible solution for serious environmental pollution problems. The highest pigment synthesis was obtained with treated samples of whey (DM and DPDM) in this study. Since the nutrients or inhibitory compounds are different in each form of whey, they might have different effects on biomass formation and product synthesis. Hence, future studies will focus on the full characterization of all whey types and the positive and negative effects of the major and minor constituents on pigment synthesis by *Monascus purpureus*.

**Author Contributions:** D.M.: Investigation, Methodology, Formal Analysis, Writing—Original Draft Preparation, N.A.P.: Calculation, Review & Editing, Y.G.: Investigation, Conceptualization, Resources, Supervision. All authors have read and agreed to the published version of the manuscript.

**Funding:** No funding received for this study.

**Institutional Review Board Statement:** Not applicable.

**Informed Consent Statement:** Not applicable.

**Data Availability Statement:** Not applicable.

**Acknowledgments:** The authors would like to thank Saisamorn Lumyong from Chiang Mai University, Department of Biology, Thailand for kindly supplying the *Monascus purpureus* CMU 001 strain.

**Conflicts of Interest:** The authors declare no conflict of interest.
