Évaluation de l'activité antioxyadante et de la qualité microbiologique de la Spiruline (Arthrospira platensis).

Abstract

Arthrospira platensis, commonly known as spirulina, is a filamentous blue-green cyanobacterium belonging to the order Oscillatoriales. It is generally classified among microalgae due to its richness in essential nutrients. Used for centuries for its nutritional properties, spirulina is now the subject of extensive research in the fields of health, human nutrition, and biotechnology. This thesis is based on a bibliographic review of the biological characteristics, biochemical composition, cultivation methods, various applications, antioxidant activity, and analytical techniques related to spirulina. It also includes an experimental study evaluating its nutritional, antioxidant, and microbiological qualities. In the experimental part, several analyses were carried out on two commercial spirulina samples, labeled A and B. To achieve our objectives, crude extracts from both samples were obtained using Soxhlet extraction with ethanol as the solvent. This allowed us to evaluate their lipid content. The dry matter content was determined by incubating the samples at 105 °C for 24 hours, followed by placement in a desiccator at 37 °C for 45 minutes before weighing. This process also enabled the determination of moisture content. The pH was measured using reactive strips at room temperature, after incubation for 15 days at 37 °C, and after 7 days at 55 °C. The biochemical evaluation included the quantification of total polyphenols, total flavonoids, and antioxidant activity using the DPPH assay. Microbiological analysis was used as a health indicator to detect total aerobic mesophilic flora, total and fecal coliforms, and Staphylococcus aureus, indicating possible bacterial contamination. The results showed that both samples, A and B, had a dry matter content estimated at 93.8% for sample A and 93% for sample B, and a moisture content of 6.2% for sample A and 7% for sample B. The pH was slightly acidic, estimated at 5.5, measured at room temperature, 37 °C, and 55 °C. The lipid content was estimated at 12.8% for sample A and 8.9% for sample B. The total polyphenol content was estimated at 1.99 mg GAE/g for sample A and 6.83 mg GAE/g for sample B. The total flavonoid content was estimated at 17.82 mg QE/g for sample A and 30.67 mg QE/g for sample B. The 50% inhibitory concentration (IC₅₀) was estimated at 0.639 mg/ml for sample A, 0.551 mg/ml for sample B, and 0.469 mg/ml for ascorbic acid. The enumeration of mesophilic aerobic flora (FTAM) in sample A was estimated at 6.3 × 10⁷ CFU/g, while the number of colonies in sample B was insufficient. The total coliform count was zero in sample A and estimated at 1.05 × 10⁶ CFU/g in sample B. Fecal coliforms were absent in both samples A and B. No growth of Staphylococcus aureus colonies was observed in sample B, while the colony count in sample A was 9.2 × 10² CFU/g. At the end of this study, both spirulina samples A and B appear to be natural sources of antioxidants, with moderate nutritional quality, which may be related to certain results from the bacteriological analysis.