Biodegradation of corn flour-based materials assessed by enzymatic, aerobic, and anaerobic tests: Influence of specific surface area

A material was produced by extrusion of corn flour with 8 wt% glycerol followed by injection-moulding. The corn flour based material biodegradation kinetics were assessed by an anaerobic biodegradation standard test (ISO 14853), an aerobic burial composting test (ISO/DIS 16929) and a test to assess the susceptibility of corn starch to hydrolysis by amylolytic enzymes. Biodegradation and hydrolysis were more rapid for corn flour based material than for native corn flour. This was probably due to corn flour starch amorphisation during thermomechanical processing at the expense of crystalline regions, which are more resistant to hydrolysis by amylolytic enzymes. This was substantiated by observations during burial composting showing that crystalline zones of this material were less degraded. A comparison of the kinetics of starch hydrolysis or biodegradation of corn flour based material samples with specific surface areas ranging from 0.67 to 30 mm−1 by amylolytic enzymes or microorganisms under anaerobic conditions in a liquid medium (ISO 14853) or aerobic conditions during burial composting (ISO/DIS 16929) allowed (i) observation that the biodegradation level by the latter method always exceeded 90% before 84 days, thus meeting this biodegradability criterion, and (ii) to propose that the test of hydrolysis by amylolytic enzymes might constitute a faster method for initial assessment of the biodegradability of starch based materials.