Evaluation of peanut shell and okara extracts as alternative culture media for Nannochloropsis oculata

Abstract

The high cost of synthetic culture media poses a significant challenge for large-scale microalgae production. This study evaluated extracts from agricultural by-products, specifically peanut shells (PN) and okara (OKR) extracts, as alternative nutrient sources for cultivating microalgae Nannochloropsis oculata, a species valued in aquaculture for its nutritional profile. N. oculata was cultured under various conditions: individual extracts, extracts supplemented with 50% or 100% f/2 medium, and combined extracts with cane molasses (CM). Results demonstrated that N. oculata could grow in all extract-based media, with positive specific growth rates (SGR) observed across treatments. The combining OKR and PN extracts with CM (OKR + PN + CM) exhibited the highest SGR (0.12 day-1) among treatments (p < 0.05) and reached peak cell density earlier (12.5 × 10⁶ cells mL-1 on day 8). This improved performance of N. oculata is likely attributable to micronutrients from the combined extracts and the additional organic carbon from cane molasses. These findings confirm that PN and OKR extracts can serve effectively for N. oculata cultivation, offering a sustainable alternative to synthetic media. Further research into nutritional composition and mixotrophic potential of these by-products is recommended to optimize their application in large-scale microalgae production systems.