Study on the biodegradability of alkaline pretreated custard apple peel (Annona squamosa Linn.) by using local cellulolytic bacteria

This study investigated custard apple peel ( Annona squamosa Linn.) as a novel raw material for sugar production through a combination of chemical and biological hydrolysis. Thermal-alkaline pretreatment was first optimized using one-factor-at-a-time (OFAT) experiments, followed by Box–Behnken Design (BBD) with Response Surface Methodology (RSM). The optimal conditions, with a NaOH concentration of 2.5 g/L, a temperature of 90 °C, and a treatment time of 70 min, yielded 3440 mg/L of reducing sugars, which is 1.8 times higher than the result obtained from single-factor optimization (1862 mg/L). The model showed a strong fit (R² = 0.9774, P < 0.05), confirming the reliability of the predicted values. In the biological approach, four cellulolytic bacterial strains, namely Alcalig-enes sp. KHM19, Staphylococcus gallinarum VC10, Bacillus safensis HL04, and Bacillus velezensis KH-08 were assessed for their enzymatic potential. Among them, B. velezensis KH-08 displayed the highest FPase activity (19.56 U/L) and produced up to 365.97 mg/L reducing sugars after 6 days. Overall, the findings provide the first evidence for the valorization of custard apple peel through integrated hydrolysis strategies and identify B. velezen-sis KH-08 as a promising novel strain for future biotechnological applications.