Production and Characterisation of Polyhydroxyalkanoates from Cocoa Mucilage Using a Wild-Type Priestia aryabhattai Strain

The accumulation of petroleum-based plastics demands sustainable alternatives such as polyhydroxyalkanoates (PHAs), biodegradable polyesters synthesised by numerous prokaryotes. However, high feedstock costs limit their commercialisation. This study evaluated cocoa mucilage, an underutilised by-product of the Ecuadorian cacao sector, as a low-cost carbon source for PHA production by a wild-type strain isolated from cocoa fruit residues. Bacteria were recovered from cocoa mucilage and pod shell fractions, screened for PHA accumulation by Sudan Black B staining with UV–Vis spectrophotometric confirmation, and identified by 16S rRNA gene sequencing. A first report of a single PHA-positive isolate, designated as Priestia aryabhattai strain NBP01-UTN, was recovered from the cocoa shell surface. Fermentation conditions were optimised using response surface methodology with a central composite design evaluating temperature, pH and ammonium sulphate concentration. The fitted quadratic model was highly significant (R² = 0.978, p < 0.0001), indentifying that temperature and nitrogen limitation were the dominant factors. Optimal conditions (40 °C, pH 7.30, 0 g·L⁻¹ (NH₄)₂SO₄) yielded 0.496 g·L⁻¹ PHA at 24 h (productivity ≈ 20.7 mg·L⁻¹·h⁻¹). FTIR and DSC analyses provided converging evidence consistent with poly(3-hydroxybutyrate). These results demonstrate the feasibility of coupling a locally isolated wild-type strain with cocoa mucilage for bioplastic production within a circular bioeconomy framework.