Effect of Nutrient Supplementation on the Biochemical Composition and Microbial Safety of Open-Pond Spirulina Cultivated in Cameroon

Spirulina (Arthrospira platensis) is globally recognized for its high nutritional value and potential as a sustainable food source. However, the influence of targeted nutrient supplementation on its biochemical composition and microbial safety under tropical open-pond conditions remains underexplored, particularly in sub-Saharan Africa. This study evaluated the effects of three nutrient supplementation regimes (compositions A, B, and C) and a control on Spirulina cultivated over 30 days in raceway ponds at the Nomayos Spirulina Production Farm in Cameroon. All treatments maintained physicochemical parameters within ranges favorable for Spirulina growth. Composition A significantly enhanced protein content (60.38 ± 0.68%), while composition C promoted carbohydrate accumulation (28.02 ± 0.41%). Microbial assessments revealed variable contamination levels, with composition B exhibiting the highest Escherichia coli (1.05 ± 0.075 × 105 CFU/g) and Salmonella/Shigella (4.09 ± 1.81 × 105 CFU/g) counts, potentially due to nutrient-induced changes or post-harvest handling factors. Correlation analyses revealed a moderate positive relationship between nitrogen input and protein synthesis (r = 0.309), which was not statistically significant (p = 0.329). Additionally, higher pH was significantly correlated with total mesophilic counts (r = 0.661, p = 0.019) and E. coli (r = 0.655, p = 0.020). These findings highlight the importance of nutrient formulation and environmental management in improving nutritional quality while minimizing microbial risks during Spirulina cultivation in tropical, low-tech settings.