Table 2. Summary of observations from recent research on developing plant based or tissue culture meat color and concerns to trigger future research

Present observations	Future research needs
Low oxygen ambience may increase myoglobin expression during culturing muscle fibers (Post and Hocquette, 2017; Simsa et al., 2019).	Need further evaluation to assess the impact of low oxygen conditions on cultured meat (Kanatous et al., 2009; Schlater et al., 2014).
Hypoxic conditions resulted better efficiency with increased glucose uptake and lactic acid production and lipids or acetic acid media showed stimulation of myoglobin expression (Moritz et al., 2015).	Need further evaluation to assess the impact of low oxygen conditions on cultured meat (Kanatous et al., 2009; Schlater et al., 2014). Possible acidification may damage the cells (Kadim et al., 2015).
Sufficient iron is mandatory in the cell for myoglobin synthesis and color development (Rubio et al., 2019).	Uptake is transferrin-dependent (Kadim et al., 2015).
Myoglobin content in cultured meat may be improved by direct inclusion of myoglobin, recently addition of metmyoglobin (the oxidized form of myoglobin) increased cell proliferation and the content of myoglobin in cells (Simsa et al., 2019).	Bioavailability of iron and inclusion limit into myoglobin needs to be studied (Simsa et al., 2019). Still, the color of cultured beef meat is pale than real beef after adding metmyoglobin.
The possibilities of artificial color or plant-derived colors are under observation but only for processed meat products. Soy leghemoglobin was able to give the color and taste of a real beef burger (Watson, 2019).	As red meat is associated with health concerns, it is wise to develop alternative colorants for cultured meat (Gamage et al., 2018).