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

<i>Spirulina</i> (<i>Arthrospira platensis</i>) 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 <i>Spirulina</i> cultivated over 30 days in raceway ponds at the Nomayos Spirulina Production Farm in Cameroon. All treatments maintained physicochemical parameters within ranges favorable for <i>Spirulina</i> 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 <i>Escherichia coli</i> (1.05 ± 0.075 × 10⁵ CFU/g) and <i>Salmonella/Shigella</i> (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 (<i>p</i> = 0.329). Additionally, higher pH was significantly correlated with total mesophilic counts (r = 0.661, <i>p</i> = 0.019) and <i>E. coli</i> (r = 0.655, <i>p</i> = 0.020). These findings highlight the importance of nutrient formulation and environmental management in improving nutritional quality while minimizing microbial risks during <i>Spirulina</i> cultivation in tropical, low-tech settings.