Enzymatic production of pectic oligosaccharides from onion peel pectin: optimization of process parameters for enhanced yield

The growing demand for sustainable bioactive ingredients has sparked interest in transforming agro-industrial byproducts into value-added prebiotics. Pectic oligosaccharides (POS) were produced enzymatically from the onion peel pectin using commercial Aspergillus niger pectinase. To maximize the yield, the process was optimized for enzyme concentration, incubation time, and solid-to-liquid ratio using a Box–Behnken response surface methodology (RSM). The quadratic RSM model demonstrated high statistical significance (R 2 = 0.9961, p < 0.0001) and a non-significant lack of fit ( p = 0.1281), indicating high model reliability. The optimized process conditions with an enzyme concentration of 0.1% (v/w), solid-to-liquid ratio of 3.5%, incubation time of 5 min, and agitation speed of 200 rpm resulted in a pectic oligosaccharide yield of 92.53 ± 0.12%. FTIR analysis confirmed the presence of hydroxyl, carbonyl, and glycosidic bonds in pectic oligosaccharides, while HPLC revealed a predominance of galacturonic acid over neutral sugars such as arabinose, rhamnose, galactose, and glucose. A low molecular weight fraction (Mw = 160 g/mol and polydispersity index = 1.176) indicates selective depolymerization. These findings show that enzymatic hydrolysis is effective at producing homogeneous, low-molecular-weight POS from onion peel waste, highlighting its potential as a long-term substrate for prebiotic and functional foods.