article · BMC Biotechnology
Whey was investigated as a growth medium to produce carotenoid pigments using the bacterium Micrococcus luteus. By statistically optimising operational conditions including whey concentration, inoculum size, pH, temperature, and agitation speed, carotenoid production reached 2.19 grams per litre. Analysis revealed twelve distinct carotenoid pigment compounds in the extract. Testing demonstrated that these carotenoids possess antioxidant activity and moderate antimicrobial effects against specific Gram-positive bacteria, including Bacillus cereus and Enterococcus faecalis, though activity against Gram-negative bacteria was limited. Biosafety assessments showed low cytotoxicity in normal mouse liver cells and an absence of substantial genotoxic effects. While heart, lung, and kidney tissues remained normal during histological analysis, some cellular changes were observed in liver tissue.
Carotenoids are widely used natural compounds with valuable antioxidant and antimicrobial properties. Utilising dairy waste such as whey to cultivate bacteria for pigment production provides a potential avenue to turn industrial by-products into high-value biochemicals. Assessing the biological activities alongside toxicity and safety profiles helps establish whether microbial pigments can be safely considered for health, food, or industrial settings.
This research represents early-stage laboratory work that could interest industrial biotechnology and bioprocessing firms seeking microbial sources of natural antioxidants and pigments. The process demonstrates that dairy whey can serve as a substrate for carotenoid synthesis, though further downstream development, in vivo validation, and safety verification regarding liver tissue effects would be required before progressing towards practical application.
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This study aimed to optimize the production of carotenoid pigments from Micrococcus luteus (ATCC 9341) through the statistical screening of media components and the characterization of antimicrobial, antioxidant, cytogenetic and cytotoxic activities. A BOX-Behnken design was used to assess the effects of whey concentration, inoculum size, pH, temperature, and agitation speed on carotenoid yield. The optimum combination increased production to 2.19 g/L, with a productivity of 0.045 g L<sup>-1</sup> h<sup>-1</sup> and a productivity yield of 0.644 g/g, as confirmed by an observed carotene production of 2.19 g/L. The final response surface model fitting the data had an R<sup>2</sup> of 0.9461. High-performance liquid chromatography (HPLC) analysis identified 12 carotenoid pigment compounds produced by M. luteus. The extracts displayed moderate antimicrobial efficacy against Gram-positive bacteria such as Bacillus cereus (ATCC 11778), Staphylococcus aureus (ATCC 6538), and E. faecalis (ATCC 19433), with inhibition zone diameters (IZD) of 29.0, 14.0, and 37.0 mm, respectively, at 1000 μg/mL. However, its effectiveness against Gram-negative bacteria is limited. In comparison, tetracycline exhibited greater antimicrobial potency. The IC<sub>50</sub> value of carotenoids was used to indicate the antioxidant activity. IC<sub>50</sub> value from the DPPH assay was 152.80 mg/100mL. An IC<sub>50</sub> cytotoxicity value greater than 300 μg/mL was found against normal mouse liver cells, with over 68% cell viability even at 300 μg/mL, indicating low toxicity. Histological structure studies revealed normal myocardial muscle tissue, lung tissue, and kidney tissue sections, whereas liver tissue sections revealed ballooning degeneration of hepatocytes and disorganization of hepatic cords. Cytogenetic parameters revealed that the carotene treatment group had a mitotic index (70%) lower than that of the control but higher than that of the positive control, mitomycin, and did not substantially increase numerical (1.2%) or structural aberrations compared with those of the control, suggesting a lack of genotoxic effects under the experimental conditions. In conclusion, optimized culture conditions enhanced carotenoid yields from M. luteus, and the extracts displayed promising bioactivity as moderate antibiotics against certain gram-positive bacteria and as antioxidants. The high IC<sub>50</sub> values demonstrate biosafety. Overall, this bioprocess for enhanced carotenoid production coupled with bioactivity profiling and low cytotoxicity support the application of M. luteus carotenoids.
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DOI: 10.1186/s12896-024-00899-6
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