Effect of cheese whey on phycobiliproteins production and FAME profile by Arthrospira platensis (Spirulina): Promoting the concept of a circular bio-economy

Despite being historically considered waste, cheese whey (CW) contains high concentrations of organic matter such as lactose which could be used by microalgae for their growth. This study explores the mixotrophic cultivation of Arthrospira platensis (Spirulina ) using CW as a sustainable substrate. The results show that the optimal CW content leading to the best growth rate and biomass yield is 0.8% v v -1 . In a 4 L glass photobioreactor, the study replicates the best CW ratio, resulting in increased biomass and productivity (1.57 g L -1 and 152 mg L -1 day -1 ) compared to the control (1.14 g L -1 and 132 mg L -1 day -1 ). Mixotrophic cultures exhibited faster growth, suggesting potential for quick biomass production. Under mixotrophy, S. platensis produces significantly more phycocyanin than in photoautotrophic conditions (3.52 mg mL -1 vs. 2.55 mg mL -1 , respectively), highlighting that CW's can boost the metabolic pathways leading to the synthesis of this relevant antioxidants which could be sold in the market at relatively high prices. The fatty acid methyl esters (FAME) profile of S. platensis in mixotrophic conditions shows minimal changes in fatty acids compared to the control, resembling olive oil with essential monounsaturated fatty acids (MUFAs). Notably mixotrophy increased the % of gamma- linolenic fatty acid omega- 6 (15.4%) compared to the control (11.2%). The study emphasizes the need to keep CW supplementation below 2.5% v v -1 for optimal nutritional and health benefits, including preventing endothelial dysfunctions and cardiovascular deseases in general. Moreover, the findings underscore the advantageous use of mixotrophic cultivation with CW for S. platensis , offering an economically viable and ecologically sustainable approach to microalgae production.