3rd Edition Of Plant Science and Molecular Biology World Conference 2026

Abstract

Cassava (Manihot esculenta) processing generates approximately 14 million tons of peels annually in Nigeria, containing 30–40% residual starch that remains largely unutilized. This study reports the isolation of an indigenous Aspergillus oryzae strain (AG10) from cassava effluent for glucoamylase production via solid-state fermentation (SSF). The strain achieved a peak enzyme yield of 49,183 U/L, representing a 1.6-fold increase over reported A. niger SSF benchmarks (38,000 U/L). A total of 20 fungal isolates from cassava dump and effluent soils were screened using serial dilution on starch-based PDA (1% starch, pH 5.6, 28°C, 96 h). AG10 demonstrated the highest hydrolytic activity, producing a 2.4 cm clearance zone following iodine staining, exceeding the 1.5 cm selection threshold. Time-course SSF on cassava peels (5 g, 65% moisture, mineral salts, pH 4.5) identified an optimal production time of 96 h, where peak activity (49,183 U/L) was observed, outperforming BG-3 (11,892 U/L) and AG2 (14,966 U/L). Morphological characteristics, including velvety green colonies (2.5–3 cm diameter) and biseriate phialides, confirmed the isolate as A. oryzae. Scale-up production was conducted using 1 kg sterile cassava peels (65% moisture, pH 4.5), inoculated with AG10 spores (10⁶/mL) and incubated statically at 28°C for 96 h. Enzyme extraction was performed using citrate–phosphate buffer (pH 4.5, 1:10 w/v), followed by muslin filtration and centrifugation (5000 × g, 20 min, 4°C), yielding a crude extract with a specific activity of 39.3 U/mg. Partial purification via ammonium sulfate precipitation (80% saturation, 4°C, 24 h) resulted in a 2.1-fold increase in specific activity to 103 U/mg, with 72% recovery. Biochemical characterization using soluble starch revealed optimal enzyme activity at pH 5.0 (126,399 U/L) and 50°C (287,352 U/L). The enzyme retained over 80% of its activity within the 40–60°C range after 2 h of incubation (pH 4–5.5). Maximum activity was observed at 9% enzyme loading (897,380 U/L), followed by a decline at 10%, indicating substrate inhibition. The SSF approach reduces reliance on submerged fermentation systems, with potential capital savings of up to 60–70%. This process presents significant potential for large-scale enzyme production while addressing environmental concerns associated with agro-industrial waste.