Optimising corn (Zea mays) cob powder as an effective sorbent for diverse gel matrices: exploring particle size and powder concentration effects

This study aims to valorise a plant waste, corn cobs (Zea mays) enriched with fibres (cellulose of 19.09–19.18% and hemicellulose of 34.04–60.13%), to create gel-like sorbents. Corn cobs (CB) were dried, grounded and sieved to obtain 500, 250 and 125 μm powder size fractions. Various CB powder concentrations (10–40% w/w) were mixed with distilled water and rice bran oil for 2 min at ambient temperature to form hydrogel-like and oleogel-like sorbents, respectively. Visual appearance indicated that selected gels formed by 250 and 125 μm CB powders were self-sustained right after mixing, while the largest particles (500 μm) could not fabricate gels at the CB concentrations studied. FTIR results suggested that the gelation process was primarily attributed to physical absorption rather than chemical binding. Comprehensive analyses of microstructure, physicochemical properties and rheological behaviour indicated that gelation was due to fibre–fibre interaction (125 μm) and oil/water–fibre interaction (250 μm). An increase in CB powder concentration enhanced the microstructural density and hardness of gels. Thus, 250 μm particles and higher absorbent concentrations resulted in brittle sorbents characterised by high hardness but low cohesiveness. The 250 μm particles also exhibit a superior antioxidant profile and lower oil/water loss than the 125 μm CB particles due to effective intra-particle trapping mechanisms.