Bioconversion of a Dairy By-Product (Scotta) into Mannitol-Stabilized Violacein via Janthinobacterium lividum Fermentation

Abstract

Violacein is a natural pigment with a wide range of biological activities, including antimicrobial, antitumor, and immunostimulatory properties. However, its industrial-scale production is hindered by low yields from microbial fermentation. This study investigated the use of scotta, a low-value by-product of the dairy industry, as an alternative and cost-effective substrate for violacein biosynthesis using Janthinobacterium lividum DSM1522. Different types of scotta, including one derived from lactose-free cheese production, were characterized and tested in flask cultures and a 2 L bioreactor. The results demonstrated that both medium dilution and increased oxygen-transfer coefficient (kLa) significantly enhanced violacein production. In the bioreactor, a final yield of 58.72 mg of violacein for each litre of diluted scotta was achieved. The pigment was then stabilized through a spray-drying process using mannitol as a carrier, resulting in a water-soluble powder that retained antibacterial activity against Bacillus subtilis. The drying process also improved pigment solubility in water, suggesting its potential application in formulations to control Gram-positive bacteria. Overall, this study highlights the potential of scotta as a sustainable fermentation substrate and presents a promising encapsulation approach for violacein stabilization. However, further investigations are needed to optimize the spray-drying process, specifically, to characterize the microgranules and to determine their storage stability.